The distribution of antigenic determinants in rat skin collagen

Immunological studies of rat skin collagen were carried out with a sensitive and quantitative radioimmunoassay. Hyperimmune rabbit antisera to rat skin collagen and isolated alpha2 chains were used. Iodine-labeled alpha chains and CNBr-produced peptides served as test antigens, and native collagen, alpha chains, and CNBr peptides were employed as inhibitors in the assay. The alpha1 and alpha2 chains were immunologically distinct. Although the alpha1 chain was not immunogenic, antibodies to alpha1 were detected in antisera to the intact collagen molecule. The major antigenic determinant of the alpha1 chain was located in alpha1-CB6 which constitutes the carboxy-terminal region of the chain. The alpha2 chain contained two non-cross-reacting antigenic determinants, one in the amino-terminal region (alpha2-CB1) and the other in the carboxy-terminal region (alpha2-CB5) of the chain. The native collagen molecule was less effective than isolated alpha chains in inhibiting binding of labeled peptides to antisera, indicating that antigenic determinants were less accessible in the triple helical molecule. These immunologic studies are consistent with preliminary comparative biochemical data which indicate that interspecies structural differences in collagen predominate at both the amino- and carboxy-terminal ends of the chains.