Human B cell precursors proliferate and express CD23 after CD40 ligation

Multifaceted roles for STAT3 in gammaherpesvirus latency revealed through in vivo B cell knockout models

Cancers associated with the oncogenic gammaherpesviruses, Epstein-Barr virus and Kaposi sarcoma herpesvirus, are notable for their constitutive activation of the transcription factor signal transducer and activator of transcription 3 (STAT3). To better understand the role of STAT3 during gammaherpesvirus latency and the B cell response to infection, we used the model pathogen murine gammaherpesvirus 68 (MHV68). Genetic deletion of STAT3 in B cells of CD19cre/+Stat3f/f mice reduced peak MHV68 latency approximately sevenfold. However, infected CD19cre/+Stat3f/f mice exhibited disordered germinal centers and heightened virus-specific CD8 T cell responses compared to wild-type (WT) littermates. To circumvent the systemic immune alterations observed in the B cell-STAT3 knockout mice and more directly evaluate intrinsic roles for STAT3, we generated mixed bone marrow chimeric mice consisting of WT and STAT3 knockout B cells. We discovered a dramatic reduction in latency in STAT3 knockout B cells compared to their WT B cell counterparts in the same lymphoid organ. RNA sequencing of sorted germinal center B cells revealed that MHV68 infection shifts the gene signature toward proliferation and away from type I and type II IFN responses. Loss of STAT3 largely reversed the virus-driven transcriptional shift without impacting the viral gene expression program. STAT3 promoted B cell processes of the germinal center, including IL-21-stimulated downregulation of surface CD23 on B cells infected with MHV68 or EBV. Together, our data provide mechanistic insights into the role of STAT3 as a latency determinant in B cells for oncogenic gammaherpesviruses.IMPORTANCEThere are no directed therapies to the latency program of the human gammaherpesviruses, Epstein-Barr virus and Kaposi sarcoma herpesvirus. Activated host factor signal transducer and activator of transcription 3 (STAT3) is a hallmark of cancers caused by these viruses. We applied the murine gammaherpesvirus pathogen system to explore STAT3 function upon primary B cell infection in the host. Since STAT3 deletion in all CD19+ B cells of infected mice led to altered B and T cell responses, we generated chimeric mice with both normal and STAT3-deleted B cells. B cells lacking STAT3 failed to support virus latency compared to normal B cells from the same infected animal. Loss of STAT3 impaired B cell proliferation and differentiation and led to a striking upregulation of interferon-stimulated genes. These findings expand our understanding of STAT3-dependent processes that are key to its function as a pro-viral latency determinant for oncogenic gammaherpesviruses in B cells and may provide novel therapeutic targets.

B cell-intrinsic STAT3-mediated support of latency and interferon suppression during murine gammaherpesvirus 68 infection revealed through an in vivo competition model

Cancers associated with the oncogenic gammaherpesviruses, Epstein-Barr virus and Kaposi sarcoma herpesvirus, are notable for their constitutive activation of the transcription factor STAT3. To better understand the role of STAT3 during gammaherpesvirus latency and immune control, we utilized murine gammaherpesvirus 68 (MHV68) infection. Genetic deletion of STAT3 in B cells of CD19cre/+Stat3f/f mice reduced peak latency approximately 7-fold. However, infected CD19cre/+Stat3f/f mice exhibited disordered germinal centers and heightened virus-specific CD8 T cell responses compared to WT littermates. To circumvent the systemic immune alterations observed in the B cell-STAT3 knockout mice and more directly evaluate intrinsic roles for STAT3, we generated mixed bone marrow chimeras consisting of WT and STAT3-knockout B cells. Using a competitive model of infection, we discovered a dramatic reduction in latency in STAT3-knockout B cells compared to their WT B cell counterparts in the same lymphoid organ. RNA sequencing of sorted germinal center B cells revealed that STAT3 promotes proliferation and B cell processes of the germinal center but does not directly regulate viral gene expression. Last, this analysis uncovered a STAT3-dependent role for dampening type I IFN responses in newly infected B cells. Together, our data provide mechanistic insight into the role of STAT3 as a latency determinant in B cells for oncogenic gammaherpesviruses.

Characterization of spleen and lymph node cell types via CITE-seq and machine learning methods

The spleen and lymph nodes are important functional organs for human immune system. The identification of cell types for spleen and lymph nodes is helpful for understanding the mechanism of immune system. However, the cell types of spleen and lymph are highly diverse in the human body. Therefore, in this study, we employed a series of machine learning algorithms to computationally analyze the cell types of spleen and lymph based on single-cell CITE-seq sequencing data. A total of 28,211 cell data (training vs. test = 14,435 vs. 13,776) involving 24 cell types were collected for this study. For the training dataset, it was analyzed by Boruta and minimum redundancy maximum relevance (mRMR) one by one, resulting in an mRMR feature list. This list was fed into the incremental feature selection (IFS) method, incorporating four classification algorithms (deep forest, random forest, K-nearest neighbor, and decision tree). Some essential features were discovered and the deep forest with its optimal features achieved the best performance. A group of related proteins (CD4, TCRb, CD103, CD43, and CD23) and genes (Nkg7 and Thy1) contributing to the classification of spleen and lymph nodes cell types were analyzed. Furthermore, the classification rules yielded by decision tree were also provided and analyzed. Above findings may provide helpful information for deepening our understanding on the diversity of cell types.

Molecular Mechanisms Driving IL-10- Producing B Cells Functions: STAT3 and c-MAF as Underestimated Central Key Regulators?

Regulatory B cells (Bregs) have been highlighted in very different pathology settings including autoimmune diseases, allergy, graft rejection, and cancer. Improving tools for the characterization of Bregs has become the main objective especially in humans. Transitional, mature B cells and plasma cells can differentiate into IL-10 producing Bregs in both mice and humans, suggesting that Bregs are not derived from unique precursors but may arise from different competent progenitors at unrestricted development stages. Moreover, in addition to IL-10 production, regulatory B cells used a broad range of suppressing mechanisms to modulate the immune response. Although Bregs have been consistently described in the literature, only a few reports described the molecular aspects that control the acquisition of the regulatory function. In this manuscript, we detailed the latest reports describing the control of IL-10, TGFβ, and GZMB production in different Breg subsets at the molecular level. We focused on the understanding of the role of the transcription factors STAT3 and c-MAF in controlling IL-10 production in murine and human B cells and how these factors may represent an important crossroad of several key drivers of the Breg response. Finally, we provided original data supporting the evidence that MAF is expressed in human IL-10- producing plasmablast and could be induced in vitro following different stimulation cocktails. At steady state, we reported that MAF is expressed in specific human B-cell tonsillar subsets including the IgD⁺ CD27⁺ unswitched population, germinal center cells and plasmablast.

