Purification and partial amino acid sequence of papain-solubilized class II transplantation antigens

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Abstract
Papain-solubilized human class II (HLA-DR) antigens were purified from cadaveric spleens by ion-exchange chromatography, gel chromatography and immunosorbent purification. The isolated papain-solubilized antigens comprised 2 subunits with apparent MW of 23,000 and 30,000, respectively. The circular dichroism spectrum for the isolated class II antigens was similar to spectra recorded for HLA-A, -B and -C antigens, Ig and Ig fragments. Class II antigens contain a considerable amount of .beta. structure. The small subunit (.beta. chain) exhibited extensive charge heterogeneity on 2-dimensional isoelectric focusing polyacrylamide gel electrophoresis, whereas the large subunit (.alpha. chain) was more homogeneous. The structural heterogeneity of .beta. chains remained after neuraminidase treatment. The NH2-terminal amino acid sequence of the .beta. chains displayed multiple residues in several positions in accordance with the genetic polymorphism displayed by this chain. The .alpha. chain also displayed multiple residues in some positions, suggesting either that some of the genetic polymorphism of the class II antigens may be endowed in this chain or that multiple loci control the expression of several .alpha. chains. Papain-solubilized class II antigen subunits were homologous in their amino acid sequences with HLA-DR antigens of defined antigenic specificity and with murine I-E/C antigens.