Immunology and Serology MCQs with Answer and Explanations | Chapter 9

Answer: Formalin killed

The pertussis vaccine uses an inactivated (killed) form of the Bordetella pertussis bacteria to stimulate the body’s immune response without causing whooping cough itself. Formalin is a common inactivating agent used in vaccines.

The other options are incorrect:

• Heat killed: While heat can be used to inactivate some viruses, it’s not typically used for bacteria like Bordetella pertussis because it can damage important antigens (molecules the immune system targets).
• Attenuated: Attenuated vaccines use a weakened or modified version of a live virus to create immunity. Pertussis vaccines don’t use this approach.
• Live: Live vaccines contain a weakened but live virus that stimulates the immune system. Pertussis vaccines don’t use live bacteria due to the risk of causing the actual illness.

Answer: Mixed vaccine

A mixed vaccine combines multiple immunizing agents targeting different diseases or strains of the same disease in a single shot. This is a convenient way to provide protection against several illnesses at once.

The other options are incorrect:

• Cellular vaccine: These vaccines are still under development and not widely used. They involve using a person’s own immune cells to fight disease.
• Recombinant vaccine: These vaccines use genetically modified organisms to produce specific antigens. While some combination vaccines might use recombinant technology, it’s not the defining characteristic of a mixed vaccine.
• Toxoid vaccine: These vaccines contain weakened or inactivated toxins produced by bacteria. While some mixed vaccines might include toxoids, they can also include whole inactivated bacteria or viral particles.

Answer: Inactivated (killed) vaccine

Inactivated (killed) vaccines contain microbes (bacteria or viruses) that have been rendered inactive through methods like heat, chemicals, or radiation. These vaccines cannot replicate and cause disease, but they still stimulate the immune system to develop immunity.

The other options are incorrect:

• Attenuated vaccines: These vaccines use a weakened or modified version of a live virus or bacteria. While weakened, they can still replicate to a limited extent, which creates a strong immune response.
• Autogenous vaccine: This is a personalized vaccine created from a specific strain of bacteria isolated from a particular patient. It’s very rare and not commonly used.
• None of these: At least some vaccines are prepared from killed microbes, making this option incorrect.

Answer: Diphtheria, Tetanus & pertusis

DPT stands for Diphtheria, Tetanus, and Pertussis (whooping cough). This combination vaccine protects against all three of these infectious diseases.

The other options are incorrect:

• Diphtheria, Tetanus: While DPT protects against both diphtheria and tetanus, it also protects against pertussis, making this option incomplete.
• Diphtheria, Pertussis: Similar to above, DPT offers protection against both diphtheria and pertussis, but it’s missing tetanus coverage.
• None of these: DPT is a well-established vaccine for the mentioned diseases, making this option incorrect.

Answer: None of these

Animals are not naturally immune to infections caused by either Vibrio cholerae (V. cholera) or Salmonella typhi (S. typhosa); these infections primarily affect humans.

The other options are incorrect:

• V. Cholera: As explained above, some animals can be susceptible to V. cholera infection.
• S. typphosa: Similar to V. cholera, S. typphosa can infect various animals.
• Both a and b: This combines the incorrect options a and b.

Answer: Artificial active immunity

Artificial active immunity is acquired when a person is inoculated with a vaccine containing living organisms of attenuated (weakened) virulence, stimulating the body’s immune response.

The other options are incorrect:

• Passive immunity: This type of immunity involves receiving antibodies directly from another source, like breast milk from a mother or immune globulin injections. It provides short-term protection.
• Natural active immunity: Natural active immunity is acquired through natural exposure to a pathogen, leading to an immune response, not through vaccination.
• Local immunity: Local immunity refers to immunity at the site of infection, such as mucosal surfaces, and is not specifically related to the inoculation of attenuated organisms.

Answer: 2 – 3 months

Passive immunity provides short-term protection because the borrowed antibodies from another source (like breast milk or immune globulin injections) gradually degrade over time. This typically lasts for around 2-3 months.

