Contribution of classic and alternative effector pathways in peanut-induced anaphylactic responses

Food allergy affects approximately 5% of children and is the leading cause of hospitalization for anaphylactic reactions in westernized countries. However, the pathways of anaphylaxis in food allergy are still relatively unknown. We investigated the effector pathways of allergic and anaphylactic responses of different strains of mice in a clinical relevant model of peanut allergy. C3H/HeOuJ, C57BL/6 and BALB/c mice were sensitized by intragastric peanut extract and challenged by intragastric or intraperitoneal injection of peanut. Peanut-specific T cell responses, IgE, IgG1 and IgG2a and mucosal mast cell degranulation were induced to different extent in C3H/HeOuJ, C57BL/6 and BALB/c mice. Interestingly, anaphylactic symptoms after systemic challenge were highest in C3H/HeOuJ followed by C57BL/6 but were absent in BALB/c mice. Mechanistic studies showed that the food allergic systemic anaphylaxis was dependent on platelets, FcRγ and mast cells, and partially dependent on platelet activating factor and monocytes/macrophages, depending on mouse strain. These data demonstrate that in three mouse strains, components of the classic and alternative anaphylactic cascade are differently expressed, leading to differential outcomes in parameters of allergic disease and food induced systemic anaphylaxis.     

Th2-dependent B cell responses in the absence of CD40-CD40 ligand interactions

CD40 is thought to play a central role in T cell-dependent humoral responses through two distinct mechanisms. CD4+ T helper cells are activated via CD40-dependent Ag presentation in which CD80/CD86 provides costimulation through CD28. In addition, engagement of CD40 on B cells provides a direct pathway for activation of humoral responses. We used a model of adenovirus-mediated gene transfer of beta-galactosidase (lacZ) into murine lung to evaluate the specific CD40-dependent pathways required for humoral immunity at mucosal surfaces of the lung. Animals deficient in CD40L failed to develop T and B cell responses to vector. Activation of Th2 cells, which normally requires CD40-dependent stimulation of APCs, was selectively reconstituted in CD40 ligand-deficient mice by systemic administration of an Ab that is agonistic to CD28. Surprisingly, this resulted in the development of a functional humoral response to vector as evidenced by formation of germinal centers and production of antiadenovirus IgG1 and IgA that neutralized and prevented effective readministration of vector. The CD28-dependent B cell response required CD4+ T cells and was mediated via IL-4. These studies indicate that CD40 signals to the B cells are not necessary for CD4+ Th2 cell-dependent humoral responses to be generated.     

Ectopic CD40 ligand expression on B cells triggers intestinal inflammation

Several studies indicate that CD4(+) T cells, macrophages, and dendritic cells initially mediate intestinal inflammation in murine models of human inflammatory bowel disease. However, the initial role of B cells in the development of intestinal inflammation remains unclear. In this study we present evidence that B cells can trigger intestinal inflammation using transgenic (Tg) mice expressing CD40 ligand (CD40L) ectopically on B cells (CD40L/B Tg). We demonstrated that CD40L/B Tg mice spontaneously developed severe transmural intestinal inflammation in both colon and ileum at 8-15 wk of age. In contrast, CD40L/B TgxCD40(-/-) double-mutant mice did not develop colitis, indicating the direct involvement of CD40-CD40L interaction in the development of intestinal inflammation. The inflammatory infiltrates consisted predominantly of massive aggregated, IgM-positive B cells. These mice were also characterized by the presence of anti-colon autoantibodies and elevated IFN-gamma production. Furthermore, although mice transferred with CD4(+) T cells alone or with both CD4(+) T and B220(+) B cells, but not B220(+) cells alone, from diseased CD40L/B Tg mice, develop colitis, mice transferred with B220(+) B cells from diseased CD40L/B Tg mice and CD4(+) T cells from wild-type mice also develop colitis, indicating that the Tg B cells should be a trigger for this colitis model, whereas T cells are involved as effectors. As it has been demonstrated that CD40L is ectopically expressed on B cells in some autoimmune diseases, the present study suggests the possible contribution of B cells in triggering intestinal inflammation in human inflammatory bowel disease.     

