Chemical, physical-chemical, and immunological properties of papain-solubilized human transplantation antigens

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Abstract
Papain-solubilized HLA-A, -B and -C antigens were isolated from cadaveric spleens. The isolated material was homogeneous and comprised subunits with the apparent MW 33,000 and 12,000. Amino acid analyses of a mixture of HLA antigen H chains obtained from spleens with different HLA antigen phenotypes revealed a composition that was very similar to that of individual HLA-A and -B antigens. The NH2-terminal 30 residues of the HLA-antigen H chain mixture were virtually identical with that recorded for individual specificities. The circular dichroism spectra for the isolated HLA antigens and for free .beta.2-microglobulin revealed similarities with spectra recorded for immunoglobulin chains and domains. The HLA-antigen H chain may contain an appreciable amount of .beta. structure. Antibodies raised against free .beta.2-microglobulin react better with .beta.2-microglobulin in free form than when bound to the HLA-A, -B and -C antigen H chains. This was due to the fact that free .beta.2-microglobulin can bind a maximum of 4 Fab fragments simultaneously. The HLA-antigen-associated .beta.2-microglobulin can bind only 2 Fab fragments without dissociating from the heavy HLA-antigen subunit.