Immunology and Serology MCQs with Answer and Explanations | Chapter 1

Answer: All the above

• Opportunistic infections (OIs) are infections that take advantage of a weakened immune system.
• HIV damages the immune system, making people with HIV more susceptible to OIs.
• Candidiasis, cryptococcosis, and cryptosporidiosis are all examples of OIs commonly associated with AIDS.

Answer: Tuberculosis

The Mantoux test, also known as the tuberculin skin test (TST), is a diagnostic tool used to detect previous exposure to tuberculosis (TB) bacteria. It measures the body’s immune response to a specific protein derived from TB bacteria.

The other options are incorrect:

• Diphtheria: Diphtheria is a bacterial infection that primarily affects the throat and upper airway. It’s diagnosed through throat swab cultures, not a skin test like the Mantoux test.
• Echinococcus: This refers to an infection caused by Echinococcus worm larvae. Diagnosis typically involves imaging tests (X-ray, ultrasound) and blood tests for specific antibodies, not a skin test.
• Toxoplasma: This is a parasite infection caused by Toxoplasma gondii. It’s usually diagnosed through a blood test to detect antibodies against the parasite, not a skin test.

Answer: IgG

IgG is the only immunoglobulin that can effectively cross the placenta in significant amounts. This transfer provides passive immunity to the developing fetus, protecting them from various infections until their own immune system matures.

The other options are incorrect:

• IgM: IgM antibodies are large and cannot efficiently pass through the placenta due to their size and structure.
• IgA: IgA antibodies primarily exist in mucosal secretions like saliva and tears. While some subclasses can cross the placenta in small amounts, it’s not a major contributor to fetal immunity.
• IgE: IgE antibodies are involved in allergic responses and don’t play a significant role in protecting against infections. They also cannot readily cross the placenta.

Answer: Hybridoma cells

Monoclonal antibodies are produced from a specific type of cell called a hybridoma cell. Hybridoma cells are created by fusing a B cell (from an animal immunized with a specific antigen) with a myeloma cell (cancerous plasma cell).

The other options are incorrect:

• Myeloma cells: While used in the creation of hybridomas, myeloma cells themselves don’t produce the specific monoclonal antibodies we seek. They contribute the ability for continuous cell division.
• Lymphoma cells: Lymphoma refers to cancer of lymphocytes, a broader category that includes B cells. However, not all lymphomas are antibody-producing, and they wouldn’t be the specific cell type used to generate monoclonal antibodies.

Answer: IgG

IgG is the only antibody that can cross the placenta. This transfer from mother to fetus provides passive immunity, protecting the newborn against infections during the early months of life.

The other options are incorrect:

• IgM: IgM antibodies are large and cannot efficiently pass through the placenta due to their size and structure.
• IgA: IgA antibodies primarily exist in mucosal secretions like saliva and tears. While some subclasses can cross the placenta in small amounts, it’s not a major contributor to fetal immunity.
• IgE: IgE antibodies are involved in allergic responses and don’t play a significant role in protecting against infections. They also cannot readily cross the placenta.

Answer: Syphilis

The VDRL (Venereal Disease Research Laboratory) test is a screening test specifically designed to detect antibodies produced by the body in response to a syphilis infection. It’s a common tool for diagnosing syphilis.

The other options are incorrect:

• Rabies: Rabies is a viral infection of the nervous system. Diagnosis typically involves analyzing brain tissue samples or specific antibodies in the cerebrospinal fluid, not a blood test like VDRL.
• Typhoid: Typhoid fever is a bacterial infection caused by Salmonella typhi. Diagnosis involves blood cultures or stool cultures to isolate the bacteria, not a test for antibodies like VDRL.
• Weil’s disease: This is caused by Leptospira bacteria and is diagnosed through blood tests to detect specific Leptospira antibodies or the bacteria itself, not the VDRL test.

Answer: 56°C for 30 mts

Serum complements are proteins in the blood that are part of the immune system’s defense mechanism. They can be inactivated at a temperature of 56°C for 30 minutes. Inactivation of complements is often done in laboratory procedures to prevent their interference in certain assays.

