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G G Klaus

Publications and source records attributed to G G Klaus.

At least 19 recordsLinked to original sources
PubMed1996

Expression of bcl-x during mouse B cell differentiation and following activation by various stimuli.

We have studied the expression of the novel anti-apoptotic protein bcl-x during mouse B cell differentiation and activation. We find that bcl-x is expressed throughout all stages of B cell differentiation in the bone marrow, and is only down-regulated in mature (sIgD+) B cells. Immature peripheral B cells express low levels of bcl-x even in adult animals, whereas mature resting B cells do not. Mature B cells re-express the protein following activation, achieving maximal levels after 36-48 h. The highest levels of bcl-x are observed with potent mitogenic stimuli (such as anti-CD40 + anti-Ig): B cells first express bcl-x in the G1 phase of the cell cycle and contain maximal levels in S phase. In addition, B cells from CBA/N mice, which do not proliferate when stimulated with anti-Ig, anti-CD40 or both, exhibited only low levels of the protein following culture with these stimuli. To investigate the functional significance of bcl-x in activated B cells, we tested their sensitivity to apoptosis induced by the Ca2+ ATPase inhibitor thapsigargin: B cell blasts activated with anti-CD40 and anti-Ig were resistant to this agent. The available data therefore suggest that bcl-x fulfils two roles in B cells: it promotes survival of immature B cells (which lack bcl-2) and secondly, it apparently plays an additional role in protecting activated mature B cells (perhaps those in germinal centers) from apoptotic stimuli.

Animals↗
PubMed1995

The role of bcl-XL in CD40-mediated rescue from anti-mu-induced apoptosis in WEHI-231 B lymphoma cells.

The phenotypically immature B cell lymphoma WEHI-231 undergoes apoptotic cell death when cultured with anti-immunoglobulin (Ig) antibodies, via a bcl-2-independent mechanism. We have therefore studied the role of the bcl-2-related protein bcl-x in controlling cell death in WEHI-231. We find that overexpression of the long form of bcl-x (bcl-XL) renders these cells refractory to anti-Ig-induced cell death. Stimulation of WEHI-231 via CD40 has similar protective effects. We show here that ligation of CD40 rapidly induces the appearance of the bcl-XL protein in WEHI-231, while stimulation via sIgM, sIgD, CD5 or CD45 receptors, or with phorbol esters plus ionomycin does not. WEHI-231 cells also rapidly undergo massive apoptosis following culture with thapsigargin, a specific inhibitor of the Ca(2+)-ATPase of the endoplasmic reticulum: this is also reversed by anti-CD40, or by overexpression of bcl-XL. We, therefore, conclude that bcl-XL plays a key role in the regulation of antigen receptor-mediated apoptosis via CD40 in WEHI-231. In addition, the fact that this protein is not induced in WEHI-231 in response to phorbol dibutyrate plus ionomycin points to a fundamental signaling defect in these cells, which could conceivably be a reflection of their immature, apoptosis-susceptible phenotype.

Animals↗
PubMed1994

Hypercross-linking surface IgM or IgD receptors on mature B cells induces apoptosis that is reversed by costimulation with IL-4 and anti-CD40.

Cross-linking of sIgM or sIgD receptors on mature B cells with appropriate anti-Ig Abs normally induces B cell activation and DNA synthesis. We show here that hypercross-linking of either class of sIg receptor on these cells by biotinylated, normally mitogenic anti-mu or anti-delta mAb by avidin rapidly induces unresponsiveness to heterologous anti-Ig, accompanied by DNA fragmentation characteristic of apoptosis. Apoptotic nuclei can be detected within 4 h after stimulation, but cells that survive for 12 to 16 h are abortively activated, as evidenced by increased levels of MHC class II Ags. Because the induction of B cell tolerance is known to be modulated by T cell-derived influences, we investigated the effects of two stimuli--IL-4 and ligation of CD40--that are known to affect B cell survival in this system. IL-4 partially reversed the induction of apoptosis, as did a mAb to CD40, and both reagents together caused almost complete reversal. We therefore conclude that in the absence of T cell help the extent of sIg receptor cross-linking on mature B cells determines whether the cells enter cycle or become deleted. We believe that this system represents a polyclonal model of clonal deletion of mature B cells induced by highly cross-linking Ags, such as type 2 T-independent polysaccharide Ags.

Animals↗
PubMed1994

B cells from CBA/N mice do not proliferate following ligation of CD40.

