Which of the following is a function of T cells in the immune system?

• A. Producing antibodies
• B. Directly killing infected host cells
• C. Acting as a first line defense
• D. Producing hormones

Answer: (B)

T cells play a crucial role in the immune response, particularly in identifying and eliminating infected or abnormal cells. One of the primary functions of certain T cells, specifically cytotoxic T cells (also known as CD8+ T cells), is to directly kill host cells that are infected with viruses or have become cancerous. This is achieved through the recognition of specific antigens on the surface of these infected or transformed cells, followed by the release of cytotoxic granules that induce apoptosis, or programmed cell death, in those target cells.

While other components of the immune system are responsible for producing antibodies, acting as a first line of defense, and producing hormones, these functions are not attributed to T cells. For instance, antibodies are produced by B cells, and the innate immune response involves physical barriers like skin and mucous membranes rather than T cell action. Furthermore, hormones related to the immune response typically involve cytokines that are produced by various immune cells, not specifically T cells. Thus, the correct answer highlights a fundamental role of T cells in targeting and eliminating infected cells from the host organism.