CD40L: a multi-functional ligand

Platelets as Key Factors in Inflammation: Focus on CD40L/CD40

Platelets are anucleate cytoplasmic fragments derived from the fragmentation of medullary megakaryocytes. Activated platelets adhere to the damaged endothelium by means of glycoproteins on their surface, forming the platelet plug. Activated platelets can also secrete the contents of their granules, notably the growth factors contained in the α-granules, which are involved in platelet aggregation and maintain endothelial activation, but also contribute to vascular repair and angiogenesis. Platelets also have a major inflammatory and immune function in antibacterial defence, essentially through their Toll-like Receptors (TLRs) and Sialic acid-binding immunoglobulin-type lectin (SIGLEC). Platelet activation also contributes to the extensive release of anti- or pro-inflammatory mediators such as IL-1β, RANTES (Regulated on Activation, Normal T Expressed and Secreted) or CD154, also known as the CD40-ligand. Platelets are involved in the direct activation of immune cells, polynuclear neutrophils (PNNs) and dendritic cells via the CD40L/CD40 complex. As a general rule, all of the studies presented in this review show that platelets are capable of covering most of the stages of inflammation, primarily through the CD40L/CD40 interaction, thus confirming their own role in this pathophysiological condition.

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.

CD40-mediated signalling influences trafficking, T-cell receptor expression, and T-cell pathogenesis, in the NOD model of type 1 diabetes

CD40 plays a critical role in the pathogenesis of type 1 diabetes (T1D). The mechanism of action, however, is undetermined, probably because CD40 expression has been grossly underestimated. CD40 is expressed on numerous cell types that now include T cells and pancreatic β cells. CD40⁺ CD4⁺ cells [T helper type 40 (TH40)] prove highly pathogenic in NOD mice and in translational human T1D studies. We generated BDC2.5.CD40^-/- and re-derived NOD.CD154^-/- mice to better understand the CD40 mechanism of action. Fully functional CD40 expression is required not only for T1D development but also for insulitis. In NOD mice, TH40 cell expansion in pancreatic lymph nodes occurs before insulitis and demonstrates an activated phenotype compared with conventional CD4⁺ cells, apparently regardless of antigen specificity. TH40 T-cell receptor (TCR) usage demonstrates increases in several Vα and Vβ species, particularly Vα3.2⁺ that arise early and are sustained throughout disease development. TH40 cells isolated from diabetic pancreas demonstrate a relatively broad TCR repertoire rather than restricted clonal expansions. The expansion of the Vα/Vβ species associated with diabetes depends upon CD40 signalling; NOD.CD154^-/- mice do not expand the same TCR species. Finally, CD40-mediated signals significantly increase pro-inflammatory Th1- and Th17-associated cytokines whereas CD28 co-stimulus alternatively promotes regulatory cytokines.

Dendritic cell function and pathogen-specific T cell immunity are inhibited in mice administered levonorgestrel prior to intranasal Chlamydia trachomatis infection

The growing popularity of levonorgestrel (LNG)-releasing intra-uterine systems for long-acting reversible contraception provides strong impetus to define immunomodulatory properties of this exogenous progestin. In initial in vitro studies herein, we found LNG significantly impaired activation of human dendritic cell (DCs) and their capacity to promote allogeneic T cell proliferation. In follow-up studies in a murine model of intranasal Chlamydia trachomatis infection, we analogously found that LNG treatment prior to infection dramatically reduced CD40 expression in DCs isolated from draining lymph nodes at 2 days post infection (dpi). At 12 dpi, we also detected significantly fewer CD4⁺ and CD8⁺ T cells in the lungs of LNG-treated mice. This inhibition of DC activation and T cell expansion in LNG-treated mice also delayed chlamydial clearance and the resolution of pulmonary inflammation. Conversely, administering agonist anti-CD40 monoclonal antibody to LNG-treated mice at 1 dpi restored lung T cell numbers and chlamydial burden at 12 dpi to levels seen in infected controls. Together, these studies reveal that LNG suppresses DC activation and function, and inhibits formation of pathogen-specific T cell immunity. They also highlight the need for studies that define in vivo effects of LNG use on human host response to microbial pathogens.

Differential Downstream Effects of Cd40 Ligation Mediated by Membrane or Soluble CD40L and Agonistic Ab: A Study on Purified Human B Cells

With the addition of various cytokines, the CD40-CD40 ligand (CD40L) system can act as a T-helper cell surrogate to permit B lymphocytes to produce large amounts of polyclonal Ig. In the present study, we tested six CD40-CD40L stimulation models: (i, ii) soluble agonistic 89 and G28.5 mAbs; (iii, iv) ‘89’ and ‘G28.5’ bound via their Fc fragments on CDw32-transfected mouse fibroblasts; (v) purified, soluble, trimeric human CD40L molecules (sCD40L); and (vi) human CD40L expressed by a CD40L-transfected mouse fibroblastic cell line (LCD40L). Target B cells consisted of purified blood and tonsillar CD19+ lymphocytes cultured in the presence of CD40 stimuli and IL-2 and IL-10, added at the onset of each B cell culture. A) There was differential expression of CD69, CD80 and CD86 exposure to sCD40L and LCD40L was ensued by the strongest % MFI changes over control. B) In blood B cells, mAbs and sCD40L induced IgA, IgM and IgG production almost equally well; LCD40L proved less efficient. In contrast, in tonsil B cells, LCD40L induced significantly more IgA, IgG 1, IgG3and IgM production than other signals. Using certain CD40/CD40L stimuli to model in vitro Ig production, a system used regularly in many laboratories, may affect the interpretation based on the cell type and on the CD40/CD40L system used.

Minocycline upregulates pro-survival genes and downregulates pro-apoptotic genes in experimental glaucoma

PURPOSE

Minocycline, a second-generation tetracycline with anti-inflammatory and anti-apoptotic properties, was reported to be neuroprotective in experimental glaucoma and optic nerve transection as well as in other neurodegenerative diseases. The purpose of this study was to investigate the mechanism underlying that neuroprotective effect in murine glaucoma.

METHODS

Elevated intraocular pressure was induced in 159 rats by the translimbal photocoagulation laser model. Minocycline 22 mg/kg or saline was injected intraperitoneally starting 3 days before the induction of glaucoma, and continued daily until the animals were sacrificed. The effect of minocycline on gene expression was evaluated using a quantitative polymerase chain reaction (PCR) array for apoptosis. The involvement of selected pro-apoptotic, pro-survival, and inflammatory genes was further analyzed by quantitative real-time PCR at multiple time points. Immunohistochemistry was used to study the effect of minocycline on microglial activation and to localize Bcl-2 changes.

RESULTS

Minocycline significantly increased the anti-apoptotic gene Bcl-2 expression at day 8 and day 14 after the induction of glaucoma (p = 0.04 and p = 0.03 respectively), and decreased IL-18 expression in the retina at day 14 and day 30 (p = 0.04 and p < 0.001 respectively). PCR arrays suggested that additional genes were affected by minocycline, including Tp53bp2, TRAF4, osteoprotegerin, caspase 1 and 4, and members of the tumor necrosis factor superfamily. Additionally, minocycline decreased the amount of activated microglia in glaucomatous eyes.

CONCLUSIONS

These results suggest that minocycline upregulates pro-survival genes and downregulates apoptotic genes, thus shifting the balance toward the anti-apoptotic side in experimental glaucoma.

Immunological profile of Fanconi anemia: a multicentric retrospective analysis of 61 patients

In this study, the immunological status of 61 patients with Fanconi anemia (FA) with advanced marrow failure before hematopoietic stem cell transplantation was analyzed by assessing the phenotype of peripheral blood lymphocytes, serum immunoglobulin (Ig) levels, and inflammatory cytokines. In patients with FA, total absolute lymphocytes (P < 0.0001), B cells (P < 0.0001), and NK cells (P = 0.003) were reduced when compared with normal controls. T cells (CD3), that is, cytotoxic T cells, naïve T cells, and regulatory T cells, showed a relative increase when compared with controls. Serum levels of IgG (P < 0.0001) and IgM (P = 0.004) were significantly lower, whereas IgA level was higher (P < 0.0001) than in normal controls. TGF-β (P = 0.007) and interleukin (IL)-6 (P = 0.0007) levels were increased in the serum of patients when compared with controls, whereas sCD40L level decreases (P < 0.0001). No differences were noted in the serum levels of IL-1β, IL-2, IL-4, IL-10, IL-13, IL-17, and IL-23 between FA subjects and controls. This comprehensive immunological study shows that patients with FA with advanced marrow failure have an altered immune status. This is in accordance with some characteristics of FA such as the proinflammatory and proapoptotic status. In addition, B lymphocyte failure may make tight and early immunological monitoring advisable.

