ABSTRACT
Lymphocytes are responsible for the specificity and memory in adaptive immune responses. They are produced in the primary lymphoid organs (Section C2) and function in the secondary lymphoid organs/tissues, where they recognize and respond to foreign antigens. The two main types of lymphocytes, T cells and B cells, mature in the thymus and bone marrow, respectively. In the resting state both types of lymphocytes have a similar morphology with a small amount of cytoplasm (Figure 1). They have specific but different antigen receptors and a variety of other surface molecules necessary for interaction with other cells (Table 1). These include molecules required for their activation and for movement into and out of the tissues of the body. This ability to migrate into the tissues and return via the lymphatic vessels to the bloodstream (recirculation) is a unique feature of lymphocytes.
