title: Characterization of a novel CD2+ human thymic B cell subset.
abstract: In the present study, it is demonstrated that functionally mature B cells are present in human thymus early during fetal life. Interestingly, 46 +/- 7% of fetal and postnatal thymic CD19+ B cells co-expressed CD2. Adult peripheral blood or splenic B cells were CD2-, and < 5% of fetal BM or fetal splenic CD19+ cells expressed CD2, indicating that CD2 is expressed preferentially on thymic B cells. Fetal thymic CD2+ B cells have a mature phenotype, because they are CD20+, CD40+, and surface IgM+, but they lack CD34 expression. They are also functionally mature because total thymic cell populations or highly purified CD2+ thymic B cells underwent Ig isotype switching and differentiation into Ig-secreting cells in a similar fashion as conventional B cells after culturing in the presence of IL-4 and activated cloned CD4+ T cells and anti-CD40 mAb cross-linked to Fc gamma RII/CDw32 transfected into murine L cells (Fc gamma RII+/L). Engagement of CD2 on thymic B cells by LFA-3+ L cell transfectants, anti-CD2 mAb cross-linked to Fc gamma RII+/L, or a mitogenic combination of anti-CD2 mAb did not result in proliferation or Ig production under the present conditions. However, anti-CD2 mAb enhanced IL-4 dependent Ig-synthesis by thymic B cells in the presence of activated CD4+ T cells, but they were ineffective when the B cells were activated by anti-CD40 mAb, suggesting that the anti-CD2 mAb stimulated antibody production indirectly via CD4+ T cells. Similarly, IL-7 enhanced IL-4-induced Ig production in the presence of CD4+ T cells. This effect of IL-7 also appeared to be indirect because no enhancement in Ig levels was observed in cultures of purified thymic B cells. Collectively, our results indicate that functionally mature B cells are present in human thymus early during fetal life, and that thymic CD2+, CD19+, sIgM+ cells represent a subset of bona fide B cells, which can be induced to Ig isotype switching and Ig production in vitro in a similar fashion as conventional B cells.
authors.affiliation: DNAX Research Institute, Human Immunology Department, Palo Alto, CA 94304-1104.
authors.forename: J
authors.initials: J
authors.lastname: Punnonen
authors.forename: J E
authors.initials: JE
authors.lastname: de Vries
mesh_terms: D000917:Antibody Formation; D015703:Antigens, CD / Q000502:physiology; D000944:Antigens, Differentiation, B-Lymphocyte / Q000502:physiology; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis*; D016175:B-Lymphocyte Subsets / Q000276:immunology*; D018801:CD2 Antigens; D019013:CD40 Antigens; D002478:Cells, Cultured; D005812:Genes, Switch; D006801:Humans; D007132:Immunoglobulin Isotypes / Q000235:genetics; D016130:Immunophenotyping; D066298:In Vitro Techniques; D008099:Liver / Q000196:embryology / Q000276:immunology; D008213:Lymphocyte Activation; D011971:Receptors, Immunologic / Q000032:analysis*; D013950:Thymus Gland / Q000166:cytology* / Q000196:embryology
chemical_list: D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; D000945:Antigens, Differentiation, T-Lymphocyte; D018801:CD2 Antigens; D019013:CD40 Antigens; D007132:Immunoglobulin Isotypes; D011971:Receptors, Immunologic