T cell polarity at the immunological synapse is required for CD154-dependent IL-12 secretion by dendritic cells

Ag-specific interaction between T lymphocytes and dendritic cells (DCs) leads to both T cell and DC activation. CD154 (CD40 ligand)/CD40 interactions have been shown to play a major, although not exclusive, role in this functional cross-talk. Interactions between T cells and DCs are structured by an immunological synapse (IS), characterized by polarization of the T cell microtubule cytoskeleton toward the interacting DCs. Yet the role T cell polarization may play in T cell-induced DC activation is mostly unknown. In this study, we address the role of T cell polarity in CD154-dependent activation of DCs in a human model, using two different tools to block T cell polarity (i.e., a microtubule depolymerizing drug and an inhibitor of atypical protein kinase C). We show that CD154 is recruited and concentrated at the IS formed between human primary T cells and autologous DCs and that this recruitment requires T cell polarity at the IS. Moreover, we show that T cell polarization at the IS controls T cell-dependent CD154-CD40 signaling in DCs as well as CD154-dependent IL-12 secretion by DCs. This study shows that T cell polarity at the IS plays a key role in CD154/CD40-dependent cross-talk between CD4(+) T cells and DCs.

Human CD14hi monocytes and myeloid dendritic cells provide a cell contact-dependent costimulatory signal for early CD40 ligand expression

CD40L on CD4(+) T cells plays a vital role in the activation of antigen-presenting cells, thus catalyzing a positive feedback loop for T-cell activation. Despite the pivotal juxtaposition of CD40L between antigen-presenting cells and T-cell activation, only a T-cell receptor stimulus is thought to be required for early CD40L surface expression. We show, for the first time, that CD40L expression on peripheral blood CD4(+) T cells is highly dependent on a cell-cell interaction with CD14(hi)CD16(-) monocytes. Interactions with ICAM-1, LFA-3, and to a lesser extent CD80/CD86 contribute to this enhancement of CD40L expression but are not themselves sufficient. The contact-mediated increase in CD40L expression is dependent on new mRNA and protein synthesis. Circulating myeloid dendritic cells also possess this costimulatory activity. By contrast, CD14(lo)CD16(+) monocytes, plasmacytoid dendritic cells, B-cell lymphoma lines, and resting, activated, and Epstein-Barr virus-immortalized primary B cells all lack the capacity to up-regulate early CD40L. The latter indicates that a human B cell cannot activate its cognate T cell to deliver CD40L-mediated help. This finding has functional implications for the role of biphasic CD40L expression, suggesting that the early phase is associated with antigen-presenting cell activation, whereas the late phase is related to B-cell activation.

Distinct roles of CD28- and CD40 ligand-mediated costimulation in the development of protective immunity and pathology during Chlamydia muridarum urogenital infection in mice

Infection with Chlamydia muridarum in the mouse urogenital tract can induce both protective immunity and inflammatory pathologies, which has been used as a model for understanding the immune and pathogenic mechanisms of C. trachomatis infection. We compared the roles of CD28- and CD40 ligand (CD40L)-mediated costimulation in C. muridarum infection. Mice with CD28 or CD80/CD86 gene knockout (KO) displayed an infection course similar to that of wild-type mice during both primary and secondary infection, suggesting that CD28-mediated costimulation is not required for protection against C. muridarum infection. However, mice deficient in CD40L or CD40 displayed a prolonged infection course after primary or secondary infection, suggesting that CD40-CD40L costimulation plays an essential role in the development of anti-C. muridarum immunity. Interestingly, the CD28- or CD80/CD86-deficient mice displayed significantly lower levels of inflammatory pathologies in the upper genital tracts after primary infection, although the attenuation in inflammation was no longer significant during secondary infection. However, the CD40L or CD40 KO mice developed inflammatory pathologies as severe as those in wild-type mice following either primary or secondary infection despite the obvious deficits in adaptive immunity in these KO mice. The resistance of CD28 or CD80/CD86 KO mice to chlamydial infection correlated with production of gamma interferon, while the development of inflammatory pathologies in CD40L or CD40 KO mice correlated with the production of other proinflammatory cytokines in mouse urogenital tracts during the early stages of the infection. These observations together suggest that C. muridarum-induced protective immunity and inflammatory pathologies can be mediated by distinct costimulatory signals.

Detecting shared pathogenesis from the shared genetics of immune-related diseases. Nat Rev Genet. 2009;10:43-55. [PMID: 19092835 DOI: 10.1038/nrg2489]

Recent genetic studies have revealed shared immunological mechanisms in several immune-related disorders that further our understanding of the development and concomitance of these diseases. Our Review focuses on these shared aspects, using the novel findings of recently performed genome-wide association studies and non-synonymous SNP scans as a starting point. We discuss how identifying new genes that are associated with more than one autoimmune or chronic inflammatory disorder could explain the genetic basis of the shared pathogenesis of immune-related diseases. This analysis helps to highlight the key molecular pathways that are involved in these disorders and the potential roles of novel genes in immune-related diseases.

CD28 and inducible costimulator (ICOS) signalling can sustain CD154 expression on activated T cells

The biological outcome of receptor-mediated signalling often depends on the duration of engagement. Because CD40 signalling is controlled by the regulated expression of its ligand, CD154, the mechanisms that regulate CD154 expression probably determine the strength and duration of CD40 signalling. Here, we demonstrate that CD154 expression on the surface of mouse CD4 T cells can be separated into an early phase, occurring between 0 and 24 hr after T-cell activation, and a later extended phase, occurring after 24 hr. The early phase of CD154 expression did not require costimulation and was probably influenced by the strength of T-cell receptor (TCR) signalling alone. However, later CD154 expression was highly dependent on costimulation through either CD28 or inducible costimulator (ICOS). Although CD28 signalling interleukin (IL)-2 secretion, ICOS not, suggesting that costimulation enhance CD154 expression independently of IL-2 production. In fact, anti-CD28 treatment could still induce late-phase CD154 on anti-CD3-stimulated CD4 T cells expressing a mutated form of CD28 that not lead to the induction of IL-2. However, this CD154 induction was somewhat weaker than that of wild-type CD28-expressing cells, suggesting that direct signalling and IL-2-mediated signalling co-operatively responsible for the levels of CD154 induced by CD28. Finally, we show that the second phase of CD154 expression negatively regulated B-cell terminal differentiation and antibody secretion. These results demonstrate that TCR signalling and costimulation each regulate different phases of CD154 expression and control the biological outcome of CD40 signalling on B cells.

Increases in circulating T lymphocytes expressing HLA-DR and CD40 ligand in patients with dilated cardiomyopathy

Inflammatory and immunological mechanisms are implicated in the development of idiopathic dilated cardiomyopathy (DCM). Since activated T lymphocytes express surface HLA-DR antigens, an increased level of these cells in the circulation could indicated an ongoing immune response. While the role of activated T lymphocytes in experimental myocarditis has been elucidated, the contribution of T lymphocyte activation in clinical DCM remains unclear. We therefore examined the role of T-cell activation in peripheral blood samples obtained from 10 patients with DCM (mean age, 49 +/- 12 years) and from 10 age-matched healthy controls. Citrated whole blood was mixed with fluorescein isothiocyanate- or phycoerythrin-conjugated specific monoclonal antibodies and analyzed using a fluorescence-activated cell sorter (FACS). The ratio (%) of histocompatibility leukocyte antigen (HLA)-DR positive cells in the FACS gated lymphocyte population was significantly higher in DCM patients than in controls (7.9% +/- 5.3% vs 2.0% +/- 0.9%; P < 0.01). The expression of CD40L on T cells determined as mean fluorescence intensity (MFI) was also significantly higher in DCM patients than in controls (3.6 +/- 2.1 vs 1.8 +/- 0.4 MFI; P < 0.05). Furthermore, the ratios of T cells expressing HLA-DR and serum brain natriuretic peptide (BNP) levels closely correlated (P = 0.0008). We showed that HLA-DR on peripheral T cells significantly correlated with serum BNP levels and that high CD40L expression on T cells was concomitant with increased BNP levels (P < 0.05). Therefore the magnitude of T-cell expression, such as increased expression of HLA-DR and CD40L, contributes to myocardial dysfunction in DCM.

