title: Isoforms of the CD45 common leukocyte antigen family: markers for human T-cell differentiation.
abstract: The diverse host defense and immunoregulatory functions of human T cells are performed by phenotypically heterogeneous subpopulations. Among the membrane antigens that are differentially expressed by reciprocal human T-cell subsets are the CD45RA and CD45RO isoforms of the common leukocyte antigen family, which have been hypothesized to identify "naive" and "memory" T cells, respectively. The CD45RA antigen is first expressed by T-lineage cells relatively late during their intrathymic maturation and continues to be expressed by most T cells in the immunologically naive neonate. With increasing age and antigenic exposure, however, CD45RA-/RO+ cells become more prevalent in the circulation and comprise the majority of cells in tissues. Analyses of the functional capabilities of CD4+CD45RA+ and CD4+CD45RO+ cells have shown that proliferative responses to "memory" recall antigens or the ability to provide help for antibody production are functions uniquely performed by CD4+CD45RA-/RO+ cells. The major immunoregulatory functions described for CD4+CD45RA+ cells involve suppression of immune responses, either directly or via the induction of suppressor activity by CD8+ cells. Two general models of differentiation have been proposed to describe the lineal relationship of these T-cell subsets. Although these subsets could represent mature, phenotypically and functionally stable progeny arising from separate differentiation pathways, there is considerable experimental support for the hypothesis that CD45RA-/RO+ cells are "memory" cells that derive from "naive" or "virgin" CD45RA+/RO- precursors via an activation-dependent postthymic differentiation pathway. Altered frequencies of CD45RA+ and CD45RO+ T cells have been observed in a variety of different clinical conditions, particularly diseases manifesting altered immune function. These findings have contributed new information concerning the physiological events regulating the in vivo generation of these T-cell subsets. In addition, they may provide clues to the pathogenetic processes associated with certain diseases.
authors.affiliation: Department of Pediatrics, UCLA School of Medicine 90024.
authors.forename: L T
authors.initials: LT
authors.lastname: Clement
mesh_terms: D015703:Antigens, CD / Q000276:immunology*; D001327:Autoimmune Diseases / Q000276:immunology; D015415:Biomarkers; D016026:Bone Marrow Transplantation / Q000276:immunology; D005312:Fetal Blood / Q000276:immunology; D006649:Histocompatibility Antigens / Q000276:immunology*; D006801:Humans; D007153:Immunologic Deficiency Syndromes / Q000276:immunology; D007519:Isoantigens / Q000276:immunology*; D017493:Leukocyte Common Antigens; D008213:Lymphocyte Activation / Q000276:immunology*; D008221:Lymphoid Tissue / Q000276:immunology; D008562:Membrane Glycoproteins / Q000276:immunology*; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D013950:Thymus Gland / Q000276:immunology
chemical_list: D015703:Antigens, CD; D015415:Biomarkers; D006649:Histocompatibility Antigens; D007519:Isoantigens; D008562:Membrane Glycoproteins; D017493:Leukocyte Common Antigens