Mediation of transitional B cell maturation in the absence of functional Bruton's tyrosine kinase

X-linked immune-deficient (Xid) mice, carrying a mutation in Bruton’s tyrosine kinase (Btk), have multiple B cell lineage differentiation defects. We now show that, while Xid mice showed only mild reduction in the frequency of the late transitional (T2) stage of peripheral B cells, the defect became severe when the Xid genotype was combined with either a CD40-null, a TCRbeta-null or an MHC class II (MHCII)-null genotype. Purified Xid T1 and T2 B cells survived poorly in vitro compared to wild-type (WT) cells. BAFF rescued WT but not Xid T1 and T2 B cells from death in culture, while CD40 ligation equivalently rescued both. Xid transitional B cells ex vivo showed low levels of the p100 protein substrate for non-canonical NF-kappaB signalling. In vitro, CD40 ligation induced equivalent activation of the canonical but not of the non-canonical NF-kappaB pathway in Xid and WT T1 and T2 B cells. CD40 ligation efficiently rescued p100-null T1 B cells from neglect-induced death in vitro. These data indicate that CD40-mediated signals, likely from CD4 T cells, can mediate peripheral transitional B cell maturation independent of Btk and the non-canonical NF-kappaB pathway, and thus contribute to the understanding of the complexities of peripheral B cell maturation.

Local Induction of B Cell Interleukin-10 Competency Alleviates Inflammation and Bone Loss in Ligature-Induced Experimental Periodontitis in Mice

Interleukin-10 (IL-10)-producing B cells (B10 cells) play a critical role in the immune system balance by negatively regulating inflammatory responses. This study was conducted to determine the effect of local B10 cell induction on periodontal inflammation and bone loss in ligature-induced experimental periodontitis in vivo Purified spleen B cells from C57BL/6J mice (8 to 10 weeks old) were cultured with CD40 ligand (CD40L) and the Toll-like receptor 9 (TLR9) agonist cytidine-phosphate-guanosine oligodeoxynucleotide (CpG) to determine effective IL-10 induction in vitro Silk ligatures (size 7-0) were tied around the mouse maxillary second molars on day 0, followed by the injection of CD40L and CpG into the palatal gingiva on days 3, 6, and 9. All the mice were sacrificed, and samples were collected on day 14. CD40L and CpG significantly increased the level of IL-10 production by B cells in vitro, although the frequencies of CD1d^hi CD5⁺ and IL-10-producing (IL-10⁺) CD45⁺ cells were decreased. IL-10 was predominantly produced by the CD1d^hi CD5⁺ subpopulation of B cells. In vivo, both IL-10 mRNA expression and the number of IL-10⁺ CD45⁺ cells were significantly increased after gingival injection of CD40L and CpG. Periodontal bone loss was significantly decreased and the gingival expression of IL-1β, tumor necrosis factor alpha, and RANKL was significantly reduced. The number of multinucleated tartrate-resistant acid phosphatase-positive cells along the alveolar bone surface was significantly decreased after gingival injection of CD40L and CpG. This study indicates for the first time that the local induction of B10 cell activity could inhibit periodontal inflammation and bone loss.

The role of CD40 ligand in systemic lupus erythematosus

CD40 ligand (CD40L, also known as CD154 or gp39) is a member of the tumor necrosis superfamily of transmembrane proteins. The interaction of CD40L on activated T cells with its receptor, CD40 on B cells, is necessary for normal immune function, including B cell differentiation, germinal center formation, and antibody isotype switching. Abnormal expressionof CD40L in patients with systemic lupus erythematosus (SLE) may contribute to autoantibody production and disease pathogenesis. Although murine models of monoclonal antibodies directed against CD40L initially showed promise, human trials either have failed to demonstrate efficacy or have been associated with adverse events. This review will summarize in vitro and murine model data and human clinical trials involving anti-CD40L monoclonal antibody.

CTLA4Fcε, a novel soluble fusion protein that binds B7 molecules and the IgE receptors, and reduces human in vitro soluble CD23 production and lymphocyte proliferation

Immunoglobulin E-mediated allergy and certain autoimmune diseases are characterized by the presence of a T helper type 2 (Th2) immune response and allergen-specific or self-reactive IgE. Soluble CD23 (sCD23) is a B-cell factor that fosters IgE class-switching and synthesis, suggesting that sCD23 may be a therapeutic target for these pathologies. We produced a recombinant protein, CTLA4Fcε, by fusing the ectodomain of the immunoregulatory molecule cytotoxic T-lymphocyte antigen 4 (CTLA-4) with a fragment of the IgE H-chain constant region. In SDS-PAGE/inmunoblot analyses, CTLA4Fcε appeared as a 70,000 MW polypeptide that forms homodimers. Flow cytometry showed that CTLA4Fcε binds to IgE receptors FcεRI and FcεRII/CD23, as well as to CTLA-4 counter-receptors CD80 and CD86. Binding of CTLA4Fcε to FcεRII/CD23 appeared stronger than that of IgE. Since the cells used to study CD23 binding express CD80 and CD86, simultaneous binding of CTLA4Fcε to CD23 and CD80/CD86 seems to occur and would explain this difference. As measured by a human CD23-specific ELISA, CTLA4Fcε - but not IgE - induced a concentration-dependent reduction of sCD23 in culture supernatants of RPMI-8866 cells. Our results suggest that the simultaneous binding of CTLA4Fcɛ to CD23-CD80/CD86 may cause the formation of multi-molecular complexes that are either internalized or pose a steric hindrance to enzymatic proteolysis, so blocking sCD23 generation. CTLA4Fcε caused a concentration-dependent reduction of lymphocyte proliferation in human peripheral blood mononuclear cell samples stimulated in vitro with concanavalin A. The ability to bind IgE receptors on effector cells, to regulate the production of sCD23 and to inhibit lymphocyte proliferation suggests that CTLA4Fcɛ has immunomodulatory properties on human Th2 responses.

Involvement of the cytoplasmic cysteine-238 of CD40 in its up-regulation of CD23 expression and its enhancement of TLR4-triggered responses

CD40, a member of the tumor necrosis factor receptor superfamily, plays a key role in both adaptive and innate immunity. Engagement of CD40 with its natural trimeric ligand or with cross-linked antibodies results in disulfide-linked CD40 (dl-CD40) homodimer formation, a process mediated by the cysteine-238 residues of the cytoplasmic tail of CD40. The present study was designed to elucidate the biological relevance of cysteine-238-mediated dl-CD40 homodimers to the expression of CD23 on B cells and to investigate its possible involvement in the innate response. Our results indicate that cysteine-238-mediated dl-CD40 homodimerization is required for CD40-induced activation of PI3-kinase/Akt signaling and the subsequent CD23 expression, as inhibition of dl-CD40 homodimer formation through a point mutation-approach specifically impairs these responses. Interestingly, cysteine-238-mediated dl-CD40 homodimers are also shown to play a crucial role in Toll-like receptor 4-induced CD23 expression, further validating the importance of this system in bridging innate and adaptive immune responses. This process also necessitates the activation of the PI3-kinase/Akt cascade. Thus, our results highlight new roles for CD40 and cysteine-238-mediated CD40 homodimers in cell biology and identify a potential new target for therapeutic strategies against CD40-associated chronic inflammatory diseases.

