Effect of B-cell receptor engagement on CD40-stimulated B cells

Activation of human B cells in vitro either by cross-linking of surface immunoglobulins (sIg) or by triggering CD40 antigen, in the presence of interleukin-10 (IL-10) and interleukin-2 (IL-2), may result in high levels of immunoglobulin secretion in vitro. We studied the combined effects of ligation of the B-cell receptor (BCR) and CD40 [with anti-CD40 monoclonal antibody (mAb)] on B-cell proliferation and production of human immunoglobulin. For this purpose highly purified splenic B cells were cultured with various combinations of anti-CD40 and IL-10/IL-2 or IL-4 in the presence of CD32-transfected L cells. Simultaneous cross-linking of the BCR was achieved by mAb held on CD32-L cells or Staphylococcus aureus (SA). We found that dual BCR and CD40 ligation with IL-10/IL-2 leads to reduced immunoglobulin G (IgG) secretion compared with B cells stimulated with either anti-CD40 and IL-10/IL-2, or compared with B cells stimulated with SA or anti-BCR mAb and IL-10/IL-2. Dual BCR and CD40 ligation with anti-immunoglobulin mAb (anti-kappa + anti-lambda light chains) but not with SA induced a similar reduction in IgM production. The reduced immunoglobulin secretion found during dual ligation is accompanied by increased proliferation. This was independent of cytokine stimulation but SA/CD40-induced proliferation was increased in the presence of IL-10/IL-2, although not with IL-4. The combination anti-kappa and anti-lambda with anti-CD40 showed a long-term suppression of IgG and IgM production (at least 14 days), while anti-kappa or anti-lambda alone, or SA, allowed a moderate recovery of immunoglobulin production by day 14. These results suggest that simultaneous B-cell antigen receptor cross-linking and CD40 engagement via CD40L on T cells induces strong initial proliferation. This may be followed later by antibody production depending on the strength of the BCR signal and the presence of the appropriate cytokines.     

Identification of two distinct CD5- B cell subsets from human tonsils with different responses to CD40 monoclonal antibody

This study investigated the response of different CD5- B cell subsets to CD40 monoclonal antibody (mAb) in various combinations with interleukin (IL)-4 or rabbit anti-human mu chain antibody (a-mu-Ab). The different CD5- B cell subsets were isolated from tonsillar B cell suspensions depleted of CD5+ B cells and subsequently fractionated on Percoll density gradients. While resting CD5+ B cells proliferated and produced IgM molecules in response to a-mu-Ab, IL-4 and CD40 mAb as well as to Staphylococcus aureus Cowan strain I (SAC) and IL-2, resting CD5- B cells, which were co-purified in the same 60% Percoll fractions, consistently failed to respond. These cells were, however, activated by the stimuli employed, as demonstrated by their capacity to express the surface activation markers CD69, CD25 and CD71. Resting CD5+ B cells had the typical phenotype of mantle zone B cells (IgM+ IgD+ CD39+ CD38- CD10- CDw75dim), whereas resting CD5- B cells were CD38- CD39- CD10- CDw75 intermediate and expressed surface IgM but relatively little surface IgD and could not be classified as mantle zone or germinal center cells. The finding that purified germinal center cells (CD38+ CD10+ CD39- CDw75bright, IgG+) responded to CD40 mAb and IL-4 and also to SAC plus IL-2 further underlined the differences to resting CD5- B cells. However, some of the data collected suggest possible relationships between CD5- B cells and germinal center cells. The CD5- B cells isolated from the 50% Percoll fraction proliferated in response to a-mu-Ab, CD40 mAb and IL-4 as well as to SAC and IL-2. These cells had the same mantle zone B cell phenotype as the CD5+ B cells, but their capacity to respond to the stimuli in vitro was unrelated to a possible contamination with CD5+ B cells, as documented by the appropriate controls. Furthermore, upon exposure to SAC or phorbol esters, the large majority of CD5- B cells from the 50% Percoll fraction did not express surface CD5 and there was very little if any accumulation of CD5 mRNA. Finally, most of the cycling cells in the stimulated CD5- B cells did not express CD5. The CD5- B cells from the 50% Percoll fraction were comprised of a consistent proportion of cells that expressed surface activation markers.(ABSTRACT TRUNCATED AT 400 WORDS)     

