title: Age-related changes in CCR9+ circulating lymphocytes: are CCR9+ naive T cells recent thymic emigrants?
abstract: The chemokine receptor CCR9 is reported to be predominantly expressed by thymocytes as well as by circulating gut-homing and resident T cells in the small intestinal mucosa. Its ligand thymus-expressed chemokine (TECK) is produced by thymic and small intestinal epithelium. Here we report that the proportion of circulating CCR9+ naive T cells (mostly CD4+) declines with age, from approximately 15% of all T cells at birth to around 1% in adults. The proportion of CCR9+ T cells lacking the classical gut-homing receptor alpha4beta7, was much higher in children than in adults. Therefore, circulating CD3+CCR9+CD45RA+ cells have most likely left the thymus quite recently. This notion was supported by the small number of CCR9+ naive T cells which was present shortly after thymectomy. Establishing a phenotypic marker for recent thymic emigrants might provide a powerful tool in the clinical assessment and follow-up after cancer chemotherapy, hematopoietic stem cell transplantation, and during antiretroviral treatment of human immunodeficiency virus (HIV)-infected patients.
authors.affiliation: Laboratory for Immunohistochemistry and Immunopathology (LIIPAT), Institute of Pathology, University of Oslo, Rikshospitalet, N-0027 Oslo, Norway.
authors.forename: R W
authors.initials: RW
authors.lastname: Olaussen
authors.forename: I N
authors.initials: IN
authors.lastname: Farstad
authors.forename: P
authors.initials: P
authors.lastname: Brandtzaeg
authors.forename: J
authors.initials: J
authors.lastname: Rugtveit
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000276:immunology*; D017252:CD3 Complex / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D002465:Cell Movement; D002648:Child; D002675:Child, Preschool; D005434:Flow Cytometry; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D017493:Leukocyte Common Antigens / Q000378:metabolism; D008875:Middle Aged; D054388:Receptors, CCR; D019707:Receptors, Chemokine / Q000378:metabolism*; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D013934:Thymectomy; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology
chemical_list: C119309:CC chemokine receptor 9; D017252:CD3 Complex; D054388:Receptors, CCR; D019707:Receptors, Chemokine; D017493:Leukocyte Common Antigens