Characterization of immunologically active cyanogen bromide peptide fragments of bovine and human retinal S-antigen.

Peptides which account for most, if not all, of the cyanogen bromide (CNBr)-generated peptide fragments of bovine retinal S-antigen have been identified and examined for their immunoreactivity with antisera raised to bovine and human S-antigen and with immune lymphocytes further selected twice in vitro with either bovine or human S-antigen. Amino-acid sequencing of a large fragment of S-antigen missing a small N-terminal peptide revealed the location of three overlapping CNBr peptides near the N-terminus. Amino-acid sequencing of several other CNBr peptides has allowed their position in a partial DNA-predicted sequence of the carboxy terminal half of the antigen to be determined. The total CNBr digest of human S-antigen was also prepared and compared with the fragments of the bovine antigen. Sera from rats immunized with bovine or human S-antigen were similar in their specificity in the enzyme-linked immunosorbent assay (ELISA) for purified bovine peptides except for the CB21 peptide which was not significantly bound by anti-human S-antigen sera. All of the other bovine peptides recognized by anti-bovine S-antigen sera were also bound by antibodies in the sera raised to the human antigen. The CNBr peptides of human and bovine S-antigen were extracted from gel slices and also assayed in the ELISA. Peptides of bovine S-antigen purified by HPLC were tested for their ability to stimulate an in vitro proliferative response in lymphocytes from Lewis rats immunized with either bovine or human S-antigen. Only quantitative differences in the proliferative response to human vs. bovine S-antigen and CNBr peptides were found. Methodology for the purification and analysis of the peptides is presented as well as the properties of the peptides.