T lymphocytes, commonly known as T cells, are crucial components of the immune system, specifically involved in cell-mediated immunity, which is a subset of adaptive immunity. This type of immunity is essential for targeting and eliminating intracellular pathogens—disease-causing agents that invade host cells. T cells are primarily developed in the thymus, a primary lymphoid organ, and once matured, they migrate to secondary lymphoid organs such as the tonsils, lymph nodes, and spleen.
There are two main types of T cells: cytotoxic T cells (TC cells) and helper T cells (TH cells). Both types require activation by antigen-presenting cells, such as dendritic cells, which display antigens on their surface. Upon activation, T cells undergo division and differentiation into various forms, including memory T cells and effector T cells. Memory T cells, which can be either memory TC or memory TH cells, are essential for mounting a rapid response to subsequent infections by the same pathogen. In contrast, effector T cells, which include effector helper T cells and effector cytotoxic T cells, are responsible for executing immune functions against pathogens.
Understanding the roles and functions of T cells is vital for comprehending the broader mechanisms of the immune response. As we delve deeper into the study of T lymphocytes, we will explore their specific functions, activation processes, and interactions with other immune cells, including B cells, which will be discussed later in the course.