Innate lymphoid cells (ILCs) are effector cells that generally reside in barrier tissues, such as the skin, the gut, and the lung. These cells closely resemble subsets of T lymphocytes, but lack a T cell antigen-receptor. Instead, these cells produce their effector molecules following stimulation by:

Correct Answer: D

Rationale: ILCs respond to cytokines from innate cells ; PAMPs are indirect, TNF-α or acute phase proteins are less specific triggers.

Correct Answer: B

Rationale: Natural killer (NK) cells release chemicals (e.g., perforin) to induce apoptosis in virus-infected cells, not phagocytosis or antibody tagging.

Correct Answer: C

Rationale: Memory cells respond to antigens in the secondary immune response, triggering a faster, stronger reaction, not hormones, antibodies, or plasma cells.

Correct Answer: B

Rationale: A second vaccination boosts memory cells, increasing antibody levels faster and stronger, not involving plasma cell survival or circulation.

Correct Answer: D

Rationale: Secondary responses are rapid (short lag) due to memory cells, stronger than primary, and don't generate new memory cells.