title: T cell-accessory cell interactions that initiate allospecific cytotoxic T lymphocyte responses: existence of both Ia-restricted and Ia-unrestricted cellular interaction pathways.
abstract: The specificity of the T-accessory cell interactions that initiate primary allospecific cytotoxic T lymphocyte (CTL) responses were found to be surprisingly diverse and of three distinct major histocompatibility complex (MHC) specificities, involving responder T cell recognition of: a) self-Ia accessory cell determinants, b) allo-Ia accessory cell determinants, or c) allo-K/D accessory cell determinants. Any one of these T-accessory cell interactions was sufficient to initiate allospecific CTL responses. It was observed that when accessory cells did not express foreign class I MHC determinants, primary allospecific CTL responses were invariably initiated by Ia-restricted T-accessory cell interactions. In contrast, it was observed that when accessory cells did express foreign class I MHC determinants, primary allospecific CTL responses could be initiated by Ia-independent T-accessory cell interactions that were specific for allogeneic, but not self, K/D determinants and that did not involve recognition of polymorphic Ia determinants. The MHC specificities of the T-accessory cell interactions that initiate primary allospecific and primary trinitrophenyl (TNP)-self CTL responses were also compared. It was observed that primary allospecific and primary TNP-self CTL responses could be initiated by self-Ia-restricted T-accessory cell interactions, and that in both responses the Ia determinants that the responding T cells recognized as self-specificities on the accessory cell surface were those that their precursors had encountered on radiation-resistant thymic elements in their differentiation environment. In contrast to the initiation of primary TNP-self CTL responses that required the activation by accessory cells of Ia-restricted T helper (TH) cells, allospecific CTL responses could also be initiated by class I-restricted T cells specific for accessory cell K/D determinants. Interestingly, such class I-restricted T cells present in primary responder cell populations were triggered only by recognition of allogeneic, but not self, K/D accessory cell determinants, even when the accessory cells were modified with TNP. Thus, the present study demonstrates that primary allospecific CTL responses, but not TNP-self CTL responses, are initiated by Ia-restricted or Ia-independent cellular interaction pathways. These results raise the possibility that unprimed class I-restricted TH cells that mediate the Ia-independent cellular interaction pathway may predominantly express an allospecific, but not a self + X-specific, receptor repertoire. Possible mechanisms by which these distinct T-accessory cell interactions initiate primary allospecific CTL responses are discuss
mesh_terms: D000818:Animals; D003602:Cytotoxicity, Immunologic; D000939:Epitopes / Q000235:genetics / Q000276:immunology*; D005802:Genes, MHC Class II; D006183:H-2 Antigens / Q000235:genetics / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000235:genetics / Q000276:immunology*; D007111:Immunity, Cellular; D008213:Lymphocyte Activation; D008211:Lymphocyte Cooperation; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D013154:Spleen / Q000166:cytology / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
chemical_list: D000939:Epitopes; D006183:H-2 Antigens; D000949:Histocompatibility Antigens Class II