CD40, but not CD154, expression on B cells is necessary for optimal primary B cell responses

CD40 is an important costimulatory molecule for B cells as well as dendritic cells, monocytes, and other APCs. The ligand for CD40, CD154, is expressed on activated T cells, NK cells, mast cells, basophils, and even activated B cells. Although both CD40(-/-) and CD154(-/-) mice have impaired ability to isotype switch, form germinal centers, make memory B cells, and produce Ab, it is not entirely clear whether these defects are intrinsic to B cells, to other APCs, or to T cells. Using bone marrow chimeric mice, we investigated whether CD40 or CD154 must be expressed on B cells for optimal B cell responses in vivo. We demonstrate that CD40 expression on B cells is required for the generation of germinal centers, isotype switching, and sustained Ab production, even when other APCs express CD40. In contrast, the expression of CD154 on B cells is not required for the generation of germinal centers, isotype switching, or sustained Ab production. In fact, B cell responses are completely normal when CD154 expression is limited exclusively to Ag-specific T cells. These results suggest that the interaction of CD154 expressed by activated CD4 T cells with CD40 expressed by B cells is the primary pathway necessary to achieve B cell activation and differentiation and that CD154 expression on B cells does not noticeably facilitate B cell activation and differentiation.     

Human B cell activation by autologous NK cells is regulated by CD40-CD40 ligand interaction: role of memory B cells and CD5+ B cells.

NK cells are a subpopulation of lymphocytes characterized primarily by their cytolytic activity. They are recognized as an important component of the immune response against virus infection and tumors. In addition to their cytolytic activity, NK cells also participate either directly or indirectly in the regulation of the ongoing Ab response. More recently, it has been suggested that NK cells have an important role in the outcome of autoimmune diseases. Here, we demonstrate that human NK cells can induce autologous resting B cells to synthesize Ig, including switching to IgG and IgA, reminiscent of a secondary Ab response. B cell activation by the NK cell is contact-dependent and rapid, suggesting an autocrine B cell-regulated process. This NK cell function is T cell-independent, requires an active cytoplasmic membrane, and is blocked by anti-CD40 ligand (anti-CD154) or CD40-mIg fusion protein, indicating a critical role for CD40-CD40 ligand interaction. Depletion studies also demonstrate that CD5+ B cells (autoreactive B-1 cells) and a heterogeneous population of CD27+ memory B cells play a critical role in the Ig response induced by NK cells. The existence of this novel mechanism of B cell activation has important implications in innate immunity, B cell-mediated autoimmunity, and B cell neoplasia.     

CD28-independent costimulation of T cells by OX40 ligand and CD70 on activated B cells.

OX40 and its ligand (OX40L) have been implicated in T cell-dependent humoral immune responses. To further characterize the role of OX40/OX40L in T-B cell interaction, we newly generated an anti-mouse OX40L mAb (RM134L) that can inhibit the costimulatory activity of OX40L transfectants for anti-CD3-stimulated T cell proliferation. Flow cytometric analyses using RM134L and an anti-mouse OX40 mAb indicated that OX40 was inducible on splenic T cells by stimulation with immobilized anti-CD3 mAb in a CD28-independent manner, while OX40L was not expressed on resting or activated T cells. OX40L was inducible on splenic B cells by stimulation with anti-IgM Ab plus anti-CD40 mAb, but not by either alone. These activated B cells exhibited a potent costimulatory activity for anti-CD3-stimulated T cell proliferation and IL-2 production. Anti-CD80 and anti-CD86 mAbs partially inhibited the costimulatory activity, and further inhibition was obtained by their combination with RM134L and/or anti-CD70 mAb. We also found the anti-IgM Ab- plus anti-CD40 mAb-stimulated B cells exhibited a potent costimulatory activity for proliferation of and IL-2 production by anti-CD3-stimulated CD28- T cells from CD28-deficient mice, which was substantially inhibited by RM134L and/or anti-CD70 mAb. These results indicated that OX40L and CD70 expressed on surface Ig- and CD40-stimulated B cells can provide CD28-independent costimulatory signals to T cells.     

CD30/CD30 ligand and CD40/CD40 ligand in malignant lymphoid disorders

CD30 and CD40 are members of the tumor necrosis factor (TNF) receptor family. These two receptors have pleiotropic biologic functions including induction of apoptosis and enhancing cell survival. This review will discuss the pattern of expression of these receptors in malignant lymphoid disorders and their prospective ligands. Understanding issues related to these two ligands and their receptors in lymphoid malignancies may help to improve the classification of these diseases and could open the doors for new treatment strategies.     

