6 UNRELATED HLA-DR-MATCHED ADULTS RECOGNIZE IDENTICAL CD4(-CELL EPITOPES FROM INFLUENZA-A HEMAGGLUTININ THAT ARE NOT SIMPLY PEPTIDES WITH HIGH HLA-DR BINDING AFFINITIES() T)

Influenza A/Beijing/32/92 (H3N2) haemagglutinin (HA)-specific short-te rm CD4(+) T cell lines were generated from six unrelated HLA-DR0701, 1 501 positive adults (aged 27-60 years) 3 months following administrati on of an influenza subunit vaccine containing HA A/Beijing/32/92. Epit ope recognition was examined using 118 HA A/Beijing/32/92-specific 16m er peptides which overlapped by 11 residues and which spanned the enti re molecule, Following influenza vaccination the donors recognized ide ntical HA peptides, The selected peptides represented HA regions which have been free from extensive drift mutation since the emergence of h uman H3N2 influenza A strains. Using DAP DR7.0701 cells (a murine cell line expressing HLA-DR0701) as antigen-presenting cells the majority of CD4(+) T cell responses were shown to be HLA-DR0701 restricted. The relationship between HA peptide recognition and relative strength of HA peptide-HLA-DR0701 binding was then explored in a competition assay with biotinylated CLIP peptide, Although peptides representing domina nt HA epitopes bound to DR0701, the relationship between relative stre ngth of binding and immunodominance was complex, and many strongly bin ding peptides, particularly those with glycosylation sites and showing inter-strain variation, were not recognized, These results illustrate the control HLA class II exerts over CD4(+) T cell HA epitope selecti on in unrelated adult humans, Immunodominance appears not to be direct ly related to the relative strength of HA peptide-HLA class II binding , and thus reflects complex interactions between antigen processing, i ntracellular competition for HLA binding, TCR repertoires and repeated exposure to different strains of influenza A viruses.