Masking of HLA class I molecules expressed on K-562 target cells can restore their susceptibility to NK cell cytolysis

The aim of our study was to follow whether class I HLA antigens play a role in the susceptibility of K-562 target cells to NK cell lysis as well as in the interaction between NK and target cells.After K-562 cells were treated with rIFN-gamma, HLA class I antigens appeared on their surface.Those HLA class I +, in comparison to HLA class I ™, K562 target cells became about 40–50% less susceptible to NK cell cytolysis.This influence of HLA class I antigens was abrogated when class I + K-562 cells were incubated with anti-HLA class I monoclonal antibodies Bra 23/9.The restoration of susceptibility of these targets to NK cell cytolysis was not caused by ADCC mechanism as determined by F(ab′) 2 fragments or by mAb CD16. Further, the percentage of conjugates between effector and target cells was not significantly altered neither when HLA class I antigens appeared on the surface of K-562 target cells nor when HLA class I + K-562 cells were incubated with anti-HLA class I monoclonal antibodies.To study this question, we used a different approach because both expression of HLA class I molecules and their masking with appropriate monoclonal antibody were done by means of the same cell line of target cells.