CD40-mediated stimulation contributes to lymphocyte proliferation, antibody production, eosinophilia, and mastocytosis during an in vivo type 2 response, but is not required for T cell IL-4 production

CD40/CD40 ligand interactions are required for the development of T cell-dependent Ab responses in vivo. The role of these cell surface molecules in contributing to T cell cytokine production and the development of effector populations other than B cells and T cells is, however, less well defined. We have examined the in vivo effects of blocking CD40/CD40 ligand interactions on the type 2 mucosal immune response that follows oral inoculation of mice with the nematode parasite, Heligmosomoides polygyrus. Administration of anti-gp39 (CD40L) mAb (MR1) blocked H. polygyrus-induced elevations in serum IgG1 levels and inhibited elevations in blood eosinophils and mucosal mast cells at day 14 after inoculation. Anti-gp39 mAb markedly inhibited B cell blastogenesis 8 days after H. polygyrus inoculation but did not inhibit elevations in B cell class II MHC expression. Maximal elevations in B7-2 expression required signaling through both CD40 and the IL-4R. Elevations in T cell cytokine gene expression and elevations in the number of IL-4-secreting cells were unaffected by treatment with anti-gp39 mAb, although IL-4 production was inhibited by anti-IL-4R mAb. These results suggest that CD40/CD40L interactions are not required to activate T cells to produce cytokines but are required for the activation and proliferation of other effector cells associated with the type 2 response.     

Monomeric IgG2 enhances Ig production and proliferation in human B cells

The effect of purified polyclonal human IgG subclasses on B-cell responses was studied using the human IgA-producing B-cell line GM-1056. IgG2 at concentrations of 0.01-1 microgram/mL enhanced both IgA production and proliferation, while IgG1, IgG3, and IgG4 each failed to do so at tested concentrations between 0.001 and 10 micrograms/mL. This enhancement was Fc gamma R mediated, since IgG2 Fc fragments enhanced IgA production and proliferation to the same extent as did the whole IgG2 molecule, whereas F(ab')2 fragments did not. However, in contrast to monomeric IgG2, aggregated IgG2, which was expected to bind Fc gamma RII on B cells, affected neither IgA production nor proliferation. Similarly, anti-CDw32 mAb (2E1, anti-Fc gamma RII), anti-CD 64 mAb (32.2 anti-Fc gamma RI), and anti-CD16 mAb (Leu 11a, anti-Fc gamma RIII) mAb each failed to stimulate GM-1056 cells, and more importantly did not block IgG2-induced stimulation. Of various cytokines tested, including IFN-alpha, IFN-gamma, IL-1 beta, IL-2, IL-3, IL-4, IL-5, and IL-6, IL-6 alone augmented IgG2-induced enhancement of IgA production and proliferation. Moreover, the IL-6 effect was lost following preabsorption with anti-IL-6 antibody but not following preabsorption with control antibody. IgG2 also enhanced Ig production and proliferation in tonsillar large activated B cells, while IgG1, IgG3 and IgG4 each failed to do so. In contrast, IgG2 had no effect on Ig production and proliferation in tonsillar small resting B cells or SAC-stimulated small B cells. IgG2-induced enhancement of Ig production and proliferation in large B cells was not blocked by 2E1, 32.2, or Leu 11a, while enhancement was augmented in a specific fashion by IL-6. These results indicate that monomeric IgG2 specifically enhances B cell responses via an Fc gamma R receptor distinct from Fc gamma RI, Fc gamma RII, and Fc gamma RIII, and that IL-6 may play a role in augmenting this response.     

Ligation of CD5 on resting B cells, but not on resting T cells, results in apoptosis

The CD5 molecule is expressed by a B cell subset. We have demonstrated that resting B cells do not proliferate in response to CD5 ligation, whereas cells preactivated with anti-IgM and IL-2 do so. Here, we specifically studied the effects of anti-CD5 and anti-IgM on apoptosis of CD5+ B cells. Both ligation of CD5 or of surface IgM (sIgM) resulted in apoptosis. This started earlier following ligation of CD5 than with sIgM, and both responses were time dependent. CD5-induced apoptosis was independent of the epitope recognized or the way the antibody was presented to the B cells. CD5+ B cells were more sensitive to IgM-induced apoptosis than CD5 B cells. Engagement of CD5 or CD3 expressed by T cells failed to induce apoptosis. Our data indicate differences in the function of CD5 molecules on tonsillar B cells, compared with blood T cells and suggest that cross-linking CD5 on B cell activates specific pathways responsible for apoptosis.     