T cell subsets and their signature cytokines in autoimmune and inflammatory diseases

CD4(+) T helper (Th) cells are critical for proper immune cell homeostasis and host defense, but are also major contributors to pathology of autoimmune and inflammatory diseases. Since the discovery of the Th1/Th2 dichotomy, many additional Th subsets were discovered, each with a unique cytokine profile, functional properties, and presumed role in autoimmune tissue pathology. This includes Th1, Th2, Th17, Th22, Th9, and Treg cells which are characterized by specific cytokine profiles. Cytokines produced by these Th subsets play a critical role in immune cell differentiation, effector subset commitment, and in directing the effector response. Cytokines are often categorized into proinflammatory and anti-inflammatory cytokines and linked to Th subsets expressing them. This article reviews the different Th subsets in terms of cytokine profiles, how these cytokines influence and shape the immune response, and their relative roles in promoting pathology in autoimmune and inflammatory diseases. Furthermore, we will discuss whether Th cell pathogenicity can be defined solely based on their cytokine profiles and whether rigid definition of a Th cell subset by its cytokine profile is helpful.

Identification and molecular characterization of the interleukin-10 receptor 1 of the zebrafish (Danio rerio) and the goldfish (Carassius auratus L.)

This is the first report of the identification and molecular characterization of an interleukin-10 receptor 1 in bony fish. By gene synteny analysis, we identified the zebrafish interleukin-10 receptor 1 (IL10R1) and using this IL10R1 sequence, we cloned the goldfish IL10R1 cDNA transcript. The identified fish IL10R1 protein sequences had a putative JAK1 binding site, only one of the two STAT3 binding sites, that are present in all other vertebrates IL10R1 proteins as well as C-terminal serine rich areas, believed to be responsible for the anti-inflammatory properties of IL10R1. Phylogenetically, the fish IL10R1 proteins grouped independently of the amphibian, avian and mammalian IL10R1s. Quantitative gene expression analysis of the IL10R1 of zebrafish and goldfish revealed highest mRNA levels in the spleen tissues. High mRNA levels were also observed in the zebrafish muscle in contrast to low mRNA levels in the muscle of the goldfish. Moderate IL10R1 mRNA levels were seen in most other tissues examined and lowest gene expression was in the liver of both fish species. Goldfish monocytes stimulated with a recombinant goldfish interleukin-10 (rgIL-10) or with heat killed fish pathogens, Aeromonas salmonicida or Trypanosoma carassii, exhibited significantly reduced mRNA levels of the IL10R1. Furthermore, we produced a recombinant form of the goldfish IL10R1 (rgIL10R1) and using in vitro binding studies, demonstrated that the dimerized rgIL-10 specifically interacted with rgIL10R1. Our results suggest that interleukin-10 system has been highly conserved throughout evolution.

CD154-CD40 interactions in the control of murine B cell hematopoiesis

Interactions between CD40 and CD154 play a very important role in control of immune responses, including the delivery of T cell help to B cells and other APCs. Thus far, there has been no role postulated for CD40-CD154 interactions in hematopoiesis. We show here that CD40 is expressed on murine pro-B cells and that its ligation enhances pro-B cell proliferation in vitro and in vivo. In addition, CD154 mRNA is present in the BM. Moreover, we show that a deficiency in CD154 expression has effects on B cell hematopoiesis. Aged, CD154-deficient mice have significantly lower levels of B hematopoietic subsets downstream of pro-B cells in the BM. In addition, B lineage cells reconstitute more slowly following BMT into CD154-deficient recipients. We hypothesize that CD154 is expressed by radio-resistant cells in the BM and plays a role in fine-tuning B cell hematopoiesis.

Accelerated atherosclerosis in systemic lupus erythematosus: role of proinflammatory cytokines and therapeutic approaches

Systemic lupus erythematosus (SLE), a chronic multisystem autoimmune disease with a broad range of clinical manifestations, is associated with accelerated atherosclerosis (AT) and increased risk of cardiovascular complications. Relevant factors directly influencing the development of AT comprise immune complex generation, complement activation, and changes in the production and activity of a complex network of cytokines, including type I and II interferons, B lymphocyte stimulator (BLyS), TNFα, IL-6, IL-17 and migration macrophage inhibitor (MIF). Autoantibodies, also responsible for cytokine expression and activation, play a supplementary key role in the development of AT. Genomic and proteomic studies have contributed to the discovery of genes and proteins involved in AT, including some that may be suitable to be used as biomarkers. All that data has allowed the development of new drugs, most of them evaluated in clinical trials: inhibitors of IFN and TNFα, B cell directed therapies, synthetic oligodeoxynucleotides, intravenous immunoglobulin, or statins. The focus of the present paper is to summarize recent evidence showing the role of cytokines in the development of AT in SLE and the rationale, and safety concerns, in the use of combined therapy to prevent AT and cardiovascular disease.

IL-7 Dependence in human B lymphopoiesis increases during progression of ontogeny from cord blood to bone marrow

IL-7 is critical for B cell production in adult mice; however, its role in human B lymphopoiesis is controversial. One challenge was the inability to differentiate human cord blood (CB) or adult bone marrow (BM) hematopoietic stem cells (HSCs) without murine stroma. Here, we examine the role of IL-7 in human B cell development using a novel, human-only model based on coculturing human HSCs on primary human BM stroma. In this model, IL-7 increases human B cell production by >60-fold from both CB and adult BM HSCs. IL-7-induced increases are dose-dependent and specific to CD19(+) cells. STAT5 phosphorylation and expression of the Ki-67 proliferation Ag indicate that IL-7 acts directly on CD19(+) cells to increase proliferation at the CD34(+) and CD34(-) pro-B cell stages. Without IL-7, HSCs in CB, but not BM, give rise to a small but consistent population of CD19(lo) B lineage cells that express EBF (early B cell factor) and PAX-5 and respond to subsequent IL-7 stimulation. Flt3 ligand, but not thymic stromal-derived lymhopoietin (TSLP), was required for the IL-7-independent production of human B lineage cells. As compared with CB, adult BM shows a reduction of in vitro generative capacity that is progressively more profound in developmentally sequential populations, resulting in an approximately 50-fold reduction in IL-7-dependent B lineage generative capacity. These data provide evidence that IL-7 is essential for human B cell production from adult BM and that IL-7-induced expansion of the pro-B compartment is increasingly critical for human B cell production during the progression of ontogeny.

Blood concentrations of the cytokines IL-1beta, IL-6, IL-10, TNF-alpha and IFN-gamma during experimentally induced swine dysentery

Background

Knowledge of the cytokine response at infection with Brachyspira hyodysenteriae can help understanding disease mechanisme involved during swine dysentery. Since this knowledge is still limited the aim of the present study was to induce dysentery experimentally in pigs and to monitor the development of important immunoregulatory cytokines in blood collected at various stages of the disease.

Methods

Ten conventional pigs (~23 kg) were orally inoculated with Brachyspira hyodysenteriae B204^T. Eight animals developed muco-haemorrhagic diarrhoea with impaired general body condition. Blood was sampled before inoculation and repeatedly during acute dysentery and recovery periods and cytokine levels of IL-1β, IL-6, Il-10, TNF-α and IFN-γ were measured by ELISA.

