title: Rapid conversion of naive to effector T cell function counteracts diminished primary human newborn T cell responses.
abstract: The reduced incidence of graft versus host disease following the use of human cord blood as a source of stem cells for bone marrow reconstitution challenges our understanding of the immunocompetence of newborn T cells. Newborn CD4+ T cells express mainly the CD45RA phenotype and have been considered to respond comparably to adult CD4+ T cells exhibiting the CD45RA phenotype. We compared the in vitro kinetics of phenotypic conversion of newborn and adult CD4+CD45RA+ T cells to CD4+CD45RO+ T cells. The cytokine profile and B cell helper activity of the converted CD4+CD45RO+ T cell population were also determined. Newborn CD4+CD45RA+ T cells were converted to CD4+CD45RO+ with significantly faster time kinetics than adult CD4+CD45RA+ T cells, following either phytohaemagglutinin (PHA) or anti-CD2 activation. Freshly purified newborn naive T cells did not produce IL-2, IL-4 or interferon-gamma (IFN-gamma) following stimulation, whereas adult naive T cells secreted IL-2 and adult-derived CD4+CD45RO+ T cells secreted all three cytokines under the same stimulatory conditions. However, newborn and adult CD4+CD45RA+ T cells, following primary stimulation and maturation in vitro, acquired the ability to secrete a Th1-type cytokine profile of IL-2 and IFN-gamma after secondary stimulation. Newborn CD4+ naive T cells that acquired the CD45RO phenotype in vitro also gained B cell helper activity equivalent to that of adult in vitro matured CD4+ naive T cells. These findings suggest that newborn and adult CD4+CD45RA+ T cell subsets are differentially responsive to various stimuli. They show that newborn CD4+CD45RA+ naive T cells can transform more quickly than their adult counterparts into functionally equivalent CD4+CD45RO+ T cells, a process that may be important to counteract the immature immune environment which exists in the newborn.
authors.affiliation: Children's Research Centre, Our Lady's Hospital For Sick Children, Crumlin, Dublin, Ireland.
authors.forename: E
authors.initials: E
authors.lastname: Early
authors.forename: D J
authors.initials: DJ
authors.lastname: Reen
mesh_terms: D000328:Adult; D001402:B-Lymphocytes / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D016207:Cytokines / Q000096:biosynthesis; D005312:Fetal Blood / Q000166:cytology / Q000276:immunology; D006801:Humans; D066298:In Vitro Techniques; D007231:Infant, Newborn / Q000276:immunology*; D007700:Kinetics; D017493:Leukocyte Common Antigens / Q000378:metabolism; D010641:Phenotype; D018417:Th1 Cells / Q000276:immunology
chemical_list: D016207:Cytokines; D017493:Leukocyte Common Antigens