Answer: They coordinate both humoral and cell-mediated immunity by secreting cytokines that activate B cells and cytotoxic T cells.
- A They are sometimes thought to directly recognize and kill virus-infected target cells without further assistance
- B They coordinate both humoral and cell-mediated immunity by secreting cytokines that activate B cells and cytotoxic T cells
- C They are sometimes mistaken for the primary cell type directly responsible for synthesizing and secreting antibodies
- D They are sometimes thought to function mainly within the thymus gland, rarely circulating beyond that organ
Correct answer: B. They coordinate both humoral and cell-mediated immunity by secreting cytokines that activate B cells and cytotoxic T cells
Explanation: T helper (Th) cells (CD4<sup>+</sup>) are the master coordinators. They recognize antigen on MHC class II, then release cytokines (interleukins, IFN-gamma) that: activate cytotoxic T cells, stimulate B cell differentiation into plasma cells, enhance macrophage killing. HIV targets these cells.
An antibody is Y-shaped, with two identical antigen-binding sites at the tips of the variable regions - each shaped to recognise one specific antigen - while the constant (Fc) region at the base is recognised by immune cells to trigger further responses.
Concept context
Innate and adaptive immunity, B cells, T cells, antibodies, vaccines, and immune disorders. Critical for NEET.