Serological analysis of the dissociation process of HLA-B and C class I molecules

Two forms of HLA class I molecules reacting differentially with the HC-10 monoclonal antibody were identified at the surface of HLA-A3, B7, Cw3 or Cw7 human cells. The HC-10-nonreactive form (which includes all HLA-A3 and a large fraction of HLA-B7, Cw3 and or Cw7 molecules) corresponds to heavy chains apparently tightly associated to beta 2-microglobulin. The HC-10-reactive form (which represents only a fraction of cell surface expressed HLA-B7, Cw3 and Cw7 molecules) corresponds to heavy chains loosely but still associated to beta 2-microglobulin. Further biochemical analyses and the study of mouse transfected cells expressing other HLA class I specificities led to the following conclusions: (a) dissociation of HLA-B and C molecules is a multistep phenomenon, the various stages being identifiable serologically; (b) acquisition of the HC-10 antigenic determinant appears as a hallmark of HLA class I molecules engaged in the process of dissociation; however, its expression does not imply complete separation of heavy and light chains; (c) only the initial stage of the dissociation process can be identified on cell surfaces, whereas (d) following addition of detergent, dissociation of HLA-B and C molecules spontaneously proceeds further, resulting in accumulation in cell lysate of cell surface-derived isolated HLA-B and C class I heavy chains.