C4b binding protein binds to CD154 preventing CD40 mediated cholangiocyte apoptosis: a novel link between complement and epithelial cell survival

Activation of CD40 on hepatocytes and cholangiocytes is critical for amplifying Fas-mediated apoptosis in the human liver. C4b-Binding Protein (C4BP) has been reported to act as a potential surrogate ligand for CD40, suggesting that it could be involved in modulating liver epithelial cell survival. Using surface plasmon resonance (BiaCore) analysis supported by gel filtration we have shown that C4BP does not bind CD40, but it forms stable high molecular weight complexes with soluble CD40 ligand (sCD154). These C4BP/sCD154 complexes bound efficiently to immobilised CD40, but when applied to cholangiocytes they failed to induce apoptosis or proliferation or to activate NFkB, AP-1 or STAT 3, which are activated by sCD154 alone. Thus C4BP can modulate CD40/sCD154 interactions by presenting a high molecular weight multimeric sCD154/C4BP complex that suppresses critical intracellular signalling pathways, permitting cell survival without inducing proliferation. Immunohistochemistry demonstrated co-localisation and enhanced expression of C4BP and CD40 in human liver cancers. These findings suggest a novel pathway whereby components of the complement system and TNF ligands and receptors might be involved in modulating epithelial cell survival in chronic inflammation and malignant disease.

Release of potential immunomodulatory factors during platelet storage

BACKGROUND

Blood platelets (PLTs) link the processes of hemostasis and inflammation. Recent studies have demonstrated that PLTs promote immunity and inflammation mainly by means of the CD40/CD40L pathway. Our objective was to describe the accumulation of cytokines in PLT concentrates during storage.

STUDY DESIGN AND METHODS

Pools of PLT concentrates were prepared, separated from plasma, and resuspended in clinical-grade storage medium; samples were taken on Days 0, 1, 2, 3, and 5 for analysis, without replacement (i.e., without soluble protein dilution). Interleukin (IL)-6, IL-8, PLT-derived growth factor (PDGF)-AA, soluble CD40 ligand (sCD40L), RANTES, and transforming growth factor-beta production were measured by specific enzyme-linked immunosorbent assays.

RESULTS

Over time, the levels of RANTES, IL-8, and IL-6 were stable. In contrast, the levels of PDGF-AA and sCD40L increased. Ex vivo production of sCD40L was quantified at levels sufficient to induce B-cell effects based on previous studies of in vitro induced B-cell activation and differentiation by sCD40L. Cytokine and/or chemokine levels were generally higher in PLT concentrate supernatants and/or PLT lysates in comparison to PLT-free plasma, allowing the determination of which cytokine and/or chemokine was absorbed or secreted by transfusion-grade PLTs over time.

CONCLUSION

Our data provide evidence that stored PLTs contain molecules with known immunomodulatory competence and secrete them differentially over time during storage for transfusion purposes.

Immunomodulation with CD40 stimulation and interleukin-2 protects mice from disseminated cryptococcosis

Cryptococcus neoformans is a ubiquitous fungus that can cause life-threatening infections during immunosuppressive states such as AIDS and after bone marrow transplantation. In this study we investigated the antifungal efficacy of an agonist antibody to CD40, an important costimulator of immune function, in combination with interleukin 2 (IL-2) in a murine model of disseminated cryptococcosis. Only the combination of anti-CD40 and IL-2 significantly prolonged the survival time of infected mice. This protection was correlated with decreased yeast burdens in the brain and kidney. Increased immune cell populations in the spleens, as well as increased serum gamma interferon (IFN-gamma) and tumor necrosis factor alpha levels were observed in infected mice treated with anti-CD40 and IL-2. Further experiments with IFN-gamma knockout mice demonstrated that the protection induced by anti-CD40 and IL-2 treatment was dependent on IFN-gamma. Depletion of CD4+ T cells did not affect the increased serum IFN-gamma levels induced by anti-CD40 and IL-2 treatment and, importantly, did not affect the antifungal effect of combination therapy. These studies indicate that immunotherapy using anti-CD40 and IL-2 has therapeutic potential in augmenting host resistance to disseminated cryptococcosis and that IFN-gamma is essential for efficacy.

Immunotherapy of high-risk acute leukemia with a recipient (autologous) vaccine expressing transgenic human CD40L and IL-2 after chemotherapy and allogeneic stem cell transplantation

CD40L generates immune responses in leukemia-bearing mice, an effect that is potentiated by IL-2. We studied the feasibility, safety, and immunologic efficacy of an IL-2- and CD40L-expressing recipient-derived tumor vaccine consisting of leukemic blasts admixed with skin fibroblasts transduced with adenoviral vectors encoding human IL-2 (hIL-2) and hCD40L. Ten patients (including 7 children) with high-risk acute myeloid (n = 4) or lymphoblastic (n = 6) leukemia in cytologic remission (after allogeneic stem cell transplantation [n = 9] or chemotherapy alone [n = 1]) received up to 6 subcutaneous injections of the IL-2/CD40L vaccine. None of the patients were receiving immunosuppressive drugs. No severe adverse reactions were noted. Immunization produced a 10- to 890-fold increase in the frequencies of major histocompatibility complex (MHC)-restricted T cells reactive against recipient-derived blasts. These leukemia-reactive T cells included both T-cytotoxic/T-helper 1 (Th1) and Th2 subclasses, as determined from their production of granzyme B, interferon-gamma, and interleukin-5. Two patients produced systemic IgG antibodies that bound to their blasts. Eight patients remained disease free for 27 to 62 months after treatment (5-year overall survival, 90%). Thus, even in heavily treated patients, including recipients of allogeneic stem cell transplants, recipient-derived antileukemia vaccines can induce immune responses reactive against leukemic blasts. This approach may be worthy of further study, particularly in patients with a high risk of relapse.

A Salmonella typhi OmpC fusion protein expressing the CD154 Trp140-Ser149 amino acid strand binds CD40 and activates a lymphoma B-cell line

CD154 is a type II glycoprotein member of the tumour necrosis factor (TNF) ligand family, which is expressed mainly on the surface of activated T lymphocytes. The interaction with its receptor CD40, plays a central role in the control of several functions of the immune system. Structural models based on the homology of CD154 with TNF and lymphotoxin indicate that binding to CD40 involves three regions surrounding amino acids K143, R203 and Q220, and that strands W140-S149 and S198-A210 are critical for such interactions. Also, it has been reported that two recombinant CD154 fragments, including amino acid residues Y45-L261 or E108-L261 are biologically active, whereas other polypeptides, including S149-L261, are not. Therefore, we decided to construct a fusion protein inserting the W140-S149 amino acid strand (WAEKGYYTMS) in an external loop of the outer membrane protein C (OmpC) from Salmonella enterica serovar Typhi and assess its ability to bind CD40 and activate B cells. The sodium dodecyl sulphate-polyacrylamide gel electrophoresis demonstrated that the chimeric OmpC-gp39 protein conserved its ability to form trimers. Binding to CD40 was established by three variants of enzyme-linked immunosorbent assay, a direct binding assay by coating plates with a recombinant CD40-Fc protein and through two competition assays between OmpC-gp39 and recombinant CD154 or soluble CD40-Fc. Flow cytometry analysis demonstrated that OmpC-gp39 increased the expression levels of major histocompatibility complex II, CD23, and CD80, in Raji human B-cell lymphoma similarly to an antibody against CD40. These results further support that the CD154/CD40 interaction is similar to the TNF/TNF receptor. This is the first report of a bacterial fusion protein containing a small amino acid strand form a ligand that is able to activate its cognate receptor.

