CD72 Ligation Regulates Defective Naive Newborn B Cell Responses

• Published in: Cellular immunology 1997-02, Vol.175 (2), p.179-188
• Main Authors: Howard, Laurence M., Reen, Denis J.
• Format: Article
• Language: English
• Subjects: Adult; Aging - immunology; Antibodies, Monoclonal - immunology; Antibody Formation - immunology; Antigens, CD - immunology; Antigens, Differentiation, B-Lymphocyte - immunology; B-Lymphocytes - immunology; Cell Differentiation; Cells, Cultured; Concanavalin A - immunology; Cytokines - immunology; Fetal Blood - cytology; Histocompatibility Antigens Class II - immunology; Humans; Interleukin-10 - immunology; Interleukin-2 - immunology; Lymphocyte Activation; Lymphocyte Cooperation; Middle Aged; T-Lymphocytes - immunology
• ISSN: 0008-8749; 1090-2163
• DOI: 10.1006/cimm.1996.1033

The biological basis for reduced Ig production by naive newborn B cells compared to adult peripheral blood B cells is not fully understood. In a Con A + IL-2 T cell-dependent system using “competent” adult T cells, adult B cells produced large amounts of IgM, IgG, and IgA, while cord B cells were restricted to low levels of only IgM production. Cord B cell activation was also diminished. The contribution of specific B–T cell contact-mediated events to the diminished cord B cell response in this system, using mAbs to CD40, CD28, CD80, and CD72, were investigated, as well as regulation of B cell Ig production by cytokines. αCD72 ligation increased cord B cell activation and IgM production, but did not affect adult B cells. Blocking αCD40 mAb inhibited cord B cell Ig production completely, but only partly inhibited adult B cell Ig production even at high concentration, suggesting a greater sensitivity of cord B cells to disruption of the CD40-CD40L interaction. Addition of IL-10 did not increase cord B cell Ig production, while adult B cell Ig production was increased. However, combined addition of IL-10 and αCD72 significantly increased cord B cell Ig production over that in the presence of either αCD72 or IL-10 alone, but had no effect on adult B cells over that of IL-10 alone. These data suggest that the diminished T cell-dependent response of cord B cells is due to reduced or absent CD72 ligation. CD72 ligation plays an important role in the induction of primary responses by naive B cells. CD72 modulation of naive B cell sensitivity to IL-10 stimulation may have implications in the induction of class switch, which is deficient in newborn B cells. Since all T cells express CD5 constitutively, these data also suggest the existence of another ligand for CD72.