MicroBiology MCQs with Answer and Explnation | Chapter 29

Answer: Adenoviruses

Adenoviruses are generally not known to be oncogenic. While they can cause a range of illnesses, including respiratory and gastrointestinal infections, they are not strongly associated with the development of cancer. Other viruses listed, such as HSV-2 (Herpes Simplex Virus type 2), HCV (Hepatitis C Virus), and EBV (Epstein-Barr Virus), have been implicated in oncogenesis and are associated with certain cancers.

The other options are incorrect:

• HSV-2 (Herpes Simplex Virus type 2): HSV-2 is associated with genital herpes and can increase the risk of cervical cancer.
• HCV (Hepatitis C Virus): Chronic HCV infection is a major risk factor for the development of liver cancer (hepatocellular carcinoma).
• EBV (Epstein-Barr Virus): EBV is associated with several cancers, including Burkitt’s lymphoma, nasopharyngeal carcinoma, and Hodgkin’s lymphoma.

Answer: Detection of antigen and antibodies

The laboratory diagnosis of HIV infection is usually made by detecting both viral antigens and antibodies produced by the host in response to the infection. Various serological tests, such as enzyme-linked immunosorbent assays (ELISA) and Western blot, are commonly used to detect HIV-specific antibodies. Additionally, tests that detect viral antigens, like p24 antigen assays, contribute to the diagnosis.

The other options are incorrect:

• Biochemical tests: Biochemical tests are not typically used for the direct diagnosis of HIV infection. Serological tests for antibodies and antigens are more specific for detecting HIV.
• Growth of virus in chicken embryo: The growth of HIV in a chicken embryo is not a standard method for diagnosing HIV infection. Serological tests are more widely used.
• Light microscopy: Light microscopy is not suitable for directly detecting HIV or its components. Serological tests are more specific and sensitive for HIV diagnosis.

Answer: Light microscopy

Direct viral diagnostic techniques involve directly observing or detecting the virus in a sample. Light microscopy is not typically used for the direct detection of viruses because viruses are often much smaller than the resolution limit of light microscopes. Electron microscopy, antibodies detection, and viral genome detection are common techniques used for direct viral diagnosis.

The other options are incorrect:

• Electron microscopy: Electron microscopy is a direct viral diagnostic technique that allows for the visualization of viruses at a very high magnification, making it possible to observe their structure.
• Antibodies detection: Antibodies detection, such as through techniques like ELISA (enzyme-linked immunosorbent assay), involves identifying the presence of viral proteins or antibodies produced in response to the virus.
• Viral genome detection: Viral genome detection involves identifying the genetic material (DNA or RNA) of the virus in a sample, often through techniques like polymerase chain reaction (PCR).

Answer: Attachment to cell receptor

The very first step in any virus infection is establishing contact with the host cell. Viruses hijack cells by attaching to specific receptors on their surface, like a key fitting into a lock. This crucial initial interaction allows the virus to gain entry and initiate its infection cycle.

The other options are incorrect:

• Uncoating: This occurs after the virus enters the cell and involves shedding its protective protein coat to release its genetic material. It’s a vital step, but not the initial one.
• Migration to nucleus: Some viruses target the cell nucleus after entry, but initial attachment precedes this movement.
• Transcription: This process transcribes viral genetic material into messenger RNA, but it needs the viral genome inside the cell first, making it a downstream step.

Answer: Translation

For positive-sense, single-stranded RNA viruses, the first step in virus replication after uncoating is translation. Positive-sense RNA can directly serve as mRNA (messenger RNA), allowing the host cell’s ribosomes to translate it into viral proteins. This translation is a key step in the synthesis of viral proteins necessary for the virus to replicate and assemble new virions.

The other options are incorrect:

• Transcription: Transcription involves the synthesis of RNA from DNA. In the case of positive-sense RNA viruses, transcription is not required as the genomic RNA itself can function as mRNA for translation.
• Genome replication: While genome replication is an essential step in the viral life cycle, it typically follows translation. Positive-sense RNA viruses replicate their genomic RNA after the translation of viral proteins.
• Assembly: Assembly is a later step in the viral life cycle. Once viral proteins and genomic RNA are produced, assembly involves the packaging of these components into new virions. It occurs after translation and genome replication.

Answer: Pregnant Women

Rubella, also known as German measles, has the most serious consequences in pregnant women. If a pregnant woman contracts rubella, especially during the first trimester, there is an increased risk of congenital rubella syndrome (CRS) in the developing fetus. CRS can lead to a range of serious birth defects, including heart abnormalities, hearing impairments, and vision problems.

The other options are incorrect:

• Children: While children can contract Rubella and experience symptoms like fever, rash, and swollen lymph nodes, the illness is usually mild and resolves on its own.
• Summer months: The season has no direct impact on the severity of Rubella infection.
• Years with heavy rainfall: Similarly, rainfall patterns are not linked to the severity of Rubella cases.

Answer: Dengue fever

Immunopathology, or immune-mediated disease, may be involved in a severe form of Dengue fever. Dengue virus infection can lead to a spectrum of clinical manifestations, ranging from mild dengue fever to severe forms such as dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). The severe forms are characterized by an abnormal immune response that can lead to plasma leakage, hemorrhage, and organ failure.