IgE production in CD40/CD40L cross-talk of B and mast cells and mediator release via TGase 2 in mouse allergic asthma

TGase 2 is over-expressed in a variety of inflammatory diseases including allergic asthma. This study aimed to investigate the role of TGase 2 on IgE production and signaling pathways in mast cell activation related to OVA-induced allergic asthma. Bone marrow-derived mast cells (BMMCs) isolated from WT or TGase 2^?/? mice were activated with Ag/Ab (refer to act-WT-BMMCs and act-KO-BMMCs, respectively). B cells isolated from splenocytes were activated with anti-mouse IgM (act-B cells), and B cells were co-cultured with BMMCs. WT and TGase 2^?/? mice were sensitized and challenged with OVA adsorbed in alum hydroxide. Intracellular Ca^2 + ([Ca^2 +]_i) levels were determined by fluorescence intensity; IgE, mediators and TGase 2 activity by ELISA; the CD138 expression by FACS analyzer; cell surface markers and signal molecules by Western blot; NF-κB by EMSA; co-localization of mast cells and B cells by immunohistochemistry; Fcε RI-mediated mast cell activation by PCA test; expression of cytokines, MMPs, TIMPs, TLR2 and Fc?RI by RT-PCR. In vitro, act-KO-BMMCs reduced the [Ca^2 +]i levels, NF-κB activity, expression of CD40/CD40L, plasma cells, total IgE levels and TGase 2 activity in act-B cells co-cultured with act-BMMCs, expression of inflammatory cytokines and MMPs2/9, release of mediators (TNF-α, LTs and cytokines), and activities of signal molecules (PKCs, MAP kinases, I-κB and PLA2), which were all increased in act-WT-BMMCs. TGase 2 siRNA transfected/activated-BMMCs reduced all responses as same as those in act-KO-BMMCs. In allergic asthma model, TGase 2^?/? mice protected against PCA reaction, OVA-specific IgE production and AHR, and they reduced co-localization of mast cells and B cells or IgE in lung tissues, expression and co-localization of surface molecules in mast cells (c-kit and CD40L) and B cells (CD23 and CD40), inflammatory cells including mast cells, goblet cells, amounts of collagen and mediator release in BAL fluid and/or lung tissues, which were all increased in WT mice. TLR expression in TGase 2^?/? mice did not differ from those in WT mice. Our data suggest that TGase 2 expression and Ca^2 + influx required by bidirectional events in mast cell activation facilitate IgE production in B cells via up-regulating mast cell CD40L expression, and induce the expression of numerous signaling molecules associated with airway inflammation and remodeling in allergic asthma.     

Soluble forms of CD40 inhibit biologic responses of human B cells.

We have expressed the CD40 surface Ag as both a soluble 28-kDa molecule and a 57-kDa Fc fusion protein containing the human IgG1 Fc region. Soluble CD40 and the Fc fusion protein inhibited the proliferative response of anti-IgM-activated human B cells to the CD40 mAb G28-5. Similarly, G28-5- and IL-4-induced IgE secretion from PBMC depleted of T cells was effectively blocked by both forms of soluble CD40. Although the soluble constructs of CD40 had only a minimal inhibitory effect on IL-4-mediated proliferation of anti-IgM-activated B cells, IL-4-induced soluble CD23 shedding from both PBMC and T cells depleted of PBMC, and IgE secretion from PBMC, were significantly reduced in a concentration-dependent manner when soluble CD40 was present in the culture. The data presented demonstrate that both soluble forms of the CD40 molecule are biologically active, and suggest that the ligand for CD40 is inducible in IL-4-stimulated cultures and that it mediates both shedding of sCD23 and IgE secretion.     

OK432-activated human dendritic cells kill tumor cells via CD40/CD40 ligand interactions

In vivo, dendritic cells (DC) are programmed to orchestrate innate and adaptive immunity in response to pathogen-derived "danger" signals. Under particular circumstances, DC can also be directly cytotoxic against tumor cells, potentially allowing them to release tumor associated Ags from dying cells and then prime antitumor immunity against them. In this study, we describe the innate characteristics of DC (OK-DC) generated in vitro after exposure of immature human myeloid-derived DC to OK432, a penicillin-inactivated and lyophilized preparation of Streptococcus pyrogenes. OK-DC produced proinflammatory cytokines, stimulated autologous T cell proliferation and IFN-gamma secretion, expressed CCR7, and migrated in response to MIP-3beta. Moreover, OK-DC displayed strong, specific cytotoxicity toward tumor cell targets. This cytotoxicity was associated with novel, OK432-induced up-regulation of CD40L on the cell surface of OK-DC, and was absolutely dependent on expression of CD40 on the tumor targets. These data demonstrate that maturation of human DC with OK432, an adjuvant suitable for clinical use, induces direct tumor cell killing by DC, and describes a novel CD40/CD40L-mediated mechanism for specific DC antitumor cytotoxicity.     

