Development of T cell clones reactive to two defined restriction elements in conjunction with two defined epitopes of antigen

A previously described pig insulin (PI)-specific T cell line of (B10 X B10.BR)F1 origin was assayed for its reactivity with species variants of insulin in the presence of antigen-presenting cells (APC) of various H-2 haplotypes. In addition to its reactivity with PI and bovine insulin (BI) in the context of syngeneic F1 (H-2b X k)-APC, a weak cross-reactivity was observed with parental B10 (H-2b)-APC and BI but not PI. The cross-reactive cells could be selected out by several restimulations with the combination of BI and B10-APC. From the resulting, strongly cross-reactive T cell line several interleukin 2-dependent sublines were developed which did not require antigen-specific restimulations for further propagation. All such sublines had retained the original cross-reactivity with BI and B10-APC but showed significant differences in their fine specificity patterns, which indicates that each subline represents a clonal population. One of the sublines was cloned by limiting dilution at one cell/culture with a cloning efficiency of 76%. Five of the clones that were tested for reactivity had the same cross-reactivity as the original subline and upon recloning at 0.1 cells/culture the pattern again remained unchanged. From an analysis of the two antigen combinations (PI/F1 and BI/B10) it can be concluded that single cells can react with different restriction elements in the context of distinct epitopes of insulin. The implications of this finding for the mechanism of T cell recognition are discussed and a model for the function of major histocompatibility complex molecules in T cell recognition is proposed.