In situ expression of CD40, CD40L (CD154), IL-12, TNF-alpha, IFN-gamma and TGF-beta1 in murine lungs during slowly progressive primary tuberculosis

The distribution and expression of CD40, its ligand CD40L (154) and related cytokines interleukin-12 (IL-12), tumour necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma) and transforming growth factor-beta1 (TGF-beta1) were studied in the lungs of B6D2F1 hybrid mice during slowly progressive primary tuberculosis (TB) by immunohistochemistry. CD40 and CD40L are implicated in cell-mediated immunity (CMI) causing activation or apoptosis of infected cells. The phenomenon of apoptosis is associated with Mycobacterium tuberculosis survival. In this study, using frozen lung sections (n = 33), our results showed increased CD40, IL-12 and TGF-beta1 expression in macrophages with progression of disease. High percentages of mycobacterial antigens (M.Ags), CD40L and IFN-gamma expression were maintained throughout infection, and TNF-alpha-expressing cells were decreased. In lymphocytes, the percentage of IFN-gamma-positive cells was increased, but CD40L and IL-12 were maintained with the progression of disease. M.Ags, CD40 and CD40L were expressed in the same areas of the lesions. We conclude that changes in the expression of CD40-CD40L and cytokines associated with M. tuberculosis infection favour the hypothesis that M. tuberculosis causes resistance of host cells to apoptosis causing perpetuation of infection.

NF-kappaB is involved in regulation of CD40 ligand expression on Mycobacterium bovis bacillus Calmette-Guérin-activated human T cells

Interaction between CD40L (CD154) on activated T cells and its receptor CD40 on antigen-presenting cells has been reported to be important in the resolution of infection by mycobacteria. However, the mechanism(s) by which Mycobacterium bovis bacillus Calmette-Guérin (BCG) up-regulates membrane expression of CD40L molecules is poorly understood. This study was done to investigate the role of the nuclear factor kappaB (NF-kappaB) signaling pathway in the regulation of CD40L expression in human CD4(+) T cells stimulated with BCG. Specific pharmacologic inhibition of the NF-kappaB pathway revealed that this signaling cascade was required in the regulation of CD40L expression on the surface of BCG-activated CD4(+) T cells. These results were further supported by the fact that treatment of BCG-activated CD4(+) T cells with these pharmacological inhibitors significantly down-regulated CD40L mRNA. In this study, inhibitor kappaBalpha (IkappaBalpha) and IkappaBbeta protein production was not affected by the chemical protease inhibitors and, more importantly, BCG led to the rapid but transient induction of NF-kappaB activity. Our results also indicated that CD40L expression on BCG-activated CD4(+) T cells resulted from transcriptional up-regulation of the CD40L gene by a mechanism which is independent of de novo protein synthesis. Interestingly, BCG-induced activation of NF-kappaB and the increased CD40L cell surface expression were blocked by the protein kinase C (PKC) inhibitors 1-[5-isoquinolinesulfonyl]-2-methylpiperazine and salicylate, both of which block phosphorylation of IkappaB. Moreover, rottlerin a Ca(2+)-independent PKC isoform inhibitor, significantly down-regulated CD40L mRNA in BCG-activated CD4(+) T cells. These data strongly suggest that CD40L expression by BCG-activated CD4(+) T cells is regulated via the PKC pathway and by NF-kappaB DNA binding activity.

CD40:CD40L interactions in X-linked and non-X-linked hyper-IgM syndromes

Hyper-IgM (HIM) syndrome is a rare immunodeficiency characterized by low or absent IgG, IgA, and IgE with normal or elevated levels of IgM. This disorder can be acquired or familial with either X-linked or autosomal patterns of inheritance. The X-linked form of the disease is a consequence of mutations in the CD40 ligand (CD40L) gene that encodes a protein expressed primarily on activated CD4+ T cells. The cognate interaction between CD40L on T cells and CD40 on antigen-stimulated B cells, macrophage, and dendritic cells is critical for the development of a comprehensive immune response. The non-X-linked form of HIM syndrome is heterogeneous and appears in some cases to be a consequence of mutations in the AlD gene which encodes a B cell specific protein required for class switch recombination, somatic mutation, and germinal center formation. However, mutations in other unidentified genes are clearly the basis of the disease in a subset of patients. In this article, we review the essential features of the X-linked and non-X-linked forms of HIM syndrome and discuss the critical role the CD40:CD40L receptor-ligand pair plays in the pathogenesis of these immune deficiencies.

Choroid plexus macrophages proliferate and release toxic factors in response to feline immunodeficiency virus

Recent observations have suggested that lentiviruses stimulate the proliferation and activation of microglia. A similar effect within the dense macrophage population of the choroid plexus could have significant implications for trafficking of virus and inflammatory cells into the brain. To explore this possibility, we cultured fetal feline macrophages and examined their response to feline immunodeficiency virus (FIV) or the T-cell-derived protein, recombinant human CD40-ligand trimer (rhuCD40-L). The rhCD40-L was the most potent stimulus for macrophage proliferation, often inducing a dramatic increase in macrophage density. Exposure to FIV resulted in a small increase in the number of macrophages and macrophage nuclei labeled with bromodeoxyuridine. The increase in macrophage density after FIV infection also correlated with an increase in neurotoxic activity of the macrophage-conditioned medium. Starting at 16-18 weeks postinfection, well after the peak of viremia, a similar toxic activity was detected in cerebrospinal fluid (CSF) from FIV-infected cats. Toxicity in the CSF increased over time and was paralleled by strong CD18 staining of macrophages/microglia in the choroid plexus and adjacent parenchyma. These results suggest that lentiviral infection of the choroid plexus can induce a toxic inflammatory response that is fueled by local macrophage proliferation. Together with the observation of increasing toxic activity in the CSF and increased CD18 staining in vivo, these observations suggest that choroid plexus macrophages may contribute to an inflammatory cascade in the brain that progresses independently of systemic and CSF viral load.

New developments in immunosuppressive therapy in renal transplantation

The introduction of new immunosuppressive agents and protocols has improved outcomes for renal transplant recipients by decreasing the risk of rejection and by increasing the function and lifespan of the allograft. This article reviews the major changes in the combinations of therapies used: calcineurin inhibitors, target of rapamycin inhibitors, mycophenolate mofetil, non-depleting monoclonal versus depleting monoclonal and polyclonal antibodies for induction and increasing emphasis on protocols for reduction or avoidance of steroids and calcineurin inhibitors. The new agents with novel immunological targets such as anti-CD40 ligand, LEA29Y, FTY720, anti-CD20 (rituximab, Rituxan, Mabthera) and anti-CH52 (alemtuzumab, Campath), which are under development but have yet to survive the rigors of clinical trials are also discussed. In the presence of low early rejection rates, immunosuppressive therapy is setting new goals such as better graft function (glomerular filtration rates), reduction in adverse effects such as hypertension, hyperlipidaemia and drug toxicity and, above all, the prevention of late graft deterioration.

Analysis of a CD40 ligand dinucleotide microsatellite in multiple sclerosis

In recent years, numerous reports have described the diverse roles of the CD40-CD40 ligand receptor-ligand pair. The interaction of these two cell-surface molecules regulates both humoral and cell-mediated immune functions. Because the CD40 ligand is known to be highly expressed on the peripheral blood mononuclear cells (PBMC) of multiple sclerosis (MS) patients, and because activated helper T cells expressing CD40 ligand have been found in the brain sections of MS patients, but not in those of normal controls, the protein is believed to be involved in MS development. We studied the influence of a polymorphic dinucleotide-repeat marker located in the 3' untranslated region of the X-linked gene encoding CD40 ligand (CD40LG) on susceptibility to and disease severity in MS. From a total cohort of 771 Nordic definite-MS patients, the most (n = 92) and least (n = 90) disabled octiles, as well as random samples of intermediately disabled males (n = 119) and females (n = 121), were genotyped; 135 ethnically matched healthy subjects were used as controls. In addition, the effect of the polymorphism on CD40 ligand mRNA expression was assessed using PBMC from 54 MS patients and 22 controls. The phenotype frequencies for the CD40LG marker did not differ significantly between gender-conditioned intermediate-MS subgroups and controls, or between gender-conditioned disability octiles. Nor did the polymorphism appear to exert any significant effect on mRNA expression in either patients or controls.

