FINE-STRUCTURE OF A VIRUS-ENCODED HELPER T-CELL EPITOPE EXPRESSED ON FBL-3 TUMOR-CELLS

Antigen peptide f(n20) representing Friend murine leukemia virus env(1 22-141) (DEPLTSLTPRCNTAWNRLKL) is recognized by two independent Friend virus-induced, FBL3 tumor-specific helper T-cell (Th) clones. We isol ated more Th clones from mice immunized with f(n20) peptide. We examin ed the fine structure of the peptide required to activate a large grou p of f(n20)-specific Th clones. A systematic analysis of peptides of d ecreasing lengths eliciting Th proliferation defined the minimum core length as 13 amino acids (LTSLTPRCNTAWN). Functional proliferation and competition assays with variant peptides with alanine substitutions p ermitted the assignment of five peptide residues in two major histocom patibility complex-interacting and three T-cell-receptor-interacting s ites. Th clones were different in their reactivities toward peptides o f various lengths and the variant peptides.