RELATIONSHIP BETWEEN ANTIBODY-DEPENDENT CELL-MEDIATED CYTOTOXICITY DUE TO ANTI-HTLV-1 AND NEGATIVE SIGNAL OF MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I ANTIGENS ON ADULT T-CELL LEUKEMIA-CELL LINES

Natural killer (NK) cells possess two types of cytotoxic activity: nat ural killer cytotoxicity (NKC) and antibody-dependent cell-mediated cy totoxicity (ADCC). The NKC is regulated by the negative signal oi the NK receptor, which recognizes major histocompatibility complex (MHC) c lass I antigens. However, it is not known whether or not the negative signal influences the ADCC. In this study, the relationship of the ADC C and negative signal was investigated. As target cells, adult T-cell leukemia (ATL) cell lines were used. When the target cells were treate d with an anti-human T-lymphotropic virus type-1 (anti-HTLV-1) antibod y, they were killed by the NK cells by means of the ADCC (ADCC/anti-HT LV-1). The killing levels were parallel with the cell surface treated with an anti-HLA, the ADCC (ADCC/anti-HLA) showed inverse correlation with the HLA antigenicity. Furthermore, when HLA polymorphic and monom orphic determinants of these target cells were blocked by F(ab')(2) fr agments of the anti-HLA and W6/32, the ADCC/anti-HLA was enhanced, but the ADCC/anti-HTLV-1 was not enhanced. These results suggest that the ADCC/anti-HLA may have an intimate relationship with the MHC class I antigens. The ADCC/anti-HLA may be suppressed by the negative signal. On the other hand, the ADCC/anti-HTLV-1 may have no relationship with the class I antigens and the negative signal may have no influence aga inst the ADCC/anti-HTLV-1. The biological mechanism of this difference remains to be investigated.