Expression of CD40 identifies a unique pathogenic T cell population in type 1 diabetes

Juvenile diabetes (type 1) is an autoimmune disease in which CD4(+) T cells play a major role in pathogenesis characterized by insulitis and beta cell destruction leading to clinical hyperglycemia. To date, no marker for autoimmune T cells has been described, although it was previously demonstrated that autoimmune mice have a large population of CD4(+) cells that express CD40. We show here that established, diabetogenic T cell clones of either the Th1 or Th2 phenotype are CD40-positive, whereas nondiabetogenic clones are CD40-negative. CD40 functionally signals T cell clones, inducing rapid activation of the transcription factor NFkappaB. We show that autoimmune diabetes-prone nonobese diabetic mice have high levels of CD40(+)CD4(+) T cells in the thymus, spleen, and importantly, in the pancreas. Finally, as demonstrated by adoptive transfers, CD4(+)CD40(+) cells infiltrate the pancreatic islets causing beta-cell degranulation and ultimately diabetes.

Bi-directional modulation of T cell-dependent antibody production by prostaglandin E(2)

T cell-dependent Ig production involves interaction between T cells and B cells. This study evaluated the effects of prostaglandin (PG) E(2) on Ig production in a system in which B cells were co-cultured with autologous CD4(+) T cell clones non-specifically activated by anti-CD3. The effects of PGE(2) on T cell-dependent Ig production differed substantially, depending on the T cells employed. We selected six T cell clones that were able to enhance Ig production (resistant T cell clones) and six T cell clones that inhibited Ig production in the presence of PGE(2) (sensitive T cell clones) for comparison. The resistant T cells produced high levels (>1000 pg/ml) of IL-2 and/or IL-4, and expressed high CD40L, OX40 and CD45RA, and low CD45RO. In contrast, sensitive T cells secreted low IL-2 (<500 pg/ml) and IL-4 (<200 pg/ml), and expressed low CD40, OX40 and CD45RA, and high CD45RO. Adding supernatant derived from resistant T cell clones restored Ig production inhibited by PGE(2), while removing IL-2, IL-4 or IL-10 using specific antibodies inhibited Ig production. In addition, we demonstrated a direct effect of PGE(2) on B cells to enhance Ig production. Consistently, in the presence of resistant T cells, PGE(2) increased B cell proliferation and differentiation. In conclusion, the effects of PGE(2) on Ig production consist of its indirect effects through T cells and its direct effects on B cells. The outcome of the effects can be up-regulatory or down-regulatory, depending whether resistant or sensitive T cells are involved.

A DAP12-mediated pathway regulates expression of CC chemokine receptor 7 and maturation of human dendritic cells

Gene targeting of the adaptor molecule DAP12 in mice caused abnormal distribution and impaired antigen presentation capacity of dendritic cells (DCs). However, the DAP12-associated receptors expressed on DCs and their functions have not been identified yet. Here we show that the triggering receptor expressed on myeloid cells-2 (TREM-2) is a cell surface receptor on human monocyte-derived DCs, which is associated with DAP12. TREM-2/DAP12 promotes upregulation of CC chemokine receptor 7, partial DC maturation, and DC survival through activation of protein tyrosine kinases and extracellular signal-regulated kinase. In contrast to Toll-like receptor-mediated signaling, TREM2/DAP12 stimulation is independent of nuclear factor-kappaB and p38 stress-activated protein kinase. This novel DC activation pathway may regulate DC homeostasis and amplify DC responses to pathogens, explaining the phenotype observed in DAP12-deficient mice.

Role of CD40 ligand in Mycobacterium avium infection

Mycobacterium avium is a common opportunistic pathogen in immunocompromised patients such as those infected with human immunodeficiency virus. Although M. avium is an intracellular organism replicating predominantly in macrophages, disseminated M. avium infection is seen in AIDS patients with CD4(+) cell counts of <50 cells/microliters, suggesting a possible involvement of a T cell-macrophage interaction for the elimination of M. avium. To determine whether CD40-CD40 ligand (CD40L) interactions play a role in M. avium infection, we studied the ability of CD40L to restrict M. avium replication in human monocyte-derived macrophages (MDM) in vitro. MDM were infected with M. avium and cocultured with CD40L-transfected 293 cells for 7 days. Intracellular growth of M. avium in these MDM was assessed by colony counting. CD40L-expressing cells inhibited growth of M. avium in MDM by 86.5% +/- 4.2% compared to MDM cultured with control cells. These findings were verified by assays using purified, soluble recombinant human CD40L (CD40LT). CD40LT (5 micrograms/ml) inhibited intracellular growth of M. avium by 76.9% +/- 18.0% compared to cells treated with medium alone. Inhibition by CD40LT was reduced by monoclonal antibodies (MAbs) against CD40 and CD40L. The inhibitory effect of CD40LT was not accompanied by enhancement of interleukin-12 (IL-12) production by M. avium-infected MDM, while CD40L-expressing cells stimulated IL-12 production by these cells. Treatment of M. avium-infected mice with MAb against murine CD40L resulted in recovery of larger numbers of organisms (0.8 to 1.0 log) from the spleens, livers, and lungs of these animals compared to infected mice which received normal immunoglobulin G. These results indicate that CD40-CD40L signaling may be an important step in host immune response against M. avium infection.

Bcl-6 expression in reactive follicular hyperplasia, follicular lymphoma, and angioimmunoblastic T-cell lymphoma with hyperplastic germinal centers: heterogeneity of intrafollicular T-cells and their altered distribution in the pathogenesis of angioimmunoblastic T-cell lymphoma

BACKGROUND

The Bcl-6 gene product, a nuclear phosphoprotein, is expressed independently of Bcl-6 gene rearrangement. In lymph nodes, expression of Bcl-6 protein is restricted to germinal center (GC) B-cells and 10% to 15% of CD3/CD4+ intrafollicular T cells. Interfollicular cells are negative for Bcl-6 protein, except for rare CD3+/CD4+ T cells. Recently, we reported cases of angioimmunoblastic T-cell lymphoma (AITL) with hyperplastic GCs (AITL/GC), and observed that borders of enlarged GCs were ill defined, with features suggestive of an outward migration of GC cells to surrounding interfollicular zones. This prompted a study of follicular borders with Bcl-6 staining in reactive follicular hyperplasias and follicular lymphomas to compare with AITL/GC.

MATERIALS AND METHODS

Formalin-fixed paraffin sections were used for immunostaining of Bcl-6. Six cases of AITL/GC, 12 nonspecific reactive follicular hyperplasia (FH), 7 HIV adenopathy, 10 follicular lymphoma (FL), and 8 typical AITL (ie, AITL without GC) were studied. Double staining for Bcl-6/CD20, Bcl-6/CD3, and Bcl-6/CD57 was performed in selected cases.

RESULTS

In FH and HIV adenopathy, staining for Bcl-6 revealed densely populated GCs with well-defined and regular GC borders, whereas Bcl-6+ cells were rare in the interfollicular areas. An occasional GC with an ill-defined border was invariably surrounded by a broad mantle zone; those with indistinct mantle zones had well-defined, regular borders. In FL, follicles were densely populated, and their borders were irregular, with some Bcl-6+ cells in the interfollicular zones. In AITL/GC, GCs were less dense, GC borders were ill defined and irregular, and the number of interfollicular Bcl-6+ cells was markedly increased. Double staining revealed that these interfollicular Bcl-6+ cells in AITL/GC were Bcl6+/CD3+/CD20-/CD57- T cells. Moreover, CD3+ intrafollicular T cells were depleted in AITL/GC, whereas they were abundant in FH. Intrafollicular CD57+ cells did not stain for Bcl-6, and were also depleted in AITL/GC. In typical AITL, some neoplastic cells were positive for Bcl-6, showing variable degrees of staining.

CONCLUSIONS

(1) GCs of AITL/GC differed from those of other reactive follicular hyperplasias and follicular lymphomas, and staining for Bcl-6 was useful to discern them. (2) Intrafollicular CD3+ T cells, many of which were also positive for Bcl-6, were markedly depleted in AITL/GC, with increased interfollicular Bcl-6+/CD3+ cells, suggesting an outward migration of intrafollicular T cells in this condition. (3) Interfollicular Bcl-6+/CD3+ cells in AITL/GC were too numerous to be accounted for by migration alone, suggesting local proliferation. (4) Intrafollicular CD57+ cells were negative for Bcl-6, indicating heterogeneity of the intrafollicular T-cell population. (5) Some neoplastic cells in AITL stained for Bcl-6, suggesting up-regulation of Bcl-6 expression in this tumor.

