Identification of overlapping class I and class II H-2d-restricted T cell determinants of influenza virus N1 neuraminidase that require infectious virus for presentation.

The requirement for endogenous viral protein synthesis in helper and cytotoxic T cell (CTL) recognition of influenza virus was studied at the level of individual epitopes. The viral envelope glycoprotein neuraminidase (NA) contains class I and class II major histocompatibility complex (MHC)-restricted T cell determinants that are presented by virus-infected antigen-presenting cells (APC). We had previously shown that recognition of NA by class II I-Ed-restricted T cells required either active viral infection of APC or introduction of uv-inactivated virus to the cytosol, similar to the well-established requirements for class I-restricted responses. Detailed mapping of T cell epitopes was undertaken using vaccinia virus vectors encoding truncated segments of the influenza NA molecule and by synthetic peptides. Class I MHC-restricted CTL were found to recognize two regions of NA: residues 69-89 in the context of Dd and 191-201 presented by Kd. Analyses of T cell proliferation and T hybridoma clones revealed that class II-restricted responses recognized the same two regions as the CTL, presented by I-Ed and I-Ad, respectively. Interestingly, both class I and class II MHC-restricted T cells showed similar requirements for endogenously synthesized antigen, responding poorly or not at all to endocytosed uv-inactivated virus. This extends previous observations that specific epitopes can be preferentially presented by class II molecules from endogenously synthesized antigens and shows that the same antigenic determinants can have access to both class I and class II antigen presentation pathways.