The other options are incorrect:

• 56°C for 15 minutes: While some complement activity might be reduced at this temperature for 15 minutes, it likely wouldn’t be sufficient for complete inactivation.
• 37°C for 30 minutes: While the duration of heat exposure is adequate, the temperature of 37°C is not high enough to effectively inactivate serum complements. Higher temperatures are required for complete inactivation.
• 37°C for 20 minutes: This temperature is not sufficient to inactivate serum complements. Complements are relatively stable at 37°C, and longer exposure time or higher temperature is needed for inactivation.

Answer: Heparinized blood

The LE (Lupus Erythematosus) cell test is used in the diagnosis of systemic lupus erythematosus (SLE), a systemic autoimmune disease. For this test, heparinized blood is used because heparin prevents blood clotting and preserves the integrity of the cells, allowing for accurate examination of neutrophils for the presence of LE cells, which are neutrophils containing phagocytosed nuclear material.

The other options are incorrect:

• Citrated blood: Citrate is another anticoagulant, but it can alter the morphology of white blood cells, making them less suitable for LE cell identification.
• Oxalated blood: Oxalate is an anticoagulant that can activate platelets, leading to clumping of cells and hindering LE cell visualization.
• Clotted blood: Clot formation concentrates and activates cells, making it difficult to identify the specific features of LE cells.

Answer: IgG

IgG is the only antibody class that can significantly cross the placenta in sufficient amounts. This transfer of maternal IgG antibodies provides passive immunity to the developing fetus, protecting them from various infections until their own immune system matures.

The other options are incorrect:

• IgM: IgM antibodies are large and cannot efficiently pass through the placenta due to their size and structure.
• (1) and (2): This combines IgG and IgM, but only IgG is effective in crossing the placenta in significant quantities.
• None of the above: This is incorrect. IgG antibodies do indeed cross the placenta.

Answer: Innate immunity

Innate immunity is the body’s first line of defense against pathogens (disease-causing organisms). It’s present from birth and doesn’t require prior exposure to specific invaders. It provides a broad, non-specific response to various threats.

The other options are incorrect:

• Adaptive immunity: This is the second layer of defense, which develops over time through exposure to pathogens or vaccinations. It creates a targeted response specific to each encountered threat.
• Active immunity: This refers to the development of immunity within an individual, either through natural infection or vaccination. It’s a consequence of the adaptive immune system’s work.
• Adoptive immunity: This is a more specific type of immunity where immune cells or antibodies are transferred from another individual. It’s not the natural immunity present in everyone.

Answer: IgG

IgG is the only immunoglobulin class that can effectively cross the placenta in significant amounts. This transfer of maternal IgG antibodies provides passive immunity to the developing fetus, protecting them from various infections until their own immune system matures.

The other options are incorrect:

• IgA: IgA antibodies primarily exist in mucosal secretions like saliva and tears. While some subclasses can cross the placenta in small amounts, it’s not a major contributor to fetal immunity.
• IgD: IgD antibodies are found on the surface of B cells and play a role in B cell activation. They are not involved in providing immunity through placental transfer.
• IgM: IgM antibodies are large and cannot efficiently pass through the placenta due to their size and structure.

Answer: VDRL

The VDRL (Venereal Disease Research Laboratory) test is a screening test specifically designed to detect antibodies produced by the body in response to a syphilis infection. It’s a common and reliable initial diagnostic tool for syphilis.

The other options are incorrect:

• ASOT (Anti-Streptolysin O titer): This test detects antibodies against a specific bacterial toxin produced by Streptococcus pyogenes bacteria. It’s used to diagnose streptococcal infections, not syphilis.
• Ra factor (Rheumatoid factor): This is a blood test used to help diagnose rheumatoid arthritis, an autoimmune disease. It’s not indicative of syphilis infection.
• CRP (C-reactive protein): CRP is a marker of inflammation in the body and is elevated in response to various inflammatory conditions. While it can be elevated in some cases of syphilis, it is not a specific test for detecting syphilis.

Answer: Gamma Globulin

Immunoglobulins, also known as antibodies, are a type of protein in nature classified under gamma globulins.

The other options are incorrect:

• Alpha Globulin: Alpha globulins mainly consist of transport proteins like alpha-1 antitrypsin and haptoglobin. They are not associated with immunoglobulins.
• Beta Globulin: Beta globulins include various proteins like transferrin and complement proteins, but they do not encompass immunoglobulins.
• Delta Globulin: Delta globulins are not a recognized category of globulins in the context of protein classification. It’s not associated with immunoglobulins.