Results

IL-1β was increased at the beginning of the dysentery period and coincided with the appearance of Serum amyloid A and clinical signs of disease. TNF-α increased in all animals after inoculation, with a peak during dysentery, and IL-6 was found in 3 animals during dysentery and in the 2 animals that did not develop clinical signs of disease. IL-10 was found in all sick animals during the recovery period. IFN-γ was not detected on any occasion.

Conclusion

B. hyodysenteriae inoculation induced production of systemic levels of IL-1β during the dysentery period and increased levels of IL-10 coincided with recovery from dysentery.

The 'short' history of regulatory B cells

The maintenance of tolerance is the sine qua non of a sophisticated regulatory apparatus to prevent or dampen overzealous immune responses. In addition to the ability of B cells to prime and activate the immune system, B cells with regulatory function (Bregs) have been identified in experimental models of autoimmunity, infections, and cancer, supporting the notion that, similar to regulatory T cells (Tregs), Breg-mediated suppression is an important means for the maintenance of peripheral tolerance. This regulatory function appears to be directly mediated by the production of IL-10 and/or TGFbeta and by the ability of B cells to interact with pathogenic T cells to inhibit harmful immune responses. The identification of their existence is of great relevance to the understanding of autoimmune diseases and to the development of new therapeutic strategies.

Systemic lupus erythematosus: multiple immunological phenotypes in a complex genetic disease

Systemic lupus erythematosus (SLE) is a complex polygenic autoimmune disease characterized by the presence of anti-nuclear autoantibodies (ANAs) that are often detectable years prior to the onset of clinical disease. The disease is associated with a chronic activation of the immune system, with the most severe forms progressing to inflammatory damage that can impact multiple organ systems in afflicted individuals. Current therapeutic strategies poorly control disease manifestations and are generally immunosuppressive. Recent studies in human patient populations and animal models have associated elements of the innate immune system and abnormalities in the immature B lymphocyte receptor repertoires with disease initiation. A variety of cytokines, most notably type I interferons, play important roles in disease pathogenesis and effector mechanisms. The genetic basis for disease susceptibility is complex, and analyses in humans and mice have identified multiple susceptibility loci, several of which are located in genomic regions that are syntenic between humans and mice. The complexities of the genetic interactions that mediate lupus have been investigated in murine model systems by characterizing the progressive development of disease in strains expressing various combinations of susceptibility alleles. These analyses indicate that genetic epistasis dramatically impact disease development and support the feasibility of identifying molecular pathways that can suppress disease progression without completely impairing normal immune function.

Inhibitory receptors CD85j, LAIR-1, and CD152 down-regulate immunoglobulin and cytokine production by human B lymphocytes

Class switching consists in the substitution of the heavy-chain constant region of immunoglobulin M (IgM) with that of IgG, IgA, or IgE. This enables antibodies to acquire new effector functions that are crucial to combat invading pathogens. Class switching usually requires engagement of CD40 on B cells by CD40 ligand (CD40L) on antigen-activated CD4(+) T cells and the production of cytokines. The process must be regulated tightly because abnormal IgG and IgA production favors the onset of autoimmunity, whereas increased switching to IgE leads to atopy. These inflammatory disorders can be triggered or exacerbated by costimulatory signals. Although thoroughly investigated on T cells, the roles of the inhibitory receptors CD85j, LAIR-1, and CD152 on B-cell functions have not been fully elucidated. In this study we show that cross-linking of the B-cell inhibitory receptors by specific monoclonal antibodies inhibits IgG and IgE production, reduces the percentage of IgG- and IgE-expressing B cells, and down-regulates interleukin 8 (IL-8), IL-10, and tumor necrosis factor alpha production. These effects were demonstrated using different B-cell stimulatory pathways (recall antigens, CD40L-transfected cells plus IL-4, and lipopolysaccharide plus IL-4). It thus appears that CD85j, LAIR-1, and CD152 play a central role for the control of IL-4-driven isotype switching.

Immuno-regulatory effects of CKBM on the activities of mitogen-activated protein kinases and the release of cytokines in THP-1 monocytic cells

CKBM is an herbal formula composed of five Chinese medicinal herbs (Panax ginseng, Schisandra chinensis, Fructus crataegi, Ziziphus jujube and Glycine Max) supplemented with processed Saccharomyces cerevisiae. Previous studies have demonstrated that CKBM is capable of triggering the release of IL-6 and TNFalpha from human peripheral blood mononuclear cells, and its anti-tumorigenic activity has been demonstrated in nude mice with gastric cancer. In this report, we utilized the THP-1 monocytic cell line as a cellular model to investigate how CKBM regulates the intracellular signaling of monocytes and the subsequent release of the produced cytokines. In terms of mitogen-activated protein kinase (MAPK) cascades, CKBM (20%) had no significant effect on ERK, but was linked to an inhibitory effect on JNK and a stimulatory effect on p38 MAPK. The differential responsiveness of JNK and p38 was dependent on the duration of treatment, as well as on the dosage of CKBM. Treatment of CKBM alone induced the release of IL-10 and IFNgamma, but not IL-1beta, IL-4, IL-6 and TNFbeta, while increase of intracellular Ca2+ concentration by A23187 triggered the release of IL-10 only. Interestingly, A23187 synergized with the activities of CKBM-treated THP-1 cells in terms of IL-1beta and IFNgamma production, while the IL-10 production showed no synergistic relationship between CKBM and A23187. This A23187-induced synergism was associated with a dose-dependent character towards CKBM administration. In view of the intracellular Ca2+ elevation during monocyte activation, our results suggest that CKBM can serve as a promoting agent for modulating the functions of monocytes.

New therapies for systemic lupus erythematosus

In the past 40 years, prognosis for patients with systemic lupus erythematosus (SLE) has improved, with 10-year survival now approximately 90%. This is due probably to a combination of earlier disease diagnosis and diagnosis of milder disease, due in part to availability of multiple serological tests for SLE, use of steroids and other immunosuppressive agents, and availability of renal dialysis and transplantation. Despite this, however, the potential for significant morbidity and mortality remains in the group of patients with partially responsive or treatment resistant disease. More recently, advancements in the understanding of molecular mechanisms involved in the pathogenesis of SLE have translated to the development of novel therapies, offering possible alternatives to this patient cohort. Discussion of these pharmacological options and ongoing research forms the basis of this review.

Loss of dopaminergic neurons by the induction of inducible nitric oxide synthase and cyclooxygenase-2 via CD40: Relevance to Parkinson's disease

A glial reaction associated with up-regulation of inflammatory molecules has been suggested to play an important role in dopaminergic neuron loss in Parkinson's disease (PD). Among inflammatory molecules, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) have been focused upon as key factors in the pathogenesis. However, the mechanism of how these molecules are induced in PD brains is not clearly understood. We focused on CD 40, which is expressed on neural cells and could be implicated in the neuroinflammation by inducing inflammatory molecules. We showed that both iNOS and COX-2 were up-regulated in microglia and astrocytes by CD 40 stimulation in association with a low dose of interferon-gamma (IFN-gamma) in vitro. Selective loss of dopaminergic neurons was induced by costimulation with CD 40 and IFN-gamma in mesencephalic cultures, which was protected by selective inhibitors of iNOS and/or COX-2. We also found in CD 40-stimulated astrocytes an increase of a low-affinity IgE receptor CD 23, which is known to induce iNOS expression. Together these data suggest that up-regulated iNOS and COX-2 via the CD 40 pathway may lead to dopaminergic neuron loss and may participate in the neuroinflammaory pathway of PD.