The other options are incorrect:

• 10 days: This is too short of a timeframe for most passive immunity derived from antibodies.
• 10 years: This duration is more characteristic of long-term immunity obtained through active immunity (vaccination or natural infection).
• None of the above: Passive immunity does offer some protection, though temporary.

Answer: All of these

All three options can be markers helpful in detecting anti-immunity (also known as autoimmune diseases):

• Hyper gamma globulinaemia: This refers to an abnormally high level of gamma globulins in the blood. Gamma globulins are proteins, including antibodies, produced by the immune system. In autoimmune diseases, the immune system overproduces antibodies that attack healthy tissues.
• Circulating antibodies: The presence of autoantibodies, which are antibodies mistakenly produced by the immune system that target the body’s own tissues, is a hallmark of many autoimmune diseases.
• Response to cortisone: Corticosteroids like cortisone are immunosuppressants that suppress the immune system’s activity. While not a definitive test, a positive response to cortisone treatment can sometimes help support an autoimmune diagnosis because it can lessen the symptoms caused by the overactive immune system.

Answer: All of these

An antigen is any substance that the immune system recognizes as foreign and can trigger an immune response. All the listed options can be antigens under the right circumstances.

• Egg albumin: The protein component of egg whites (albumin) can be antigenic for some people, leading to an egg allergy.
• RBC and serum: Red blood cells (RBCs) can have specific surface molecules (antigens) that are recognized as foreign by the immune system if someone receives a blood transfusion with an incompatible blood type. Serum, the liquid portion of blood, can also contain proteins that act as antigens in certain situations.
• Vegetable protein: Some people can develop allergies to specific vegetable proteins, such as those found in peanuts, soy, or gluten.
• Snake venom: Snake venom contains proteins and other molecules that are potent antigens, leading to an immune response.

Answer: Passive

An antitoxin is a substance containing antibodies specifically designed to neutralize a specific toxin produced by bacteria or other pathogens. Antitoxins are used for passive immunization.

The other options are incorrect:

• Active: Active immunization involves stimulating the body’s own immune response, not introducing pre-made antibodies.
• Both a and b: Antitoxins are primarily used for passive immunization.
• None of these: Antitoxins do have a specific use in passive immunization.

Answer: All of these

All of the listed factors contribute to the pathology of asthma, allergic rhinitis, and urticaria, although the exact mechanisms may differ slightly between these conditions. Here’s a breakdown:

• Local vasodilation: This refers to the widening of blood vessels in the affected tissues. In all three conditions, this can lead to swelling, redness, and increased mucus production.
• Increased capillary secretion: Capillaries are tiny blood vessels. Increased secretion from these capillaries can contribute to swelling and inflammation in the affected areas.
• Excess eosinophils in tissue secretion and blood: Eosinophils are a type of white blood cell involved in allergic reactions. In these conditions, there’s an increase in eosinophils, which contribute to inflammation and tissue damage.

Answer: Schick tests

The Schick test is a historical skin test used to determine susceptibility to diphtheria toxin. It involved injecting a small amount of diluted diphtheria toxin under the skin. If the person lacked immunity (antibodies) against the toxin, a localized reaction would develop at the injection site within 48-72 hours.

The other options are incorrect:

• Dick test: The Dick test was used to diagnose scarlet fever, not diphtheria. It detected antibodies against a specific toxin produced by some strains of Streptococcus pyogenes, the bacteria causing scarlet fever.
• V-P test: The VDRL (Venereal Disease Research Laboratory) test is used to screen for syphilis, a sexually transmitted infection. It doesn’t assess diphtheria susceptibility.
• Precipitin test: Precipitin tests are used to detect antibodies against various antigens, but they are not specific for diphtheria toxin.

Answer: Display cytotoxic effect on tumour cell

Natural killer (NK) cells are a type of lymphocyte that belongs to the innate immune system. They are capable of recognizing and killing tumor cells and virus-infected cells without prior antigen exposure.

The other options are incorrect:

• Belongs to B-cell lineage: B cells are responsible for producing antibodies, a different immune response mechanism.
• Belongs to T-cell lineage: As mentioned earlier, NK cells have a separate lineage from B and T cells.
• Require previous antigen exposure for activation: NK cells can act without prior exposure, unlike T cells that require antigen presentation.