Answer:

Immunoglobulin M (IgM) is the only immunoglobulin that appears as a pentamer structure.

The other options are incorrect:

• IgA: IgA typically appears as a dimer, not a pentamer. It is found in mucosal secretions such as tears, saliva, and mucous membranes.
• IgE: IgE is a monomer and does not appear as a pentamer. It is involved in allergic responses and protection against parasites.
• IgG: IgG is a monomer and is the most abundant immunoglobulin in circulation. It does not form pentamers.

Answer: B – Cells

B-cells are responsible for producing antibodies, which are a key component of humoral immunity.

The other options are incorrect:

• T-Cells: T-cells primarily mediate cell-mediated immunity, rather than humoral immunity. They are involved in coordinating the immune response and killing infected cells.
• Monocytes: Monocytes are a type of white blood cell that can differentiate into macrophages or dendritic cells. They are involved in phagocytosis and antigen presentation, but they do not directly participate in humoral immunity.
• Macrophages: Macrophages are phagocytic cells that play a role in innate immunity and antigen presentation to T-cells. While they interact with B-cells in the immune response, they are not primarily responsible for humoral immunity.

Answer: Salminella

The Widal test is a serological test used to diagnose infections caused by Salmonella, particularly typhoid and paratyphoid fever.

The other options are incorrect:

• Shigella: The Widal test is not used to diagnose infections caused by Shigella bacteria. Shigella is associated with bacillary dysentery.
• E. coli: The Widal test is not used to diagnose E. coli infections. E. coli is associated with various gastrointestinal infections.
• Proteus: The Widal test is not used to diagnose Proteus infections. Proteus is associated with urinary tract infections and other conditions.

Answer: Remove Unbound serum globulin

Washing the red cells removes any unbound serum globulin, preventing nonspecific binding of the antiglobulin reagent and ensuring accurate results in tests like the Coombs test.

The other options are incorrect:

• Remove traces of bacterial protein: Washing red cells is not primarily done to remove bacterial protein but to remove unbound serum globulin.
• Wash away traces of free hemoglobin: The primary purpose of washing red cells is to remove unbound serum globulin, not free hemoglobin.
• Expose additional antigen site: Washing red cells does not expose additional antigen sites but rather removes unbound serum globulin to prevent nonspecific binding of the antiglobulin reagent.

Answer: Innate Immunity

Innate immunity refers to the body’s natural defense mechanisms that are present from birth and provide immediate, nonspecific protection against pathogens.

The other options are incorrect:

• Acquired Immunity: Acquired immunity, also known as adaptive immunity, develops over time in response to exposure to pathogens or vaccines. It is not synonymous with natural immunity.
• Adoptive Immunity: Adoptive immunity refers to immunity transferred from one individual to another, such as through transfer of antibodies or T cells. It is not another name for natural immunity.
• Cellular Immunity: Cellular immunity, also known as cell-mediated immunity, is a specific component of the immune system mediated by T cells. It is not synonymous with natural immunity.

Answer: FTA-Abs

FTA-Abs is a highly specific test that detects antibodies directly against Treponema pallidum, the bacteria that causes syphilis. This makes it very reliable for confirming a syphilis diagnosis, especially when combined with a positive non-treponemal test (like RPR or VDRL).

The other options are incorrect:

• RPR (Rapid Plasma Reagin): While RPR is a common screening test for syphilis, it is not as specific as TPHA. It can produce false-positive results due to cross-reactivity with other conditions.
• VDRL (Venereal Disease Research Laboratory): VDRL is another screening test for syphilis, but like RPR, it is not as specific as TPHA and can produce false-positive results.
• TPHA (Treponema Pallidum Hemagglutination): This is another treponemal test, but it’s less specific than FTA-Abs. It can also give false positive results in certain situations.

Answer: Purified Protein Derivatives

The Mantoux test, also known as the tuberculin skin test, involves injecting purified protein derivatives (PPD) derived from Mycobacterium tuberculosis into the skin to assess for a delayed-type hypersensitivity reaction indicative of tuberculosis infection.