Interleukin-10 suppression of myeloid cell activation--a continuing puzzle

Efforts to identify the signal transduction pathways used by interleukin-10 (IL-10) have resulted in limited success. The anti-inflammatory effects elicited by IL-10, and the mechanisms by which these are mediated, are still relatively unknown. Understanding the signalling mechanisms behind the suppression of cytokine expression by IL-10 could be of potential therapeutic interest. Although the consensus is that the Janus kinase, Jak1, as well as the signal transducer and activator of transcription STAT3 are central, much controversy exists about the participation and roles of many other signalling pathways targeted by IL-10. The mechanisms of cytokine suppression proposed by various groups have included transcriptional, post-transcriptional and post-translational regulation of IL-10 target genes; nevertheless no unifying model has emerged thus far. Here we would like to highlight novel findings and discuss their implications in the context of current understanding of IL-10 signalling.

Isolation of high-affinity human IgE and IgG antibodies recognising Bet v 1 and Humicola lanuginosa lipase from combinatorial phage libraries

Allergen-specific Fab fragments isolated from combinatorial IgE and IgG libraries are useful tools for studying allergen-antibody interactions. To characterise the interaction between different allergens and antibodies we have created recombinant human phage antibody libraries in the Fab format. Human IgE and IgG libraries have been created from patients allergic to birch pollen or lipase. These libraries have been used to select binders recognising the major birch pollen allergen Bet v 1 and Humicola lanuginosa lipase. A panel of allergen-specific IgE and IgG antibodies were identified; these were further characterised by allergen binding studies using Biacore and competition studies using human sera and antibodies purified from human sera. Affinities in the nM range were recorded and a competition with human sera for allergen binding was observed.

Effects of low concentrations of cadmium on immunoglobulin E production by human B lymphocytes in vitro

Exposure to cadmium (Cd) can cause a variety of biological effects including alterations of immune responses in animals and humans. Both immunosuppression and immunoenhancement have been reported. The present study was aimed at investigating the consequences of exposure to Cd on the human immunoglobulin (Ig) E synthesis, using purified peripheral blood B lymphocytes and IL-4 and anti-human CD40 monoclonal antibody (a-CD40 mAb) as stimuli. Low concentrations of Cd (0.1-10 microM) markedly inhibited production of IgE in a concentration-dependent manner. IgG production, in contrast to IgE, showed a tendency towards being enhanced by Cd, although with a certain individual variability; IgM production was not affected. Cd failed to alter immediate surface expression of the activation markers CD69 and CD23 indicating that early activation events were not impaired. However, the portion of activated B cells was diminished by Cd after stimulation for more than 24 h, paralleled by a concomitant decrease in viability and a subsequent reduction in proliferation. These data suggest that the mechanism of Cd action on activated B cells involved pathways that interrupted an effectively initiated cell activation and induced a cytotoxic signal. Results from this study thus provide further evidence for and new information on the immunotoxic and immunomodulatory effects of Cd on human immune responses.

Carcinogenicity testing of IL-10: principles and practicalities

IL-10 is a cytokine with actions at many levels of the immune system. In the course of development of recombinant human IL-10 (rhuIL-10) as a potential treatment for a number of chronic diseases of man, the question 'What about its carcinogenicity testing?' was repeatedly asked, based on scientific evaluation by toxicologists, beliefs about regulatory requirements, and questions considered likely to be raised by physicians, patients, and lawyers. The feasibility of various approaches to the carcinogenicity testing of rhuIL-10 is critically discussed here as a contribution to rational consideration of the general need for and value of such testing, and its particular feasibility for a recombinant human protein with profound effects on the immune system. The physiological functions of IL-10 in man and rodents are reviewed in detail, as there are notable differences between species in its normal activities, followed by detailed evaluation of the potential procedures and practical problems of its carcinogenicity testing as a heterologous, immunogenic protein in rodents. The value of information that might be obtained from transgenic mice is also evaluated, and so are the results of studies exploring its actions on human tumour cell biopsies and rodent and human cell lines. It is concluded that despite the probable popular and regulatory expectations that carcinogenicity test results would be provided, all the physiological and pathological information reveals no indication that rhuIL-10 would pose a carcinogenic risk to humans on prolonged administration, and that it would not be feasible to undertake such experimentation. It is argued that in this, as in other instances, professional and popular expectations have run beyond practical feasibility or theoretical justification. Cautious and critical evaluation should be made every time shorter or longer term toxicity studies of any candidate drug are planned or even considered, especially if it is a recombinant protein, to decide on objective grounds whether the studies are really necessary and whether they can be done in a way that will give meaningful results that will help in risk assessment.

The role of interleukin-10 in autoimmune disease: systemic lupus erythematosus (SLE) and multiple sclerosis (MS)

Interleukin-10 (IL-10) is an immunoregulatory cytokine that plays a crucial role in inflammatory and immune reactions. It has potent anti-inflammatory and immunosuppressive activities on myeloid cell functions which forms a solid basis for its use in acute and chronic inflammatory diseases. Here, we discuss the role of IL-10 in autoimmune diseases and examine its beneficial effects in cellular-based autoimmune diseases such as multiple sclerosis (MS) or its involvement in humoral-based autoimmune diseases such as systemic lupus erythematosus (SLE). Inhibition of the immune stimulatory activities of IL-10 may provide novel approaches in the treatment of humoral autoimmune diseases, infectious diseases and cancer.

Cooperation of multiple signaling pathways in CD40-regulated gene expression in B lymphocytes

CD40/CD40L interaction is essential for multiple biological events in T dependent humoral immune responses, including B cell survival and proliferation, germinal center and memory B cell formation, and antibody isotype switching and affinity maturation. By using high-density microarrays, we examined gene expression in primary mouse B lymphocytes after multiple time points of CD40L stimulation. In addition to genes involved in cell survival and growth, which are also induced by other mitogens such as lipopolysaccharide, CD40L specifically activated genes involved in germinal center formation and T cell costimulatory molecules that facilitate T dependent humoral immunity. Next, by examining the roles of individual CD40-activated signal transduction pathways, we dissected the overall CD40-mediated response into genes independently regulated by the individual pathways or collectively by all pathways. We also found that gene down-regulation is a significant part of the overall response and that the p38 pathway plays an important role in this process, whereas the NF-kappa B pathway is important for the up-regulation of primary response genes. Our finding of overlapping independent control of gene expression modules by different pathways suggests, in principle, that distinct biological behaviors that depend on distinct gene expression subsets can be manipulated by targeting specific signaling pathways.

Does CD40 ligation induce B cell negative selection?

