Apoptosis induced by the antigen receptor and Fas in a variant of the immature B cell line WEHI-231 and in splenic immature B cells

Abstract

Signaling by the BCR causes proliferation and resistance to Fas-induced apoptosis in mature B cells, but growth arrest and apoptosis in immature B cells. We have identified a variant of the immature B cell line WEHI 231 that retains the apoptotic response to the BCR but has acquired susceptibility to Fas-induced apoptosis. The Fas susceptibility was associated with increased Fas expression on the cell surface and down-regulated IgD expression. These cells exhibited a distinctive functional relationship in response to signals from the BCR, Fas and CD40: BCR stimulation markedly promoted Fas-mediated apoptosis (and vice versa) and Fas-induced apoptosis was not subject to modulation by CD40 signaling. While BCR-induced apoptosis was effectively rescued by CD40, it was not affected by the expression of a dominant-negative FADD. The mechanistic distinctions between BCR- and Fas-induced apoptosis were further characterized by the differential effects of different caspase inhibitors on these two processes which imply the involvement of different subsets of caspases. For BCR-induced apoptosis, we provide evidence that the final apoptotic destruction phase can be inhibited by the pan-caspase inhibitor BOC-Asp-FMK (BD) and that, in the presence of BD, the BCR only induces growth arrest which is reversible. The striking enhancing effects of Fas on BCR-induced apoptosis seen in the variant cells prompted us to examine if a similar cooperation in induction of apoptosis occurs in the highly tolerizable immature B cells of the spleen. We found that the splenic immature B population contains a significant number of Fas-expressing cells, but neither Fas-induced apoptosis nor an enhancing effect of Fas on BCR-induced apoptosis of these cells was detected in vitro.

The anti‐apoptotic factor Bcl‐2 can functionally substitute for the B cell survival but not for the marginal zone B cell differentiation activity of BAFF

“…Consistent with our result, immature splenic B cells are insensitive to Fas triggering [28]. In contrast to FLIP, Tg expression of Bcl-2 restored B cell maturation and function in TACI-Ig-Tg mice, as judged by the rescue of mature lymph node B cells and the ability to mount a Tdependent antibody response.…”

“…TACI-Ig-Tg mice immunized with the T-dependent model antigen NP 28 -chicken gamma globulin (NP-CGG) had a severely impaired anti-NP humoral response, consistent with their deficit in mature B cells. In contrast, TACI-Ig×Bcl-2 dTg mice readily mounted T-dependent humoral responses, indicating that expression of Bcl-2 rescues not only the presence but also the function of B cells (Fig.…”

Environmental Chemical-Induced Bone Marrow B Cell Apoptosis: Death Receptor-Independent Activation of a Caspase-3 to Caspase-8 Pathway

“…Studies performed with transformed and primary immature sIg ϩ B cells have begun mapping apoptosis pathways invoked during clonal deletion (Wu et al, 1996a(Wu et al, , 1998Andjelic and Liou, 1998;Doi et al, 1999;Ruiz-Vela et al, 1999;Tian et al, 2001). Our previous studies with nontransformed, bone marrow stromal cell-dependent, primary pre-B cells and pro-/pre-B cell lines have shown that a similar but clearly distinct set of events leads to apoptosis at an earlier stage of B cell development when cultures are exposed to immunosuppressive environmental chemicals (Yamaguchi et al, 1997a;Mann et al, 1999Mann et al, , 2001Ryu et al, 2003).…”

“…Some of the signaling pathway leading to immature B cell death and clonal deletion has been mapped in model systems in which transformed cells (e.g., WEHI-231) (Wu et al, 1996a(Wu et al, , 1998Andjelic and Liou, 1998;Doi et al, 1999;Ruiz-Vela et al, 1999) or immature splenic B cells (Andjelic and Liou, 1998;Tian et al, 2001) were induced to undergo apoptosis after immunoglobulin cross-linking. In these systems, contributions of nuclear factor-B and c-Myc down-regulation (Wu et al, 1996a,b);p53, p27 Kip1 , and p21 WAF1 up-regulation (Wu et al, 1998); mitochondrial activation (Doi et al, 1999); and protease (calpain, cathepsin, and caspase) activation (Ruiz-Vela et al, 1999) have begun to be defined.…”

B cells from aged mice exhibit reduced apoptosis upon B-cell antigen receptor stimulation and differential ability to up-regulate survival signals

“…Considering that Fas expression not necessarily correlate with Fas-mediated apoptosis susceptibility [32] and that B cells from aged-animals present lower Fas+ B cells than those from young mice, we examined the susceptibility of BCRstimulated B cells from aged animals to anti-Fas killing. Thus, purified splenic B cells from young and aged mice were cultured with F(ab) 2 anti-μ during 48 h, re-cultured with anti-Fas antibody or control hamster IgG during 12 h and stained with PI to determine the percentage of apoptotic cells by FCM.…”