When a B-cell undergoes immunoglobulin class switching

Correct Answer: C

Rationale: When a B-cell undergoes immunoglobulin class switching, the variable region of the heavy chain remains the same but its constant region changes. This process allows the B-cell to produce antibodies with different effector functions while maintaining the same antigen specificity. By changing the constant region of the heavy chain, the B-cell can switch from producing IgM to IgG, IgA, or IgE antibodies. Choices A, B, and D are incorrect because they do not accurately describe the specific changes that occur during immunoglobulin class switching in B-cells.

Correct Answer: B

Rationale: The correct answer is B because immunoglobulins can indeed recognize conformational antigens on viral particles. Immunoglobulins have variable regions that can bind to a wide range of antigen shapes. Choice A is correct as Ig structure consists of two light and two heavy chains. Choice C is incorrect as immunoglobulins can also bind to internal epitopes. Choice D is incorrect as Ig expression starts during the late B cell development stage.

Correct Answer: D

Rationale: The correct answer is D because Signal 2 is essential for the activation of naïve T cells. Signal 1 provides the antigen recognition, while Signal 2, typically provided by co-stimulatory molecules, is required for full T cell activation. A is incorrect because Signal 2 is not specifically for memory T cell re-activation. B is incorrect because Signal 2 is not related to self-tolerance, which is typically maintained by regulatory T cells. C is incorrect because CD3 is a component of the T cell receptor complex, not the primary mediator of Signal 2.

Correct Answer: B

Rationale: The correct answer is B because mature naïve T cells that leave the thymus can include self-reactive T cells that have not been tolerized against a specific antigen. This is because the process of negative selection in the thymus eliminates most self-reactive T cells but does not catch all of them. Some self-reactive T cells may escape negative selection and circulate as mature naïve T cells. Therefore, it is possible for mature naïve T cells leaving the thymus to include self-reactive T cells that have not been tolerized against a specific antigen. Choices: A: This is incorrect because although negative selection in the thymus eliminates most self-reactive T cells, it does not catch all of them, so some self-reactive T cells may still be present in the mature naïve T cell population. C: This is incorrect because mature naïve T cells already have the ability to recognize antigens presented by MHC, which is developed in the th

Correct Answer: D

Rationale: The correct answer is D, "All of the above A, B, and C". Step 1: Induction of a neutralizing antibody response (A) is crucial as it helps prevent the virus from infecting cells. Step 2: Induction of a cytotoxic T cell response (B) is important to eliminate infected cells and stop the spread of the virus. Step 3: Protection against multiple strains (C) is desirable to ensure broad coverage against different flu strains. Combining A, B, and C in a vaccine would provide comprehensive protection against the flu by targeting different aspects of the immune response. Choices A, B, and C are incorrect individually as they each address only one aspect of a desirable flu vaccine, whereas the correct answer D encompasses all three crucial features.