title: Expression of CD8alpha identifies a distinct subset of effector memory CD4+ T lymphocytes.
abstract: Circulating CD4+ CD8+ T lymphocytes have been described in the peripheral blood of humans and several animal species. However, the origin and functional properties of these cells remain poorly understood. In the present study, we evaluated the frequency, phenotype and function of peripheral CD4+ CD8+ T cells in rhesus macaques. Two distinct populations of CD4+ CD8+ T cells were identified: the dominant one was CD4hi CD8lo and expressed the CD8alphaalpha homodimer, while the minor population was CD4lo CD8hi and expressed the CD8alphabeta heterodimer. The majority of CD4hi CD8alphalo T cells exhibited an activated effector/memory phenotype (CCR5lo CD7- CD28- HLA-DR+) and expressed relatively high levels of granzyme B. Intracellular cytokine staining assays demonstrated that the frequency of cytomegalovirus-specific T cells was enriched five-fold in CD4hi CD8alphalo T cells compared to single-positive CD4+ T cells, whereas no consistent enrichment was observed for simian immunodeficiency virus (SIV)-specific T cells. Cross-sectional studies of SIV-infected animals demonstrated that the frequency of CD4hi CD8alphalo T cells was lower in wild-type SIV-infected animals compared to uninfected controls, although prospective studies of SIV-infected animals demonstrated depletion of CD4hi CD8alphalo lymphocytes only in a subset of animals. Taken together, these data suggest that CD4+ T cells expressing CD8alpha represent an effector/memory subset of CD4+ T cells and that this cell population can be depleted during the course of SIV infection.
authors.affiliation: New England Primate Research Center, Department of Immunology, Harvard Medical School, Southborough, MA 01772, and Infectious Disease Unit and Partners AIDS Research Center, Massachusetts General Hospital, Charlestown, USA.
authors.forename: Iole
authors.initials: I
authors.lastname: Macchia
authors.forename: Marie-Claire
authors.initials: MC
authors.lastname: Gauduin
authors.forename: Amitinder
authors.initials: A
authors.lastname: Kaur
authors.forename: R Paul
authors.initials: RP
authors.lastname: Johnson
mesh_terms: D000818:Animals; D000956:Antigens, Viral / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D016827:CD8 Antigens / Q000097:blood*; D016207:Cytokines / Q000096:biosynthesis; D005434:Flow Cytometry / Q000379:methods; D019672:Genes, T-Cell Receptor; D007156:Immunologic Memory; D016130:Immunophenotyping; D008213:Lymphocyte Activation / Q000276:immunology; D008253:Macaca mulatta; D016097:Simian Acquired Immunodeficiency Syndrome / Q000276:immunology*; D015302:Simian Immunodeficiency Virus / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000276:immunology*
chemical_list: D000956:Antigens, Viral; D016827:CD8 Antigens; C431698:CD8alpha antigen; D016207:Cytokines