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Genetics of the immune response to ferredoxin : assessment of control at the determinant level Sikora, Lydia Kazimiera Jadwiga


Ferredoxin (Fd), a fifty-five amino acid electron transport protein of the anaerobe Clostridium pasteurianum, has been chosen as the ideal probe for immunoregulation studies. Its critical feature is that it contains two antigenic determinants satisfying the hypothetical minimum requirement for immunogenicity. It was found that both the antibody (as measured by ELISA) and the lympho-proliferative responses to Fd are linked exclusively to the MHC of mice, mapping to K/I-A. Analysis of the response was undertaken at the determinant level with selective enzyme cleavage products of trypsin and carboxypeptidase A which yield respectively a 52 residue C-determinant peptide (devoid of a functional N-determinant), "C", and a 53 residue N-determinant peptide (devoid of a functional C-determinant peptide), "N",. Through the use of these two molecules ("N" and "C") and a doubly digested molecule, "M", the immune response to Fd was dissected. At first, anti-Fd antibody from high responder, H-2[sup=k], mice was shown to be 10-20% "N" specific with the balance of the response "C" directed, while intermediate responder haplotypes, H-2[sup=b] and H-2[sup=s]. demonstrate equal specificity for the two determinants. H-2 mice were uniformly non-responsive. Fd immune T-cells demonstrated lymphoproliferative capacity mirroring the antibody response of B10.BR (H-2[sup=k]) mice: "C" induced proliferation comparable to that with the native molecule, "N" inducing a much lower response, one matched by the "M" peptide. Next, the "N", "C" and "M" molecules were assessed for their immunogenicity in B10.BR, C57BL/10 (H-2[sup=b])and B10.D2 (H-2[sup=d]) mice. "N" was found to induce limited, if any, antibody production whereas it primes for a very good proliferative response (B10.BR only). "M" induced no antibody response in any strain, and minimal proliferation in B10.BR. "C" induced at least two-fold higher antibody in B10.BR and C57BL/10 as compared to native Fd, and converted the B10.D2 non-responders into responders. "C" induced a weak proliferative response in B10.BR. The data suggest that two determinants exist at the B-cell level, while three determinants account for the T-cell response.

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