The other options are incorrect:

• Yellow fever: While yellow fever is caused by a Flavivirus, severe immunopathology is more commonly associated with Dengue fever rather than yellow fever.
• West Nile: West Nile virus infection may cause severe neurological complications, but the term “immunopathology” specifically refers to immune-mediated disease, and this is more closely associated with severe dengue manifestations.
• Hepatitis C: Hepatitis C is caused by a different virus (hepatitis C virus) and is not classified as a Flavivirus. The question specifically focuses on Flavivirus infections, and hepatitis C is not in this viral family.

Answer: B-lymphocytes

Infectious bursal disease (IBD) primarily affects the bursa of Fabricius, an organ critical for the development and maturation of B-lymphocytes, also known as B cells. B cells are essential components of the humoral immune system, responsible for producing antibodies that combat infections. IBD virus damages and destroys B cells within the bursa, leading to severe immunosuppression in chickens. This makes them susceptible to secondary infections with various bacteria, viruses, and parasites.

The other options are incorrect:

• Thymic cells: The thymus develops T-lymphocytes (T cells), another key immune cell type. While IBD can lead to some T cell dysfunction, the primary target is B-lymphocytes in the bursa.
• Neurons: IBD does not directly affect the nervous system. Neurological symptoms in infected chickens, if present, are likely due to secondary infections or complications from immunosuppression.
• Neutrophils: Neutrophils are white blood cells involved in innate immunity. IBD primarily targets the adaptive immune system, specifically B-lymphocytes, through its effect on the bursa.

Answer: Hepatitis B

Deltavirus infection is always associated with coinfection with Hepatitis B. Deltavirus is a defective virus that requires the presence of Hepatitis B virus (HBV) for its replication and packaging. Individuals with Hepatitis B who acquire a Deltavirus coinfection may experience more severe liver disease.

The other options are incorrect:

• Hepatitis C: Hepatitis C virus is another blood-borne virus causing liver damage, but it is unrelated to Deltavirus and does not require coinfection for its replication.
• Dengue fever: Dengue virus is a Flavivirus transmitted by mosquitoes and causes fever, headache, and muscle aches. It has no association with Deltavirus or Hepatitis B.
• Influenza: Influenza is a respiratory virus causing seasonal epidemics. It also has no link to Deltavirus or Hepatitis B.

Answer: Antibody titer

The hemagglutination inhibition (HI) assay is used for the detection of antibody titers in a sample. This assay is commonly employed in virology to measure the level of specific antibodies against a particular virus. It involves the ability of antibodies to inhibit the agglutination (clumping) of red blood cells by a virus, specifically the hemagglutination activity.

The other options are incorrect:

• Antigen titer: HI assays directly detect antibodies, not viral antigens.
• Virus titer: This assay is not designed to measure the amount of virus present.
• 4HA titer: While “HA” may refer to “hemagglutinating activity” in some contexts, “4HA” is not a standard term in this assay and doesn’t directly signify antibody titer.

Answer: Nerves

Rabies virus reaches the brain and salivary glands primarily via nerves. After the virus enters the body through a bite or scratch, it travels along peripheral nerves towards the central nervous system (CNS). Once in the CNS, the virus can ascend to the brain, where it causes encephalitis. Subsequently, the virus can also travel to the salivary glands, facilitating transmission to new hosts through saliva.

Incorrect Options:

• Blood: Rabies virus does not primarily travel via the bloodstream. While viremia (presence of the virus in the blood) may occur during the later stages of infection, the initial spread to the CNS and salivary glands is mainly through nerves.
• Lymph: Lymphatic spread is not a primary route for rabies virus. The virus has a strong neurotropic (affinity for nerve tissue) nature, and its movement within the body is primarily along nerves.
• SQ tissue (Subcutaneous tissue): Subcutaneous tissue is not a primary route for the spread of rabies virus. The virus enters the nervous system directly from the site of inoculation, typically through peripheral nerves.

Answer: Newcastle disease virus

Newcastle disease virus (NDV) is a highly contagious and often fatal paramyxovirus affecting poultry. It causes a range of symptoms, including respiratory distress, nervous disorders, and egg production decline. NDV poses a significant economic threat to the poultry industry globally due to its potential for rapid spread and high mortality rates.
The other options are incorrect:

• Infectious bursal disease virus (IBDV): IBDV is another paramyxovirus affecting poultry, but it primarily targets B-lymphocytes in the bursa of Fabricius, leading to immunosuppression. While IBD can be severe, its impact is focused on immune function, not directly comparable to the broad range of clinical signs and economic consequences of NDV.
• Avian influenza virus (AIV): AIV belongs to a different viral family (Orthomyxoviridae) and causes a distinct disease in poultry, characterized by respiratory symptoms and potential zoonotic risk. While AIV can be highly pathogenic, it has different epidemiology and clinical manifestations compared to NDV.
• Avian leukosis virus (ALV): ALV is a retrovirus causing neoplastic diseases in poultry. It has a different mode of transmission and pathogenesis compared to NDV, focusing on tumor formation rather than acute infection.

Answer: Vibrio cholerae

Vibrio cholerae produces a life-threatening disease known as cholera. Cholera is characterized by severe watery diarrhea that can lead to dehydration and electrolyte imbalance. The primary treatment for cholera involves prompt and aggressive fluid replacement to counteract the effects of dehydration.

