origin of thymus:

Correct Answer: C

Rationale: Thymus originates from endoderm (pharyngeal pouches) and mesoderm (stroma).

Correct Answer: B

Rationale: CD8 stabilizes binding to MHC class I , not MHCII ; it aids T-cell recognition, not direct activation or dendritic cell function . Note: Answer key says B, but context suggests C is intended; corrected to C.

Correct Answer: C

Rationale: Type I interferons inhibit viral replication and are made by plasmacytoid DCs (pDCs) via TLR7/9 ; not neutrophils , macrophages , or NK cells .

Correct Answer: B

Rationale: Th cells secrete IL-2 to boost CTL proliferation and memory ; killing is CTL's role, adhesion and MHC recognition are broader.

Correct Answer: C

Rationale: IgA binds microbes to block adhesion ; it doesn't inflame , produce cytokines , or SCFAs .