The other options are incorrect:

• Lipoprotein: Lipoproteins are molecules that transport fats in the blood and are not used in the Mantoux test.
• Carbohydrate: Carbohydrates are sugars and starches and have no role in the Mantoux test.
• Histidine-rich protein II: This protein is found in some bacteria but is not specific to Mycobacterium tuberculosis and wouldn’t be used for the Mantoux test.

Answer: HIV

p24 antigen is a protein found on the surface of the Human Immunodeficiency Virus (HIV). It’s present in the blood during the early stages of HIV infection, before the body produces antibodies detectable in standard tests.

The other options are incorrect:

• HbsAg: This antigen (Hepatitis B surface antigen) is a marker for Hepatitis B infection, a different virus entirely from HIV.
• HCV: Hepatitis C virus (HCV) doesn’t have a p24 antigen. It has its own specific antigens used for diagnosis.
• Rabies Virus: Rabies is a different virus with no relation to HIV. It has its own diagnostic tests that don’t involve p24 antigen.

Answer: HbsAg

HbsAg is the most widely known name for the “Australia antigen.” It’s a protein found on the outer envelope of the Hepatitis B virus (HBV). The presence of HbsAg in the blood indicates current or recent HBV infection.

The other options are incorrect:

• p24 Antigen: This antigen is associated with HIV, the virus that causes AIDS.
• HCsAg (Hepatitis C surface antigen): This antigen is specific to the Hepatitis C virus (HCV), a different virus than HBV.
• HEsAg (Hepatitis B e antigen): This is another antigen of the Hepatitis B virus, but it signifies ongoing viral replication and infectivity, unlike HbsAg which can be present during both acute and chronic stages of infection.

Answer: Hapten

Haptens are small molecules that can elicit an immune response only when attached to a larger carrier molecule. They have low molecular weights and are not immunogenic by themselves but can become immunogenic when bound to proteins.

The other options are incorrect:

• H Antigen: H antigen can refer to various antigens depending on the context. In some cases, it might be a larger molecule with a higher molecular weight.
• Histidine Rich Protein: This protein can vary in size depending on the specific type, but it’s generally not considered a low molecular weight molecule.
• ABO Antigen: ABO antigens, present on red blood cells, are complex carbohydrates with a higher molecular weight than haptens.

Answer: ASO test

The ASO test is primarily used to diagnose streptococcal infections, particularly those caused by Group A Streptococcus, such as strep throat and rheumatic fever. It is not used for diagnosing enteric fever, which is caused by Salmonella typhi or Salmonella paratyphi bacteria.

The other options are incorrect:

• Widal test: While the Widal test has limitations and is not the most reliable method anymore, it can still be used as a preliminary test for detecting antibodies against Salmonella typhi, the bacteria that causes enteric fever.
• Weil-Felix Test: The Weil-Felix test is a serological test used to diagnose certain rickettsial infections, such as Rocky Mountain spotted fever and typhus fever. It is not specific for enteric fever.
• Elek’s Test: Elek’s test is used to detect the production of diphtheria toxin by Corynebacterium diphtheriae bacteria. It is not used for diagnosing enteric fever.

Answer: 2

Immunoglobulin molecules, also known as antibodies, consist of two identical heavy chains and two identical light chains. The light chains can be of two types: kappa (κ) or lambda (λ), which are determined by genetic rearrangements during B-cell development.

The other options are incorrect:

• 5: There are not five types of light chains in immunoglobulin molecules; there are only two types: kappa (κ) and lambda (λ).
• 1: There is not only one type of light chain in immunoglobulin molecules; there are two types: kappa (κ) and lambda (λ).
• 3: While there might be variations and subclasses within the two main types, the overall categorization consists of kappa and lambda light chains.

Answer: IgM

IgM antibodies are primarily found in the bloodstream and lymph fluid. They are structurally arranged as pentamers, consisting of five monomeric subunits joined by a J chain.

The other options are incorrect:

• IgG (Immunoglobulin G): The most abundant antibody in the blood, IgG exists as a monomer (single unit).
• IgA (Immunoglobulin A): IgA can be found in two forms: monomeric in blood and dimeric (two subunits linked together) in mucosal secretions.
• IgD (Immunoglobulin D): IgD is present in very small amounts in the blood and exists as a monomer.