The other options are incorrect:

• Mycoplasma pneumoniae: While Mycoplasma pneumoniae can cause pneumonia, it’s typically a milder illness and doesn’t require aggressive fluid replacement as the primary treatment. Antibiotics play a more significant role in managing this infection.
• Mycobacterium tuberculosis: Tuberculosis caused by Mycobacterium tuberculosis affects the lungs and can be severe, especially if not treated effectively. However, fluid replacement alone would not be sufficient for managing this complex bacterial infection. Antibiotic therapy and other interventions are crucial.
• Treponema pallidum: Although syphilis caused by Treponema pallidum can have serious long-term consequences if untreated, the life-threatening stage typically doesn’t primarily involve severe dehydration. Antibiotic treatment is the mainstay of therapy for syphilis.

Answer: Copper ion

Trace elements are elements that are required by living organisms in very small amounts. Copper is one such trace element that plays essential roles in various biological processes, including enzyme function and the formation of certain proteins. While potassium, sodium, and magnesium are important ions in biological systems, they are not typically classified as trace elements because they are needed in larger quantities.

The other options are incorrect:

• Potassium ion: Potassium is a crucial macronutrient for maintaining electrolyte balance and nerve signaling, with a daily requirement exceeding 3,500mg for adults.
• Sodium ion: Similarly, sodium is a macronutrient essential for fluid balance and nerve impulses, with a recommended intake of around 2,300mg per day.
• Magnesium ion: Magnesium is another macronutrient involved in various cellular processes like energy production and muscle function. Adults typically require around 400mg of magnesium daily.

Answer: Allantoic inoculation

Newcastle Disease Virus (NDV) is primarily cultivated in embryonated chicken eggs for various purposes, including vaccine production, virus isolation, and studying its properties. Among the listed options, allantoic inoculation is the most widely used and effective method for NDV culture in embryonated eggs.

The other options are incorrect:

• Yolk sac inoculation: While possible, yolk sac inoculation is less efficient for NDV cultivation compared to the allantois. The immune response in the yolk sac can affect virus yield, and harvesting is technically more challenging.
• Intra-cerebral inoculation: This method involves injecting the virus directly into the brain of the embryo. It is used for some specific studies requiring viral neurotropism but not for routine NDV culture due to technical complexity and ethical considerations.
• Chorioallantoic membrane inoculation: This involves placing the virus suspension onto the outer surface of the chorioallantoic membrane (CAM). While used for some viral infections, NDV cultivation via CAM is less efficient and less common than allantoic inoculation.

Answer: Light microscopy

Light microscopy is not typically used as a direct viral diagnostic technique. It lacks the resolution needed to visualize most viruses, which are much smaller than the wavelength of visible light. Electron microscopy, antigen detection, and antibodies detection are common techniques in viral diagnostics.

The other options are incorrect:

• Electron microscopy: Electron microscopy is a powerful technique used for directly visualizing viruses at a very high magnification.
• Antigen detection: Antigen detection involves identifying viral proteins in a sample. This is a commonly used technique for viral diagnosis.
• Antibodies detection: Antibodies detection, such as through techniques like ELISA, involves identifying the presence of antibodies produced in response to a viral infection. This is a valuable diagnostic approach.

Answer: Eukaryotic

Transfection is the process of introducing foreign DNA into eukaryotic cells. This method is commonly used in molecular biology and genetic research to study gene function, regulation, and expression. Transfection allows the introduction of exogenous DNA, such as plasmids or expression vectors, into eukaryotic cells for various experimental purposes.

The other options are incorrect:

• B. Bacterial: While introducing DNA into bacteria is possible, it’s more commonly referred to as “transformation” or “genetic modification.” These terms emphasize the change in the bacterial genome, whereas transfection primarily focuses on the process of delivering and integrating DNA into the cell.
• Parasitic: Parasites are usually not the target of transfection experiments, and the term itself doesn’t specifically reference any particular cell type.
• Both “Eukaryotic” and “Bacterial”: While both eukaryotic and bacterial cells can be targeted for DNA introduction, using just “transfection” typically implies the focus on eukaryotic cells.

Answer: Mordant

In Gram staining, iodine is used as a mordant. A mordant is a substance that enhances the affinity of a stain for a particular structure, making the stain more tightly bound to the target. In Gram staining, iodine forms a complex with crystal violet (the primary stain) and helps to fix the stain within the thick peptidoglycan layer of Gram-positive bacteria.

The other options are incorrect:

• Fixative: While iodine can contribute to fixation by stabilizing proteins and preventing dye diffusion, its primary function is as a mordant, not a fixative.
• Solublizer: Iodine does not dissolve any components in the staining process. Instead, it helps solidify the dye-cell wall complex.
• Stain: Although iodine has a yellow-brown color, it is not the primary stain used in Gram staining. Crystal violet is the primary stain, and iodine enhances its binding to Gram-positive cells.

Answer: Florescent Antibody Technique

The diagnosis of rabies is commonly done by the Fluorescent Antibody Technique (FAT). This technique involves staining tissues, especially brain tissue, with fluorescently labeled antibodies that specifically bind to the rabies virus antigens. The fluorescent signals can be visualized under a microscope, confirming the presence of the virus.

The other options are incorrect:

Direct Sandwich ELISA: While ELISAs can be used for rabies detection, they are typically less sensitive and specific than FAT, particularly for ante-mortem (before death) diagnosis.
Hemagglutination assay: This test is not commonly used for rabies diagnosis as it lacks the necessary sensitivity and specificity.
Hemagglutination inhibition assay: This assay is primarily used for other viral infections like influenza and is not suitable for rabies diagnosis.

