Association of human and bovine beta 2-microglobulins with detergent solubilized HLA-A,B antigens

The association of human and bovine beta 2-microglobulins with detergent solubilized HLA-A,B antigens was analyzed by a direct binding assay using radiolabeled beta 2-microglobulin and an immunoadsorbent containing a monoclonal antibody to the HLA-A,B heavy chains. Binding of beta 2-microglobulin to HLA-A,B heavy chains could be saturated with respect to the amount of membrane glucoprotein in the system and reached steady state after 6 h at 37 degrees C. Inhibition of [125I]beta 2-microglobulin binding to HLA-A,B heavy chains by beta 2-microglobulin purified from human urine or bovine colostrum resulted in identical inhibition curves and apparent dissociation constants of 1 X 10(-8) M. This evidence suggests that beta 2-microglobulins from different species have similar binding sites for HLA-A,B heavy chains.