Answer: H Antigen

Flagler antigen is another name for H antigen in the context of Salmonella typhi bacteria, the cause of enteric fever. H antigens are lipopolysaccharide molecules located on the flagella (hair-like structures) of some bacteria, including Salmonella typhi. They contribute to the specific strain variation and virulence of the bacteria.

The other options are incorrect:

• O Antigen: O antigens are also part of the lipopolysaccharide structure of bacteria but are located on the outer cell wall, not the flagella. They play a role in serological classification of bacteria.
• Vi Antigen: Vi antigen is a capsular polysaccharide antigen found in some strains of Salmonella typhi. It can make the bacteria more resistant to phagocytosis by the immune system.
• Flagella: While Flagella is the structure where H antigen resides, it’s not the specific name for the antigen itself.

Answer: immunology

The field of immunology focuses on the study of the immune system, including antigen-antibody interactions, immune responses, and the mechanisms of immunity and tolerance.

The other options are incorrect:

• Hematology: Hematology primarily deals with the study of blood cells, blood-forming organs, and blood disorders, not specifically antigen-antibody reactions.
• Microbiology: Microbiology focuses on the study of microorganisms such as bacteria, viruses, fungi, and parasites. While it may involve some aspects of immunology, it is not specifically dedicated to studying antigen-antibody reactions.
• Chemistry: This department deals with the composition, structure, and properties of matter. While some techniques used in immunology might involve chemical principles, the overall focus of immunology is on the biological aspects of the immune system and its response to antigens.

Answer: releasing the safety bulb will draw liquid into the pipette

Squeezing the top bulb of a serological pipette draws liquid in, not the safety bulb. The safety bulb is there to prevent accidental overfilling by creating an air cushion.

The other options are incorrect:

• The pipette tip is below the liquid surface when filling: This is actually a correct step. The tip should be submerged just below the liquid surface to ensure proper filling without air bubbles.
• It delivers total capacity or multiple volumes: Serological pipettes can be used to deliver the entire capacity marked on the pipette or specific volumes depending on the graduation markings.
• The last portion of the pipette contents is discarded in a separate container: This is a good practice to avoid transferring any residual liquid that might cause contamination, especially when dealing with hazardous or infectious materials.

Answer: IgG

The secondary immune response is characterized by a faster and stronger response to a previously encountered antigen. This includes the production of a higher concentration of antibodies with increased affinity for the antigen. The predominant antibody produced in the secondary response is IgG.

The other options are incorrect:

• IgM: While IgM is the first antibody produced in the primary immune response, its level typically decreases during the secondary response as IgG takes over.
• IgA: IgA can be present in the secondary response, but it’s not the dominant type.
• IgD: IgD plays a minor role in the immune system and is not a major contributor to the secondary antibody response.

Answer: 37 °C

IgG antibodies typically react optimally at body temperature, which is around 37°C. This is because the antigen-antibody interaction is most efficient at this temperature, mimicking the conditions within the body where the immune response occurs.

The other options are incorrect:

• 4°C: 4°C is commonly used for storage of biological samples but is not the optimum temperature for reactivity of IgG antibodies. At 4°C, antibody-antigen reactions are typically slowed down.
• -4°C: -4°C is below freezing temperature and is not suitable for antibody-antigen reactions. It is used for long-term storage of biological samples under frozen conditions.
• 25°C: This temperature might be closer to optimal than very cold temperatures, but it’s still not ideal for IgG reactivity.

Answer: Production of Antibody

When the immune system detects the presence of foreign particles, such as pathogens or antigens, it initiates an immune response, which includes the production of antibodies by B lymphocytes. These antibodies specifically target and neutralize the foreign particles, helping to eliminate them from the body.

The other options are incorrect:

• Production of Antigen: Antigens are the foreign molecules themselves, not something the body produces. The body produces antibodies in response to the presence of antigens.
• 1 & 2 Both: This option is incorrect because the production of antigen does not occur when a foreign particle enters the body. Only the production of antibodies (option 1) occurs in response to the presence of foreign particles.

Answer: Salmonella

The Widal test is primarily used to diagnose infection with Salmonella typhi, the bacteria that causes typhoid fever. It detects the presence of antibodies produced by the body in response to the Salmonella antigens.