Evaluation of CD40, its ligand CD40L and Bcl-2 in psoriatic patients

Psoriasis is a chronic, recurrent, inflammatory disease. Recent investigations indicate an autoimmune pathogenesis of the disease. Apoptosis plays an important role in the regulation of immune mechanisms in many autoimmune diseases. Although CD40, CD40L, and Bcl-2 have already been studied in psoriatic skin lesions, little is known about their circulating forms. The aim of the present study was to evaluate the serum concentrations of Bcl-2, soluble CD40 and CD40L in psoriatic patients. The study was performed using ELISA kits in 39 psoriatic patients before treatment and after two weeks of topical ointment. Data was analyzed with respect to severity of psoriasis, duration of the disease, and coexisting psoriatic arthritis. Our results revealed that serum concentrations of soluble CD40 and CD40L before and after treatment were significantly higher (p < 0.01 and p < 0.001) in patients with psoriasis compared to the control group. Topical treatment of psoriatic lesions with dithranol ointment failed to decrease serum of CD40 and CD40L, which has not been described until now. There was no significant difference in serum Bcl-2 concentration between the compared groups. We did not find significant differences in serum concentrations of Bcl-2, CD40 or CD40L between patients with mild or severe psoriasis, nor any correlation between disease duration and the presence of psoriatic arthritis symptoms. Our data indicates upregulation of the CD40/CD40L system in psoriatic patients despite topical treatment and suggests their possible role in the pathogenesis of psoriasis.     

A multimerized form of recombinant human CD40 ligand supports long-term activation and proliferation of B cells

Background aimsCD40-activated B cells have long been studied as potent antigen-presenting cells that can potentially be used for cancer immunotherapy. Nevertheless, their use in human clinical trials has been limited by the lack of a Good Manufacturing Practice–grade soluble human CD40 ligand that is able to induce activation and proliferation of primary B cells. We describe an in vitro method to effectively generate and expand B cells through the use of a multimerized form of human recombinant CD40 ligand (rCD40L).MethodsHuman B cells were isolated from healthy donors and cultivated with either rCD40L or on a monolayer of murine NIH3T3 cells stably expressing human CD40L (NIH3T3/tCD40L) as a widely used standard method. Morphology, expansion rate, immune phenotype and antigen presentation function were assessed.ResultsB cells efficiently proliferated in response to rCD40L over 14 days of culture in comparable amounts to NIH3T3/tCD40L. B-cell division in response to CD40L was also confirmed by carboxyfluorescein succinimidyl ester dilution. Moreover, rCD40L induced on B cells upregulation of co-stimulatory molecules essential for antigen presentation. Additionally, proliferation of T cells from allogeneic healthy volunteers confirmed the immunostimulatory capacities of CD40-activated B cells.ConclusionsWe demonstrated that B cells with potent antigen presentation capacity can be generated and expanded by use of a non-xenogeneic form of CD40L that could be implemented in future human clinical settings.     

T cells can induce somatic mutation in B cell receptor-engaged BL2 Burkitt's lymphoma cells independently of CD40-CD40 ligand interactions

The B cell surface trigger(s) and the molecular mechanism(s) of somatic hypermutation remain unknown, partly because of the lack of amendable in vitro models. Recently, however, we reported that upon B cell receptor cross-linking and coculture with activated T cells, the Burkitt's lymphoma cell line BL2 introduces mutations in its IgVH gene in vitro. We now confirm the relevance of our culture model by establishing that the entire spectrum of somatic mutations observed in vivo, including insertions and deletions, could be found in the DNA of BL2 cells. Additionally, we show that among four human B cell lines, only two with a centroblast-like phenotype can be induced to mutate. Triggering of somatic mutations in BL2 cells requires intimate T-B cell contacts and is independent of CD40-CD40-ligand (CD40L) interactions as shown by 1) the lack of effect of anti-CD40 and/or anti-CD40L blocking Abs on somatic mutation and 2) the ability of a CD40L-deficient T cell clone (isolated from an X-linked hyper-IgM syndrome patient) to induce somatic mutation in B cell receptor-engaged BL2 cells. Thus, our in vitro model reveals that T-B cell membrane interactions through surface molecules different from CD40-CD40L can trigger somatic hypermutation.     