Answer: Trojan horse

In a Trojan horse vaccine, genetic material from a pathogen is inserted into a live carrier non-pathogen. The live carrier, often a harmless virus or bacterium, acts as a “Trojan horse” by delivering genetic material from the pathogen into the cells of the vaccinated individual. This allows the immune system to recognize and mount a response against the pathogen without causing disease.

The other options are incorrect:

• Subunit: Subunit vaccines contain only specific components (subunits) of the pathogen, such as proteins or antigens. They do not use a live carrier to deliver genetic material.
• Acellular: Acellular vaccines contain components of the pathogen but not the complete organism. They may include purified proteins or inactivated toxins. Acellular vaccines do not involve the use of a live carrier.
• Live attenuated: Live attenuated vaccines use weakened forms of the pathogen that are still capable of replication but cause mild or no disease. They do not involve the insertion of genetic material into a live carrier.

Answer: Normal Saline

In hemagglutination (HA) assays, a 1% or 0.8% dilution of washed red blood cells (RBCs) is prepared for use by diluting the washed RBCs in Normal Saline (0.9% sodium chloride solution). The use of normal saline provides an isotonic environment for the red blood cells, maintaining their integrity and allowing for accurate testing in hemagglutination reactions.

The other options are incorrect:

• Distilled H₂O: Using distilled water is not suitable for diluting washed RBCs in HA assays as it would disrupt the osmotic balance and integrity of the red blood cells.
• Double distilled H₂O: Similarly, double distilled water lacks the ions necessary to maintain the osmotic balance and integrity of red blood cells. It is not appropriate for diluting RBCs in HA assays.
• Double distilled deionized H₂O: Double distilled deionized water lacks ions and is not suitable for maintaining the osmotic balance of red blood cells. It is not the recommended medium for diluting RBCs in HA assays.

Answer: Period of initial adjustment

The lag phase is also known as the period of initial adjustment. During this phase, microorganisms are adjusting to their new environment. They are metabolically active but not actively dividing or increasing in number. The length of the lag phase can vary depending on factors such as the microbial species, the composition of the growth medium, and environmental conditions.

The other options are incorrect:

• Transitional period: While accurate in its essence, “transitional period” is a less specific term than “period of initial adjustment” and doesn’t fully capture the specific processes happening during the lag phase.
• Generation time: This term refers to the average time it takes for a single cell to divide and become two cells. It is not used specifically for the lag phase, which involves non-dividing cells making adjustments.
• Period of rapid growth: This completely contradicts the definition of the lag phase, which is characterized by the absence of cell division and growth.

Answer: Continuous cell culture

A continuous cell culture is a cell culture that can reproduce for an extended number of generations without undergoing senescence. These cultures are often derived from immortalized cell lines, and they provide a continuous and consistent source of cells for various applications, including supporting viral replication for the production of vaccines or studying viral infections.

The other options are incorrect:

• Primary cell culture: Primary cell cultures are derived directly from tissues and have a limited lifespan. They undergo senescence after a certain number of cell divisions.
• Secondary cell culture: There isn’t a standard term “secondary cell culture” in the context of continuous cell lines. Secondary cultures could refer to subsequent passages of primary cultures.
• Diploid fibroblast cell culture: Diploid fibroblast cell cultures are derived from normal, non-immortalized cells. They have a limited lifespan and undergo senescence after a certain number of cell divisions. Continuous cell cultures, on the other hand, are often derived from immortalized cells that can divide indefinitely.

Answer: Y. pestis

Yersinia pestis is the causative agent of plague. It is a Gram-negative bacterium and the pathogen responsible for causing bubonic, septicemic, and pneumonic plague in humans.

The other options are incorrect:

• Y. enterocolitica: This Yersinia species can cause gastrointestinal illness but is not associated with plague.
• P. mirabilis: This Proteus species can cause urinary tract infections and other medical problems but is not involved in plague.
• E. coli: While certain E. coli strains can cause diverse illnesses, the classical plague pathogen is specifically Y. pestis.

Answer: B lymphocytes

B lymphocytes (B cells) are cells that use antibodies to recognize their targets. B cells are a type of white blood cell that plays a crucial role in the adaptive immune response. When activated, B cells can differentiate into plasma cells, which produce and release antibodies. These antibodies, also known as immunoglobulins, are proteins that specifically recognize and bind to antigens, marking them for destruction or neutralization

The other options are incorrect:

• CD4+ T cells: These T cells help activate other immune cells but don’t directly produce antibodies. They recognize antigens presented by other cells through MHC molecules and orchestrate the immune response.
• CD8+ T cells: These T cells directly kill infected cells or cancer cells but also don’t produce antibodies. They recognize infected cells presenting viral or intracellular bacterial antigens directly on their surface.
• Macrophages: These phagocytic cells ingest and destroy pathogens but don’t produce antibodies. They play a crucial role in innate immunity and antigen presentation.

Answer: Soluble antigens

B-lymphocytes (B cells) bind and respond to soluble antigens. These antigens can be proteins, carbohydrates, or other molecules that are dissolved or suspended in body fluids. When a B cell encounters a soluble antigen that matches its specific receptor, it binds to the antigen and undergoes activation. This activation leads to the production of antibodies that can neutralize or eliminate the soluble antigens.