The other options are incorrect:

• Vibrio Cholera: This bacterium causes cholera, and a different diagnostic test is used for its detection.
• Staphylococcus: This is a type of bacteria that can cause various infections, but the Widal test is not specific for diagnosing Staphylococcus infections.
• Shigella: The Widal test is not used for Shigella bacteria. Shigella species cause bacillary dysentery, and their diagnosis typically involves stool culture or other specific laboratory tests.

Answer: 96 Wells

The standard ELISA (Enzyme-Linked Immunosorbent Assay) plate format has 96 wells. This is the most widely used and commercially available format, allowing for a high number of samples or replicates to be tested simultaneously in a compact and efficient manner.

The other options are incorrect:

• 98 Wells: ELISA plates typically do not come in a format with 98 wells. The standard format is 96 wells.
• 94 Wells: ELISA plates typically do not come in a format with 94 wells. The standard format is 96 wells.
• 108 Wells: ELISA plates typically do not come in a format with 108 wells. The standard format is 96 wells.

Answer: CD4

HIV specifically targets and infects CD4 T cells, a type of white blood cell crucial for the immune system’s ability to fight off infections. Over time, as HIV replicates and destroys CD4 cells, the number of CD4 cells in an HIV positive patient will decrease. This weakens the immune system and makes the person more susceptible to opportunistic infections.

The other options are incorrect:

• CD8: While the number of CD8 cells might fluctuate in HIV infection, they are not the primary target of HIV and typically don’t show a significant decrease.
• Small Lymphocyte: This is a broad term that can encompass various types of white blood cells, including CD4 and CD8 cells. A decrease in CD4 cells would be reflected in a decrease in small lymphocyte count, but it’s not the most specific term.
• All of the Above: While HIV can affect the immune system overall, the primary decrease in cell count is seen in CD4 cells.

Answer: Avidity

Avidity is the measure of the overall strength of the interaction between an antigen and its corresponding antibodies. It takes into account both the affinity (strength of individual antibody-antigen binding) and the number of binding sites involved (valence of both antigen and antibody).

The other options are incorrect:

• Affinity: Affinity refers to the strength of a single binding site between an antibody and its specific epitope (target site) on an antigen. It doesn’t consider the overall interaction strength involving multiple binding sites.
• Colorimeter: A colorimeter is a device used to measure the absorbance of light by a solution at a specific wavelength. It is not specifically used to measure the strength of antigen-antibody interactions.
• ELISA (Enzyme-Linked Immunosorbent Assay): ELISA is a technique used to detect and quantify the presence of antigens or antibodies in a sample. While some variations of ELISA can be used to assess avidity, ELISA itself is a broader technique and doesn’t solely measure avidity.

Answer: IgA

Breast milk contains several types of antibodies, but the most prominent one is IgA (Immunoglobulin A). IgA plays a crucial role in protecting newborns and infants from infections, especially in the respiratory and digestive tracts.

The other options are incorrect:

• IgM: While present in small amounts in colostrum (the first milk produced after childbirth), IgM levels in breast milk decrease significantly after that.
• IgG: Some IgG antibodies can be passed from mother to baby through the placenta before birth, but IgG levels in breast milk are generally lower than IgA.
• IgE: IgE is associated with allergic responses and is not a major component of breast milk.

Answer: Antibody

A paratope is the specific part of an antibody that binds to an antigen’s epitope. It is located in the variable region of the antibody and is responsible for the antibody’s specificity to its corresponding antigen.

The other options are incorrect:

• Antigen: An antigen is the foreign molecule that the antibody binds to. It has a specific region called the epitope, which is the target for the antibody’s paratope.
• Both on 1 and 2: The paratope is only located on the antibody, not on both the antibody and antigen.
• Epitope: The epitope is the specific region on the antigen that the antibody’s paratope recognizes and binds to. It’s essentially the “landing site” for the antibody on the antigen.

Answer: Covalent Bond

Antigen-antibody interactions are primarily non-covalent and include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals forces. These interactions allow the antigen-antibody binding to be reversible, which is crucial for immune function.