CD40 stimulation promotes human secondary immunoglobulin responses in HuPBL-SCID chimeras

Antibodies to CD40 have been demonstrated to promote B-cell growth and differentiation in vitro. In order to determine if CD40 stimulation could promote antigen-specific human immunoglobulin (Ig) production in vivo, we examined the effects of anti-human CD40 MoAb in an in vivo system where human peripheral blood lymphocytes (huPBL) were engrafted into mice with severe combined immune deficiency (SCID). The huPBL-SCID mice were then given various doses of diphtheria-tetanus toxoid (DT) vaccine and were examined for the presence of human DT-specific antibodies by ELISA. Surprisingly, treatment with anti-CD40 significantly lowered background DT responses versus untreated chimeras in unimmunized huPBL-SCID mice. However, after immunization, huPBL-SCID mice treated with anti-CD40 MoAb responded to a significantly greater extent in response to the vaccine compared with control huPBL-SCID mice, although total Ig levels were sometimes lower in anti-CD40-treated mice. The predominant Ig isotype induced after immunization was IgG. Thus, CD40 stimulation promotes human secondary IgG responses in huPBL-SCID mice. These data demonstrate that CD40 stimulation is capable of promoting antigen-specific human B-cell responses in vivo.

Induction and Inhibition of CD40-CD40 Ligand Interactions: A New Strategy Underlying Host-Virus Relationships

Interaction between CD40 and the CD40 ligand (CD40L) is required for mouse mammary tumor virus (MMTV) propagation. We found that Fas was expressed on B cells and CD40L on a small subset of viral superantigen-cognate T cells 12 h after MMTV(SW) infection. CD40L and Fas were down-regulated after 24 h. All CD4 T cells then became resistant to anti-CD3-induced CD40L induction in vitro for 2 wk. Initiation of CD40L expression and its rapid shut-off was associated with IL-12 production and was controlled by IFN-γ and shedding of soluble CD40. These results suggest that a rapid, transient CD40-CD40L interaction involving a small number of cells is sufficient for MMTV propagation. Modulation of CD40L expression may be a major mechanism regulating the balance between viral propagation and host defenses, allowing mutual survival.

CD40 Ligand/Trimer DNA Enhances Both Humoral and Cellular Immune Responses and Induces Protective Immunity to Infectious and Tumor Challenge

CD40/CD40 ligand interactions have a central role in the induction of both humoral and cellular immunity. In this study, we examined whether a plasmid expressing CD40 ligand/trimer (CD40LT) could enhance immune responses in vivo. BALB/c mice were injected with plasmid expressing β-galactosidase DNA with or without CD40LT DNA or IL-12 DNA, and immune responses were assessed. Mice vaccinated with β-gal DNA plus CD40LT DNA or IL-12 DNA had a striking increase in Ag-specific production of IFN-γ, cytolytic T cell activity, and IgG2a Ab. The mechanism by which CD40LT DNA enhanced these responses was further assessed by treating vaccinated mice with anti-IL-12 mAb or CTLA-4 Ig (CTLA4Ig). Production of IFN-γ and CTL activity was abrogated by these treatments, suggesting that CD40LT DNA was mediating its effects on IFN-γ and CTL activity through induction of IL-12 and enhancement of B7 expression, respectively. Physiologic relevance for the ability of CD40LT DNA to enhance immune responses by the aforementioned pathways was shown in two in vivo models. First, with regard to CTL activity, mice vaccinated with CD40LT DNA did not develop metastatic tumor following challenge with lethal dose of tumor. Moreover, in a mouse model requiring IL-12-dependent production of IFN-γ, mice vaccinated with soluble Leishmania Ag and CD40LT DNA were able to control infection with Leishmania major. These data suggest that CD40LT DNA could be a useful vaccine adjuvant for diseases requiring cellular and/or humoral immunity.

Cutting Edge: CD40 Ligand Is Not Essential for the Development of Cell-Mediated Immunity and Resistance to Mycobacterium tuberculosis

It has been proposed that the induction of cellular immunity and resistance to intracellular pathogens is dependent upon CD40 ligand (CD40L). In the present study we show that this proposal is not ubiquitously supported. Mice genetically deficient in CD40L (CD40LKO) were resistant to i.v. infection with Mycobacterium tuberculosis when assessed by survival and bacteriologic burden in the spleen, liver, and lungs. Infected CD40LKO mice developed granulomas that lacked epithelioid cells and were less numerous and markedly smaller than those observed in control mice. Upon stimulation with purified protein derivative of M. tuberculosis,CD4+ T cells from infected CD40LKO mice proliferated and produced high levels of IFN-γ but not IL-4. Finally, spleen cells from CD40LKO mice stimulated with M. tuberculosis produced IL-12, TNF, and nitric oxide levels comparable to those produced by control cells. In contrast to original proposals, these data clearly show that protective Th1 immunity can be achieved against intracellular pathogens (e.g., Mycobacterium) independently of CD40L.

Human Purified Protein Derivative-Specific CD4+ T Cells Use Both CD95-Dependent and CD95-Independent Cytolytic Mechanisms

CTL, both CD4+ and CD8+, are essential in the eradication of intracellular pathogens. Data generated using murine T cells have suggested a critical role for CD95 (Fas, Apo-1) in CD4+ T cell-induced apoptosis of target cells. In contrast, CD8+ CTL predominantly use the perforin/granzyme lytic pathway. At present little is known about the mechanism of CD4+ CTL lytic function during intracellular infection in humans. We have used human CD4+ T cells specific for purified protein derivative (PPD) of Mycobacterium tuberculosis to explore whether CD95 is the dominant cytolytic mechanism. PPD-reactive CD4+ clones efficiently lysed Ag-pulsed autologous monocytes, adherent macrophages, and EBV-transformed B cells. Addition of an antagonistic CD95 Ab had a minimal effect on cytolysis, whereas addition of MgEGTA to block perforin/granzyme resulted in complete inhibition of killing. In contrast, lysis of activated peripheral blood B cells could be partially blocked with the antagonistic CD95 Ab. Supporting these observations, monocytes, macrophages, and EBV-transformed B cells were not lysed by an agonistic CD95 Ab. Activated B cells were readily lysed by the agonistic CD95 Ab. T cell clones triggered through the TCR with anti-CD3 were capable of lysing the CD95-sensitive Jurkat T cell line in a CD95-dependent manner, but were also able to release granzymes. We conclude that human CD4+ T cells are capable of lysing PPD-pulsed targets using both perforin/granzyme and CD95 pathways. The contribution of CD95 is strictly dependent on target cell susceptibility to CD95-mediated killing.

Elevated levels of biologically active soluble CD40 ligand in the serum of patients with chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is an indolent lymphoproliferative disorder manifested by low growth fraction and prolonged survival of the malignant cells. The mechanisms that enable CLL cells to live longer and to resist apoptosis remain unclear. Because the malignant CLL cells express CD40 and Fas receptors, which can transduce cell-survival and cell-death signals, we examined the role of CD40 in the growth regulation of CLL cells and its interaction with Fas-mediated and fludarabine-induced apoptosis in vitro. Primary CLL cells underwent spontaneous apoptosis in culture, which was enhanced by exogenous human Fas ligand (FasL) or fludarabine. Exogenous CD40L rescued CLL cells from spontaneous apoptosis in a dose-dependent manner, and caused CLL cells to resist apoptosis induced by FasL or fludarabine. Patients' autologous plasma rescued CLL cells from spontaneous apoptosis, an effect that could be reversed with anti-CD40 ligand (CD40L) antibodies. The levels of soluble CD40 ligand in the sera of 51 CLL patients and 55 healthy donors were determined by enzyme-linked immunosorbent assay. The mean soluble CD40L level in normal donors was 0.29 ng/ml compared to a mean value of 0.80 ng/ml in CLL patients (P < 0.001). CD40L up-regulated bcl-X(L) mRNA but not bcl-2 in CLL cells within 3-6 h in culture. Our results demonstrated that serum of patients with CLL contained elevated levels of biologically active soluble CD40L, and that CD40L can prolong survival of CLL cells and mediate their resistance to FasL and fludarabine in vitro.