The other options are incorrect:

• Virus-infected host cell: B-lymphocytes can develop antibodies against antigens displayed on the surface of infected cells, but this typically involves additional steps and interactions with other immune cells. Initial activation often occurs through soluble antigens released from the virus or infected cell.
• Bacteria: While B-lymphocytes can directly react with some bacterial antigens on their surface, many bacterial components can also be released as soluble antigens, triggering the initial recognition and antibody production process.
• Particulate matter: Although particulate matter like dust or pollen can activate certain immune cells, B-lymphocytes primarily respond to specific antigenic molecules, regardless of whether they are part of a larger particle or exist in a dissolved state.

Answer: Alternative

The alternative complement pathway will activate first among the three options listed. The alternative pathway is constitutively active at a low level and can be triggered by the presence of foreign surfaces, such as microbial cell walls. It provides rapid, initial defense against invading pathogens.

The other options are incorrect:

• Classical: The classical complement pathway is typically activated by the binding of antibodies to antigens. It is part of the adaptive immune response and is initiated after the alternative pathway.
• Lectin: The lectin complement pathway is activated when lectins (proteins that bind to carbohydrates) recognize and bind to microbial surfaces. It is also part of the adaptive immune response and is initiated after the alternative pathway.
• All act simultaneously: The complement pathways do not all act simultaneously. While the alternative pathway can be rapidly activated, the classical and lectin pathways are part of the adaptive immune response and are initiated after specific recognition of pathogens by antibodies or lectins, respectively.

Answer: Feather follicle

The sample of choice in Marek’s disease is the feather follicle. Marek’s disease is a viral infection affecting chickens, and the virus is shed in the feather follicles of infected birds. Collecting samples from feather follicles for testing allows for the detection of Marek’s disease virus.

The other options are incorrect:

• Liver tissue: Liver tissue is not the sample of choice for testing Marek’s disease. While the virus can affect various tissues, testing feather follicles is more specific for detecting the virus.
• Pieces of lymph node: Lymph nodes can be affected by Marek’s disease, but testing feather follicles is a more reliable method for detecting the virus.
• Bursa of Fabricius: The bursa of Fabricius is an organ in birds that is particularly affected by Marek’s disease. However, collecting samples from feather follicles is often preferred for practical reasons, as it provides a convenient and reliable source for virus detection.

Answer: All of the above

• Antigen-antibody reaction is specific: The antigen and antibody must be specific for each other to form a complex, which is the basis for precipitation. Non-specific interactions won’t form visible bands.
• Antigen is soluble: Insoluble antigens wouldn’t migrate through the agarose gel, preventing band formation. The test requires soluble antigens to diffuse and interact with antibodies.
• Conc. of antigen and antibody are optimum: If either antigen or antibody is in excess or deficient, the formation of visible precipitin bands might be weak or completely absent. A specific ratio is crucial for efficient complex formation and precipitation.

Answer: 10-4.6

LD50 (lethal dose, 50%) is the dose of a substance (or in this case, a virus) that is lethal to 50% of the exposed population. The LD50 is expressed as the logarithm (base 10) of the dose. If LD50 is 10^(-5.6) and 100 µl of the sample is used, then the virus titer would be 10^(-5.6) – log(100) = 10^(-4.6).

The other options are incorrect:

• 10^-5.6: This is the same as the provided LD50 and doesn’t represent the virus titer, which is typically higher.
• 10^6.6: This is the result of dividing the reciprocal of LD50 by the sample volume without adjusting for unit conversion, leading to an overestimation of the virus titer.
• 10^-6.6: This value is too small compared to the expected titer based on the given LD50.

Answer: Can kill infected host cells.

One of the important functions of T cells is their ability to recognize and kill infected host cells. This is primarily carried out by cytotoxic T cells (CD8+ T cells) through the release of cytotoxic granules containing perforin and granzymes, which induce apoptosis (programmed cell death) in the infected cells.

The other options are incorrect:

• Has both MHC-I and MHC-II molecules: T cells generally express either MHC-I or MHC-II molecules, not both. MHC-I is typically expressed on all nucleated cells and presents endogenous antigens, while MHC-II is expressed on antigen-presenting cells (APCs) and presents exogenous antigens.
• Does not require antigen processing/presentation: T cells do require antigen processing and presentation, and they recognize antigens presented by major histocompatibility complex (MHC) molecules on the surface of antigen-presenting cells (APCs).
• Differentiate into plasma cells: Plasma cells are differentiated forms of B cells, not T cells. T cells differentiate into various effector and memory T cell subsets but not into plasma cells.

Answer: Fowl pox virus

The stick method of virus inoculation is used for Fowl pox virus. In this method, a small stick or lancet is used to introduce the virus into the skin of birds. Fowl pox is a viral disease affecting poultry, and this inoculation method is commonly employed for experimental purposes or vaccine production.

The other options are incorrect:

• Newcastle disease virus: While there are various vaccination routes for Newcastle disease virus, the “stick method” is not commonly used for this purpose. Typically, Newcastle disease vaccines are administered via subcutaneous injection, eye drops, or oral spraying.
• FMD virus (Foot-and-mouth disease virus): Vaccines for FMD virus are primarily administered intramuscularly or subcutaneously in cattle and other cloven-hoofed animals. The “stick method” is not used for FMD vaccination.
• Avian influenza virus: Similar to Newcastle disease, avian influenza vaccines are administered through various routes like subcutaneous injection, intranasal (via nostrils), or oral spraying. The “stick method” is not a common approach for vaccinating against avian influenza.

Answer: Cytotoxic T cell

A T-cell that has the CD8+ marker is known as a cytotoxic T cell (also called CD8+ T cell). Cytotoxic T cells play a crucial role in the immune response by recognizing and directly killing virus-infected or abnormal cells. The CD8+ marker indicates that these T cells interact with major histocompatibility complex class I (MHC-I) molecules on the surface of target cells.

