Lymphoma models for B cell activation and tolerance. V. Anti-Ig mediated growth inhibition is reversed by phorbol myristate acetate but does not involve changes in cytosolic free calcium.
ABSTRACT B cell lymphomas which can be growth inhibited by crosslinking their surface IgM receptors by anti-Ig reagents provide models for normal B cell regulation and tolerance. WEHI-231 and CH31 are two independently derived lines that are exquisitely sensitive to negative signalling by antibodies specific for mu or kappa chains, but are unaffected by antibodies against MHC class 1 or 2 antigens. In order to determine the mechanism of this growth inhibition as a model for tolerance, we have examined the roles played by protein kinase C activation and calcium mobilization/influx during negative signalling in these cells. We found that growth inhibition caused by anti-mu crosslinking was reversed in the presence of either phorbol myristate acetate (PMA) or by lipopolysaccharide (LPS) from E. coli. The effect of PMA on negative signalling was a true reversal since phorbol esters could be added after anti-mu treatment, thus allowing nearly normal cellular progression into the S phase of the cell cycle. In contrast, pretreatment with PMA did not provide protection against the growth inhibition from anti-mu. Indeed, a "desensitization" protocol demonstrated that PMA pretreatment actually decreased reversal by both PMA and LPS of the effects of anti-mu on B lymphoma growth. These studies suggest that both LPS and PMA act via at least one common intermediate, which is assumed to involve activation and translocation of protein kinase C. Analysis of changes in calcium ion concentration after treatment with anti-Ig reagents showed both mobilization from internal stores and influx via calcium channels in WEHI-231, as has been reported for normal B cells. However, these changes did not correlate with negative signalling for the several reasons. Firstly, anti-mu inhibition of the growth of WEHI-231 could be induced in the relative absence of extracellular Ca++ or in quin-2 loaded (buffered) cells. Secondly, pretreatment with high concentrations of PMA ablated calcium mobilization, yet failed to modulate growth inhibition in WEHI-231 cells. Moreover, LPS provided protection from the effects of anti-mu yet did not alter cellular [Cai++]. In addition, PMA posttreatment (under conditions causing a reversal of the effects of anti-mu) can be applied as long as four hours after the initial exposure to anti-mu and the rapid measurable changes in calcium flux. Indeed, such changes in intracellular free calcium occurred in elutriated WEHI-231 lymphoma cells at all phases of the cell cycle, although we have previously identified early G1 as the only critical period in which negative signalling can be delivered.(ABSTRACT TRUNCATED AT 400 WORDS)
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ABSTRACT: Summary The antigen receptors on T and B lymphocytes can transduce both agonist and antagonist sig- nals leading either to activation/survival or anergy/death. The outcome of B lymphocyte anti- gen receptor (BCk) triggering depends upon multiple parameters which include (a) antigen concentration and valency, (b) duration of BCP,. occupancy, (c) receptor affinity, and (d) B cell differentiation stages. Herein, using anti-immunoglobulin K and k light chain antibodies, we analyzed the response of human naive, germinal center (GC) or memory B cells to BCR cross- linking regardless of heavy chain Ig isotype or intrinsic BCR specificity. We show that after CD40-activation, anti-BCR.(K+k) can elicit an intracellular calcium flux on both GC and non-GC cells. However, prolonged BCP, cross-linking induces death of CD40-activated GC B cells but enhances proliferation of naive or memory cells. Anti-K antibody only kills K + GC B cells without affecting surrounding k + GC B cells, thus demonstrating that BCR-mediated killing of GC B lymphocytes is a direct effect that does not involve a paracrine mechanism. BCR-mediated killing of CD40-activated GC B cells could be partially antagonized by the ad- dition of IL-4. Moreover, in the presence of IL-4, prestimulation through CD40 could prevent subsequent anti-Ig-mediated cell death, suggesting a specific role of this combination in selec- tion of GC B cells. This report provides evidence that in human, susceptibility to BCP, killing is regulated along peripheral B cell differentiation pathway.
Journal of Experimental Medicine 01/1994; 179(1):221-228. DOI:10.1084/jem.179.1.221 · 13.91 Impact Factor
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ABSTRACT: CD40, a glycoprotein expressed on B lymphocytes plays an important role in B cell development, growth and differentiation. The ligand for the CD40 is a 39-kDa glycoprotein (CD154) expressed onthe surface of activated T lymphocytes and is essential for thymus-dependent humoral immunity. The expression of CD154 is tightly regulated and its transient expression reduces the chances of potentially deleterious bystander activation of B cells. Stimulation through CD40 has been studied in vitro by using antibodies against CD40, by membranes of activated T cells or lately, by CD154 transfected cells. In this work we have evaluated the outcome of CD40-CD40 ligand interaction in vitro and in vivo by using CD154-transfected L929 cells. In vitro assaysshowed that CD154-L929 cells can induce on B cells: IL-4-dependent proliferation, up-regulation of CD23, CD54 and class II molecules and can also rescue WEHI-231 B cell lymphoma from anti-IgM-induced apoptosis. Interestingly, in vivo assays revealed that when CD154-L929 cells were inoculated into the spleen, mice developed a strong but transient production of anti-erythrocyte autoantibodies. Through B lymphocyte activation with CD154-transfected L929 cells both in vitro and in vivo, our data reveal that enforced and prolonged expression of CD40 ligand overcomes the tightly regulated mechanisms of B cell activation, triggering the production of autoantibodies. This system might be used to evaluate the early steps of an autoimmune response and the role of CD40-CD154 in the induction of primary responses in vivo.European Journal of Immunology 12/2001; 31(12):3484 - 3492. DOI:10.1002/1521-4141(200112)31:12<3484::AID-IMMU3484>3.0.CO;2-5 · 4.52 Impact Factor