What distinguishes adaptive immunity from innate immunity?

Correct Answer: C

Rationale: The correct answer is C because adaptive immunity involves T and B lymphocytes that provide specific immune responses tailored to particular pathogens. T and B lymphocytes are key players in adaptive immunity, recognizing and targeting specific antigens. Choice A is incorrect because macrophages are part of innate immunity. Choice B is incorrect because innate immunity is nonspecific and immediate, while adaptive immunity is specific and takes time to develop. Choice D is incorrect because physical barriers are a characteristic of innate immunity, not adaptive immunity.

Correct Answer: A

Rationale: Step 1: Selective genetic pressure refers to the process where specific genetic traits are favored due to environmental factors. Step 2: Rroma populations and their genetic response to Yersinia pestis demonstrate selective genetic pressure as they have developed genetic adaptations to resist the plague bacterium. Step 3: This adaptation is a result of prolonged exposure to the pathogen, leading to the survival and reproduction of individuals with genetic variations that confer resistance. Step 4: Other choices are incorrect because mutation rates in viruses like the flu (B) do not necessarily involve genetic pressure, increased pathogen diversity in unvaccinated populations (C) is a consequence of lack of immunity, and non-specific activation of innate immunity (D) is not a selective process based on genetic traits.

Correct Answer: B

Rationale: The correct answer is B: Jules Hoffman. He is credited with identifying Toll-like receptors (TLRs) in innate immunity. Hoffman's research provided crucial insights into how the immune system recognizes pathogens and triggers immune responses. Paul Ehrlich is known for his work on antibodies, Edward Jenner for developing the smallpox vaccine, and Louis Pasteur for his contributions to germ theory and vaccination. However, none of them are specifically associated with the discovery of Toll-like receptors in innate immunity.

Correct Answer: C

Rationale: The correct answer is C. NK cells kill target cells by releasing perforin and granzyme. Perforin creates pores in the target cell's membrane, allowing granzyme to enter and induce apoptosis. Antibodies (choice A) are produced by B cells, not NK cells. Cytokines (choice B) regulate immune responses but do not directly kill cells. Phagocytosis (choice D) involves engulfing and digesting pathogens, which is not how NK cells kill target cells.

Correct Answer: C

Rationale: The correct answer is C: Lymphoid lineage. NK cells are a type of lymphocyte that is part of the innate immune system. They are derived from common lymphoid progenitors in the bone marrow. NK cells play a crucial role in recognizing and killing infected or abnormal cells. Myeloid lineage (A) gives rise to cells like macrophages and granulocytes, not NK cells. Erythroid lineage (B) produces red blood cells, and granulocyte lineage (D) gives rise to neutrophils, basophils, and eosinophils, not NK cells. Therefore, the correct choice is C as NK cells originate from the lymphoid lineage.