Answer: IgE

Immunoglobulin E (IgE) is associated with anaphylactic and delayed hypersensitivity reactions. It plays a central role in allergic reactions by triggering the release of histamine and other inflammatory mediators from mast cells and basophils.

The other options are incorrect:

• IgA: IgA is primarily found in mucosal secretions like saliva and tears and plays a role in protecting these surfaces from pathogens. While it can be involved in some allergic reactions, it’s not typically associated with anaphylaxis.
• IgD: The exact function of IgD is still being researched, but it’s believed to play a minor role in the immune system. It’s not a major contributor to anaphylaxis.
• IgM: IgM is the first antibody produced by B cells in response to a new antigen. It’s essential for the initial immune response but not directly linked to anaphylaxis.

Answer: Both b & c

Patients with AIDS commonly exhibit decreased CD4+ T cells, which are crucial for coordinating the immune response. Additionally, they often have increased CD8+ T cells, as these cells attempt to compensate for the loss of CD4+ T cells. Hypergammaglobulinemia, or increased levels of gamma globulins (antibodies), can also be observed as part of the immune response to HIV infection.

The other options are incorrect:

• Decreased CD4 + T cells: This statement is actually a correct immune abnormality seen in patients with AIDS, so it doesn’t belong in the list of incorrect options.

Answer: IgE

IgE is the immunoglobulin that cannot activate complement. Instead, it primarily mediates allergic reactions by binding to mast cells and basophils, triggering the release of histamine and other inflammatory mediators.

The other options are incorrect:

• IgM: IgM is a potent activator of the complement system, playing a crucial role in the classical pathway of complement activation.
• IgA: IgA can activate the complement system through the alternative pathway, especially when it forms immune complexes.
• IgG: IgG is the most abundant immunoglobulin in serum and can activate complement through both the classical and alternative pathways.

Answer: IgE

The Prausnitz-Küstner (P-K) reaction is generated by IgE antibodies. It is an in vivo skin test used to detect allergic hypersensitivity to specific antigens.

The other options are incorrect:

• IgA: IgA is the main antibody found in mucosal secretions and plays a role in protecting these surfaces from pathogens. It’s not typically involved in the PK reaction.
• IgG: IgG is the most abundant antibody and plays a central role in the immune response by neutralizing pathogens and activating other immune mechanisms. It’s not directly involved in the PK reaction.
• IgD: The exact function of IgD is still being researched, but it’s believed to play a minor role in the immune system. It’s not involved in the PK reaction.

Answer: IgE

Elevated levels of IgE antibodies are found in asthma. IgE plays a central role in allergic reactions, including those associated with asthma, by triggering the release of histamine and other inflammatory mediators from mast cells and basophils.

The other options are incorrect:

• IgA: IgA is the main antibody found in mucosal secretions and plays a role in protecting surfaces like the respiratory tract from pathogens. While it might be involved in some aspects of asthma, it’s not typically elevated in the context of allergic asthma.
• IgM: IgM is one of the first antibodies produced in a primary immune response and is not typically associated with allergic asthma.
• IgD: The exact function of IgD is still being researched, but it’s believed to play a minor role in the immune system and is not a major contributor to allergic asthma.

Answer: A compliment fixation

Both IgM and IgG antibodies can fix complement, which is a crucial step in the immune response against pathogens.

