title: A novel subpopulation of primed T cells in the human fetus.
abstract: Virgin and memory T cells reciprocally express high levels of the RA or the RO isoforms of CD45, respectively. In an examination of T cell expression of these two CD45 isoforms during human development, the RO+RA- "memory" T cells were infrequent in the newborn blood and spleen, but comprised approximately half of the T cells in adult tissues. These anticipated findings probably reflect the immunologic naivete of the newborn. Surprisingly, however, RO+RA- T cells were relatively abundant in fetal spleen and in cord blood samples from premature births, comprising approximately 25% and 10% of the T cells in these tissues, respectively. This early peripheral wave of RO+RA- T cells was composed of polyclonal T cells in both the CD4 and CD8 subpopulations. The fetal RO+ cells of CD4+ phenotype frequently expressed the CD25-alpha chain subunits that characterize high affinity IL-2 receptors, and were able to proliferate in response to exogenous IL-2. In further contrast with their RO+ memory T cell counterparts in adults, the fetal T cells were unresponsive to mitogenic anti-CD2 and anti-CD3 antibodies. We conclude that the data suggest an embryonic population of autoreactive T cell clones with anergic characteristics.
authors.affiliation: Department of Medicine, University of Alabama at Birmingham 35294.
authors.forename: J A
authors.initials: JA
authors.lastname: Byrne
authors.forename: A K
authors.initials: AK
authors.lastname: Stankovic
authors.forename: M D
authors.initials: MD
authors.lastname: Cooper
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002478:Cells, Cultured; D002648:Child; D002675:Child, Preschool; D005260:Female; D005333:Fetus / Q000276:immunology*; D006801:Humans; D016130:Immunophenotyping; D007223:Infant; D017493:Leukocyte Common Antigens / Q000032:analysis; D008875:Middle Aged; D011247:Pregnancy; D016176:T-Lymphocyte Subsets / Q000276:immunology*
chemical_list: D017493:Leukocyte Common Antigens