Proliferation and differentiation of human CD5⁺ and CD5⁻ B cell subsets activated through their antigen receptors or CD40 antigens

Abstract

The pan-T cell antigen CD5 has been shown to delineate two different mouse B cell subsets, originating from distinct progenitors. In man, on average, 30% of the tonsillar B cell pool expresses this antigen. In the present report, a detailed comparison of the CD5+ and CD5- B cell response to cytokines, following activation via surface immunoglobulins (sIg) or CD40 antigen, was undertaken. CD5+ B cells were positively selected by panning or by sorting from tonsils. Two-color immunofluorescence analysis performed on tonsillar B cell populations showed that CD5+ B cells displayed most of the phenotypic features of mantle zone B cells. CD5+ B cells could be stimulated for DNA synthesis by mitogenic concentrations of Staphylococcus aureus, Cowan I strain (SAC), insolubilized anti-IgM antibodies, immobilized anti-CD40 antibodies and phorbol 12-myristate 13-acetate (PMA). The growth-response of small dense CD5- B cells to these T cell-independent mitogens was comparable to that of CD5+ B cells, whereas the low-density, in vivo-activated, CD5- B cells were only marginally stimulated by Ig-cross-linking agents and PMA. Following ligation of sIg, both B cell subsets proliferated essentially in response to interleukin (IL)-2 and IL-4. When used in co-stimulation with immobilized anti-CD40 antibodies, IL-4 promoted growth of CD5+ and CD5- B cells, whereas IL-2 displayed only moderate stimulatory effects. CD5+ and CD5- B cells differentiated into Ig-secreting cells when they were co-cultured with SAC or cross-linked anti-CD40 antibodies and IL-2. However, IgM constituted the major component of the Ig response of CD5+ B cells, whereas high levels of IgG were secreted by CD5- B cells.

Modulation of E2F Complexes during G0 to S Phase Transition in Human Primary B-lymphocytes

“…The B-lymphocytes captured by the magnetic beads were then released using Detachabeads (Dynall). As the control, small dense B-lymphocytes were also isolated by flow cytometric sorting from human tonsils, as described (45). The freshly purified B-lymphocytes were seeded at 10 6 cells/ml in culture medium containing 15% fetal calf serum in RPMI and incubated for at least 36 h at 37°C before stimulation by the addition of PMA at 30 g/ml.…”

“…Moreover, little is known about the roles of the E2F and pRB families of proteins during B-lymphocyte activation. The present report describes the modulation of E2F complexes during human Blymphocyte activation through stimulation by PMA 1 (45,46) and explores the molecular mechanisms involved.…”

Identification of TRAF6, a Novel Tumor Necrosis Factor Receptor-associated Factor Protein That Mediates Signaling from an Amino-terminal Domain of the CD40 Cytoplasmic Region

“…CD40 is expressed in late B cells in bone marrow, mature B cells, and certain accessory cells, including bone marrow-derived dendritic cells and follicular dendritic cells (8 -10), and is a receptor for CD40 ligand (CD40L) present on activated CD4 ϩ T cells (11). Signals through CD40 rescue B cells from apoptosis induced by cross-linking of the surface immunoglobulin M complex (12) and also induce B cells to differentiate and to undergo Ig isotype switching (13,14).…”

Two differently regulated nuclear factor κB activation pathways triggered by the cytoplasmic tail of CD40

“…CD40 is expressed in late B cells in bone marrow, mature B cells, and certain accessory cells, including bone marrow-derived dendritic cells and follicular dendritic cells (2,3), and is a receptor for CD40 ligand (CD40L), which is present on activated CD4 ϩ T cells (4). Signaling through CD40 rescues B cells from apoptosis induced by crosslinking of the surface IgM complex (5), induces B cells to undergo Ig isotype switching (6,7), and activates antigen-presenting cells to prime cytotoxic T lymphocytes (8)(9)(10).…”