The other options are incorrect:

• Placental transport: IgG antibodies can cross the placenta, providing passive immunity to the fetus, but IgM antibodies typically cannot cross the placenta.
• Heat stability at 56oC: IgG antibodies are stable at higher temperatures (such as 56°C) due to their structure, but IgM antibodies are more sensitive to heat.
• Sedimentation coefficient: IgM antibodies typically have a higher sedimentation coefficient compared to IgG antibodies, reflecting their larger size and pentameric structure.
• a

Answer: All of these

Cell-mediated immunity can be identified by all of the listed methods:

• Sheep red blood cell (SRBC) rosette formation: This test measures the ability of T lymphocytes (a key cell in cell-mediated immunity) to bind to sheep red blood cells. In a positive test, T cells form rosettes around the sheep red blood cells, indicating the presence of functional T lymphocytes.
• Microphage migration inhibition factor (MIF) assay: MIF is a substance produced by activated T cells that can inhibit the migration of macrophages. This test measures the production of MIF, which indirectly reflects T cell activity.
• Skin test for delayed hypersensitivity: This test involves injecting a small amount of a specific antigen into the skin. In individuals with cell-mediated immunity to that antigen, a localized area of swelling and induration (hardening) develops within 24-48 hours, indicating a T cell-mediated reaction.

Answer: Alkaline phosphate

In the ELISA (Enzyme-Linked Immunosorbent Assay) technique, antibodies are often labeled with enzymes such as alkaline phosphatase. These enzymes produce a detectable signal when they react with their substrate, indicating the presence of the target antigen.

The other options are incorrect:

• Acridine orange: Acridine orange is a fluorescent dye used for staining nucleic acids (DNA and RNA) and is not typically used for labeling antibodies in ELISA.
• Neutral red: Similar to acridine orange, neutral red is another dye used for staining cells and tissues and not for antibody labeling in ELISA.
• Bromothymol blue: Bromothymol blue is a pH indicator and not an enzyme used in ELISA.

Answer: Agamma globulinemia

Agammaglobulinemia is a genetic disease characterized by a total or partial inability to synthesize immunoglobulins (antibodies), which are a major component of the globulin fraction in blood. This deficiency leads to a weakened immune system and recurrent infections.

The other options are incorrect:

• Apitosis: Apitosis is not a recognized medical term. It might be a misspelling of apoptosis, which is a programmed cell death process not directly related to immunoglobulin deficiency.
• Gammaglobulinemia: This term itself refers to the presence of globulins in the blood. It wouldn’t specify an inability to synthesize them.
• Sickle-cell anemia: Sickle-cell anemia is a genetic disease affecting red blood cells, not immunoglobulin production. It’s characterized by abnormal hemoglobin causing misshapen red blood cells.

Answer: Both a and b (Proteins and Glycoproteins)

Viral antigens are primarily composed of two main types of molecules.

• Proteins: Many viruses have protein capsids (shells) that enclose their genetic material. These capsid proteins often serve as important viral antigens, allowing the immune system to recognize and target the virus.
• Glycoproteins: Some viruses have envelope membranes surrounding the capsid. These envelopes contain embedded glycoproteins (proteins with sugar molecules attached). These glycoproteins can also be important viral antigens.

Incorrect Option:

• Lipoproteins: While some viruses may incorporate lipids (fats) into their envelopes, lipoproteins (complexes of proteins and lipids) are not the primary structural components or antigens of most viruses.

Answer: AIDS

ELISA (Enzyme-Linked Immunosorbent Assay) test is commonly used for the identification of antibodies to HIV (Human Immunodeficiency Virus), aiding in the diagnosis of AIDS (Acquired Immunodeficiency Syndrome).

The other options are incorrect:

• Janudice: Although some tests might use ELISA principles, ELISA is not the primary diagnostic tool for jaundice, which is a condition characterized by yellowing of the skin and eyes due to excess bilirubin in the blood.
• Cancer: While some cancer research applications might utilize ELISA, it’s not a standard diagnostic test for most cancers.
• Diabetes: ELISA is not commonly used for diagnosing diabetes. Blood sugar tests are the primary diagnostic tools for diabetes.

Answer: Frei test

The Frei test, also known as the intradermal test, is employed for the diagnosis of lymphogranuloma venereum (LGV), a sexually transmitted infection caused by the bacterium Chlamydia trachomatis.

The other options are incorrect:

• Mantoux test: The Mantoux test is used for the diagnosis of tuberculosis (TB), not for LGV.
• Schick test: The Schick test is used to determine susceptibility to diphtheria, not for LGV.
• Dick test: The Dick test is used for the diagnosis of scarlet fever, not for LGV.