Binding of CD154 to its receptor, CD40, provides costimulation for mature B cell activation and differentiation in response to Ag receptor signals. In mice, early B cell precursors express CD40, but its function at this stage is unknown. We examined the effects of CD40 ligation during B cell ontogeny in transgenic mice constitutively expressing CD154 on B cells (kappaEP-CD154). Precursors beyond pro-B cells were absent in adult bone marrow but were increased in the fetal liver. Newborn kappaEP-CD154 mice had largely increased numbers of peripheral B cells, which were CD154+, and that 36 h after birth expressed high surface levels of CD23 and MHC class II, resembling activated mature B cells. Nevertheless, kappaEP-CD154 mice were hypogammaglobulinemic, indicating that the expanded population of apparently activated B cells was nonfunctional. Further analysis revealed that soon after birth, kappaEP-CD154 mice-derived B cells became CD5+/Fas+, after which progressively decreased in the periphery in a CD154-CD40-dependent manner. These results indicate that CD40 ligation during B cell ontogeny induces negative selection characterized by either hyporesponsiveness or an arrest in maturation depending on the time of analysis and the anatomic site studied.

Delayed Vaccination Does Not Improve Antibody Responses in Splenectomized Rats Experiencing Hypovolemic Shock

Delayed vaccination after splenectomy has been shown to increase the antibody response in normotensive rats. The purpose of this experiment was to study the effect of timing of vaccination on antibody responses in rats undergoing splenectomy and experiencing hypovolemic shock. Sixty male Sprague-Dawley rats weighing 250 to 400 g underwent either a sham abdominal surgery or splenectomy after a 30-minute period of controlled hypovolemic shock. All rats then received pneumococcal vaccinations one day, 7 days, or 28 days postoperatively. Antibody levels were determined by enzyme-linked immunosorbent assay 3 weeks after vaccination. Results were compared by analysis of variance. Animals vaccinated one day postoperatively had similar or higher antibody responses than did rats receiving delayed vaccinations after 7 or 28 days. These results were similar for immunoglobulins G and M and more importantly were consistent for animals undergoing splenectomy and sham operations. Delayed vaccinations failed to improve antibody responses when hypovolemic shock preceded splenectomy. We propose that this is the result of complex cytokine responses to hypovolemic shock. These responses have been studied extensively in the setting of septic shock but not in the setting of hypovolemic or hemorrhagic shock.

Interleukin-10 and the interleukin-10 receptor

Interleukin-10 (IL-10), first recognized for its ability to inhibit activation and effector function of T cells, monocytes, and macrophages, is a multifunctional cytokine with diverse effects on most hemopoietic cell types. The principal routine function of IL-10 appears to be to limit and ultimately terminate inflammatory responses. In addition to these activities, IL-10 regulates growth and/or differentiation of B cells, NK cells, cytotoxic and helper T cells, mast cells, granulocytes, dendritic cells, keratinocytes, and endothelial cells. IL-10 plays a key role in differentiation and function of a newly appreciated type of T cell, the T regulatory cell, which may figure prominently in control of immune responses and tolerance in vivo. Uniquely among hemopoietic cytokines, IL-10 has closely related homologs in several virus genomes, which testify to its crucial role in regulating immune and inflammatory responses. This review highlights findings that have advanced our understanding of IL-10 and its receptor, as well as its in vivo function in health and disease.

Interleukin-10 and the Interleukin-10 Receptor

Interleukin-10 (IL-10), first recognized for its ability to inhibit activation and effector function of T cells, monocytes, and macrophages, is a multifunctional cytokine with diverse effects on most hemopoietic cell types. The principal routine function of IL-10 appears to be to limit and ultimately terminate inflammatory responses. In addition to these activities, IL-10 regulates growth and/or differentiation of B cells, NK cells, cytotoxic and helper T cells, mast cells, granulocytes, dendritic cells, keratinocytes, and endothelial cells. IL-10 plays a key role in differentiation and function of a newly appreciated type of T cell, the T regulatory cell, which may figure prominently in control of immune responses and tolerance in vivo. Uniquely among hemopoietic cytokines, IL-10 has closely related homologs in several virus genomes, which testify to its crucial role in regulating immune and inflammatory responses. This review highlights findings that have advanced our understanding of IL-10 and its receptor, as well as its in vivo function in health and disease.

Characterization of cytokine, growth factor receptor, costimulatory and adhesion molecule expression patterns of bone marrow blasts in relapsed childhood B cell precursor all

Relapse of childhood acute lymphoblastic leukaemia (ALL) comprises a leading challenge of investigation. Characterization of leukaemic cells regarding their potency to express growth factors and surface molecules can provide insight into their aberrant biology. Thus, we analyzed bone marrow blasts from 10 children with relapsed B cell precursor ALL. The gene and protein expression of essential haematopoietic growth factors (IL-2, IL-4, IL-7, IL-10, IL-15, IFN-gamma, G-CSFR), their corresponding receptors as well as the expression pattern of adhesion molecules (ICAM-1, CD58) and costimulatory proteins (CD40, CD40L, B7.1, B7.2, CD28, MHC-I and II) was analyzed by RT-PCR and flow cytometry. Constitutive gene expression was found for IL-7, IL-10, IL-15 and IFN-gamma and their corresponding receptors. Flow-cytometric analysis showed that IL-10R, IL-7Ralpha, IL-4Ralpha and the gamma(c)chain are constitutively expressed, and that some cells bear the G-CSFR. IL-10 and IL-15 protein-producing leukaemic cells were easily detectable. The neoplastic cells mainly lack B7.1, and ICAM-1 is mostly decreased. Furthermore, high CD40, and, surprisingly, CD40L expression could be found. These studies show that ALL cells are likely to be sensitive to many growth factors and some factors are produced by the neoplastic cell itself. The secretion of IL-10 by leukaemic cells, and the absence or downregulation of conventional adhesion and costimulatory molecules might represent an effective mechanism of escape of immune surveillance in relapsed ALL.

Hodgkin disease: pharmacologic intervention of the CD40-NFκB pathway by a protease inhibitor

The malignant Reed-Sternberg cell of Hodgkin disease is an aberrant B cell that persists in an immunolgically mediated inflammatory infiltrate. Despite its nonproductive immunoglobulin genes, the Reed-Sternberg cell avoids the usual apoptotic fate of defective immune cells through an unknown mechanism. A likely candidate is the surface receptor, CD40, consistently expressed by Reed-Sternberg cells, and the first link in the pathway to NF-κB activation, the central regulator of cytokine production and apoptosis. CD40 signaling in B lymphocytes coordinates the immune response, including immunoglobulin isotype switch and Fas-mediated apoptosis. CD40-induced NF-κB activation is mediated by adapter proteins, the TNF receptor (TNFR)-associated factors (TRAFs), especially TRAFs 2, 3, and 5. Using a Hodgkin cell line, this study demonstrates that CD40 activation of NF-κB is mediated by proteolysis of TRAF3. Results further demonstrate that the pathway can be blocked by treatment with pharmacologic doses of a specific protease inhibitor, pepstatin-A, even in the presence of a mutated NF-κB inhibitor, I-κBα. The stability of TRAF3 regulates CD40/NF-κB–mediated control of the immune response, which is central to the biologic activity of the Reed-Sternberg cell. Prevention of TRAF3 proteolysis may be an entry point for design of novel pharmaceuticals to treat Hodgkin disease and immune system disorders.

