Abstract

A lymphocyte is a type of white blood cell in the vertebrate immune system. The three major subtypes of lymphocytes are natural killer cells (NK cells), T cells and B cells. The pivotal role of NK cells is the protection against infected cells or tumor cells which are recognized by the altered expression of surface molecules presented by the MHC (major histocompatibility complex) class I type. NK cells are mobilized and activated by hormones, cytokines, and interferons. Target cells are eliminated by the release of cytotoxic granules. T cells and B cells represent the major cellular components of the adaptive immune response. Both cell types are able to recognize non-self-antigens during the process of antigen presentation. Verf.-Referat (gekürzt)