Fas (CD95)-transduced signal preferentially stimulates lupus peripheral T lymphocytes

Fas (CD95) is a cell surface receptor whose biological function in circulating peripheral T cells is not well understood. To address the question of abnormal T cell sensitivity to Fas stimulation in systemic lupus erythematosus (SLE), we studied Fas-transduced stimulation and apoptosis in peripheral blood T cells from patients with SLE and normal control. Immobilized anti-Fas monoclonal antibodies (mAb) (imCH-11; IgM type) significantly stimulated SLE T cell proliferation compared to T cells from normal donors and patients with rheumatoid arthritis (p < 0.003 and p < 0.005, respectively). The soluble form of CH-11 and other immobilized anti-Fas mAb (UB-2, ZB-4; IgG type) failed to stimulate lupus T cells while immobilized human Fas ligand did. Furthermore, imCH-11 induced IL-2 and IL-6 mRNA expression. However, imCH-11 activation failed to induce expression of the T cell activation surface molecules CD25 and CD69. Addition of exogenous ceramide, a second messenger for Fas-mediated apoptosis signaling, also induced T cell proliferation in SLE and normal controls. Moreover, fumonisin B1, a specific ceramide synthase inhibitor, and caspase inhibitors markedly suppressed imCH-11 induced T cell proliferation, suggesting that the ceramide pathway may be involved in Fas-transduced stimulation signals in SLE T cells. These results show that SLE T cells have an alteration in the Fas signal transduction pathway leading to cell proliferation. This defect may be important in Fas-mediated peripheral immune homeostasis.     

Autologous bone marrow support and bone disease in metastatic breast cancer

Production of IgM, IgG and IgA was induced from human blood B lymphocytes by culturing with a CD40 MoAb and IL-2 for 9 days. Replacement of IL-2 by IL-10 markedly enhanced production of all three isotypes. High levels of immunoglobulin production also occurred when activated irradiated autologous T cells replaced the CD40 MoAb, and when IL-10 replaced IL-2 in these cultures a spectacular increase in IgG production occurred. The effectiveness of the T cell stimulus depended on the mode of purification of the T cells and the nature of the stimulant used to activate them. Differences in the kinetics and level of expression of CD40L on the various T cell preparations were observed, but did not account for variations in immunoglobulin-inducing efficiency. Immunoglobulin production from sIgD+ and sIgD- B cells was investigated. IgG and IgA were found in sIgD+ cultures, indicating that some isotype switching had occurred, but the major part of the IgG and IgA secreted was from cells already committed to these isotypes. Anti-IgD or anti-IgM MoAbs enhanced the proliferation of B cells induced by anti-CD40 antibody, but immunoglobulin production was not enhanced. Factors affecting the balance of proliferation and differentiation are discussed.     

CD154/CD40 and CD70/CD27 interactions have different and sequential functions in T cell-dependent B cell responses: enhancement of plasma cell differentiation by CD27 signaling

CD40, a TNF receptor family member, plays a central role in T cell-mediated B cell activation. We have recently demonstrated that CD27, another TNF receptor family member, was also involved in B cell regulation and enhanced Ig production. In this report we compare CD27 and CD40 signals in B cell function. We selectively mimicked the effect of T cell help by addition to peripheral blood B cells activated with Staphylococcus aureus Cowan I strain and IL-2 of irradiated 300-19 cells transfected with either the CD70 (CD27 ligand) gene or the CD154 (CD40 ligand) gene, the vector alone, or both CD70 and CD154 genes. CD27 ligation induced only a slight increase in B cell proliferation compared with the dramatic enhancement induced by CD40 ligation; double ligation proved to be less efficient than CD40 ligation alone. In contrast, IgG production was increased only by CD27 ligation alone. Moreover, the CD27 signal was more efficient when it was given on day 2 of the culture rather than on day 0. Phenotypic analysis of the activated cells showed that CD27 ligation increased the percentage of cells showing a plasma cell profile (CD19-, CD38+), whereas upon CD40 ligation most of the cells still had a germinal center-like phenotype (CD19+, CD38+). Our results suggest that the CD27 and CD40 signals are not synergistic but, rather, are complementary and involve distinct steps of T cell-dependent B cell activation. CD27 may be more important in the induction of plasma cell differentiation at a time when the expansion phase has already occurred.     

