Single amino acid residues in a synthetic peptide of influenza haemagglutinin, HA 1 177-199, distinguish I-Ad- and I-Ed-restricted T-cell epitopes.

A majority of Iad-restricted, CD4+ T-cell clones, derived from BALB/c mice infected with X31 (H3N2) influenza virus and specific for the HA 1 subunit of the viral haemagglutinin (HA), has previously been shown to recognize the synthetic peptide HA 1 177-199, corresponding to the primary amino acid sequence of a major antibody binding site. Here it is demonstrated that both I-Ad- and I-Ed-restricted T-cell clones recognize HA 1 177-199, and that inter- and intra-allelic differences in Iad-restricted recognition are defined by single amino acid residues. A panel of truncated HA 1 synthetic peptides defined three distinct but overlapping CD4+ epitopes within the common antigenic site (HA 1 177-199): two I-Ad-restricted epitopes mapped within HA 1 186-198 and HA 1 177-199, and peptide HA 1 178-195 identified an I-Ed-restricted epitope. Moreover, fine specificity differences in the recognition of synthetic peptides, truncated at the carboxy terminus of HA 1 177-199, identified residues HA 1 A 198 and HA 1 S 199 as being critical for defining inter- and intra-allelic differences, respectively, in the Iad-restricted T-cell recognition of HA.

The structural requirements for class II (I-Ad)-restricted T cell recognition of influenza hemagglutinin: B cell epitopes define T cell epitopes.

A majority of I-Ad-restricted CD4+ clones elicited by influenza X31 (H3N2) virus infection, recognize a synthetic peptide of hemagglutinin (HA) corresponding to an antibody binding region of the HA1 subunit (site B: HA1 177-199). The structural requirements for class II-restricted T cell recognition were investigated by determining the proliferative responses of representative CD4+ clones to truncated HA1 peptides and synthetic peptide analogues. Two distinct T cell epitopes were identified and CD4+ clones, specific for either determinant, were sensitive to the same single amino acid substitutions in synthetic peptides at HA1 193 S----N or HA1 198 A----E, that had featured in antigenic drift and abrogated antibody binding to native HA. Competitive inhibition studies, between stimulatory HA1 peptides and non-stimulatory analogue peptides, for antigen presentation to CD4+ clones established that the 193 S----N and 198 A----E substitutions could affect either interaction with the T cell receptor or class II molecule, according to the specificity of the CD4+ clone examined. The structural requirements for class II-restricted T cell recognition of the linear sequence determinants of HA are, therefore, integrally linked to conformation-dependent antibody recognition of the native molecule.