Hodgkin disease: pharmacologic intervention of the CD40-NFκB pathway by a protease inhibitor

The malignant Reed-Sternberg cell of Hodgkin disease is an aberrant B cell that persists in an immunolgically mediated inflammatory infiltrate. Despite its nonproductive immunoglobulin genes, the Reed-Sternberg cell avoids the usual apoptotic fate of defective immune cells through an unknown mechanism. A likely candidate is the surface receptor, CD40, consistently expressed by Reed-Sternberg cells, and the first link in the pathway to NF-κB activation, the central regulator of cytokine production and apoptosis. CD40 signaling in B lymphocytes coordinates the immune response, including immunoglobulin isotype switch and Fas-mediated apoptosis. CD40-induced NF-κB activation is mediated by adapter proteins, the TNF receptor (TNFR)-associated factors (TRAFs), especially TRAFs 2, 3, and 5. Using a Hodgkin cell line, this study demonstrates that CD40 activation of NF-κB is mediated by proteolysis of TRAF3. Results further demonstrate that the pathway can be blocked by treatment with pharmacologic doses of a specific protease inhibitor, pepstatin-A, even in the presence of a mutated NF-κB inhibitor, I-κBα. The stability of TRAF3 regulates CD40/NF-κB–mediated control of the immune response, which is central to the biologic activity of the Reed-Sternberg cell. Prevention of TRAF3 proteolysis may be an entry point for design of novel pharmaceuticals to treat Hodgkin disease and immune system disorders.

CD40-ligand stimulates myelopoiesis by regulating flt3-ligand and thrombopoietin production in bone marrow stromal cells

CD40 ligand (CD40L)/CD40 interactions play a central role in T-cell–dependent B-cell activation as previously shown by in vitro studies, the phenotype of CD40L knockout mice and the defective expression of CD40L in patients who have X-linked immunodeficiency with hyper-IgM. The distribution of CD40 in cells other than of myeloid and lymphoid lineages has suggested additional functions for this receptor/ligand couple. Here we show that CD40L stimulates myelopoiesis with a noticeable effect on megakaryocytopoiesis in cocultures of hematopoietic progenitor cells and bone marrow stromal cells. These results suggest a mechanism by which T-cell or platelet-associated or soluble CD40L may regulate myelopoiesis.

Sustained expression of CD154 (CD40L) and proinflammatory cytokine production by alloantigen-stimulated umbilical cord blood T cells

Recent data suggests that graft-versus-host disease (GVHD) is initiated by host APCs. Blockade of CD40:CD154 interactions between APCs and T cells in vivo induces T cell tolerance to host alloantigen and dramatically reduces GVHD. Because allogeneic cord blood (CB) transplantation results in a lower incidence and severity of acute GVHD compared with bone marrow transplantation, we have investigated whether CB T cells can express CD154 in response to stimulation by allogeneic monocyte-derived dendritic cells (MDDC) and have used 5- (and 6-)carboxyfluorescein diacetate succinimidyl ester (CFSE) labeling in combination with intracellular cytokine analysis to assess the proliferation and cytokine profiles of alloantigen-responsive cells. CB T cells stimulated with allogeneic MDDC showed stronger proliferation than adult blood T cells. Surface CD154 expression was detected in the actively dividing CFSElow populations of both the CD4+ and CD4- subsets and was brightest in cells that had divided the most. Assessment of supernatants from MDDC-stimulated CB and adult blood T cells showed no significant difference in the levels of either IFN-gamma or TNF-alpha, but CB T cell supernatants did show a significant lack of detectable IL-2. Intracellular cytokine analysis revealed that dividing CB T cells had been primed to produce IFN-gamma, TNF-alpha, and IL-2 on restimulation. Further phenotype analysis showed that 75% of CB T cells producing IFN-gamma were CD8+. These data suggest that MDDC-stimulated CB T cells express functional CD154 and provide enough costimulation for dendritic cells to prime naive CD8+ CB T cells and induce type 1 cytokine production.

CD40-ligand stimulates myelopoiesis by regulating flt3-ligand and thrombopoietin production in bone marrow stromal cells

CD40 ligand (CD40L)/CD40 interactions play a central role in T-cell–dependent B-cell activation as previously shown by in vitro studies, the phenotype of CD40L knockout mice and the defective expression of CD40L in patients who have X-linked immunodeficiency with hyper-IgM. The distribution of CD40 in cells other than of myeloid and lymphoid lineages has suggested additional functions for this receptor/ligand couple. Here we show that CD40L stimulates myelopoiesis with a noticeable effect on megakaryocytopoiesis in cocultures of hematopoietic progenitor cells and bone marrow stromal cells. These results suggest a mechanism by which T-cell or platelet-associated or soluble CD40L may regulate myelopoiesis.

The influence of CD40-CD154 interactions on the expressed human V(H) repertoire: analysis of V(H) genes expressed by individual B cells of a patient with X-linked hyper-IgM syndrome

Analysis of the V(H)DJ(H) repertoire of peripheral blood IgM(+) B cells from a patient with X-linked hyper-IgM syndrome (X-HIgM) was undertaken to determine whether the distribution of V(H) families in the productive repertoire might be regulated by in vivo CD40-CD154 interactions. The distribution of V(H) genes in the non-productive repertoire of IgM(+) B cells was comparable in X-HIgM and normals. Unlike the normal productive V(H) repertoire, however, in the X-HIgM patient the V(H)4 family was found at almost the same frequency as the V(H)3 family. This reflected a diminution in the positive selection of the V(H)3 family observed in normals and the imposition of positive selection of the V(H)4 family in the X-HIgM patient. Unique among the V(H)3 genes, V(H)3-23/DP-47 was positively selected in both normals and the X-HIgM patient. No major differences in the usage of J(H) or D segments or the complementarity-determining region (CDR) 3 were noted, although the foreshortening of the CDR3 noted in the mutated V(H) rearrangements of normals was absent in the X-HIgM patient. Finally, a minor degree of somatic hypermutation was noted in the X-HIgM patient. These results have suggested that specific influences on the composition of the V(H) repertoire in normals require CD40-CD154 interactions.

CD40 ligand in CLL pathogenesis and therapy

Advances in immunology during the past three decades have facilitated our understanding of the biology of specific lymphoid neoplasms including chronic lymphocytic leukemia (CLL). Investigations in our laboratory have focused on CD40, a critical regulator of B cell survival and differentiation, and its ligand, CD154 (CD40L). We have established that in some cases of CLL the malignant cells express both CD40 and CD154, and on the basis of those observations, proposed a model for CLL tumor growth due to CD40-CD154 interactions within and among the malignant cells, and for the occurrence of autoimmune syndromes in some cases of CLL. Here, we include an update on our studies regarding CD154 expression in CLL, a review of the data regarding the consequences of CD40 engagement in CLL B cells, and a discussion of these findings in the context of the complex and potentially opposite outcomes that have been reported for CD40-mediated signals in CLL. The implications for therapy, such as by impedance to CD154-CD40 interaction using antibody to CD154, or by selective inhibitors of NF-kappa B, are considered.

