Clonal analysis of the major histocompatibility complex restriction and the fine specificity of antigen recognition in the T cell proliferative response to cytochrome C.

Abstract

Experiments were performed with pigeon cytochrome c-specific T cell lines and clones from H-2 congenic B10.A and B10.S(9R) mice in order to assess the influence of Ia molecules on the genetic control and fine specificity of the T cell proliferative response. Families of clones that were derived from the long-term lines of both strains were all shown to respond to a dominant carboxyterminal determinant on the immunogen in the context of homologous I-A/E(β):I-E(α) Ia molecules expressed on antigen-presenting cells (APC). One dominant clonal phenotype was found in the B10.A and two in the B10.S(9R). However, minor phenotypic variants could be discerned in three separate ways: a) by difference in the fine specificity of antigen recognition in the context of syngeneic Ia; b) by the presence or absence of degeneracy in major histocompatibility complex restriction for antigen recognition; and c) by the presence in some clones of concomitant alloreactivity. Among the latter clones was one restricted in antigen recognition to the syngeneic I-A/E(β)(k):I-E(α)(k) Ia molecule but simultaneously alloreactive against an Ia molecule encoded within a different I subregion (I-A(β)(s)I-A(α)(s). Another antigen-specific clone displaying concomitant alloreactivity was shown to mount a significant additional antigen-specific proliferative response in the context of the same allogeneic Ia molecule. Thus, a single T cell clone recognized an Ia molecule as both an alloantigen and as a restriction element for nominal antigen recognition. In the case of the T cell clones capable of responding to pigeon cytochrome c in the context of either B10.A or B10.S(9R) APC, the fine specificity of antigen-induced activation was shown to vary with the haplotype of the APC, confirming that the Ia molecule must contribute to the fine specificity of antigen-induced T cell activation. Such variation in antigen dose-response patterns with APC haplotype was also observed in the comparative proliferative response of a single B10.A T cell clone to pigeon cytochrome c and its carboxyterminal fragment 81-104, which indicated that the whole molecule and its fragment behave as distinct antigens in T cell recognition. In addition, the influence of the I-region gene products on the clonally expressed T cell receptor repertoire was demonstrated by the absence of overlap between clonotypes from the B10.A and B10.S(9R), even among the clones capable of responding to pigeon cytochrome c in the presence of APC from either strain. Finally, the identification of families of closely related, though phenotypically distinct, T cell clonotypes specific for the same globular protein antigen provided suggestive evidence for the presence of somatic mutational mechanisms in the generation of T cell receptor diversity.