CD40 ligand inhibits Fas/CD95-mediated apoptosis of human blood-derived dendritic cells

Dendritic cells (DC) are considered to be the most potent antigen-presenting cells (APC) in the immune system. In this study, we analyzed the regulation of apoptosis of human peripheral blood-derived DC. DC were generated from adherent peripheral blood mononuclear cells that had been cultured for 7 days with granulocyte-macrophage colony-stimulating factor and interleukin-4. These cells displayed phenotypic properties of DC, including dendritic processes, expression of CD1a and lack of expression of CD14, and were very potent at presenting soluble antigens to T cells. Blood-derived DC were demonstrated to express the Fas/CD95 antigen and an agonist antibody to CD95 strongly induced apoptotic cell death in these cells. Soluble trimeric CD40 ligand potently inhibited both CD95-mediated and spontaneous apoptosis in DC. The data suggest that interactions between members of the tumor necrosis factor family of ligands expressed by T cells with their receptors on DC play an important role in the regulation of apoptosis in DC during antigen presentation and may, therefore, regulate the duration of T cell expansion and cytokine production.

Reed-Sternberg cells and the TNF family of receptors/ligands

Treatment of cancer with means other than chemo- and radiation therapy becomes more and more important. Through the better understanding of tumor biology approaches towards the cure of cancer interfering with the pathophysiological mechanisms of malignancy can be considered. Hodgkin's disease is a good example for the role of the immune system in cancer. The Reed-Sternberg (RS) cells, malignant cells of Hodgkin's disease (HD), are surrounded by tumor infiltrating lymphocytes (TILs) and still evade immunesurveillance. In this respect the importance of the superfamily of tumor necrosis factor (TNF) receptors and ligands is becoming more and more clear. Ligand-receptor interaction either leads to death or survival signals. Many of these receptors and ligands are expressed by the RS cells and the surrounding lymphocytes. Their expression and function in HD are discussed and future directions for possible therapeutical investigations are proposed.

A Leishmania protein that modulates interleukin (IL)-12, IL-10 and tumor necrosis factor-alpha production and expression of B7-1 in human monocyte-derived antigen-presenting cells

LeIF, a gene homologue of the eukaryotic initiation factor 4A was first described as a leishmanial antigen that induced a Th1-type T cell response in peripheral blood mononuclear cells (PBMC) from leishmaniasis patients. Moreover, the interferon (IFN)-gamma production by PBMC was found to be interleukin (IL)-12 dependent. Herein, we characterize the effects of LeIF on cytokine production and expression of surface molecules by normal human monocytes as well as by monocyte-derived macrophages and dendritic cells (MoDC). LeIF was a strong inducer of IL-12 and, to a lesser extent, of IL-10 and tumor necrosis factor (TNF)-alpha in macrophages and MoDC. IL-12 production did not require CD40 triggering, confirming that the ability of LeIF to induce IL-12 was not mediated through an effect on T cells. However, addition of soluble CD40 ligand (L) synergistically augmented IL-12 production in macrophages and MoDC. The cytokine-inducing activity of LeIF is located in the N-terminal portion of the molecule and was both proteinase K sensitive and polymyxin B resistant. LeIF, lipopolysaccharide and fixed Staphylococcus aureus all induced comparable amounts of IL-12, validating the potent cytokine-inducing effects of LeIF. Moreover, of these stimuli, LeIF had the highest IL-12/IL-10 and IL-12/TNF-alpha ratio demonstrating the preference of LeIF for IL-12 induction. Studies investigating the expression of surface molecules showed that LeIF up-regulated B7-1 and CD54 (ICAM-1) on macrophages and MoDC. To our knowledge this is the first report describing IL-12 production, up-regulation of co-stimulatory and intercellular adhesion molecules by monocytic antigen-presenting cells in response to a protein from a pathogenic microorganism. These immunomodulatory characteristics of LeIF might be excellent properties for a Th1-type adjuvant.

Immunologic and hematopoietic effects of CD40 stimulation after syngeneic bone marrow transplantation in mice

CD40 is a molecule present on multiple cell types including B lymphocyte lineage cells. CD40 has been shown to play an important role in B cell differentiation and activation in vitro, although little is known concerning the effects of CD40 stimulation in vivo. We therefore examined the effects of CD40 stimulation in mice using a syngeneic bone marrow transplantation (BMT) model in an effort to augment B cell recovery after high dose therapy with hematopoietic reconstitution. After the BMT, mice were treated with or without 2-6 microg of a soluble recombinant murine CD40 ligand (srmCD40L) given intraperitoneally twice a week. A significant increase in B cell progenitors (B220+/ surface IgM-) was observed in the bone marrow of mice receiving the srmCD40L. The treated recipients also demonstrated improved B-cell function with increases in total serum immunoglobulin and increased splenic mitogen responsiveness to LPS being noted. Additionally, srmCD40L treatment promoted secondary lymphoid organ repopulation, accelerating germinal center formation in the lymph nodes. Total B cell numbers in the periphery were not significantly affected even with continuous srmCD40L administration. Lymphocytes obtained from mice treated with the ligand also had increases in T cell mitogen and anti-CD3 mAb responsiveness and acquired the capability to produce IL-4. Surprisingly, treatment with srmCD40L also produced hematopoietic effects in mice, resulting in an increase of BM and splenic hematopoietic progenitor cells in the mice after BMT. Treatment with srmCD40L significantly increased granulocyte and platelet recovery in the peripheral blood. Incubation of BMC with srmCD40L in vitro also resulted in increased progenitor proliferation, demonstrating that the hematopoietic effects of the ligand may be direct. Thus, stimulation of CD40 by its ligand may be beneficial in accelerating both immune and hematopoietic recovery in the setting of bone marrow transplantation.

CD40/CD40 ligand interactions in normal, reactive and malignant lympho-hematopoietic tissues

CD40 is a 48 Kd integral membrane protein expressed by cells of B cells, origin, dentritic cells, monocytes, epithelial cells, endothelial cells and tumor cells including carcinomas, B cell lymphomas/leukemias and Hodgkin and Reed-Sternberg (HRS) cells of Hodgkin's disease (HD). CD40 has been clustered as a member of the nerve growth factor (NGF)/tumor necrosis factor (TNF) receptor superfamily with the corresponding counterstructure, the CD40 ligand (L) being mainly expressed by activated CD4+ T cells, but also some activated CD8+ T cells, basophils, eosinophils, mast cells and stromal cells. CD40L shares significant amino acid homology with TNF particularly in its extracellular domain ("TNF homology region") and is therefore viewed as a member of the TNF ligand superfamily. Binding of CD40L+ T cells to CD40+ B cells is thought to play a major role in T cell-dependent B cell activation, B cell proliferation, Ig isotype switching, memory B cell formation and rescue of B cells from apoptotic death in germinal centers. Mutations of the CD40L gene have been associated with the X-linked hyper-IgM immunodeficiency syndrome, pointing to the critical role of the CD40/CD40L interaction in the T cell-B cell interplay. Accordingly, expression of CD40 by human lympho-hematopoietic tumors has been shown in most of the B cell neoplasias, H-RS cells and HD and some carcinomas. In contrast, CD40L+ tumor cells are almost invariably restricted to CD4+/CD8- T cell lymphomas. Overall, functional CD40/CD40L interactions appear to be critical for cellular activation signals during immune responses and neoplastic tumor cell growth. The understanding of the biology of CD40L has improved our diagnostic and therapeutic repertoire in the management of several human diseases, including CD40+ tumors.

Effects of CD40 stimulation in the prevention of human EBV-lymphomagenesis

CD40 is a molecule present on B lineage cells, both normal and neoplastic. Signalling through CD40 has been demonstrated to promote B cell growth and differentiation in vitro. In contrast to its effects on normal B cells, we have found that CD40 stimulation can inhibit the growth of various aggressive histology human B cell lymphomas both in vitro and in vivo. Moreover, using a human/mouse chimera model in which human EBV-induced B cell lymphomas can spontaneously arise, we have found that CD40 stimulation an prevent the occurrence of this human lymphoma in mice. However, normal human B cell engraftment and function was not adversely affected in these mice by CD40 stimulation. This indicates that CD40 stimulation is selective in its effects on aggressive histology B cell lymphomas. Thus, CD40 stimulation either by antibody or a recombinant soluble ligand, may be of potential clinical use, not only in the treatment of EBV-induced B cell lymphomas, but also in their prevention.

