Which part of the immune system do T lymphocytes primarily belong to?

T lymphocytes are primarily a component of adaptive immunity, which is the part of the immune system that adapts its response to specific pathogens through a memory-based mechanism. Unlike innate immunity, which provides a rapid but non-specific response to infection, adaptive immunity involves a slower response that can specifically target pathogens.

T lymphocytes, or T cells, are essential for recognizing and responding to specific antigens presented by infected or abnormal cells. They play key roles in orchestrating the immune response by helping other immune cells and directly killing infected cells. This specificity and the ability to retain memory of past infections characterize adaptive immunity.

While T cells are involved in cellular immunity—another answer choice—they are part of the broader adaptive immune system. Therefore, classifying T lymphocytes under adaptive immunity captures their role within the overall immune response more accurately. Humoral immunity, on the other hand, primarily refers to B cells and the antibodies they produce, which is a different aspect of adaptive immunity focused on secreted antibodies.