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 but is stably expressed at room temperature. This cell line has been utilized to study the conformation dependence of MHC class I in the modulation of target cell sensitivity to natural killing. Surface expression of MHC class I molecules was monitored by the antibodies W6/32 (detecting a pan-class I specificity that is beta 2-microglobulin and conformation 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 reduced temperature to induce cell surface expression of class I molecules, and then the temperature was shifted to 37 degrees C. During the first 2 h at 37 degrees C, C1R.Aw68 delta 242 displayed a higher level of HC.10 reactivity than W6/32. Conjugation of C1R.Aw68 delta 242 to NK cells correlated inversely with W6/32 expression, but not with 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 function of temperature, and the level of C1R.Aw68 delta 242 cytolysis correlated inversely with W6/32 expression but not HC.10. The fact that both the conjugation rate and target cell cytolysis increased with decreased 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).