Which cells undergo negative selection in the thymus?

Correct Answer: B

Rationale: T cells undergo negative selection; B cells are in marrow, macrophages and neutrophils don't.

Correct Answer: A

Rationale: The encircled region is a secondary lymphatic nodule, characterized by a germinal center.

Correct Answer: C

Rationale: Afferent vessels enter at the convex surface, efferent vessels and veins exit at the concave hilum of the lymph node.

Correct Answer: C

Rationale: PALS (periarteriolar lymphatic sheath) contains only T-lymphocytes.

Correct Answer: D

Rationale: Epithelial reticular cells secrete hormones , form barriers , and nurse T-cells ; all apply.