MHC CLASS-I UP-REGULATION PROTECTS SOME BUT NOT ALL TARGETS AGAINST LAK-MEDIATED LYSIS - POSSIBLE IMPLICATIONS FOR THE EXISTENCE OF LAK CELL SUBPOPULATIONS USING DIFFERENT RECOGNITION STRATEGIES

The effect of gamma-interferon (gamma-IFN) was examined on the lymphokine-activated killer (LAK) cell susceptibility and the levels of major histocompatibility complex (MHC) class I antigen expression on YAC, P815 and EL4 cells. IFN induced a marked increase in the MHC class I antigen expression on all target cells, a concomitant decrease in LAK sensitivity was observed for YAC and P815 cells but not for EL4 cells. In competition experiments, lysis of YAC cells by LAK cells was inhibited by control or IFN-treated YAC and P815 cells, but not by control or IFN-treated EL4 cells. Moreover, lysis of EL4 cells was not inhibited by control or IFN-treated YAC cells. Our results suggest that the effectors killing EL4 are distinct from those killing YAC and/or P815 and that the former are not influenced by the levels of MHC class I antigens on target cells.