Mapping of a protective helper T cell epitope of human influenza A virus hemagglutinin

The synthetic peptide comprising the 317-341 region of human influenza A vi rus (H1N1 subtype) hemagglutinin elicits peptide-specific antibody and help er T cell responses and confers protection against lethal virus infection. Molecular mapping of the 317-329 region, which encompasses the epitope reco gnized by peptide-specific T cells, revealed that the minimal size required for T cell activation was the 317-326 segment. The most likely peptide ali gnment, which placed 320Leu to pocket 1 of the I-E-d peptide binding groove , was predicted by molecular mechanics calculations performed with the pare ntal and with the Ala-substituted analogs. In Line with the prediction data , the results of the peptide binding assay, where the relative binding effi ciency to I-E-d molecules expressed on the surface of antigen-presenting ce lls was monitored, identified the 320-326 core sequence interacting with th e major histocompatibility class II peptide binding groove. Functional anal ysis of Ala-substituted variants by functional assays and by calculating th e surface-accessible areas of the single peptidic amino acids in the I-E-d- peptide complexes demonstrated that 324Pro is a primary contact residue for the T cell receptor. Our results show that this type of analysis offers a suitable tool for molecular mapping of helper T cell epitopes and thus prov ides valuable data for subunit vaccine design. (C) 2000 Academic Press.