Tolerance and hematopoietic stem cell transplantation 50 years after Burnet's theory

OBJECTIVE

In 1949, the original formulation of Burnet's theory on the mechanisms responsible for the capacity of the immune system to discriminate between foreign antigens (i.e., the "non-self") and the cells of its own body (i.e., the "self") was published. Since then, further refinements and reconsiderations of the basic concepts underlying the achievement of a state of tolerance toward a certain antigen have been reported. Here, we attempt to analyze critically new clinical and experimental strategies aimed at inducing alloantigen-specific unresponsiveness.

DATA SOURCES

The data discussed in this review are drawn from articles and abstracts published in journals covered by the Science Citation Index and Medline.

STATE OF THE ART

Induction of tolerance toward alloantigens still remains one of the most elusive goals of clinical immunology. Until now, nonspecific immunosuppressive drugs have been used to successfully perform both solid organ and hematopoietic stem cell transplantation. However, using this approach, patients given an allograft are exposed to the threat of infections, tumors, and other side effects. Moreover, in solid organ transplant recipients, permanent tolerance toward the graft's alloantigens is never achieved. Recently, considerable progress has been made in expanding our knowledge of transplant tolerance. The traditional model of central tolerance, derived from Burnet's concept, has been complemented by knowledge of mechanisms of peripheral tolerance.

CONCLUSIONS

New experimental and therapeutic trials based on the blockade of costimulatory molecules, as well as on generation and infusion of either regulatory or nonimmunogenic cells, have been recently proposed for inducing alloantigen-specific tolerance.The achievements obtained in understanding the mechanisms of unresponsiveness toward non-self antigens are fundamental prerequisites for successful allogeneic transplants, and they could open a new exciting era of specific, immunosuppressive therapies.

Effective priming of cytotoxic T lymphocyte precursors by subcutaneous administration of peptide antigens in liposomes accompanied by anti-CD40 and anti-CTLA-4 antibodies

Recently it has been shown that modulation of CD40 molecules on antigen (Ag) carrying dendritic cells (DC) can bypass T cell help, resulting in priming cytotoxic T lymphocytes (CTL) specific for the Ag. In the present study we attempted to prime peptide Ag-specific CTL by a new method in which a peptide Ag in liposome (liposomal peptide), consisting of phosphatidylserine and phosphatidylcholine (3:7), was administrated subcutaneously with anti-CD40 and/or CTLA-4 monoclonal antibodies (mAb) to mice. We found that the subcutaneous administration of the liposomal peptide with both anti-CD40 and anti-CTLA-4 mAb enhanced CTL responses comparing with those induced by the liposomal peptide alone or the liposomal peptide plus each mAb. It was shown that liposomes were critical for induction of the CTL activity. Flow cytometry analysis of a peptide-bearing DC in lymph nodes (LN) and measurement of serum IL-12 indicated that anti-CD40 mAb promoted migration of DC to the LN, where DC might differentiate and acquire ability of priming CTL. These findings provide a possibility that our procedure is applicable to cancer patients.

CD40 ligand upregulates expression of the IL-3 receptor and stimulates proliferation of B-lineage acute lymphoblastic leukemia cells in the presence of IL-3

The proliferative response of B cell precursor acute lymphoblastic leukemia (BCP-ALL) cells to IL-3 is dependent on the expression of functional IL-3 receptors (IL-3R). Here we report that CD40 ligand (CD40L) in the presence of recombinant IL-3 increased proliferation of BCP-ALL cells by upregulating expression of IL-3R. Upregulation of IL-3R in BCP-ALL cells was observed as early as 1 h after treatment with CD40L, and a 50- to 500-fold increase of IL-3R expression after 24 h was detected in all 12 cases studied. Moreover, expression of receptors for IL-7 (IL-7R) and stem cell factor (SCF-R, c-Kit) was also induced by CD40L in the majority of BCP-ALL cases examined; however, levels of induction were low compared to those for IL-3R. To test the functional activity of upregulated receptors for IL-3, SCF and IL-7, we evaluated the proliferation and growth of BCP-ALL cells cultured in serum-free media with CD40L plus these factors. When CD40L was added with either a single cytokine (IL-3, SCF and IL-7) or their combinations, cell proliferation was significantly increased as detected by DNA synthesis assay. Combinations of CD40L plus IL-3 and either SCF or IL-7 were able to support long-term growth of BCP-ALL cells for at least 8 weeks in three of the seven cases studied. Immunophenotyping and gene rearrangement studies indicated that cells in long-term cultures were monoclonal and retained their original phenotypes. The leukemic cells remained primarily dependent on the presence of IL-3 and its receptor for long-term growth, as shown by selective withdrawal of growth factors or antibody blockade of receptors. These results suggest an important role for CD40L in upregulating expression of IL-3R on BCP-ALL cells and enabling these cells to proliferate in long-term cultures in the presence of IL-3 and either SCF or IL-7.

Accessory cells, cytokine loops and cell-to-cell interactions in chronic lymphocytic leukemia

In addition to the extensive work that has been conducted in order to understand better the biological features of the leukemic population in B-cell chronic lymphocytic leukemia (CLL), over the years considerable interest has been directed towards other related studies that may have important implications for the accumulation of the leukemic clone and for the immunoparesis typical of this disease. In the present review article, we discuss some of these areas of investigation and, in particular, we focus on: (1) the multiple abnormalities recorded within the T and cytotoxic compartment of patients with CLL; (2) cytokine loops occurring in this disease, with particular emphasis on the cytokines that appear to play a more critical role; and (3) the cell-to-cell cross talk that may be actively operational in CLL. These findings will be discussed in relation with the possible implications that each of them have in the expansion and clinical behavior of a disease that is increasingly proving its heterogeneity.

Membrane-bound CD154, but not CD40-specific antibody, mediates NF-kappaB-independent IL-6 production in B cells

CD40, a member of the tumor necrosis factor receptor (TNF-R) superfamily, is expressed on the surface of B cells, where its engagement results in IL-6 secretion. In this study, we characterize the specific molecular requirements for CD40-mediated IL-6 production. Engagement of CD40 on either a B cell line or normal mouse splenic B cells with a membrane-bound form of CD154 (also known as CD40L or gp39) induced IL-6 secretion as well as up-regulation of IL-6 mRNA, but cross-linking CD40 with agonistic anti-CD40 mAb did not, although these mAb induce many other CD40 activation events, including the nuclear translocation of the transcription factor NF-kappaB. Using a mouse B cell line stably transfected with various human CD40 (hCD40) cytoplasmic truncation and point mutants, we show that the region from amino acids 202 to 225 in the cytoplasmic domain of CD40 is necessary for IL-6 secretion. However, the carboxy-terminal 32 amino acids are not, although these residues are required for CD40-mediated NF-kappaB activation. In addition, CD40 mutants previously shown to lack binding to TRAF2 and -3 are fully capable of inducing IL-6 production. Thus, CD40-mediated IL-6 induction is independent of NF-kappaB activation and the binding of TRAF2 and -3, but CD40 must be engaged by trimeric CD154 on cell membranes to activate production of IL-6.