Answer: All of these

All the listed vaccines – Influenza, Rabies, and Russian Spring-Summer Encephalitis – are inactivated viral vaccines. This means they contain viruses that have been rendered inactive (killed) and can no longer cause disease. They still trigger the immune system to recognize and fight off the real virus if encountered later.

Answer: Influenza virus

Antigenic variation, which refers to the ability of a pathogen to change its surface antigens to evade the immune response, is most extensive in the influenza virus. This variation is why new flu vaccines are needed each year to match the circulating strains.

The other options are incorrect:

• Smallpox virus: Smallpox has been eradicated, and the virus exhibits minimal antigenic variation.
• Measles virus: Measles virus shows some degree of antigenic variation, but it’s less extensive compared to influenza.
• Herpes virus: Herpesviruses can undergo some antigenic variation, but not to the same extent as influenza. Their latency and ability to hide within the host contribute to immune evasion strategies.

Answer: mumps

The mumps vaccine, also part of the MMR (Measles, Mumps, Rubella) vaccine, is a live attenuated vaccine. This means it contains a weakened (attenuated) form of the mumps virus that can trigger an immune response but is not strong enough to cause the actual disease in healthy individuals.

The other options are incorrect:

• Pertussis: The whooping cough vaccine (DTaP, Tdap) is an inactivated vaccine containing killed pertussis bacteria and components.
• Cholera: The cholera vaccine can be either an inactivated oral vaccine or a live attenuated vaccine depending on the specific type.
• Rabies: The rabies vaccine is an inactivated vaccine containing rabies virus particles that have been rendered inactive.

Answer: Whooping cough, tetanus and Diphtheria

Triple toxoid vaccine provides protection against three diseases: pertussis (whooping cough), tetanus, and diphtheria. It contains inactivated toxins (toxoids) of these bacteria, stimulating the immune system to produce antibodies against them.

The other options are incorrect:

• Diphtheria, tetanus and rabies: This combination is incorrect as the triple toxoid vaccine does not provide protection against rabies.
• Tetanus, whooping cough, Tuberculosis: Tuberculosis is caused by a bacterium, Mycobacterium tuberculosis, and is not prevented by the triple toxoid vaccine. Additionally, the order of diseases listed here is incorrect.
• Whooping cough, cancer and T.B.: Cancer and tuberculosis are not prevented by the triple toxoid vaccine. Additionally, the order of diseases listed here is incorrect.

Answer: Delayed

Organ transplant rejection is a type of delayed hypersensitivity (type IV hypersensitivity). This reaction involves T cells of the immune system recognizing the donor organ’s tissues as foreign and attacking them. It typically takes days to weeks after the transplant for this reaction to develop.

The other options are incorrect:

• Immediate Hypersensitivity: This type of hypersensitivity (type I) involves IgE antibodies and mast cells, causing allergic reactions like anaphylaxis. It wouldn’t be involved in transplant rejection.
• Allergy: Allergy is a broader term encompassing various immune system reactions to harmless substances. While organ rejection involves the immune system, it’s not a typical allergy response.
• None of these: Rejection is a well-documented immune response to organ transplants. Delayed hypersensitivity is the specific type involved.

Answer: Formalin

Formalin, a solution of formaldehyde in water, is the primary agent used to convert diphtheria toxin into diphtheria toxoid. Formaldehyde inactivates the toxin’s ability to cause disease while preserving its antigenicity, allowing the body to develop immunity.

The other options are incorrect:

• Aldehyde: While formaldehyde is a type of aldehyde, it’s the specific aldehyde used in diphtheria toxoid production.
• Phenols: Phenols are disinfectants with different mechanisms of action and are not typically used for diphtheria toxoid preparation.
• None of these: Formaldehyde is the standard method for inactivating diphtheria toxin for vaccine development.

Answer: Bovine tubercle bacilli

The BCG vaccine is made from a weakened strain of Mycobacterium bovis, the bovine tubercle bacillus. This weakened strain cannot cause active tuberculosis in humans but stimulates the immune system to develop defenses against the related human tuberculosis bacteria, Mycobacterium tuberculosis.

