Changes in conformation with loss of alloantigenic determinants of a histocompatibility antigen (HLA-B7) induced by monoclonal antibodies.

Two conformations of HLA-B7 have been characterized. In one conformation B7 has epitopes that are: specific to B7, shared with B27, shared with B40, and common to many HLA-B locus products. In the second conformation the B7-specific and B7/B27 cross-reactive epitopes are effectively lost and an additional epitope that is shared with B40 has been acquired. The conformation of papain-solubilized and cell surface B7 can be reversibly changed by monoclonal antibodies against the appropriate epitopes. Antibody bivalency is not an important factor in these changes. In the second conformation B7 is antigenically indistinguishable from B40. It is suggested that conformational changes of this magnitude could contribute to the adaptability of histocompatibility antigens in forming functional complexes with many pairs of T cell receptors and foreign antigens.