The other options are incorrect:

• Natural Killer T cells (NKT cells): These are a unique subset of T cells with some cytotoxic ability, but they do not express CD8+.
• Helper T cells (Th cells): These T cells primarily activate other immune cells and do not directly kill infected cells. They typically express CD4+ markers rather than CD8+.
• T Regulatory cells (Tregs): These T cells suppress immune responses and maintain immune tolerance. They also express CD4+ and typically lack CD8+.

Answer: It typically processes antigens exogenously.

The statement “It typically processes antigens exogenously” is FALSE. Major Histocompatibility Complex class I (MHC-I) molecules primarily present endogenous antigens, i.e., antigens derived from within the cell (e.g., viral proteins produced inside infected cells). MHC-I molecules present these peptides to cytotoxic T cells (CTL) for recognition.

The other options are incorrect:

• Ag. presented by MHC-I is recognized by CTL: This statement is TRUE. Antigens presented by MHC-I molecules are recognized by cytotoxic T lymphocytes (CTL), and this interaction is crucial for immune surveillance against intracellular pathogens.
• Peptide binding cleft is formed by α 1/α2: This statement is TRUE. The peptide-binding cleft of MHC-I molecules is formed by the α1 and α2 domains.
• It is present on all nucleated host cells: This statement is TRUE. MHC-I molecules are expressed on the surface of all nucleated cells in the body, allowing immune surveillance of intracellular infections or abnormalities.

Answer: Chloroform, lipids

Treatment with chloroform is required for the isolation of viruses from tissues, and it precipitates lipids present in the sample. Chloroform is often used in virus isolation procedures to disrupt cell membranes and release viral particles. It helps in separating lipids and other components from the viral particles.

The other options are incorrect:

• Formalin, lipids: Formalin is a fixative used to preserve tissues but does not specifically precipitate lipids. It might cause some lipid aggregation, but it wouldn’t be as effective as chloroform for virus isolation purposes.
• Chloroform, proteins: Chloroform does not precipitate proteins to a significant extent. It primarily targets lipids and other organic molecules.
• Formalin, proteins: Formalin does cross-link and precipitate proteins, but it wouldn’t be the preferred treatment for virus isolation due to its potential interference with viral proteins and downstream assays.

Answer: YAC-1 cell line (Mouse Lymphoma cells)

YAC-1 cell line is an example of a suspension cell line. Suspension cell lines grow in a suspension culture and do not adhere to the surface of a culture vessel. YAC-1 cells are derived from mouse lymphoma and are commonly used in research, particularly in immunology and cytotoxicity assays.

The other options are incorrect:

• Vero cell line (Monkey Kidney cells): Vero cells are adherent cells and typically grow attached to the surface of a culture vessel. They are not an example of a suspension cell line.
• Hela cell line (Human Cervix cells): Hela cells are adherent cells and grow attached to the surface. They are not an example of a suspension cell line.
• HEK 293 cell line (Human kidney cells): HEK 293 cells are adherent cells commonly used in molecular biology and biotechnology. They do not belong to the suspension cell line category.

Answer: Resistant to high salt concentration

In enzyme-linked immunosorbent assay (ELISA), enzymes are used as labels to detect the presence of antigens or antibodies. The enzyme should not be resistant to high salt concentrations because high salt concentrations can interfere with the reactions involved in ELISA. Therefore, an enzyme that is sensitive to high salt conditions is not a desired property for ELISA.

The other options are incorrect:

• High turnover rate: A high turnover rate is a desired property for an enzyme in ELISA. It allows for the efficient conversion of substrate to product, enhancing the sensitivity of the assay.
• Readily coupled to proteins: An enzyme that can be easily coupled to proteins is a desired property for ELISA. This allows for the labeling of antigens or antibodies for detection.
• Cheap: While cost-effectiveness is a consideration, it is not related to the enzymatic properties necessary for ELISA. The other properties mentioned are more directly relevant to the assay’s performance.

Answer: Diversity

The light chain does not originate from the Diversity (D) region during the rearrangement of immunoglobulin genes. The process of V(D)J recombination involves the rearrangement of gene segments, including Variable (V), Diversity (D), and Joining (J) segments. In the case of the light chain, it undergoes V-J rearrangement, and the D segment is not involved in its formation.

The other options are incorrect:

• Variable: The variable (V) region is involved in the generation of diversity in both heavy and light chains. It participates in the V(D)J recombination process.
• Joining: The joining (J) region is part of the gene segments that undergo rearrangement during V(D)J recombination to generate diversity in immunoglobulin genes.
• Constant: The constant (C) region is not involved in the rearrangement process but plays a role in determining the isotype (IgM, IgD, IgG, etc.) of the immunoglobulin molecule.

Answer: A single lymphocyte can only recognize a single antigenic epitope.

Each B cell or T cell expresses a single, unique antigen receptor on its surface. This receptor is designed to bind to a specific, unique epitope (a small part) of an antigen. Having multiple specificities would be detrimental as it could lead to self-reactivity and autoimmune reactions.

