The major role of helping B cells to produce antibodies of high affinity by the dual ability of secreting either Th1 or Th2 cytokines is characteristic of which type of T cell

Correct Answer: A

Rationale: T follicular helper (TFH) cells aid B cells in germinal centers, secreting Th1/Th2 cytokines for affinity maturation.

Correct Answer: D

Rationale: Attenuated microbes are live, weakened for vaccines; toxoids are inactivated toxins.

Correct Answer: B

Rationale: T cells mature in the thymus ; produced in bone marrow.

Correct Answer: D

Rationale: Pattern recognition receptors (PARs) are genomically determined to bind to molecules widely expressed by microbes but not by host cells. Consequently, PARs cannot recognize host-associated molecules such as MHC class I molecules or cells of host origin such as B, T, or natural killer lymphocytes.

Correct Answer: C

Rationale: IgE is the least prevalent, primarily involved in allergies and parasite defense.