The CBA/N mouse carries the X-linked immunodeficiency xid, resulting in defective B cell development. B cells from these animals cannot mount antibody responses to type 2 T-independent antigens, and do not synthesize DNA when stimulated with anti-immunoglobulin (Ig) antibodies which are mitogenic for normal B cells. The primary antibody responses of CBA/N mice to T-dependent antigens have also been reported to be abnormal. Here we describe the results of experiments which demonstrate that the B cells from these animals respond abnormally to ligation of CD40, a B cell surface molecule now known to play a key role during T cell-B cell interactions, via its interaction with the counterligand (CD40L) expressed by activated T cells. Hence, xid B cells fail to proliferate when cultured with preactivated T helper type 2 (Th2)T cells (known to express CD40L), with a soluble CD40L-CD8 fusion protein, or in response to monoclonal antibodies to CD40, even in the presence of IL-4 and/or anti-Ig reagents. However, xid B cells do receive abortive activation signals following ligation of CD40, as manifested by up-regulation of class II major histocompatibility complex and CD23 antigens. Since the xid defect has now been identified as a point mutation in the protein tyrosine kinase Btk, our results point to an important role for this kinase in the downstream signaling cascade elicited in response to ligation of either surface Ig or CD40.

Animals↗
PubMed1994

Plastic-immobilized anti-mu or anti-delta antibodies induce apoptosis in mature murine B lymphocytes.

It is widely accepted that extensive cross-linking of surface immunoglobulin (sIg) receptors on mature B cells promotes their activation and progression through the cell cycle. A commonly employed method to maximize receptor cross-linking via anti-receptor antibodies is to immobilize them on tissue culture plastic. We show here that immobilizing monoclonal anti-mu or anti-delta antibodies, which are mitogenic in solution, on plastic abrogates their capacity to induce DNA synthesis in mature murine B cells, even in the presence of interleukin-4 (IL-4). The cells do become abortively activated, as evidenced by up-regulation of major histocompatibility complex class II antigen levels, but subsequently virtually all of them die, manifesting DNA fragmentation characteristic of apoptosis. The induction of apoptosis is abrogated by the inclusion of either IL-4 or anti-CD40 antibodies in the cultures, with the two stimuli acting in concert. We believe that the system represents a polyclonal model of clonal deletion tolerance in mature B cells, such as may be induced under physiological conditions by antigens with repeating epitopes.

Animals↗
PubMed1994

Properties of mouse CD40: cellular distribution of CD40 and B cell activation by monoclonal anti-mouse CD40 antibodies.

We describe here the derivation of a rat monoclonal antibody (mAb) against mouse CD40 (designated 3/23), which stains 45-50% of spleen cells of adult mice, approximately 90% of which are B cells. Interestingly, some 5-10% of both CD4+ and CD8+ T cells in the spleens of (some, but not all) adult, unimmunized mice are also CD40+, whereas CD40+ cells were not detectable in the thymus, even following collagenase digestion. Some 35-40% of lymphoid cells in the bone marrow of adult mice are CD40+ and virtually all of these are B220+, and hence of the B cell lineage: triple-color flow cytometry showed that CD40 is expressed at low levels on some 30% of pre-B cells, at intermediate levels on 80% of immature B cells and on essentially all mature B cells in the bone marrow. These results, therefore, suggest that in the mouse CD40 is expressed relatively late during the process of B cell differentiation. The mAb induced marked up-regulation of major histocompatibility complex class II molecules, CD23 and B7.2 antigens on mature B cells. It also stimulated modest levels of DNA synthesis in mature B cells by itself: this was markedly enhanced by suboptimal concentrations of mitogenic (but not non-mitogenic) anti-mu and anti-delta mAb, and moderately enhanced by co-stimulation with interleukin-4. Hypercross-linking of CD40 (using biotinylated mAb and avidin) also enhanced the proliferative response to anti-CD40.

Animals↗
PubMed1994

Properties of mouse CD40: the role of homotypic adhesion in the activation of B cells via CD40.

Stimulation of human B cells via CD40 is known to induce their homotypic aggregation. We show here that anti-mouse CD40 monoclonal antibodies (mAb) also induce B cells to form large, spherical, extremely stable clusters. This clustering is markedly enhanced by co-stimulation with either interleukin-4 (IL-4) or anti-immunoglobulin (Ig). The aggregation is slow in onset, and is largely (but not completely) abrogated by anti-LFA-1 mAb, but not by mAb directed against other potentially important adhesion molecules on B cells. Anti-LFA-1 mAb also partially suppressed DNA synthesis induced by anti-CD40, but not by other B cell mitogens, suggesting that clustering is an important component of B cell activation via CD40. This concept is supported by analyses of the phenotype of clustered B cells: the cells within clusters express higher levels of various activation markers, and also more of them are in cell cycle than non-clustered cells. These results therefore suggest that CD40 stimulation may either induce B cells to secrete soluble factors which act in an autocrine way to promote B cell activation, or that clustering generates cell contact-mediated signals which are important in the activation cascade.