CD40-CD40 ligand interaction between dendritic cells and CD8+ T cells is needed to stimulate maximal T cell responses in the absence of CD4+ T cell help

Stimulation of CD40 on APCs through CD40L expressed on helper CD4+ T cells activates and "licenses" the APCs to prime CD8+ T cell responses. Although other stimuli, such as TLR agonists, can also activate APCs, it is unclear to what extent they can replace the signals provided by CD40-CD40L interactions. In this study, we used an adoptive transfer system to re-examine the role of CD40 in the priming of naive CD8+ T cells. We find an approximately 50% reduction in expansion and cytokine production in TCR-transgenic T cells in the absence of CD40 on all APCs, and on dendritic cells in particular. Moreover, CD40-deficient and CD40L-deficient mice fail to develop endogenous CTL responses after immunization. Surprisingly, the role for CD40 and CD40L are observed even in the absence of CD4+ T cells; in this situation, the CD8+ T cell itself provides CD40L. Furthermore, we show that although TLR stimulation improves T cell responses, it cannot fully substitute for CD40. Altogether, these results reveal a direct and unique role for CD40L on CD8+ T cells interacting with CD40 on APCs that affects the magnitude and quality of CD8+ T cell responses.     

Role of CD40 ligand and CD28 in induction and maintenance of antiviral CD8+ effector T cell responses

The primary aim of this report was to evaluate the immune responses of CD40 ligand-deficient (CD40L-/-) mice infected with two viruses known to differ markedly in their capacity to replicate in the host. Lymphocytic choriomeningitis virus (LCMV) is a natural mouse pathogen that replicates widely and extensively, whereas vesicular stomatitis virus (VSV) spreads poorly. We found that the primary response of CD40L-/- mice toward VSV is significantly impaired; proliferation of both CD4+ and CD8+ cells is reduced 2- to 3-fold, few CD8+ cells acquire an activated phenotype, and little functional activity is induced. Very similar results were obtained in VSV-infected, CD28-deficient mice. In contrast, neither CD40L nor CD28 was required for induction of a primary CD8+ response toward LCMV. Surprisingly, lack of CD4+ T cells had no impact on the primary immune response toward any of the viruses, even though the CD40 ligand dependence demonstrated for VSV would be expected to be associated with CD4 dependence. Upon coinfection of VSV-infected mice with LCMV, the requirement for CD40 ligand (but not CD28) could be partially bypassed, as evidenced by a 3-fold increase in the frequency of VSV-specific CD8+ T cells on day 6 postinfection. Finally, despite the fact that the primary LCMV-specific CD8+ response is virtually unimpaired in CD40L-/- mice, their capacity to maintain CD8+ effector activity and to permanently control the infection is significantly reduced. Thus, our results demonstrate that the importance of CD40/CD40L interaction for activation of CD8+ T cells varies between viruses and over time.     

CD40 ligand (CD40L) does not stimulate proliferation of vascular smooth muscle cells

The present study investigates the effects of CD40 ligand (CD40L) on mitogenic signalling, proliferation, and migration of cultured bovine coronary artery smooth muscle cells (SMC). A time- and concentration-dependent phosphorylation of the extracellular signal-regulated kinases-1/2 (ERK-1/2) and the mitogen-activated protein kinase p38 (p38-MAPK) was observed upon stimulation with soluble CD40L (sCD40L). This phosphorylation was inhibited by neutralizing antibodies against the CD40 and CD40L, respectively. Activation of the phosphatidylinositol-3-phosphate (PI-3) kinase pathway by sCD40L, as determined by the measurement of Akt phosphorylation, was not detected. However, there was evidence for direct activation of the NFkappaB system (degradation of IkappaBalpha and nuclear translocation of the p65 NFkappaB subunit) by sCD40L. Accordingly, sCD40L caused a small but significant increase in DNA synthesis. However, sCD40L-induced DNA synthesis was not followed by proliferation (increase in cell number). Furthermore, sCD40L did not potentiate SMC mitogenesis induced by known mitogens such as platelet-derived growth factor-BB, thrombin or serum. The lack of cell proliferation was not caused by a concomitant induction of SMC apoptosis by sCD40L. The possible role of membrane-bound CD40L in SMC mitogenesis was also studied using different membrane preparations (platelets, lymphocytes). However, no mitogenic effects of membrane-bound CD40L were detected. Finally, sCD40L did not induce SMC migration. From these data it is concluded that CD40L activates mitogenic signalling and DNA synthesis but does not contribute to proliferation or migration of vascular SMC.     

