HLA - D REGION - ASSOCIATED DETERMINANTS HLA Typing

After in vitro mixed lymphocyte culture, cytotoxic lymphocytes develop which have specificity for components of the main histocompatibility complex (MHC) 1 of the stimulating lymphocyte population (1, 2). The effector cells were found to be directed mainly against class I histocompatibility antigens, that is, the H2-K and H2D antigens in the mouse (3), and the HLA-A or HLA-B antigens in man (4). Cytotoxicity against HLA-C was quite weak (5). The role of class II antigens was thought to be that of providing a necessary amplifying effect (6, 7), however, it became clear later that incompatibility at HLA-D was not necessary for cell-mediated lysis (CML) to occur (8). In mice, class I antigens (H2-K and H2-D) alone, or class II antigens (H2-I) alone, were able to generate strong CML (9). Most investigators who have performed studies with human lymphocytes have concluded that HLA-D region products do not serve as targets for CML (6, 7, 10). However, cytotoxicity directed at MHC products other than the known class I (HLAA, B, or C) specificities has frequently been observed (8, 11-13). In spite of the failure to detect cytotoxicity against HLA-D products, the question of their role was not considered resolved by several authors (14-16). In view of the analogy between HLAD and the I region in the mouse, reports that products of H2-I serve as strong targets for CML (17-19) were particularly relevant to this question. In the present experiments the possibility that products of the HLA-D region may act as target antigens in CML was investigated by using monocytes as target cells. The effector cells were generated in vitro by culture with stimulating cells from unrelated donors, matched in the HLA-A and B regions, but mismatched for HLAD. The results obtained with a variety of target cells, showed that cytotoxicity correlated with HLA-D, as determined by serologic typing. Specific blocking experiments with unlabeled monocytes have confirmed that products of HLA-D were recognized by the cytotoxic lymphocytes.