Animals↗
PubMed1994

Properties of mouse CD40. Ligation of CD40 activates B cells via a Ca(++)-dependent, FK506-sensitive pathway.

The immunosuppressive drugs cyclosporine A (CsA) and FK506 selectively abrogate Ca(++)-regulated activation pathways in both T cells and B cells. We show here that anti-CD40-induced murine B cell proliferation, in the presence or absence of interleukin-4 (IL-4) is, like the response to anti-immunoglobulin (Ig), abrogated by 1-5 ng/ml (concentration causing 50% inhibition ca. 1 nM) FK506. However, the effects of the drug on proliferative responses elicited by anti-Ig or anti-CD40 differ significantly: firstly, the response to anti-CD40 + IL-4 becomes completely FK506-resistant within 24 h, whilst that to anti-Ig remains sensitive significantly longer. Secondly, stimulating B cells concurrently via CD40, surface Ig (sIg) and IL-4 receptors invokes an FK506-resistant activation pathway. We previously reported that ligation of either sIg or CD40 receptors, in conjunction with IL-4, induces the transcription factor, nuclear factor of activated T cells (NF-AT) in B cells, via a CsA/FK506-sensitive pathway. However, NF-AT induction elicited by anti-Ig/anti-CD40/IL-4 is still FK506 sensitive, implying that the drug resistance of the response to these three stimuli involves additional components than NF-AT. These results indicate that CD40 activates murine B cells via a Ca(++)-dependent pathway. In agreement with this, anti-CD40 induces a modest increase in intracellular Ca++ levels in these cells, which appears to be largely due to Ca++ influx through the plasma membrane.

Animals↗
PubMed1994

Induction of NF-AT in normal B lymphocytes by anti-immunoglobulin or CD40 ligand in conjunction with IL-4.

We show here that ligation of surface immunoglobulin or CD40 receptors in conjunction with interleukin-4 induces the nuclear factor of activated T cells (NF-AT) in normal murine B cells, which is inhibited by cyclosporin (CsA). Lipopolysaccharide, which activates B cells by a Ca(2+)-independent, CsA-resistant pathway, does not induce NF-AT. The NF-AT complex in T cells and B cells appears to be identical, comprising both Fos and Jun proteins and the 120 kDa cytosolic component of NF-AT (NF-ATp). Our transfection experiments using a trimerized NF-AT site linked to the minimal IL-2 promoter driving luciferase activity demonstrate that NF-AT is functional in A20 B-lymphoma cells. These results therefore suggest that the induction of NF-AT forms part of the B cell response to both cross-linking antigens and T cell-generated signals.

Animals↗
PubMed1993

Cross-linking of surface IgM, but not surface IgD receptors, by soluble monoclonal antibodies primes murine B cells to secrete immunoglobulin in response to lymphokines.

We have previously reported the development of a two-step culture system in which soluble anti-mu monoclonal antibodies prime small resting murine B cells to secrete immunoglobulin (Ig) in response to restimulation with a mixture of interleukin-4 (IL-4) and IL-5. Here we have extended these studies to investigate the effects of engaging surface IgD (sIgD). We find that, unlike anti-mu, three different anti-delta monoclonal antibodies did not prime B cells to secrete Ig. In addition, these anti-delta antibodies inhibited anti-mu-stimulated priming for Ig secretion, while enhancing DNA synthesis in response to anti-mu. Furthermore, anti-delta antibodies still inhibited anti-mu-induced priming when added 24-48 h after anti-mu. These results therefore suggest that triggering of sIgD on B cells induces a dominant inhibitory signal which is not necessarily dependent upon co-ligation of sIgM and sIgD receptors. In addition, these findings raise the possibility that ligating sIgM or sIgD receptors on mature B cells in the absence of T cell help, may produce different downstream effects.

Animals↗
PubMed1993

Polyclonal activation of immature B cells by preactivated T cells: the role of IL-4 and CD40 ligand.