p40 molecule regulates NK cell activation mediated by NK receptors for HLA class I antigens and TCR-mediated triggering of T lymphocytes

p40 was previously described as a regulatory molecule capable of inhibiting both the natural and the CD16-mediated cytotoxicity of NK cells. In this study, we analyze the effect of p40 molecule engagement on the NK cell triggering induced by activating HLA class I-specific NK receptors (NKR) or on TCR alpha beta-mediated T cell activation. CD3-CD16+ NK cell clones expressing activating NKR (either CD94 or p50) were analyzed in a redirected killing assay using P815 target cells and appropriate mAb. A strong target cell lysis was detected in the presence of anti-NKR or anti-CD16 mAb alone. Addition of anti-p40 mAb resulted in a strong inhibition of both anti-NKR or anti-CD16 mAb-induced cytolysis. mAb specific for either CD45 or lymphocyte function associated antigen-1 did not exert any inhibitory effect in the same experimental system. Free intracellular calcium ([Ca2+]i) increase induced by mAb cross-linking of activating CD94 or p50 was inhibited by simultaneous engagement of p40 molecules, but not of other NK surface molecules including CD44 and CD56. In addition, cross-linking of p40 molecules strongly inhibited the CD94-induced tumor necrosis factor-alpha and IFN-gamma production. Analysis of TCR alpha beta or gamma delta T cell clones revealed that the engagement of p40 molecules, using specific mAb, induced some degree of inhibition only on anti-V beta (but not anti-V delta or anti-CD3) mAb-induced cytotoxicity. On the other hand, the p40 molecule engagement prevented T cell proliferation induced by either anti-V beta 8 or anti-V delta 2 mAb. A similar inhibitory effect was found on the IL-2-induced NK cell proliferation. Taken together, our present findings suggest that p40 may play a role in the regulation of NK and T lymphocyte activation and proliferation.     

Signaling via major histocompatibility complex class II molecules and antigen receptors enhances the B cell response to gp39/CD40 ligand

Activated T cells induce proliferation and differentiation of resting B cells in vitro through their CD40 molecules and lymphokine receptors. However, despite constitutive B cell expression of CD40 and lymphokine receptors, widespread nonspecific polyclonal B cell activation by activated T cells is seldom observed in vivo. The present study was designed to test the hypothesis that signals delivered via the B cell antigen (Ag) receptor (membrane immunoglobulin, mIg) and major histocompatibility complex (MHC) class II molecules enhance B cell responsiveness to CD40-mediated signals, providing specificity to the Ag-nonspecific, MHC-unrestricted CD40 signal. To test this hypothesis, both an Ag-specific mouse B cell clone CH12.LX, and freshly isolated resting splenic B cells were cultured with either soluble or membrane-bound forms of the T cell ligand for CD40 (CD40L), in the presence or absence of additional signals provided by Ag or anti-IgM, interleukin-4, and class II-specific monoclonal antibody (mAb). Differentiation of CH12.LX cells and proliferation of splenic B cells in response to both forms of CD40L was greatly enhanced by exposure to mIg-mediated signals, with greatest enhancement seen when cells were cultured with Ag prior to receiving other signals. Response to CD40L was further enhanced by concurrent culture with class II-specific, but not class I-specific mAb. Enhancement was greatest at limiting concentrations of CD40L. The ability of class II MHC-mediated signals to enhance Ag-specific B cell responsiveness to CD40-mediated signaling may selectively promote the activation of B cell clones capable of cognate interactions with helper T cells.     

Mouse germinal center B cells with the xid mutation retain responsiveness to antimouse CD40 antibodies but diminish IL-5 responsiveness

The germinal center (GC) develops in secondary lymphoid tissues in response to thymus-dependent (TD) antigens. To investigate the molecular mechanism of B cell differentiation in GC, we enriched GC B cells from spleen of TD antigen-immunized wild-type and X-linked immunodeficient (XID) mice, and examined the differentiation of GC B cells into antigen-specific IgG1 antibody-forming cells (AFC) in response to anti-CD40 mAb and cytokines. A significant proportion of freshly purified GC B cells expressed receptors for IL-4 and IL-5. Anti-CD40 mAb sustained the viability of GC B cells and IL-4 co-operated with anti-CD40 mAb for further enhancement of the cell viability. Anti-CD40 mAb and IL-4 were essential for inducing differentiation of GC B cells into antigen-specific IgG1-AFC and IL-5 efficiently enhanced their differentiation. GC B cells with the xid mutation responded for proliferation to CD40 ligation to a lesser extent and for the IgG1-AFC response to anti-CD40 mAb together with IL-4, but they showed impaired responsiveness to IL-5, regardless of enhanced expression of IL-5R in response to anti-CD40 mAb and IL-4. These results suggest that anti-CD40 mAb, IL-4 and IL-5 play a critical role in the differentiation of mouse GC B cells. The GC B cells from XID mice show a functional defect with respect to IL-5-mediated differentiation.     