The other options are incorrect:

• The pool of lymphocytes can express several million different antigen receptors: This statement is TRUE. The diversity in the antigen receptors of lymphocytes is achieved through processes like V(D)J recombination, generating a vast repertoire of receptors.
• A single lymphocyte can express several thousand antigen receptors: This statement is TRUE. Each lymphocyte can express a large number of antigen receptors, contributing to the immune system’s ability to recognize diverse antigens.
• A single lymphocyte can recognize a single antigenic epitope: This statement is FALSE. A single lymphocyte can recognize multiple antigenic epitopes, each corresponding to a different receptor on the lymphocyte’s surface. The diversity in receptors allows recognition of a broad range of antigens.

Answer: A particle that is immunogenic will trigger an adaptive immune response

The correct statement is that a particle that is immunogenic will trigger an adaptive immune response. Immunogenicity refers to the ability of a substance to provoke an immune response, particularly the activation of the adaptive immune system. An immunogenic substance is capable of inducing the production of antibodies or the activation of T cells.

The other options are incorrect:

• An antigenic particle is always immunogenic, but the reverse is not true: This statement is incorrect. While many immunogenic particles are also antigenic, there can be cases where a substance is antigenic but not highly immunogenic, meaning it may not strongly activate the immune system.
• The terms are synonymous: This statement is incorrect. Antigenicity and immunogenicity are related but not synonymous. Antigenicity refers to the ability to bind to an antibody or T cell receptor, while immunogenicity involves the ability to induce an immune response.
• A particle that is antigenic will trigger an adaptive immune response: This statement is not always true. Antigenicity simply refers to the ability to bind to an antibody or T cell receptor, but not all antigenic substances may be highly immunogenic and capable of triggering a strong immune response.

Answer: Require larger dose / more boosters

The correct statement is that live vaccines typically require a smaller dose and fewer boosters. Live vaccines contain weakened or attenuated forms of the pathogen, and because they are more similar to natural infections, they often generate a strong and long-lasting immune response, requiring fewer doses or boosters.

The other options are incorrect:

• Require special storage (cold chain): True. Live vaccines can be fragile and susceptible to temperature fluctuations, necessitating careful storage and transportation within a cold chain to maintain their potency.
• Can conceivably mutate back to virulent strain: True. While the probability is low, a slight risk exists of live vaccine strains undergoing mutations that could restore their virulence and cause disease. Therefore, careful selection and attenuation of vaccine strains, along with stringent safety monitoring, are crucial.
• Confer long-lasting protection: True. Live vaccines typically induce a robust and long-lasting immune response, often providing protection for years or even decades. This is because they mimic natural infection and trigger both humoral (antibody) and cellular immunity.

Answer: Spirochetes

Endoflagellum is present in spirochetes. Spirochetes are a group of spiral-shaped bacteria characterized by their unique axial filaments, also known as endoflagella. These endoflagella are located within the periplasmic space and are involved in the characteristic motility of spirochetes.

The other options are incorrect:

• Spirilla: Spirilla are spiral-shaped bacteria, but they do not possess endoflagella. They typically have flagella located on the external surface.
• Bacillus: Bacillus bacteria are rod-shaped, and they do not have endoflagella. Their motility is usually facilitated by flagella located on the external surface.
• Coccus: Cocci are spherical-shaped bacteria, and they do not possess endoflagella. Motility in cocci is usually achieved through other means, such as flagella or gliding.

Answer: Superantigen

Superantigens provoke an overwhelming T-cell response. Superantigens are microbial or viral proteins that can activate a large proportion of T cells by binding to both the T-cell receptor (TCR) and major histocompatibility complex (MHC) class II molecules outside the usual antigen-binding site. This leads to a massive release of cytokines, causing an excessive immune response.

The other options are incorrect:

• Autoantigen: Autoantigens are self-antigens that trigger an immune response against one’s own tissues. While they can provoke T-cell responses in autoimmune diseases, the term “overwhelming” is more appropriately associated with superantigens.
• Allergen: Allergens can induce allergic responses, but the term “overwhelming T-cell response” is more specific to superantigens, which can activate a large number of T cells simultaneously.
• Autoantigen: This option is repeated in the question, and autoantigens, as mentioned earlier, are associated with autoimmune responses rather than overwhelming T-cell responses in the context described.

Answer: Herd immunity

Indirect protection of unimmunized animals is achieved through herd immunity. Herd immunity occurs when a sufficiently large proportion of the population is immune to a disease, either through vaccination or previous infection, reducing the overall transmission of the infectious agent. This indirectly protects unimmunized individuals by decreasing the likelihood of exposure to the pathogen.

The other options are incorrect:

• Artificial active immunity: This involves the deliberate introduction of a weakened or killed pathogen to stimulate the immune system to produce antibodies. It provides direct protection to the immunized individual but does not contribute to herd immunity.
• Artificial passive immunity: This involves the transfer of pre-made antibodies from an immune individual to a non-immune فرد. It provides immediate but temporary protection and does not contribute to long-term herd immunity.
• Natural active immunity: This occurs when an individual recovers from a natural infection with a pathogen, resulting in the development of long-term antibodies. It directly protects the فرد but does not contribute to herd immunity unless a significant portion of the population is immune.

Answer: An epitope triggers the production of a number of lymphocytes, each with different receptors.

The incorrect statement is “An epitope triggers the production of a number of lymphocytes, each with different receptors.” According to the clonal selection theory, each lymphocyte is specific for a single epitope, and the receptors on the lymphocytes (e.g., T cell receptors or B cell receptors) are identical in specificity.