It is well-established that preactivated CD4+ T cells can activate mature B cells in a polyclonal, MHC-unrestricted fashion. We have used this system to investigate the effects of T cell-derived signals on immature B cells purified from the spleens of neonatal mice, since these cells are unresponsive to many polyclonal activators and are exquisitely sensitive to tolerization. We show that immature B cells can be induced to proliferate by anti-CD3 activated, fixed Th1 and Th2 cells, although the latter induce a greater response than the former. Antibodies to IL-4 partially blocked stimulation by Th2 cells, whereas antibodies to IL-2 and IL-5 had no effect on responses to Th1 cells. This suggested that molecules in addition to IL-4 contribute to the capacity of T cells to induce B cell activation, one likely candidate being the ligand for CD40. We therefore generated mouse erythroleukemia (MEL) transfectants which express CD40 ligand (CD40L). These transfectants also induced proliferation of immature B cells, which is enhanced by IL-4. Unlike the situation with mature B cells, both anti-mu and anti-delta antibodies inhibited the activation of immature B cells by CD40L-MEL cells. However, this inhibition was reversed by IL-4, which synergized with signals delivered through CD40 to render immature B cells refractory to negative signals delivered through sIg. Taken together these data suggest that immature B cells can be activated by T cell-derived contact signals and that CD40L-CD40 interactions, in the presence of IL-4, are capable of abrogating the negative signals generated via sIgM and sIgD receptors expressed by these cells.

Animals↗
PubMed1992

Soluble anti-mu monoclonal antibodies prime resting B cells to secrete immunoglobulins in response to interleukins-4 and -5.

Soluble anti-immunoglobulin (Ig) antibodies have been generally found to inhibit Ig secretion in B cells, via largely unknown mechanisms. To investigate this phenomenon further a two-step culture system was used in which B cells are primed for 24-72 h with various soluble monoclonal or polyclonal anti-Ig antibodies: after washing the cells were placed in readout cultures with a combination of interleukin (IL)-5 and IL-4. Using this protocol B cells primed with (mitogenic or nonmitogenic) anti-mu monoclonal antibodies differentiated into large numbers of IgM-secreting cells, comparable to responses to lipopolysaccharide. In contrast, priming with polyclonal rabbit anti-Ig or monoclonal anti-kappa antibodies, markedly inhibited Ig secretion induced by IL-4 + IL-5. In addition, anti-mu was markedly inhibitory if left in the readout cultures with the two lymphokines. These results, therefore, indicate that appropriate cross-linking of surface IgM receptors on B cells can prime the cells to secrete Ig when they are restimulated by T cell-derived lymphokines in the absence of anti-mu. In contrast co-ligation of both surface IgM and surface IgD receptors apparently results in powerful inhibition of Ig secretion, which is not reversed by stimulation with IL-4 plus IL-5.

Animals↗
PubMed1992

Inhibition of lipopolysaccharide-induced activation of immature B cells by anti-mu and anti-delta antibodies and its modulation by interleukin-4.

Soluble anti-Ig or anti-mu antibodies completely abrogate the lipopolysaccharide (LPS)-stimulated proliferation of purified B cells obtained from spleens of 5-7 day old mice. This provides further evidence for the powerful nature of the negative signals transduced by sIgM receptors on immature B cells. In addition, ligation of sIgD receptors (expressed by approximately 30% of these cells) by two out of three monoclonal anti-delta antibodies inhibits the response to LPS by some 50%. Ligation of sIgD on purified sIgD+ B cells (greater than 98% sIgD+) completely inhibited the LPS response of these cells. The inclusion of IL-4 in these cultures partially (with anti-mu), or completely (with anti-delta), restored the proliferative response. Immobilized anti-mu or anti-delta caused comparable levels of inhibition as the soluble antibodies: IL-4 again rescued the inhibition caused by immobilized anti-delta, but not that induced by anti-mu. These results therefore indicate that engaging either sIgM or sIgD receptors on developing B cells delivers negative (tolerogenic) signals. They also implicate IL-4 as a major (although not the only) T cell-derived influence which can modulate these signals. Finally, the data suggest that extensive cross-linking of sIgM (by immobilized anti-mu) causes more profound unresponsiveness in immature B cells, which cannot be rescued by IL-4 alone.

Animals↗
PubMed1991

IL-4 promotes anti-Ig-mediated protein kinase C translocation and reverses phorbol ester-mediated protein kinase C down-regulation in murine B cells.

