NKT CELLS AS A CONNECTING ELEMENT BETWEEN INNATE AND ADAPTIVE IMMUNITY

Natural killer T cells (NKT cells) are T lymphocytes revealing the expression of both T-cell receptors (TCRs) and NK cell specific receptors on the cell surface. They recognize lipid antigens bound to CD1d molecules, which are not recognized by conventional T lymphocytes. NKT cells function in the innate immune responses being rapidly activated upon antigenic stimulation. They subsequently secrete large amounts of cytokines that in turn modulate the developing adaptive immune response. Therefore NKT cells are regarded to represent a subset of lymphocytes that bridge the innate and adaptive immune systems. NKT lymphocytes are divided into subpopulations according to the structure of their T-cell receptor and expression of the surface receptor CD161. NKT populations differ also in their effector functions. Both mode of activation and localization of NKT cells were shown to affect their activities which may be described as pro-inflammatory or anti-inflammatory as observed in autoimmune diseases. Due to the regulatory properties of NKT cells they may play an important protective role in the processes of aging and carcinogenesis.