The other options are incorrect:

• Human tubercle bacilli: BCG is not derived from the virulent human strain to avoid causing disease in the recipient.
• Avian tubercle bacilli: This strain infects birds and is not used in BCG vaccine production.
• Atypical mycobacteria: These are a group of environmental mycobacteria not used in BCG vaccine development. They can cause infections but are distinct from the bacteria causing tuberculosis.

Answer: VDRL test

The VDRL (Venereal Disease Research Laboratory) test is a specific test for syphilis. It is a non-treponemal test that detects antibodies produced by the body in response to infection with Treponema pallidum, the bacterium that causes syphilis.

The other options are incorrect:

• ELISA: ELISA (Enzyme-Linked Immunosorbent Assay) is not a specific test for syphilis. While it can be used in the diagnosis of various infectious diseases, including HIV, it is not typically used as a primary test for syphilis.
• FTA: FTA (Fluorescent Treponemal Antibody Absorption) test is a treponemal test used for confirming syphilis infection, but it is not the specific test typically used for primary screening. The VDRL test is more commonly used for this purpose.

Answer: Slide flocculation test

The VDRL (Venereal Disease Research Laboratory) test is a type of slide flocculation test. In this test, a suspension of inactivated syphilis bacteria is mixed with the patient’s serum. If antibodies against syphilis are present, they will clump together with the bacteria, forming visible aggregates on a slide. This clumping (flocculation) indicates a potential syphilis infection.

The other options are incorrect:

• Agglutination test: Agglutination tests are similar to flocculation tests but use red blood cells or latex particles instead of bacteria for detection. While there might be some overlap in terminology, slide flocculation is the more specific term for VDRL.
• Precipitation test: Precipitation tests involve forming an insoluble precipitate between antigen and antibody. While some flocculation tests might involve some precipitation, slide flocculation specifically refers to the clumping of antigen-antibody complexes observed on a slide.

Answer: Semple vaccine

The Semple vaccine, a historical rabies vaccine derived from sheep brain tissue, was known to have a higher risk of neurological complications compared to modern rabies vaccines. This is because the Semple vaccine contained some neural tissue components, which could rarely trigger an autoimmune reaction in the nervous system.

The other options are incorrect:

• Chick embryo vaccine: This type of rabies vaccine uses chick embryos to grow the rabies virus for vaccine production. It’s a safer alternative to the Semple vaccine with a lower risk of neurological complications.
• HDCS vaccine: The Human Diploid Cell Rabies Vaccine (HDCV) utilizes human cells to grow the rabies virus. It’s a safe and effective rabies vaccine with minimal risk of neurological complications.
• BPL vaccine: The Purified Vero Cell Rabies Vaccine (PVRV) or BPL vaccine is another modern rabies vaccine produced using Vero cells, a lineage of monkey kidney cells. It’s a safe and effective option with a low risk of neurological complications.

Answer: FTA

he Fluorescent Treponemal Antibody (FTA) test specifically detects antibodies to the bacterium Treponema pallidum, the causative agent of syphilis.

The other options are incorrect:

• VDRL test: This is a non-specific test for syphilis, detecting antibodies not specific to Treponema pallidum.
• ELISA: This is a general technique that can be used for many different tests but is not specific to syphilis.
• None of these: This option is incorrect as FTA is the specific test for syphilis.

Answer:Slide flocculation test

The VDRL (Venereal Disease Research Laboratory) test is a slide flocculation test that detects the presence of reagin antibodies produced in response to syphilis.

The other options are incorrect:

• Agglutination test: This type of test involves the clumping of particles and is not used in the VDRL test.
• Precipitation test: This test involves the formation of a precipitate in a solution and is not the method used in the VDRL test.
• None of these: This option is incorrect because the VDRL test is indeed a slide flocculation test.

Answer: Induces antibodies

The sporozoite vaccine for malaria works by inducing the production of antibodies that target the sporozoite stage of the Plasmodium parasite, helping to prevent infection.