Immunological studies on PD-1 deficient mice: implication of PD-1 as a negative regulator for B cell responses

PD-1, an Ig superfamily member, contains an immunoreceptor tyrosine-based inhibitory motif in the cytoplasmic tail. It is expressed in a minor fraction of CD4-CD8- normal thymocytes and induced in peripheral lymphocytes following activation. To assess the possible roles of PD-1 in the immune responses, PD-1-deficient (PD-1-/-) mice were generated by a gene-targeting strategy. PD-1-4- mice developed and grew normally. Although the thymus was apparently normal, PD-1-/- mice showed moderate but consistent splenomegaly, which reflected the increased cellularity of both lymphoid and myeloid cells. The proliferative response of B cells by anti-IgM antibodies, but not of T cells by an anti-CD3 (145-2C11) mAb in vitro, was augmented in PD-1-/- mice as compared with control littermates. PD-1-/- mice showed increased serum levels of IgG2b, IgA and most strikingly IgG3, while those of IgM and IgG1 were comparable with control mice. Furthermore, PD-1-/- mice exhibited significantly augmented IgG3 anti-DNP antibody response to a type 2 T-independent antigen, DNP-Ficoll, with comparable IgM and IgG1 antibody responses with littermate controls. In the peritoneal cavity, the B-1 cell population in PD-1-/- mice exhibited significantly reduced expression of CD5, a negative regulator of B-1 cell activation, despite a marginal increase in the number of B-1 cells. Thus, PD-1 was suggested to be involved in the negative regulation for particular aspects of B cell proliferation and differentiation including class switching.     

Regulation of adhesion and migration in the germinal center microenvironment

T cell dependent humoral immune responses are initiated by the activation of naive B cells in the T cell areas of the secondary lymphoid tissues. This primary B cell activation leads to migration of germinal center (GC) cell precursors into B cell follicles where they engage follicular dendritic cells (FDC) and T cells, and differentiate into memory B cells or plasma cells. Both B cell homing to the GC and interaction with FDC critically depend on integrin-mediated adhesion. We have recently indentified the c-met-encoded receptor tyrosine kinase and its ligand, the growth and motility factor hepatocyte growth factor/scatter factor (HGF/SF), as a novel paracrine signalling pathway regulating B cell adhesion (van der Voort et al., 1997, J. Exp. Med. 185, 2121-2131). The c-Met protein is expressed on B cells localized in the dark zone of the GC (centroblasts) and is induced by CD40 plus BCR ligation. Stimulation of c-Met with HGF/SF, which is produced at high levels by tonsillar stromal cells and FDC, leads to receptor phosphorylation and to enhanced integrin-mediated adhesion of B cells to both VCAM-1 and fibronectin. Interestingly, these responses to HGF/SF are promoted by heparan-sulfate proteoglycan forms of CD44 (CD44-HS). Like c-Met, CD44-HS is induced on B cells by CD40 ligation. It efficiently binds HGF/SF and strongly promotes signalling through c-Met. We conclude that integrin regulation during antigen specific B cell differentiation involves cross-talk between the HGF/SF-c-Met pathway and CD44-HS.     