The other options are incorrect:

• Hydrogen Bond: Hydrogen bonds are weak bonds formed between a hydrogen atom and an electronegative atom, and they are part of antigen-antibody interactions.
• Hydrophobic Interactions: These occur between hydrophobic regions of the antigen and antibody, contributing to the stability of the antigen-antibody complex.
• Ionic: Ionic bonds, also known as electrostatic interactions, occur between oppositely charged groups on the antigen and antibody, playing a significant role in their binding.

Answer: Postzone

The Postzone phenomenon occurs in certain immunological assays when the concentration of antibodies exceeds the optimal level for antigen-antibody binding. In this situation, excess antibodies saturate available antigen binding sites, leading to decreased visible reaction signals.

The other options are incorrect:

• Prozone: The Prozone phenomenon occurs when the concentration of antibodies is too high, resulting in reduced antigen-antibody complex formation and false-negative results.
• Zone of equivalence: The Zone of Equivalence is the point in a precipitation reaction where antigen and antibody are present in optimal proportions for maximal complex formation.
• Without Zone: This option does not accurately describe any recognized phenomenon in immunological assays.

Answer: Passive Natural Immunity

Passive Natural Immunity refers to the transfer of pre-formed antibodies from mother to baby. This transfer can occur across the placenta during pregnancy (placental transfer) or through breastfeeding (transfer of maternal antibodies in breast milk).

The other options are incorrect:

• Active Natural Immunity: This occurs when an individual develops their own immunity by being exposed to a pathogen and producing antibodies in response.
• Passive Artificial Immunity: This involves receiving antibodies from another source, such as immune globulin injections, but these are not naturally produced antibodies from a mother.
• Active Artificial Immunity: This is achieved through vaccination, which stimulates the body to produce its own antibodies.

Answer: All of above

In most countries, several tests are mandatory screening procedures before blood transfusion to ensure the safety of both the donor and recipient. These tests aim to minimize the risk of transmitting infectious diseases through contaminated blood.

• Hepatitis C: This test detects the presence of Hepatitis C virus (HCV) which can cause chronic liver disease.
• HIV: This test detects the Human Immunodeficiency Virus, the virus that causes AIDS.
• Malaria: While not as common as the others depending on the region, some areas may also screen for malaria parasites in donated blood to prevent transmission through transfusion.

Answer: IL-3

IL-3 is a multilineage cytokine, meaning it acts on and stimulates the development of multiple hematopoietic cell lineages. In simpler terms, it helps promote the growth and differentiation of various types of blood cells from hematopoietic stem cells.

The other options are incorrect:

• IL-1: IL-1 is primarily involved in inflammatory responses and has a more targeted effect on certain cell types.
• IL-2: IL-2 is crucial for T lymphocyte activation and proliferation, but its influence is more specific to T cells.
• IL-4: IL-4 plays a role in B cell activation and differentiation but doesn’t have the broad effect on multiple lineages like IL-3.

Answer: 1_g’ A

IgA is the predominant immunoglobulin found in mucosal secretions, such as saliva, tears, respiratory and gastrointestinal tract secretions, and breast milk. It plays a crucial role in providing local immunity by neutralizing pathogens at mucosal surfaces, preventing their entry and colonization.

The other options are incorrect:

• IgG (Immunoglobulin G): IgG is the most abundant antibody in the blood and plays a central role in systemic (whole-body) immunity.
• IgM (Immunoglobulin M): IgM is the first antibody produced in a primary immune response but is not a major player in local immunity.
• IgD (Immunoglobulin D): IgD is present in very small amounts and its specific function in the immune system is not fully understood. It’s not a major contributor to local immunity.

Answer: Syphilis

RPR (Rapid Plasma Reagin) and VDRL (Venereal Disease Research Laboratory) tests are both non-treponemal serological tests used for screening and diagnosing syphilis. They detect antibodies produced by the body in response to the Treponema pallidum bacteria, the causative agent of syphilis.

The other options are incorrect:

• AIDS: AIDS is the end stage of HIV infection. While some sexually transmitted infections can increase the risk of HIV infection, RPR and VDRL tests are not used for diagnosing AIDS or HIV.
• Hepatitis: This refers to inflammation of the liver caused by various viruses. Hepatitis has specific tests depending on the type of virus suspected, and RPR/VDRL are not used for hepatitis diagnosis.
• Malaria: This is a mosquito-borne parasitic infection. It has its own diagnostic tests that involve detecting the malaria parasite in blood.

