The immune response to ferredoxin: characterization of a major idiotype in serum using monoclonal antibody derived by cell fusion

Abrogation and reconstitution of nonresponsiveness: a correlation with high network connectivity

A monoclonal antibody (Fd-B2) to ferredoxin, which bears an idiotype scarcely expressed in any of a wide variety of mouse strains, is able to markedly enhance the response to ferredoxin of both high-responder and intermediate-responder strains. A rabbit anti-idiotype serum to Fd-B2 also specifically enhances the response to ferredoxin in such mice. Most remarkably, the treatment of nonresponder T cells by either the idiotype (Fd-B2) plus complement or anti-idiotype antiserum plus complement causes them to be responsive in adoptive transfer experiments. The two responding populations (idiotype-treated and anti-idiotype-treated) can then be combined to reconstitute the nonresponsive state. When the nonresponders are treated with either Fd-B2 idiotype plus complement or anti-idiotype plus complement and subsequently respond, the idiotype of the anti-ferredoxin antibody produced does not bear the Fd-B2 idiotype. We interpret the results as being consistent with a model in which the unresponsive state for ferredoxin is a state of high network connectivity of the ferredoxin-specific T cells.

Identification of an idiotypic marker of a major regulatory T cell of the immune response in B10.BR mice to ferredoxin. The relationship of idiotypic regulation to conventional hapten-carrier effects

An anti-idiotypic antiserum was raised in rabbits to a monoclonal antibody (Fd-1) with specificity for one (the N epitope) of the two antigenic epitopes found on the ferredoxin (Fd) molecule. The anti-idiotypic antiserum (anti-Fd-1) was used to demonstrate that the Fd-1 idiotype was expressed at significant levels in most anti-Fd antisera raised in B10.BR mice. Examination of antisera raised in other mouse strains demonstrated that expression of this idiotype mapped to the IgH gene complex and was found in the antisera of all mouse strains examined with the Ig-1 allotype. When splenocytes from Fd-immune B10.Br mice were treated with anti-Fd-1 and transferred to irradiated syngeneic recipients, the adoptive secondary response was significantly higher in animals receiving treated cells as opposed to control animals, which received normal rabbit serum-treated cells. This response produced a net increase in antibody to both determinants, and the relative amount of Fd-1 idiotype was not significantly altered. Further studies with separated cell populations showed that the overall increase of anti-Fd antibody produced was attributable to the effects of the anti-idiotypic serum on a population(s) of T cells. Treatment of mice with the Fd-1 monoclonal antibody (which should react with anti-idiotypic cells) had an analogous effect to that of the anti-idiotype, in that mice so treated produced higher concentrations of anti-Fd antibodies when they were immunized and these antibodies exhibited net increases to both determinants. A model is presented to explain these results.

The use of unideterminant fragments of ferredoxin in the genetic mapping of determinant specificity of the immune response

The ferredoxin (Fd) molecule is a small non-mammalian immunogenic protein containing 55 amino acid residues with only two major antigenic determinants located with the NH2-terminal heptapeptide and the COOH-terminal pentapeptide. Selective enzyme cleavages of Fd with either trypsin or carboxypeptidase A result in the inactivation of the antigenic determinants by the removal of a tripeptide at the NH2-terminal and two amino acid residues at the COOH-terminal, effectively leaving 52 and 53 amino acid fragments respectively, each containing a single antigenic determinant. Fd digested with both enzymes yielded a 50 amino acid peptide with both determinants inactivated. Purity of these digests was assessed using monoclonal antibodies in standard and antigen-blocking ELISAs. The doubly digested peptide had virtually no reactivity with anti-Fd sera, reconfirming that the central cysteine-rich region is serologically silent. It was found that the sum of the reactivities of the N- and C-determinant-bearing peptides as equal to that of the native Fd and that the ratio of the reactivities could be used to assess determinant selectivity in the response to Fd in congenic recombinant strains of mice. This method was used in mapping the determinant selectivity in the antibody response to the MHC of mice to the left of the I-B subregion. Use of the B10.HTT strain indicated that separate genes mapping to the same subregion code for the magnitude of the antibody response and the determinant selectivity of the response.