CD40 ligation induces Apo-1/Fas expression on human B lymphocytes and facilitates apoptosis through the Apo-1/Fas pathway.

Abstract

SummaryThe Apo-1/Fas antigen (CD95) mediates programmed cell death of lymphocytes when bound by Fas ligand or anti-Apo-1/Fas antibody. In contrast, the CD40 antigen provides a potent activation and survival signal to B lymphocytes when it is engaged by its T cell ligand (CD40L, gp39) or cross-linked by anti-CD40 antibody. In this study, we use human tonsillar B cells and the Ramos Burkitt's lymphoma B cell line, which serves as a model for human germinal center B lymphocytes, to study the effectors of Apo-1/Fas expression and apoptosis of human B cells. We found that Apo-1/Fas expression was upregulated on both malignant and normal human B lymphocytes after CD40 ligation induced by (a) cognate T helper-B cell interaction mediated by microbial superantigen (SAg); (b) contact-dependent interaction with CD40L +, but not CD40L-Jurkat mutant T cell clones; and (c) monoclonal anti-CD40, but not any of a panel of control antibodies. Enhanced B cell Fas/Apo-1 expression is functionally significant. Coculture of Ramos Burkitt's lymphoma line cells with irradiated SAg-reactive CD4 + T cells with SAg or CD40L + Jurkat T cells results in B cell apoptosis, evidenced by reduced cell viability and DNA laddering. This process is augmented by the addition ofanti-Apo-1/Fas monoclonal antibody, consistent with an acquired susceptibility to Apo-1/Fas-mediated apoptosis. These data support an immunoregulatory pathway in which seemingly contradictory signals involving the B cell proliferation/survival antigen CD40, as well as the Apo-1/Fas molecule, which mediates programmed cell death oflymphocytes, are linked in the process of human B cell activation.Po-1/Fas (CD95) is a 48-kD cell surface antigen of the TNF/nerve growth factor (NGF) 1 receptor superfamily that mediates apoptosis of T and B lymphocytes (1). The interaction of Apo-1/Fas and its ligand have been shown to play a central role in the regulation of programmed cell death of mature peripheral murine and human T lymphocytes. Defects in both Fas and its ligand have been described in murine models of lymphoproliferative disease characterized by features of SLE (2-4), suggesting that this pathway may be responsible for the deletion ofautAbbreviations used in this paper: CD40L, CD40 ligand; MAM, Mycoplasma arthritidis-derived microbial superantigen; MHC II, MHC class II; NGF, nerve growth factor; SAg, microbial superantigen; TSST-1, toxic shock syndrome toxin 1; TMAMxr, irradiated MAM-reactive CD4 § cells; TTSSTxF, TSST-l-reactive CD4 + cells. toreactive clones. In peripheral T lymphocytes, TCR signaling leads to upregulation of Apo-1/Fas and, on Thl cells, Fas ligand expression, resulting in fratricide or even suicide of antigen-activated T cells (5-8). Although Apol/ Fas expression occurs early after antigen stimulation, susceptibility to Apo-1/Fas-mediated apoptosis develops slowly (9), allowing for the clonal expansion and effector function of antigen-activated T cells before their apoptotic elimination. B lymphocytes also express the Apo-1/Fas receptor (10, 11), and they a...

Sensitivity to Fas-mediated apoptosis is null or weak in B-cell non-Hodgkin's lymphomas and is moderately increased by CD40 ligation

“…CD40 is a membrane molecule expressed on both normal and malignant B cells (Banchereau et al, 1994). Binding of its ligand (CD40L) transduces activation and survival signals, and can lead to an increase in Fas expression (Banchereau et al, 1994;Schattner et al, 1995;Castigli et al, 1996). Normal B cells were reported to be initially resistant to killing via the Fas pathway, and to become sensitive upon CD40 activation, which results in a gradual increase in Fas expression (Garrone et al, 1995;Choe et al, 1996).…”

“…Like Fas, CD40 belongs to the TNFR superfamily, and regulates B-cell activation and differentiation (Banchereau et al, 1994; Castigli et al, 1996). CD40 can induce Fas up regulation on the surface of B cells (Schattner et al, 1995).…”

“…Like Fas, CD40 belongs to the TNFR superfamily, and regulates B-cell activation and differentiation (Banchereau et al, 1994; Castigli et al, 1996). CD40 can induce Fas up regulation on the surface of B cells (Schattner et al, 1995).Understanding the regulation of Fas-mediated apoptosis therefore appears critical for the development of new therapies against NHLs. In this report we tried to characterize the susceptibility of NHL cells to Fas-induced killing and its possible modulation.…”

Rapid CD40‐mediated rescue from CD95‐induced apoptosis requires TNFR‐associated factor‐6 and PI3K

“…CD40 signals allow B cells to proliferate, differentiate, switch isotype, form GC, and become memory cells [3][4][5]. CD40 stimulation also induces upregulation of other members of the TNFR family, including the death receptor CD95/Fas [6].The importance of CD95 in maintaining lymphocyte homeostasis and tolerance is highlighted by the human disease autoimmune lymphoproliferative syndrome (ALPS), caused by mutations in the CD95 signaling pathway [7,8] autoantibodies are produced, and systemic autoimmunity develops [9]. Expression of the CD95 transgene exclusively in T cells of lpr/lpr mice is sufficient to decrease lymphadenopathy, splenomegaly, and the accumulation of abnormal T cells, but these mice still produce autoantibodies, causing deposition of immune complexes in kidney glomeruli [10].…”

“…TRAF6 has been shown to be important in B cells for CD40-mediated IL-6 production, Ig secretion, and CD80 up-regulation, but its role in NF-jB activation may be partially redundant with TRAF2 [23,24]. It is not known which TRAF molecules are required for CD40 rescue from CD95 apoptosis.The relationship between activation of CD40 and CD95-induced apoptosis is complex, because CD40 signals up-regulate CD95 and can thus enhance B cell sensitivity to CD95-mediated death [6]. However, it would be disadvantageous to induce cell death before B cell activation is complete.…”