Which organ is central to adaptive immunity?

Correct Answer: C

Rationale: Lymph nodes activate adaptive responses; spleen filters, thymus matures T cells, marrow produces.

Correct Answer: A

Rationale: The presence of white pulp and central artery indicates this is from the spleen.

Correct Answer: D

Rationale: Lymph node capsule has smooth muscle at hilum , adipose tissue , and is pierced by afferent vessels ; it divides into cortex and medulla, but not regularly (D is incorrect).

Correct Answer: A

Rationale: Littoral cells line blood sinusoids in the spleen; Kupffer cells are in the liver.

Correct Answer: D

Rationale: Epithelial reticular cells have tonofilaments and desmosomes for structural support.