Paracrine regulation of germinal center B cell adhesion through the c-met-hepatocyte growth factor/scatter factor pathway

T cell-dependent humoral immune responses are initiated by the activation of naive B cells in the T cell areas of the secondary lymphoid tissues. This primary B cell activation leads to migration of germinal center (GC) cell precursors into B cell follicles where they engage follicular dendritic cells (FDC) and T cells, and differentiate into memory B cells or plasma cells. Both B cell migration and interaction with FDC critically depend on integrin-mediated adhesion. To date, the physiological regulators of this adhesion were unkown. In the present report, we have identified the c-met-encoded receptor tyrosine kinase and its ligand, the growth and motility factor hepatocyte growth factor/scatter factor (HGF/SF), as a novel paracrine signaling pathway regulating B cell adhesion. We observed that c-Met is predominantly expressed on CD38(+)CD77(+) tonsillar B cells localized in the dark zone of the GC (centroblasts). On tonsil B cells, ligation of CD40 by CD40-ligand, induces a transient strong upregulation of expression of the c-Met tyrosine kinase. Stimulation of c-Met with HGF/SF leads to receptor phosphorylation and, in addition, to enhanced integrin-mediated adhesion of B cells to both VCAM-1 and fibronectin. Importantly, the c-Met ligand HGF/SF is produced at high levels by tonsillar stromal cells thus providing signals for the regulation of adhesion and migration within the lymphoid microenvironment.     

CD40 activation boosts T cell immunity in vivo by enhancing T cell clonal expansion and delaying peripheral T cell deletion

In this report we show that activation of APC with an agonist anti-CD40 mAb profoundly alters the behavior of CD4 T cells in vivo. Stimulation of mice with anti-CD40 2 days before, but not 1 day after, administration of superantigen (SAg) enhanced CD4 and CD8 T cell clonal expansion by approximately threefold. Further, CD40 activation also delayed peripheral T cell deletion after activation. Dying, activated T cells were quantitated by detecting extracellular phosphatidylserine with concomitant staining for SAg-reactive T cells using a TCR Vbeta-specific mAb. Upon close examination, it was shown that CD40 activation delayed the death of the activated T cells. Additionally, it was found that enhanced survival of CD4 T cells was equally dependent on APC expression of B7-1 and B7-2. This is in contrast to CD8 T cells, which did not depend as much on B7-1 as B7-2. Thus, CD40 activation indirectly promotes T cell growth and delays the death of SAg-stimulated CD4 T cells in vivo. These data suggest that one way CD40 activation promotes a more robust immune response is by indirectly increasing the production of effector T cells and by keeping them alive for longer periods of time.     

Requirement of CD28-CD86 co-stimulation in the interaction between antigen-primed T helper type 2 and B cells

The interaction between CD28 and its ligands, CD80 and CD86, is crucial for an optimal activation of antigen-specific T cells. However, the requirement of CD80 or CD86 co-stimulation in Th2 cell differentiation and activation is controversial. Freshly isolated murine CD4+ and CD8+ T cells were incubated with P815 transfectants expressing a similar level of either CD80 or CD86 in the presence of anti-CD3 mAb. Both CD80 and CD86 co-stimulated the proliferation of CD4+ and CD8+ T cells at comparable time-kinetics and magnitude, but CD86 alone was able to co-stimulate IL-4 and especially IL-10 production in CD4+ T cells. In typical Th2-dependent immune responses elicited by Nippostrongylus brasillensis infection, the anti-CD86 mAb treatment but not the anti-CD80 mAb treatment efficiently inhibited antigen-specific IgE and IgG1 production, which was accompanied with the reduced IL-4 production. Our results suggest that CD86 co-stimulation plays a dominant role not only in the primary activation of Th2 cells but also in the secondary interaction between antigen-primed Th2 cells and B cells.     

IL-12 up-regulates CD40 ligand (CD154) expression on human T cells

IL-12 is a heterodimeric cytokine produced by APC that promotes the development of CD4+ Th1 cells and their IFN-gamma production after TCR/CD3 triggering. We here investigated the capacity of IL-12 to modify the expression on T cells of CD40 ligand (CD40L or CD154), a molecule transiently expressed on activated T cells and known to be of utmost importance for cognate interaction with B cells and for activation of dendritic cells and macrophages. Our data demonstrate that IL-12 up-regulates CD40L expression on anti-CD3-activated human peripheral blood T cells. For optimal induction of CD40L, IL-12 synergizes with IL-2 as well as with other costimulatory interactions, such as B7/CD28. The effect of IL-12 was observed at both the protein and the mRNA level. T cells costimulated by IL-12 provided more efficient help for IL-4-dependent B cell proliferation and for IgG production than when activated in the absence of IL-12. This helper activity was blocked by an mAb against CD40L, indicating that the effect of IL-12 on B cells is mediated indirectly through CD40L. The data thus suggest that the effects of IL-12 on cellular and humoral immune responses are partly mediated through CD40L induction.     

