T cells mature in the thymus and primarily function to:

• A. Attack infected cells in the body
• B. Produce antibodies
• C. Circulate antibodies in body fluids
• D. Attack parasites and infected cells via cell-mediated responses

Answer: (D)

T cells mature in the thymus to mediate cell-mediated immunity, which relies on direct cellular attacks rather than antibodies roaming in body fluids. They do not produce antibodies—this is the job of B cells in humoral immunity. Instead, cytotoxic T cells recognize infected or abnormal cells via MHC I and kill them directly, while helper T cells release cytokines to coordinate the broader immune response. This direct attack on infected cells and intracellular pathogens is why the best description is that T cells attack infected cells and parasites via cell-mediated responses.