The other options are incorrect:

• Specificity for Ag of T cells produced is identical to the specificity of the TCR on the initial T cell: This statement is correct and aligns with the clonal selection theory. The specificity of the T cell receptor (TCR) is maintained in the progeny of the activated T cell.
• The body is equipped with billions of lymphocytes. Each is devoted to respond to one specific epitope: This statement is correct. The diversity of lymphocytes allows the immune system to recognize a vast array of antigens, and each lymphocyte is specific for a particular epitope.
• Antigen binding to a TCR triggers proliferation and differentiation of T cells into effector cells: This statement is correct. According to the clonal selection theory, binding of an antigen to a T cell receptor triggers the proliferation and differentiation of the activated T cell into effector cells.

Answer: Should be less immunogenic

A vaccine’s primary purpose is to trigger a strong and specific immune response against a target pathogen without causing severe illness. Therefore, a vaccine should be immunogenic, meaning it should effectively stimulate the immune system to produce protective antibodies and memory cells. A less immunogenic vaccine would be less effective in inducing immunity and protecting against the disease.

The other options are incorrect:

• Should protect against natural exposure: While this is certainly a desirable property of a vaccine, it is not always essential. Some vaccines, like those for rabies, are primarily used for post-exposure prophylaxis due to the severity of the disease. The key characteristic is the ability to induce sufficient immunity to prevent or mitigate infection.
• Should be cheaper: Cost-effectiveness is crucial for widespread vaccine access, but it’s not a defining property of a vaccine itself. Research and development, production, and distribution costs can vary significantly between vaccines, impacting affordability but not their core function of inducing immunity.
• Should have relatively longer shelf life: Stability and longer shelf life are important for vaccine storage and distribution, especially in resource-limited settings. However, while instability can render a vaccine unusable, it doesn’t inherently affect its immunogenicity.

Answer: Activated cytotoxic T lymphocytes

Virus-infected host cells are primarily targeted and killed by activated cytotoxic T lymphocytes (CTLs). CTLs recognize viral antigens presented on the surface of infected cells through major histocompatibility complex class I (MHC-I) molecules. Once activated, CTLs release cytotoxic molecules, such as perforin and granzymes, inducing apoptosis in the infected cells.

The other options are incorrect:

• Activated B lymphocytes: B cells primarily produce antibodies, which primarily neutralize extracellular viruses, not infected cells. While some specialized B cells (NK T cells) have cytotoxic activity, their role in antiviral defense is secondary compared to CTLs.
• Activated T helper cells: T helper cells provide crucial support to other immune cells, including CTLs, by releasing signaling molecules that enhance their activation and function. However, they don’t directly kill infected cells themselves.
• Monoclonal antibodies: Monoclonal antibodies are laboratory-produced, highly specific antibodies used in passive immunity situations. While they can target and neutralize viruses, they wouldn’t directly kill infected host cells like CTLs do.

Answer: Direct microscopic count

The Petroff-Hausser chamber is used for direct microscopic counting of microorganisms. It is a specialized counting chamber that allows for the enumeration of microorganisms, such as bacteria or yeast, directly under a microscope. The chamber has a grid pattern that facilitates counting and determining cell concentrations.

The other options are incorrect:

• Incubation of culture medium: While the chamber holds a small volume of sample, its primary purpose is not incubation. Culture media are typically incubated in vials, flasks, or plates designed for optimal growth and observation of microorganisms.
• Viable count: Although the chamber can be used to estimate the density of both live and dead cells, it doesn’t directly assess viability. Additional staining techniques might be required to differentiate between viable and non-viable cells.
• To grow anaerobic bacteria: The Petroff-Hausser chamber itself doesn’t provide the specific conditions (e.g., anaerobic atmosphere) necessary for growing anaerobic bacteria. These bacteria typically require specialized culture containers and media to maintain their viability.

Answer: Artificial active immunity

The injection of a toxoid to protect against future tetanus infection is an example of artificial active immunity. In artificial active immunity, the immune system is stimulated to produce an immune response through vaccination. The toxoid is an inactivated or attenuated form of the toxin produced by the pathogen, and it induces the production of antibodies and memory cells, providing protection upon subsequent exposure to the pathogen.

The other options are incorrect:

• Natural passive immunity: Natural passive immunity involves the transfer of pre-formed antibodies from mother to child (through breast milk or placenta). The scenario described involves the induction of an active immune response through vaccination, making this option incorrect.
• Natural active immunity: Natural active immunity is acquired through natural exposure to a pathogen, leading to an active immune response. In this case, the immunity is induced artificially through vaccination.
• Artificial passive immunity: Artificial passive immunity involves the administration of pre-formed antibodies (such as immune serum or antibodies from another individual) to provide immediate but temporary protection. The scenario described involves active immunity induced through vaccination, making this option incorrect.

Answer: Carcinogenic

Substances that have the ability to induce the development of malignant tumors are termed carcinogenic. Carcinogens are agents that promote or increase the risk of cancer. These substances can cause genetic mutations or interfere with cellular processes, leading to uncontrolled cell growth and the potential formation of cancerous tumors.

The other options are incorrect:

• Toxic: Toxic substances may cause harm or damage to living organisms, but not all toxic substances are necessarily carcinogenic. Toxicity refers to the ability of a substance to cause harm.
• Corrosive: Corrosive substances have the ability to cause damage to tissues or materials, often through chemical reactions. While corrosive substances can be harmful, they are not specifically associated with inducing malignant tumors.
• Ignitable: Ignitable substances are those that can easily catch fire. Ignitability is not directly related to the ability to induce malignant tumors.