FUNCTION AND SPECIFICITY OF HUMAN NATURAL-KILLER-CELL RECEPTORS

In humans, natural killer lymphocytes express HLA class I-specific inh ibitory receptors belonging to at least two different molecular famili es. The first is represented by members of the Ig superfamily that are involved in the recognition of different groups of HLA class I allele s, and the second is represented by a molecular complex formed by CD94 and NKG2A that displays a broad specificity for various class I molec ules including the 'non-classical' HLA-G molecules. In addition to the inhibitory receptors, a series of activating receptors has been ident ified. Some display the same specificities as the corresponding inhibi ting receptors and can be viewed as HLA class I-specific activating re ceptors. Another group of activating receptors appear to be involved i n the cytolytic activity against HLA-'negative' target cells. These re ceptors are clearly non-MHC specific and, under physiological conditio ns, their function is suppressed by the HLA class I-specific inhibitor y receptors.