Abstract
Natural killer (NK) cells exist in each individual in the absence of any intentional immunization. They are able to kill a wide range of targets from tumoral as well as from normal origin. However, their exact physiologic role is not clearly understood. In this study we report results about a human Epstein-Barr virus-transformed B-cell line from which variants perturbed in the expression of HLA molecules have been derived. Our results indicate that in these cell lines an inverse relationship exists between expression of HLA antigens and susceptibility to NK lysis. The original cell line is highly resistant to NK lysis. On the contrary, the variant perturbed in class I antigen expression is highly susceptible. Variant perturbed in class II antigen expression is intermediate in susceptibility. Interferon, which induces HLA class I expression and NK resistance in the unrelated classical K-562 target cells, does not change either HLA expression or NK susceptibility in the variant cell lines. The difference between the original cell line and the variants does not reside in the ability to be bound by NK effectors. Our results suggest a different role for HLA molecules. By some unknown mechanism discussed here, the presence of HLA molecules at the surface of a cell would prevent this cell from being killed by NK cells. The loss of this "good health" signal would lead to the elimination of the cell through NK lysis.