The Separate Roles of Hapten and of Carrier in the Conformation of T Cell-Reactive Determinants on Aba-Protein Conjugates

Abstract

Abstract When new antigenic determinants were formed on a protein by modifying it with p-azobenzenearsonate (ABA), those of the new determinants that were recognized by and activated a T cell-immune response contained functionally separate contributions from the hapten and from the carrier protein. Those parts of the determinant that actually reacted with the T cell recognition site were contributed by the carrier molecule, whereas the hapten contribution was toward specifying the structural arrangement of those parts of the carrier molecule. The indirect nature of the haptenic contribution to the conjugate determinant explains why p-azobenzenearsonic acid on the autologous carrier guinea pig albumin (GPA) cross-reacted with p-azobenzoic acid on the same protein, whereas p-azobenzenearsonic acid in its free form on tyrosine did not cross-react with conjugates of p-azobenzoic acid. Although identity of the hapten components of the autologous albumin conjugates were not necessary for inducing cross-reactive immunity, neither was identity of both hapten and protein moiety sufficient to induce cross-reaction, since ABA-GPA did not induce immunity to ABA-Actyr GPA, and ABA-Actyr-GPA induced only a very weak immunity to ABA-GPA. Thus, the manner or site of attachment of ABA to protein was a major factor in determining the conformation of the determinant that it induced on the protein. In spite of the finding of some cross-reaction between different protein conjugates of ABA, there was no evidence that the conjugate determinants had induced T cell immunity to any structure containing the hapten in an immunologically recognizable form. ABA-protein immune cells did not respond to ABA-amino acids nor to ABA on the amino acid copolymers GT or GL. Enrichment of the cross-reactive population of ABA-OA or ABA-GPA immune T cells by in vitro selection on macrophage pulsed with the cross-reacting antigen did not amplify any small population of hapten-reactive cells that might have been undetectable by direct testing of an unenriched cell population with ABA-amino acids.