Absence of major histocompatibility complex restriction in the interaction between processed basic protein and Ia of two rat strains.

Antigen fragments, biologically degraded by antigen-presenting cells (APC), combine with Ia positive moieties (IPM) to stimulate antigen-specific T lymphocyte lines. The main objective of this study was to evaluate whether this interaction was determined by the major histocompatibility complex (MHC) genotype of the APC, thus genetically restricting antigen-specific T lymphocyte proliferative responses. To do so, we assayed the capacity of processed basic protein, associated with IPM, to stimulate basic protein specific T lymphocyte lines derived from the Lewis (LW), Brown Norway (BN), and (LW x BN)F1 rat strains. Our findings are that: (a) IPM replaced the requirement for intact APC in proliferative responses of T lymphocytes to processed basic protein; (b) processed basic protein, irrespective of the genotype of APC from which it was prepared, was fully reconstituted by all IPM genotypes tested. Hence, the interaction between processed antigen and IPM was not found to be MHC-restricted. The possible implication of this conclusion is discussed.