Molecular, structural, and biological characteristics of the tumor necrosis factor ligand superfamily

The tumor necrosis factor receptor superfamily at present consists of ten different transmembrane (type I) glycoproteins with characteristic limited sequence homology for the cysteine-rich repeats in the extracellular domain. In parallel the tumor necrosis factor ligand super-family has been recognized by discovery of ligands for all members of the receptor superfamily. These molecules are also transmembrane (type II) glycoproteins, with the exception of lymphotoxin-alpha which is the only entirely secreted protein of the tumor necrosis factor-like proteins. Several members of the ligand superfamily, including tumor necrosis factor and CD95L also exist in a biologically active soluble form. The tumor necrosis factor ligand superfamily contains at present ten different proteins. In addition, NGFR p75 binds to a second family of proteins (neurotrophins). These nerve growth factor-like dimeric soluble molecules are basic neurotrophic factors and the five members (NGF, BDNF, NT-3, NT-4, NT-5) are not related to the tumor necrosis factor superfamily ligands. The members of the tumor necrosis factor ligand superfamily (TNF, LT-alpha, LT-beta, CD27L, CD30L, CD40L, CD95L, 4-IBB, OX40L, TRAIL) share common biological activities, but some properties are shared by only some ligands, while others are unique. The diverse biological activities triggered through tumor necrosis factor receptors have been linked to the regulation of cellular activation, including immune responses and inflammatory reactions, but also with the pathology of a series of human diseases.

Increased responsiveness of rheumatoid factor-producing B cells in seronegative and seropositive rheumatoid arthritis

OBJECTIVE

To compare the frequencies and responsiveness of rheumatoid factor (RF)-producing B cells in the peripheral blood of patients with seronegative and seropositive rheumatoid arthritis (RA).

METHODS

Frequencies of IgM+, IgG+, and RF+ B cells were determined by limiting-dilution analysis of purified peripheral blood B cells from 6 patients with seropositive RA, 8 patients with seronegative RA, and 7 normal controls. B cell help was provided by cloned T helper cells, which were stimulated by either anti-CD3 or the bacterial superantigen staphylococcal enterotoxin D (SED). IgM and IgG antibodies and RF in culture supernatants were detected by enzyme-linked immunosorbent assay.

RESULTS

In the presence of anti-CD3-stimulated T helper cells, 2-10% of B cells from normal individuals secreted IgM and IgG antibodies. The frequency of RF+ B cells was low and ranged from 1:182 to 1:885 (RF+: IgM+) B cells. In patients with seropositive RA, the numbers of Ig-producing B cells were reduced by a factor of 2, while the fraction of RF+ B cell precursors was expanded by more than 50-fold (7-20% of IgM+ B cells; P = 0.004). Patients with seronegative RA had higher frequencies of RF-producing B cells (1.5-6% of IgM+ B cells) than normal individuals (P = 0.002), but not to the same extent as seropositive patients (P = 0.002). Stimulation of B cells using SED preferentially induced RF+ B cells in normal controls and in patients with seronegative and seropositive RA.

CONCLUSION

B cell precursors with the potential to secrete RF were detectable in high frequencies in normal individuals and in patients with seropositive and seronegative RA. In all donors, these B cells could be stimulated with the bacterial superantigen SED. In normal individuals, RF+ B cells remained nonresponsive to help provided by anti-CD3-activated T cells, but were responsive in RA patients. Seronegative and seropositive RA form a continuous spectrum of disease, with a higher number of RF-secreting B cells in the seropositive patients.

Fas (CD95)/Fas ligand interactions regulate antigen-specific, major histocompatibility complex-restricted T/B cell proliferative responses

The effect of Fas ligand (FasL) cytotoxicity on T/B collaboration was examined in vitro using cloned T helper 1 cells and antigen-pulsed, activated B cells. We compared antigen-pulsed B cells that had been activated through different membrane receptors (IgM, CD14 and CD40) for their ability to induce T cell proliferation and to respond to T cell help. We also used a Fas-Ig fusion protein, an inhibitor of FasL-mediated cytotoxicity, to determine the effect of FasL cytotoxicity on the T and B cell proliferative responses. The data show that the extent of both T and B cell proliferative responses correlate with the relative resistance of activated B cell populations to FasL cytotoxicity. Moreover, both T and B cell proliferation could be enhanced by Fas-Ig. Our results demonstrate that FasL cytotoxicity is a negative regulatory mechanism for both T and B cell proliferative responses and that Fas-Ig can be an immunopotentiating agent for both T and B cell immunity.

CD40/CD40 ligand interactions are required for T cell-dependent production of interleukin-12 by mouse macrophages

We have previously shown that T cell receptor-activated mouse T helper (Th)1 clones induce the production of interleukin (IL)-12 by splenic antigen-presenting cells (APC). Here, we show that the expression of CD40L by activated T cells is critical for T cell-dependent IL-12 production by mouse macrophages. IL-12 was produced in cultures containing alloreactive Th1 clones stimulated with allogeneic peritoneal macrophages, or in cultures of splenocytes stimulated with anti-CD3. Anti-CD40L monoclonal antibodies (mAb) inhibited the production of IL-12, but not IL-2, in these cultures by approximately 90% and had dramatic inhibitory effects on antigen-dependent proliferation of Th1 clones. In addition, both activated T cells and a Th1 clone derived from CD40L knockout mice failed to induce IL-12 production from splenic APC or peritoneal macrophages. Finally, macrophages cultured in the absence of T cells produced IL-12 upon stimulation with soluble recombinant CD40L in combination with either supernatants from activated Th1 clones or with interferon-gamma and granulocyte/macrophage colony-stimulating factor. Thus, both CD40L-dependent and cytokine-mediated signals from activated T cells are required to induce the production of IL-12 by macrophages. A blockade at the level of IL-12 production may explain, at least in part, the dramatic ability of anti-CD40L mAb to inhibit disease in animal models that are dependent upon the generation of a cell-mediated immune response. Moreover, a defect in T cell-dependent induction of IL-12 may contribute to the immune status of humans that lack functional CD40L.

Costimulation and the regulation of antimicrobial immunity

The regulated expression of costimulatory molecules is a major factor limiting T-cell responses to self-antigens. However, the development of effective antimicrobial immunity requires that these molecules be induced on a variety of tissues, but most notably on macrophages. Here, Paul Kaye discusses the regulation of costimulatory molecules on macrophages and suggests that microbial interference in this process has important implications for immune regulation.

Recombinant CD30 ligand and CD40 ligand share common biological activities on Hodgkin and Reed-Sternberg cells

The CD30 ligand (CD30L) and CD40L are members of the tumor necrosis factor (TNF) protein superfamily, CD30L and CD40L are mainly expressed as membrane-bound proteins by activated T cells. CD30L and CD40L are costimulatory for T cell proliferation and activation. Further, CD40L is a critical signal for T cell-dependent activation of B cells. Primary and cultured Hodgkin and Reed-Sternberg (H-RS) cells, the neoplastic component of Hodgkin's disease (HD), express high levels of the counterreceptors CD30 and CD40. We have found that both the recombinant CD30L and CD40L enhanced interleukin (IL)-6, TNF and lymphotoxin (LT)-alpha release from cultured H-RS cells. In addition, CD40L, but not CD30L, induced IL-8 secretion. CD30L and CD40L seem to share some redundant biological activities involved in the deregulated secretion of cytokines known to play a central role in the clinical presentation and pathology of HD. Further, CD30L enhanced surface expression of intercellular adhesion molecule-1 (ICAM-1/CD54) on cultured H-RS cells, which is frequently overexpressed on primary H-RS cells. CD30L- and CD40L-enhanced CD54 surface expression is followed by elevated shedding of CD54, as shown by detection of elevated 82-kDa soluble (s) CD54 levels in culture supernatants after stimulation with both ligands. CD30L and CD40L share common pleiotropic biological activities on CD30+/CD40+ H-RS cells and are elements of the cytokine and cell contact-dependent activation network typical for HD, a tumor of cytokine producing cells.