Co-stimulation of B lymphocytes with IL-4 plus nonmitogenic concentrations of anti-Ig antibodies, or protein kinase C (PKC) activators, drives resting B cells into DNA synthesis. Although cross-linking of the sIg receptors provokes the generation of the intracellular second messengers, inositol 1,4,5-trisphosphate (IP3) and diacylglycerol, the molecular mechanism utilized by IL-4R in murine B cells has not, as yet, been defined. In human B cells IL-4 has been shown to induce a transient rise in IP3 followed by a sustained elevation of cAMP. However, in murine B cells, IL-4 does not induce the release of IP3, Ca2+ mobilization, PKC translocation, or indeed modify signaling via the phosphoinositide pathway induced by ligation of sIg receptors. We now present evidence that, in murine B cells, IL-4 synergizes with nonmitogenic concentrations of anti-Ig to provoke translocation of PKC from the cytosol to membranes. In addition, the lymphokine up-regulates PKC levels and activity and prevents phorbol ester-induced PKC down-regulation in B cells. We therefore propose that (unknown) signals generated via IL-4R potentiate and/or prolong sIg-induced PKC activation. These observations may therefore provide a biochemical basis for explaining how IL-4 and anti-Ig synergize to induce B cell activation.

Animals↗
PubMed1991

Effects of anti-immunoglobulin antibodies, interleukin-4 and second messenger agonists on B cells from neonatal mice.

Crosslinking of surface Ig receptors on mature B cells with mitogenic anti-Ig antibodies stimulates phosphoinositide breakdown with subsequent activation of protein kinase C (PKC) and elevation of [Ca2+]i leading to B-cell activation. This response can be mimicked using second messenger agonists such as phorbol 12,13-dibutyrate (PDB) plus a Ca2+ ionophore. Furthermore, interleukin-4 (IL-4) synergizes with sub-mitogenic concentrations of anti-Ig (or with PDB) to activate adult B cells. In contrast anti-Ig does not activate neonatal B cells but rather desensitizes or kills them. The nature of the signals involved in these effects on neonatal B cells is poorly understood. Here we have investigated the proliferative responses of small, resting B cells from 1-, 4-, 8-, and 12-week-old mice stimulated with combinations of anti-Ig, PDB, ionomycin and IL-4. We find that B cells from 8- and 12-week-old mice show an adult pattern of reactivity. B cells from 4-week-old mice respond to high doses of anti-Ig, anti-Ig + IL-4 and also to PDB + ionomycin + IL-4, but not to PDB + ionomycin alone. Neonatal (1-week-old) B cells respond only to the combination of PDB, ionomycin and IL-4. Most strikingly, pre-incubation of neonatal cells with anti-Ig completely abrogates this response, whilst IL-4 renders them refractory to such anti-Ig mediated inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Antigen receptor-mediated phosphoinositide hydrolysis in murine T cells is not initiated via G-protein activation.

Ligation of the antigen receptors on both T and B lymphocytes induces phosphoinositide (PI) hydrolysis, Ca(2+)-mobilization and protein kinase C activation. The activation of the phosphoinositide-specific phosphodiesterase (PPI-PDE) following crosslinking of surface Ig receptors on B cells is controlled by an uncharacterized guanine nucleotide-regulatory (G) protein. Here we have used permeabilized murine T cells (both resting T cells and a conalbumin-specific CD4-positive T cell clone) to investigate a role for G protein(s) in coupling the TCR to the PPI-PDE. We found that anti-TCR McAb (or processed antigen)-induced PI hydrolysis cannot be uncoupled by permeabilizing T cells, as occurs with classical G protein-linked receptors. Furthermore, the TCR-mediated release of inositol phosphates in permeabilized T cells was not enhanced by non-hydrolyzable analogs of GTP, nor inhibited by GDP analogs. These findings therefore argue strongly against the concept that TCR-mediated PI hydrolysis is G-protein controlled.

Animals↗
PubMed1990

Anti-immunoglobulin antibodies induce apoptosis in immature B cell lymphomas.

WEHI-231 and CH31 are phenotypically immature sIgM+ murine B cell lymphomas whose growth is inhibited by anti-immunoglobulin (Ig) antibodies. These lines have therefore been used as models for studying the role of surface Ig receptors in the induction of B cell tolerance. We show here that anti-mu antibodies induce DNA cleavage into oligonucleosomal fragments characteristic of programmed cell death (apoptosis) in both cell lines, although WEHI-231 cells are less susceptible than CH31. This effect was reversed by lipopolysaccharide, in agreement with the known effects of lipopolysaccharide on anti-Ig-induced growth inhibition. These results therefore indicate that these lymphomas afford a potentially interesting model to study the mechanisms of programmed cell death induced by ligation of the antigen receptors on normal B cells.

Antibodies, Anti-Idiotypic↗