The other options are incorrect:

• Prevents only asexual forms with reproduction: This is incorrect because the sporozoite vaccine targets the sporozoite stage, not the asexual stages of the parasite.
• No effects on clinical illness: This is incorrect as the vaccine aims to prevent the infection and thereby can have a significant impact on clinical illness.
• None of the above: This is incorrect because the correct answer is that the sporozoite vaccine induces antibodies.

Answer:plasma cells

Plasma cells are derived from B lymphocytes and are responsible for producing antibodies, thus providing humoral immunity.

The other options are incorrect:

• T Lymphocyte: These cells are involved in cell-mediated immunity, not in the production of antibodies.
• None of the above: This option is incorrect because plasma cells do form antibodies and provide humoral immunity.

4o

Answer: mast cell

IgE antibodies bind to the surfaces of mast cells, which play a key role in allergic responses by releasing histamine and other chemicals when activated.

The other options are incorrect:

• Melanocyte: These cells are responsible for producing melanin, the pigment in the skin, and are not involved in allergic responses.
• Fibrocyte: These cells are involved in the formation of connective tissue and collagen, not in allergic responses.
• Macrophage: These cells are involved in phagocytosis and the immune response but do not have a primary role in allergic responses mediated by IgE.

Answer: Mucosal epithelium

The secretory piece of IgA, known as the secretory component, is synthesized by epithelial cells in mucosal tissues. It helps transport IgA across the mucosal surface and provides protection against degradation.

The other options are incorrect:

• T-cells: These cells are involved in cell-mediated immunity but do not synthesize the secretory component of IgA.
• B-cells: These cells produce IgA antibodies but not the secretory component itself.
• Lymph nodes: While they are sites of immune cell activation and antibody production, they do not synthesize the secretory component of IgA.

Answer: C5b, C6, C7, C8, C9

The membrane attack complex (MAC) in the complement pathway is formed by the sequential assembly of the components C5b, C6, C7, C8, and C9, which create a pore in the target cell membrane leading to cell lysis.

The other options are incorrect:

• C5b, C6: These are part of the initial steps in forming the MAC but are not sufficient by themselves to complete the complex.
• C6, C7: These components are involved in the formation of the MAC but do not form the entire complex.
• C8, C9: These are the later components that help complete the formation of the MAC but are not sufficient alone to initiate its assembly.

Answer: Immunoblotting is also called as Northern blotting

Immunoblotting is also known as Western blotting, not Northern blotting. Northern blotting is a technique used to detect RNA.

The other options are incorrect:

• ELISA can detect antigen and antibody both: This is true. ELISA (Enzyme-Linked Immunosorbent Assay) can be used to detect the presence of both antigens and antibodies.
• Immunofluorescence test uses Fluorescein iso thiocyanate: This is true. Immunofluorescence tests commonly use fluorescein isothiocyanate (FITC) as a fluorescent dye to label antibodies.
• Immunoferritin is used in Immunoelectron microscopy: This is true. Immunoferritin, which is ferritin conjugated to antibodies, is used as a marker in immunoelectron microscopy to visualize antigens.

Answer: IgG antibody against Fc fragment of IgG

Rheumatoid factor is most commonly an IgM antibody that targets the Fc region of IgG, but for the sake of the given options, it should be considered as IgG against the Fc fragment of IgG.

The other options are incorrect:

• IgD antibody against Fc fragment of IgG: This is incorrect as rheumatoid factor is not an IgD antibody.
• IgM antibody against Fc fragment of IgM: This is incorrect because rheumatoid factor typically targets IgG, not IgM.
• IgE antibody against Fc fragment of IgM: This is incorrect as rheumatoid factor is not an IgE antibody and does not target IgM.

Answer: It inhibits the normal progress of complement cascade

C1 esterase inhibitor (C1-INH) regulates the complement system by inhibiting the proteases C1r and C1s, but it does not inhibit the normal progress of the complement cascade; rather, it prevents its uncontrolled activation.

