title: CD8 alpha is an activation marker for a subset of peripheral CD4 T cells.
abstract: Rat CD4 T lymphocytes express CD8 alpha upon activation. Here, we show that double-positive cells express CD8 alpha alpha homodimers, and we study their phenotype and function. Most activated CD4(+) lymphocytes expressing CD8 alpha are recent thymic emigrants. Accordingly, most activated CD4 single-positive thymocytes express CD8 alpha, and thymectomy and aging decrease the frequency of CD4(+)CD8 alpha(+) lymphocytes. However, CD8 induction is not restricted to CD4(+) recent thymic emigrants. CD4(+)CD8 alpha(+) and CD4(+)CD8 alpha(-)cells were generated in vitro from naive or from primed donors and, to study their function, were transferred to normal rats. Both cell types helped primary humoral responses, but only CD4(+)CD8 alpha(-) cells promoted secondary responses. Thus, memory CD4 T cells mediating antibody responses and some naive CD4(+) lymphocytes do not express CD8 alpha. In addition, CD4(+)CD8 alpha(+) cells produce mainly Th1 cytokines while CD4(+)CD8 alpha(-) cells produce IL-10 and showed a sustained proliferative response. Hence, CD8 alpha expression after activation distinguishes two distinct CD4 T cell subsets.
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford, GB.
authors.forename: Emma
authors.initials: E
authors.lastname: Kenny
authors.forename: Don
authors.initials: D
authors.lastname: Mason
authors.forename: Abdelhadi
authors.initials: A
authors.lastname: Saoudi
authors.forename: Ana
authors.initials: A
authors.lastname: Pombo
authors.forename: Francisco
authors.initials: F
authors.lastname: Ramírez
mesh_terms: D000818:Animals; D015415:Biomarkers; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D016827:CD8 Antigens / Q000276:immunology / Q000378:metabolism*; D002455:Cell Division / Q000502:physiology; D006086:Graft vs Host Disease / Q000276:immunology; D051381:Rats; D018800:Thy-1 Antigens / Q000378:metabolism; D013950:Thymus Gland / Q000378:metabolism / Q000601:surgery
chemical_list: D015415:Biomarkers; D016827:CD8 Antigens; C409469:CD8 antigen, alpha chain; D018800:Thy-1 Antigens