Immunology MCQs

1. In an antigen, haptens are:

a. Immunogenic b. Non-immunogenic c. Antigenic d. None of these

Correct Answer: b. Non-immunogenic

Explanation: Haptens are small molecules that are antigenic (can be recognized by antibodies) but non-immunogenic on their own, meaning they cannot induce an immune response unless they are chemically coupled to a larger carrier protein.

2. The antibody that is first formed after infection is:

a. IgG b. IgM c. IgD d. IgE

Correct Answer: b. IgM

Explanation: IgM is the first immunoglobulin class produced during the primary immune response to an antigen. Its pentameric structure allows it to bind effectively to pathogens early in the infection before IgG is produced in large quantities.

3. Antibodies in our body are produced by:

a. B-lymphocytes b. T-lymphocytes c. Monocytes d. RBC’s

Correct Answer: a. B-lymphocytes

Explanation: Antibodies are produced by B-lymphocytes. When a B-cell encounters its specific antigen and receives help from T-cells, it differentiates into a plasma cell, which is an “antibody factory.”

4. The antibody class/type which can cross placenta is:

a. IgE b. IgG c. IgA d. IgM

Correct Answer: b. IgG

Explanation: IgG is the only antibody class capable of crossing the placenta to provide passive immunity to the fetus, thanks to specific neonatal Fc receptors (FcRn) in the placental tissue.

5. Monoclonal antibodies are produced by:

a. Hybridoma technology b. Biotechnology c. Fermentation Technology d. None of these

Correct Answer: a. Hybridoma technology

Explanation: Hybridoma technology involves fusing a specific antibody-producing B-cell with an immortal myeloma (cancer) cell. The resulting hybrid cell can grow indefinitely and produce a single type of monoclonal antibody.

6. First site of entry of antigen is:

a. Antibody molecules b. Unbroken skin c. Antigen molecules d. Phagocytic cells

Correct Answer: d. Phagocytic cells

Explanation: When an antigen enters the body, phagocytic cells (like macrophages and dendritic cells) are typically the first to “enter” into contact with and engulf the antigen to initiate the immune response.

7. The cellular immune response is mediated by:

a. B cells b. T cell c. BT cells d. Endothelial cells

Correct Answer: b. T cell

Explanation: T-lymphocytes (specifically Cytotoxic T-cells and Helper T-cells) are the primary mediators of cell-mediated immunity, whereas B-cells mediate humoral (antibody) immunity.

8. The reaction of soluble antigen with antibody is known by:

a. Precipitation b. Flocculation c. Agglutination d. Complement fixation

Correct Answer: a. Precipitation

Explanation: When a soluble antigen interacts with its specific antibody at an optimal concentration, they form an insoluble lattice that drops out of solution; this is called precipitation. If the antigen is particulate (like a cell), the reaction is called agglutination.

9. Interferon is composed of:

a. Lipids b. Lipoprotein c. Glycoprotein d. Nucleic acid

Correct Answer: c. Glycoprotein

Explanation: Interferons are signaling proteins belonging to the cytokine family. Chemically, they are glycoproteins produced by host cells in response to the presence of viruses or other pathogens.

10. Active immunity is induced by:

a. Infection b. Placental transfer of antibodies c. Injection of antibodies d. Injection of gamma- globulins

Correct Answer: a. Infection

Explanation: Active immunity is induced when the host’s own immune system responds to an antigen, such as during a natural infection or through vaccination. The other options describe passive immunity.

11. Immunity is life long following:

a. Diphtheria b. Tetanus c. Measles d. Yellow fever

Correct Answer: d. Yellow fever

Explanation: Recovery from Yellow fever (or vaccination against it) typically provides lifelong immunity. Measles also provides very long-lasting immunity, but Yellow fever is a classic example used in immunology for permanent protection.

12. To prepare vaccine for small pox, the material used by Edward Jenner is:

a. Small pox material b. Chicken pox material c. Cow-pox material d. Measles material

Correct Answer: c. Cow-pox material

Explanation: Edward Jenner observed that milkmaids who contracted cow-pox were immune to smallpox. He used the fluid from cow-pox pustules to create the first successful vaccination.

13. Antibody present in colostrums is:

a. IgG b. IgA c. IgM d. IgE

Correct Answer: b. IgA

Explanation: While the composition varies by species, secretory IgA is the predominant immunoglobulin in human colostrum and milk, providing mucosal protection to the neonate’s gut.

14. Anthrax vaccine is prepared by:

a. Attenuated bacilli b. Killing the bacilli c. Live bacilli d. None of these

Correct Answer: a. Attenuated bacilli

Explanation: The Sterne strain vaccine for Anthrax (used in livestock) consists of attenuated (weakened) live bacilli that have lost their ability to produce a capsule, making them non-virulent but immunogenic.

15. Example for cell-mediated immunity are:

a. Tuberculin type b. Contact dermatitis c. Granulomatous d. All of these

Correct Answer: d. All of these

Explanation: All the listed options are forms of Delayed-Type Hypersensitivity (Type IV), which is the classic clinical manifestation of cell-mediated immunity.

16. DPT is used as vaccine for:

a. Diphtheria b. Pertussis vaccine c. Tetanus toxoid d. All of these

Correct Answer: d. All of these

Explanation: The DPT (or DTaP) vaccine is a combination vaccine that protects against three infectious diseases: Diphtheria, Pertussis (whooping cough), and Tetanus.

17. If the microbes used in the vaccine are obtained from patient, they are:

a. Anti viral vaccines b. Anti bacterial vaccines c. Autogenous vaccines d. None of these

Correct Answer: c. Autogenous vaccines

Explanation: Autogenous vaccines are prepared from specific pathogens isolated from a diseased individual (or herd) and then administered back to that same individual to provide targeted immunity.

18. Following substance may act as an antigen:

a. Egg albumin b. RBC and serum c. Vegetable protein d. Snake venom e. All of these

Correct Answer: e. All of these

Explanation: Any foreign substance (usually a protein or large polysaccharide) that can be recognized by the immune system can act as an antigen. This includes animal proteins, plant proteins, and complex venoms.

19. Which antibody class is majorly involved in mucosal immunity?

a. IgY b. IgA c. IgD d. IgE