Direct evidence that a class II molecule and a simple globular protein generate multiple determinants.

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Abstract
We have examined the individual contributions of the I-A.alpha.k chain, the I-A.beta.k chain, and the foreign antigen hen egg-white lysozyme (HEL) in the formation of the determinant being recognized by the T cell receptor. As functional probes we have used (a) a panel of 10 HEL-specific T cell hybridomas, (b) a panel of antigen-presenting cells (APC) possessing mutations in either the I-A.alpha.k or I-A.beta.k chains, and (c) proteolytic fragment of HEL and related synthetic peptides. The ability of the I-A.beta.k and I-A.alpha.k mutant cell lines to present antigen to the 10 T cell hybridomas divided these T cells into six distinct groups. These HEL-specific T cells therefore appear to recognize several distinct domains on the I-Ak molecule. The 10 T cell hybrids were then shown to recognize at least three distinct determinants on the HEL molecule, with 8 of the 10 hybrids recognizing one of two major determinants HEL(46-61) or HEL(34-45). Combining the response patterns to the panel of I-Ak mutant APC lines with the antigen specificity revealed that the 10 T cell hybrids recognized at least eight unique determinants formed by the I-A.alpha.k chains, I-A.beta.k chains, and HEL peptides. This analysis provides direct evidence that a large number of different determinants or T cell receptor ligands can be generated from a single Ia molecule and a simple globular protein.

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