Signal 2 for T cell activation is

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: 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.

Correct Answer: C

Rationale: The correct answer is C: Increasing pathogen reproduction. The immune system's main function is to protect the body from pathogens and foreign invaders, not to promote their reproduction. A: Promoting wound healing is correct as the immune system helps in tissue repair. B: Fighting cancer is correct as the immune system plays a role in recognizing and destroying cancerous cells. D: Eliminating cell debris is correct as the immune system helps in clearing out dead or damaged cells to maintain tissue health.

Correct Answer: B

Rationale: The correct answer is B: Dendritic cells. Dendritic cells are sentinel cells in tissues that detect pathogens and activate the immune response. They are crucial in initiating adaptive immune responses by presenting antigens to T cells. T lymphocytes (A) are involved in adaptive immunity, not innate immunity. B lymphocytes (C) mature into plasma cells (D) which produce antibodies, but they are not sentinel cells in tissues like dendritic cells.

Correct Answer: B

Rationale: The correct answer is B because modern immunology indeed builds on the groundbreaking contributions of scientists like Jenner and Pasteur. Their work laid the foundation for understanding concepts like vaccination and immune responses. Choice A is incorrect because modern immunology encompasses both innate and adaptive immunity. Choice C is incorrect as immunology extends beyond tissue healing to include immune responses to pathogens and self-cells. Choice D is incorrect as immunology is a rapidly evolving field with significant advancements in understanding immune mechanisms and developing new treatments.