A re-evaluation of the frequency of CD8(+) T cells specific for EBV in healthy virus carriers

EBV is a gammaherpesvirus that can establish both nonproductive (latent) an d productive (lytic) infections within the cells of its host. Although T ce ll responses to EBV latent proteins have been well characterized, little is known about the importance of responses to lytic proteins in long term vir us carriers. Here we have compared the frequencies of CD8(+) T cells specif ic for EBV latent and lytic Ags in healthy virus carriers, using three tech niques: limiting dilution analysis, enzyme-linked immunospot assay, and FAC S staining with tetrameric MHC-peptide complexes. T cells specific for EBV lytic protein epitopes were readily detectable in all donors and were usual ly more abundant than those specific for latent epitopes, We infer that dir ect T cell control of viral replicative lesions is maintained in long term carriers of EBV and is an important component of the immune response to thi s virus. Estimates of CD8(+) T cell frequencies varied considerably accordi ng to methodology; values obtained from MHC-peptide tetramer staining were, on the average, 4.4-fold higher than those obtained from enzyme-linked imm unospot assays, which were, in turn, on the average, 5.3-fold higher than t hose obtained from limiting dilution analysis. Tetramer staining showed tha t as many as 5.5% circulating CD8(+) T cells in a virus carrier were specif ic for a single EBV lytic protein epitope. Such values are much greater tha n previously imagined and illustrate how antigenic challenge from a persist ent herpesvirus can influence the composition of the host's CD8(+) T cell p ool.