The other options are incorrect:

• It inhibits Hageman factor: This is true. C1-INH inhibits Factor XII (Hageman factor), which is involved in the activation of the complement, coagulation, and kinin systems.
• It inhibits plasmin: This is true. C1-INH also inhibits plasmin, a key enzyme in the fibrinolytic system.
• It is alpha-neuraminoglycoprotein: This is true. C1-INH is a glycoprotein, specifically an alpha-neuraminoglycoprotein.

Answer: Corynebacterium diphtheriae and glial cells

Molecular mimicry refers to the process where microbial antigens resemble host antigens, leading to immune responses against both the microbe and host tissues. Corynebacterium diphtheriae does not mimic host glial cells; instead, it produces toxins that cause damage.

The other options are incorrect:

• Shigella flexneri and HLA B27: Shigella flexneri infection has been associated with reactive arthritis in individuals with HLA B27.
• Cosackie B virus and Myocardium: Coxsackie B virus infection has been implicated in myocarditis, where the viral antigens may mimic myocardial antigens.
• Mycobacterium tuberculosis and joint membranes: In tuberculosis-associated arthritis, antigens from Mycobacterium tuberculosis may cross-react with joint tissue antigens, leading to inflammation.

Answer: 0,3,7,14,30 and 90 day optional

The recommended schedule for post-exposure prophylaxis against rabies involves receiving the rabies vaccine on days 0, 3, 7, 14, and 28 or 30. An additional dose may be administered on day 90 for immunocompromised individuals or those at higher risk of exposure.

The other options are incorrect:

• 0,3,7,14 and 30 day optional: This option misses the recommended dose on day 28 or 30, which is necessary for completing the vaccination series.
• 0,7,14,30 and 90 day optional: This option does not include the dose on day 3, which is crucial for the timely administration of the rabies vaccine.
• 0,7,14 and 30 day optional: This option also misses the recommended doses on days 3 and 28 or 30, which are necessary for adequate protection against rabies.

111

Answer: Antibody producing cells. Memory B cell

In the primary immune response, B cells are activated and differentiate into plasma cells, which produce antibodies specific to the encountered antigen. Additionally, memory B cells are generated during the primary response, which enables a faster and more robust response upon re-exposure to the same antigen.

The other options are incorrect:

• Involves IgG: This is incorrect. In the primary immune response, IgM is the predominant antibody class produced initially, followed by a switch to IgG production.
• No lag period: This is incorrect. The primary immune response typically involves a lag period during which the immune system mounts a response to the newly encountered antigen.
• Slow and sluggish: While the primary immune response may be slower compared to secondary responses, describing it as “slow and sluggish” is not entirely accurate, as it is an essential process in initiating the immune response against a novel antigen.

Answer: 10 mm in diameter

A positive tuberculin test, also known as the Mantoux test, is indicated by an area of induration (firm swelling or bump) on the skin measuring greater than 10 mm in diameter. This reaction indicates exposure to the tuberculosis (TB) bacterium, Mycobacterium tuberculosis.

The other options are incorrect:

• <5mm in diameter: This size of induration typically indicates a negative result, suggesting no significant exposure to TB.
• 6-9 mm in diameter: This size of induration may indicate a positive result in certain populations, such as individuals with HIV infection or recent contacts with active TB cases, but it is not the standard criterion for a positive result.
• No induration: The absence of induration indicates a negative tuberculin test result, meaning no significant exposure to TB.

Answer: CD4T cell count

The CD4 T cell count is considered the best indicator of HIV prognosis. As HIV attacks and destroys CD4 T cells, monitoring the CD4 T cell count provides valuable information about the status of the immune system and the progression of HIV infection.

The other options are incorrect:

• CD8 T cell count: While CD8 T cells play a role in the immune response to HIV, the CD4 T cell count is a more direct indicator of HIV prognosis.
• HIV RNA: HIV RNA, also known as viral load, measures the amount of HIV virus in the blood. While it is important for monitoring HIV infection and treatment effectiveness, it is not considered the best indicator of prognosis on its own.
• ELIS: ELIS (Enzyme-Linked Immunosorbent Assay) is a type of test used to detect HIV antibodies or antigens, but it is not a direct indicator of HIV prognosis.