Ex vivo analysis of phenotype and TCR usage in relation to CD45 isoform expression on cytomegalovirus-specific CD8(+) T lymphocytes

Human cytomegalovirus (CMV) is a ubiquitous pathogen which sets up a lifelo ng persistent infection and which can lead to significant disease in the im munosuppressed. The immunological mechanisms controlling CMV in the long te rm are not defined completely, but CD8(+) T lymphocytes are thought to play an important role. Antiviral CD8(+) T lymphocytes may exist in very large pools in healthy individuals. Although the detailed composition of these po ols is not completely understood, there is known to be heterogeneity, in pa rticular of CD45 isoform expression. We have therefore investigated the CD8 (+) T-lymphocyte response against CMV directly ex vivo using Class I tetram ers combined with stains for a range of phenotypic markers followed by four -colour flow cytometric analysis. In particular, we examined expression of these phenotypic markers in relation to the expression of CD45 isoforms. We found that a spectrum of phenotypes exists stably, from CD45R0(high)/RA(lo w) through CD45RA(high)/R0(low), and that expression of other surface marke rs such as CD28 and CD62L, and also TCR usage, may vary in parallel with CD 45 isoform expression. In some individuals, expansions of antigen-specific CD8(+) T lymphocytes bearing specific TCR V beta chains were restricted to cells of particular CD45 isoforms. Immunity against CMV comprises a large p opulation of CD8(+) T lymphocytes with heterogeneous potential, a spectrum in which CD45 isoform expression may play a central role.