CONFORMATION DEPENDENCE OF MHC CLASS-I IN THE MODULATION OF TARGET-CELL SENSITIVITY TO NATURAL KILLING

C1R.Aw68 Delta 242 is a human B cell line expressing a mutant class I molecule that is defective in assembly and transport at 37 degrees C b ut is stably expressed at room temperature. This cell line has been ut ilized to study the conformation dependence of MHC class I in the modu lation of target cell sensitivity to natural killing. Surface expressi on of MHC class I molecules was monitored by the antibodies W6/32 (det ecting a pan-class I specificity that is beta(2)-microglobulin and con formation dependent) and HC.10 (detecting free HLA-B heavy chain and a subset of HLA-A heavy chains). C1R.Aw68 Delta 242 was cultured at red uced temperature to induce cell surface expression of class I molecule s, and then the temperature was shifted to 37 degrees C. During the fi rst 2 h at 37 degrees C, C1R.Aw68 Delta 242 displayed a higher level o f HC.10 reactivity than W6/32. Conjugation of C1R.Aw68 Delta 242 to NK cells correlated inversely with W6/32 expression, but not wit-h HC.10 reactivity as revealed by flow cytometry. The sensitivity of the C1R. Aw68 Delta 242 cells to NK-mediated lysis was also examined as a funct ion of temperature, and the level of C1R.Aw68 Delta 242 cytolysis corr elated inversely with W6/32 expression but not HC.10. The fact that bo th the conjugation rate and target cell cytolysis increased with decre ased reactivity with the conformation-dependent antibody W6/32 and not with HC.10, is consistent with the hypothesis that NK cell inhibitory receptors (KIR) detect a conformation-dependent epitope(s). (C) Ameri can Society for Histocompatibility and Immunogenetics, 1998. Published by Elsevier Science Inc.