p38 MAPK is required for CD40-induced gene expression and proliferation in B lymphocytes

We have investigated the activation of the p38 MAPK pathway in response to CD40 engagement in multiple B cell lines and in human tonsillar B cells to define the role of p38 MAPK in proliferation, NF-kappaB activation and gene expression. Cross-linking CD40 rapidly stimulates both p38 MAPK and its downstream effector, MAPKAPK-2. Inhibition of p38 MAPK activity in vivo with the specific cell-permeable inhibitor, SB203580, under conditions that completely prevented MAPKAPK-2 activation, strongly perturbed CD40-induced tonsillar B cell proliferation while potentiating the B cell receptor (BCR)-driven proliferative response. SB203580 also significantly reduced expression of a reporter gene driven by a minimal promoter containing four NF-kappaB elements, indicating a requirement for the p38 MAPK pathway in CD40-induced NF-kappaB activation. However, CD40-mediated NF-kappaB binding was not affected by SB203580, suggesting that NF-kappaB may not be a direct target for the CD40-induced p38 MAPK pathway. In addition, SB203580 selectively reduced CD40-induced CD54/ICAM-1 expression, whereas CD40-dependent expression of CD40 and CD95/Fas and four newly defined CD40-responsive genes cIAP2, TRAF1, TRAF4/CART and DR3 were unaffected. Our observations show that the p38 MAPK pathway is required for CD40-induced proliferation and that CD40 induces gene expression via both p38 MAPK-dependent and -independent pathways.     

Influenza virus hemagglutinin induces differentiation of mature resting B cells and growth arrest of immature WEHI-231 lymphoma cells

We have investigated the functional requirements for the B cell "mitogenicity" of the influenza virus hemagglutinin (HA). Murine B cell proliferative responses were inducible by either infectious or inactivated virus, and by infected, paraformaldehyde-fixed cells. Viruses of the 12 different HA-subtypes displayed marked differences in their activation potential, classifying them as high (H2, H4, H6, H12), medium (H3, H5, H8, H9), or low (H1, H7, H10, H11) B cell activators. HA-mediated proliferation of resting B cells induced a vigorous Ig synthesis, with a predominance of IgG2b, IgG3, and IgM production. In this activation mode the B cell receptor (BCR) complex seems to be involved because 1) virus-triggered B cell proliferation was blocked by anti-Ig Abs, 2) B cell responses could be competitively inhibited by unfractionated high dose Igs, and 3) addition of BCR-modulating anti-CD45 mAb abrogated subsequent stimulation by HA. Furthermore, 4) influenza viruses were able to induce a growth arrest in the anti-mu sensitive B cell line WEHI-231. Most interestingly, the "tolerogenic" capacity correlated with the B cell stimulatory subtype of the virus, because highly stimulatory HA-subtypes were highly "tolerogenic" whereas low stimulatory subtypes were only marginally effective. Collectively, these observations raise the hypothesis that influenza viruses can cause polyclonal proliferation/differentiation of mature B cells and inactivation/tolerance induction in immature B cells by a mechanism that seems to mimic certain aspects of the physiologic BCR complex-mediated B cell activation.     

Perspective evaluation of the post-graduate courses of the Nursing Department at UFRN (1980-1992)

Superantigens have been used to study peripheral tolerance in CD4+ T cells. The superantigen SEB induces T cell anergy by promoting the differentiation of SEB-activated virgin T cells into anergic memory T cells. Memory T cells from SEB or antigen-primed mice do not proliferate when they are cultured with SEB. The present studies were performed to determine whether memory T cells fail to interact with SEB antigen-presenting cells or whether SEB promotes incomplete or negative signals in memory T cells. When murine virgin and memory T cells were separated on the basis of CD45RB expression and cultured with SEB-pulsed B cells, SEB induced the expression of CD25, which then mediated proliferation when IL-2 was added to the cultures. In addition, SEB promoted the expression of the CD40L, which is required for T helper cell function. Finally, PMA induced a costimulatory signal leading to the proliferation of these cells. Surprisingly, the agents, i.e., IL-2 and PMA, which induced TM cell proliferation in conjunction with SEB failed to induce lymphokine secretion. However, in the presence of IL-4 plus IL-5, the T memory cells induced the SEB-pulsed B cells to secrete IgM and IgG. These results suggest that memory T cells are not simply unresponsive to SEB but are actively anergized.