Twelve monoclonal antibodies (HC-MoAb) were prepared against a mixture of denatured HLA-B7 and -B40 heavy chains and were characterized by biochemical methods. The patterns of reactivity of 11 out of 12 of these MoAb were very similar and showed marked preference for the HLA-B locus heavy chains. A single antibody, HC-3, reacted with a subset of the HLA class I heavy chains recognized by the other HC-MoAb, which react with all HLA-B locus heavy chains tested. In pulse-chase experiments, only biosynthetic intermediates consisting of free class I heavy chains were precipitated by the HC MoAb. In addition to free HLA-B and minor quantities of some HLA-A heavy chains, additional class I polypeptides were recognized by the HC-MoAb. A number of these additional class I polypeptides showed a striking correlation with HLA-C as determined serologically. None of these polypeptides could be clearly identified in immunoprecipitations prepared from continuously labeled cells with the MoAb W6/32, previously thought to recognize all HLA-A, B, and C specificities. These findings suggest that in human cells, HLA-C locus products may be associated only weakly with B2m, explaining some of the difficulties encountered in biochemical studies of HLA-C antigens.

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