Ligation of CD28 in vivo induces CD40 ligand expression and promotes B cell survival.

Functional activation of T cells requires ligation of Ag receptors with specific peptides presented by MHC molecules on APCs concurrent with appropriate contacts of cell surface accessory molecules. Among these accessory molecules, interactions between CD28/CTLA-4 with B7 family members (CD80 and CD86) and CD40 with CD40 ligand (CD40L) play a decisive role in regulating the progression of balanced immune responses. However, most information regarding the role of accessory molecules in immune responses has been derived in the context of signals from the TCRs. Little understanding has been achieved regarding the consequence of ligation of costimulation molecules in absence of signals from the TCR. By employing an in vivo murine system, we show, herein, that ligation of CD28 alone with anti-CD28 Abs leads to a dramatic enlargement of the peripheral lymphoid organs characterized primarily by the expansion of B cells. B cells from anti-CD28-treated mice are resistant to spontaneous and anti-IgM-induced apoptosis. These cells are also unsusceptible to FasL-mediated apoptosis. Interestingly, this in vivo effect of CD28 on B cells is largely mediated by inducing the expression of CD40L, since coadministration of a blocking Ab against CD40L inhibited CD28-mediated B cell survival and expansion. Therefore, CD28-mediated expression of CD40L may play an important role in the regulation of lymphocyte homeostasis.     

Generation of Human CD40-activated B cells

CD40-activated B cells (CD40-B cells) have been identified as an alternative source of immuno-stimulatory antigen-presenting cells (APC) for cancer immunotherapy ^1-3. Compared to Dendritic cells (DCs), the best characterized APC, CD40-B cells have several distinct biological and technical properties. Similar to DCs, B cells show an increased expression of MHC and co-stimulatory molecules (Fig.1b), exhibit a strong migratory capacity and present antigen presentation efficiently to T cells, after stimulation with interleukin-4 and CD40 ligand (CD40L). However, in contrast to immature or mature DCs, CD40-B cells express the full lymph node homing triad consisting of CD62L, CCR7/CXCR4, and leukocyte function antigen-1 (LFA1, CD11a/CD18), necessary for homing to secondary lymphoid organs (Fig.1a) ³. CD40-B cells can be generated without difficulties from very small amounts of peripheral blood which can be further expanded in vitro to very large amounts of highly-pure CD40-B cells (>10⁹ cells per patient) from healthy donors as well as cancer patients (Fig.1c,d) ^1,4.In this protocol we demonstrate how to obtain fully activated CD40-B cells from human PBMC. Key molecules for the cell culture are CD40 ligand, interleukin-4 (IL-4) and cyclosporin A (CsA), which are replenished in a 3-4 day culture cycle. For laboratory purposes CD40-stimulation is provided by NIH/3T3 cells expressing recombinant human CD40 ligand (tCD40L NIH/3T3) ⁵. To avoid contamination with non-transfected cells, expression of the human CD40 ligand on the transfectants has to be checked regularly (Fig.2).After 14 days CD40-B cell cultures consist of more than 95% pure B cells and an expansion of CD40-B cells over 65 days is frequently possible without any loss of function ^{1, 4}. CD40-B cells efficiently take up, process and present antigens to T cells ⁶. They do not only prime naϊve, but also expand memory T cells ^7,8. CD40-activated B cells can be used to study B-cell activation, differentiation and function. Moreover, they represent a promising tool for therapeutic or preventive vaccination against tumors ⁹.Download video file.^{(152M, mp4)}     

CD40-CD40 ligand costimulation is required for generating antiviral CD4 T cell responses but is dispensable for CD8 T cell responses.

This study documents a striking dichotomy between CD4 and CD8 T cells in terms of their requirements for CD40-CD40 ligand (CD40L) costimulation. CD40L-deficient (-/-) mice made potent virus-specific CD8 T cell responses to dominant as well as subdominant epitopes following infection with lymphocytic choriomeningitis virus. In contrast, in the very same mice, virus-specific CD4 T cell responses were severely compromised. There were 10-fold fewer virus-specific CD4 T cells in CD40L-/- mice compared with those in CD40L+/+ mice, and this inhibition was seen for both Th1 (IFN-gamma, IL-2) and Th2 (IL-4) responses. An in vivo functional consequence of this Th cell defect was the inability of CD40L-/- mice to control a chronic lymphocytic choriomeningitis virus infection. This study highlights the importance of CD40-CD40L interactions in generating virus-specific CD4 T cell responses and in resolving chronic viral infection.