T lymphocytes are primarily involved in which immune response?

• A. Humoral antibody production
• B. Cellular immune response and act directly against antigens
• C. Phagocytosis of bacteria in the blood
• D. Production of plasma cells

Answer: (B)

T lymphocytes drive the cellular immune response, meaning they act directly against antigens rather than relying on antibodies carried in the blood or fluids. They include cytotoxic T cells that recognize infected or abnormal cells presented with antigens by MHC class I and kill them, and helper T cells that coordinate and amplify other immune cells’ activities. This direct, cell-focused action is the hallmark of cell-mediated immunity, which is distinct from humoral immunity that relies on B cells producing antibodies. Phagocytosis is carried out by macrophages and neutrophils, not T cells, and plasma cells (antibody-producing cells) arise from B cells—not T lymphocytes. So the primary role of T lymphocytes is the cellular immune response with direct involvement against antigen-bearing cells.