have peripheral dark small lymph with germinal center that have high B-lymph. low T-lymph.

Correct Answer: B

Rationale: Secondary follicles have germinal centers with high B-lymphocytes and low T-lymphocytes, staining dark peripherally.

Correct Answer: B

Rationale: Thymic factor controls helper and suppressor T-cell multiplication.

Correct Answer: D

Rationale: Context suggests thymus (CD4+ and CD3+ T-cell production, D); spleen degrades RBCs , lymph nodes have vessels , tonsils produce antibodies .

Correct Answer: C

Rationale: Cytokines from macrophages signal and coordinate immune responses ; they don't destroy pathogens directly , form vesicles , or primarily affect blood flow .

Correct Answer: C

Rationale: Co-stimulatory molecules (e.g., B7) bind CD28 on T cells for activation ; pattern recognition , DC activation , and killing are distinct.