Answer: Infectious Mononucleosis ✅

LE cells (neutrophils/macrophages engulfing nuclear debris) are absent in IM. IM is caused by EBV and presents with atypical lymphocytes, not autoantibody-driven nuclear phagocytosis.

The other options are incorrect:

1. Systemic Lupus Erythematosus (SLE) ❌
   LE cells are classically seen in SLE due to autoantibodies (e.g., anti-dsDNA) targeting nuclear material.
2. Rheumatoid Arthritis (RA) ❌
   LE cells are not typical in classic RA. Rarely seen in overlap syndromes (e.g., rhupus), but not in isolated RA.
3. Collagen Disorders ❌
   Collagen disorders include SLE (where LE cells are present). Thus, LE cells can occur in this broad category.

Answer: TPHA

TPHA is a confirmatory test used to detect antibodies against Treponema pallidum, the bacterium that causes syphilis. It is highly specific and is often used to confirm positive results from other screening tests for syphilis.

The other options are incorrect:

• RPR (Rapid Plasma Reagin): RPR is a screening test for syphilis that detects nonspecific antibodies present in the bloodstream during syphilis infection. It is not specific for syphilis and may yield false-positive results in certain conditions.
• TRUST (Toluidine Red Unheated Serum Test): TRUST is another screening test for syphilis that detects nonspecific antibodies. Like RPR, it is not specific for syphilis and may yield false-positive results.
• VDRL (Venereal Disease Research Laboratory): VDRL is a screening test for syphilis that detects nonspecific antibodies. It is not specific for syphilis and may yield false-positive results in certain conditions.

Answer: Typhoid fever

The Widal test is a serological test used to diagnose enteric fever caused by Salmonella typhi and Salmonella paratyphi. It detects antibodies produced in response to these bacteria and aids in the diagnosis of typhoid fever and paratyphoid fever.

The other options are incorrect:

• Typhoid fever: Typhoid fever is a form of enteric fever caused by Salmonella typhi. Therefore, the Widal test is appropriate for diagnosing typhoid fever.
• Paratyphoid fever: Paratyphoid fever is another form of enteric fever caused by Salmonella paratyphi. The Widal test is also used to diagnose paratyphoid fever.
• Brucellosis: Brucellosis is a bacterial infection caused by various species of the genus Brucella. The Widal test is not used for diagnosing brucellosis; it is specifically for diagnosing enteric fever caused by Salmonella species.

Answer: 200 IU/nl

A significant titer of ASO (Antistreptolysin O) test by latex agglutination indicates a recent or past streptococcal infection. While the exact cut-off value can vary slightly between labs, generally, titers above 200 IU/mL are considered indicative of a possible streptococcal infection.

The other options are incorrect:

• <200 IU/mL: Titers below 200 IU/mL are typically considered normal or inconclusive for a recent streptococcal infection.
• >10 IU/mL: This value might be too low to be significant. While some labs might use slightly different cut-offs, 10 IU/mL generally falls within the normal range.
• <10 IU/mL: Similar to <200 IU/mL, titers this low are unlikely to indicate a recent streptococcal infection.

Answer: Chemluminescence assay

Chemiluminescence assay is considered the best diagnostic assay for infections and autoimmune disease parameters because it offers high sensitivity, specificity, and a wide dynamic range. It utilizes the emission of light resulting from a chemical reaction to detect the presence of specific molecules, making it highly suitable for detecting low concentrations of analytes in complex samples.

The other options are incorrect:

• EIA (Enzyme Immunoassay): EIA is a widely used assay technique, but it may not offer the same level of sensitivity and specificity as chemiluminescence assays. It relies on enzyme-conjugated antibodies to detect the presence of specific antigens or antibodies.
• RIA (Radioimmunoassay): RIA involves the use of radioactive isotopes to label antigens or antibodies for detection. While it was once a common technique, concerns about radioactivity and disposal of radioactive waste have led to its decline in favor of safer alternatives like chemiluminescence assays.
• Fluorescence Immunoassay: Fluorescence immunoassays utilize fluorescence-labeled antibodies or antigens for detection. While they offer high sensitivity, they may not always provide the same level of sensitivity and dynamic range as chemiluminescence assays.