Interleukin-4 biases differentiation of B cells from Trypanosoma cruzi-infected mice and restrains their fratricide: role of Fas ligand down-regulation and MHC class II-transactivator up-regulation

Requirements of IL-4 during the Generation of B Cell Memory

IL-4 has long been established as a key regulator of Th cells and for promoting effective B cell survival and isotype class switching. Yet, despite having been extensively studied, the specific role of IL-4 in generating humoral memory in vivo is unclear. In this review, we explore the recent studies that unravel the cellular sources and spatiotemporal production of IL-4, the relationship between IL-4 and IL-21 during germinal center responses and the formation of Ab-secreting cells, and the current understanding of whether IL-4 promotes or suppresses memory B cell generation in vitro and in vivo.

Galectins in Chagas Disease: A Missing Link Between Trypanosoma cruzi Infection, Inflammation, and Tissue Damage

Trypanosoma cruzi, the protozoan parasite causative agent of Chagas disease, affects about seven million people worldwide, representing a major global public health concern with relevant socioeconomic consequences, particularly in developing countries. In this review, we discuss the multiple roles of galectins, a family of β-galactoside-binding proteins, in modulating both T. cruzi infection and immunoregulation. Specifically, we focus on galectin-driven circuits that link parasite invasion and inflammation and reprogram innate and adaptive immune responses. Understanding the dynamics of galectins and their β-galactoside-specific ligands during the pathogenesis of T. cruzi infection and elucidating their roles in immunoregulation, inflammation, and tissue damage offer new rational opportunities for treating this devastating neglected disease.

Immunosuppressive Mechanisms of Regulatory B Cells

Regulatory B cells (Bregs) is a term that encompasses all B cells that act to suppress immune responses. Bregs contribute to the maintenance of tolerance, limiting ongoing immune responses and reestablishing immune homeostasis. The important role of Bregs in restraining the pathology associated with exacerbated inflammatory responses in autoimmunity and graft rejection has been consistently demonstrated, while more recent studies have suggested a role for this population in other immune-related conditions, such as infections, allergy, cancer, and chronic metabolic diseases. Initial studies identified IL-10 as the hallmark of Breg function; nevertheless, the past decade has seen the discovery of other molecules utilized by human and murine B cells to regulate immune responses. This new arsenal includes other anti-inflammatory cytokines such IL-35 and TGF-β, as well as cell surface proteins like CD1d and PD-L1. In this review, we examine the main suppressive mechanisms employed by these novel Breg populations. We also discuss recent evidence that helps to unravel previously unknown aspects of the phenotype, development, activation, and function of IL-10-producing Bregs, incorporating an overview on those questions that remain obscure.

Effects of sotrastaurin, mycophenolic acid and everolimus on human B-lymphocyte function and activation

Humoral rejection processes may lead to allograft injury and subsequent dysfunction. Today, only one B-cell-specific agent is in clinical use and the effects of standard and new immunosuppressant substances on B-cell activation and function are not fully clarified. The impact of sotrastaurin, mycophenolic acid and everolimus on human B-lymphocyte function was assessed by analysing proliferation, apoptosis, CD80/CD86 expression and immunoglobulin and IL-10 production in primary stimulated B cells. In addition, B-cell co-cultures with pre-activated T cells were performed to evaluate the effect of the different immunosuppressive agents on T-cell-dependent immunoglobulin production. Sotrastaurin did not inhibit B-cell proliferation, CD80/CD86 expression, and IgG production and had only minor effects on IgM levels at the highest concentration administered. In contrast, mycophenolic acid and everolimus had strong effects on all B-cell functions in a dose-dependent manner. All immunosuppressive agents caused decreased immunoglobulin levels in T-cell-dependent B-cell cultures. The data provided here suggest that mycophenolic acid and everolimus, but not sotrastaurin, are potent inhibitors of human B-lymphocyte function and activation.

FcγRIIb and BAFF differentially regulate peritoneal B1 cell survival

B1 cells produce most natural Abs in unimmunized mice and play a key role in the response to thymus-independent Ags and microbial infection. Enlargement of B1 cell number in mice is often associated with autoimmunity. However, the factors that control peripheral B1 cell survival remain poorly characterized. Mice lacking the inhibitory receptor FcγRIIb exhibit a massive expansion in peritoneal B1 cells, implicating this receptor in B1 cell homeostasis. In this study, we show that peritoneal B1 cells express the highest levels of FcγRIIb among B cell subsets and are highly susceptible to FcγRIIb-mediated apoptosis. B1 cells upregulate FcγRIIb in response to innate signals, including CpG, and the B cell homeostatic cytokine BAFF efficiently protects activated B1 cells from FcγRIIb-mediated apoptosis via receptor downregulation. BAFF-transgenic mice manifest an expansion of peritoneal B1 cells that express lower levels of FcγRIIb and exhibit reduced susceptibility to apoptosis. Whereas both peritoneal B1 cells from wild-type and BAFF-transgenic mice immunized with CpG exhibit an increase in FcγRIIb levels, this change is blunted in BAFF-transgenic animals. Our combined results demonstrate that FcγRIIb controls peritoneal B1 cell survival and this program can be modulated by the BAFF signaling axis.

In vitro study of the effects of Angiostrongylus cantonensis larvae extracts on apoptosis and dysfunction in the blood-brain barrier (BBB)

It has been hypothesized that blood-brain barrier (BBB) dysfunction in Angiostrongylus cantonensis infection might be due to the apoptosis of the hosts' BBB cells. Here, we evaluated this hypothesis through several methods, all based on an in vitro mouse BBB model consisting of primary culture brain microvascular endothelial cells (BMECs) and brain astrocytic cells (BACs). In the present study, a four-hour percolation and HRP permeability experiment showed that A. cantonensis larvae extracts can increase the permeability of the BBB. Apoptosis among BMECs and BACs after exposure to larvae extracts was monitored by TUNEL and annexin-V-FITC/PI double staining. A. cantonensis larvae extracts were found to induce apoptosis in both BMECs and BACs. For this reason, we concluded that the induction of apoptosis might participate in the BBB dysfunction observed during angiostrongyliasis. Improved fundamental understanding of how A. cantonensis induces apoptosis may lead to new approaches to the treatment or prevention of this parasitic disease.

Hepatocyte proliferation/growth arrest balance in the liver of mice during E. multilocularis infection: a coordinated 3-stage course

Background

Alveolar echinococcosis (AE) is characterized by the tumor-like growth of Echinococcus (E.) multilocularis. Very little is known on the influence of helminth parasites which develop in the liver on the proliferation/growth arrest metabolic pathways in the hepatocytes of the infected liver over the various stages of infection.

Methodology/Principal Findings

Using Western blot analysis, qPCR and immunohistochemistry, we measured the levels of MAPKs activation, Cyclins, PCNA, Gadd45β, Gadd45γ, p53 and p21 expression in the murine AE model, from day 2 to 360 post-infection. Within the early (day 2–60) and middle (day60–180) stages, CyclinB1 and CyclinD1 gene expression increased up to day30 and then returned to control level after day60; Gadd45β, CyclinA and PCNA increased all over the period; ERK1/2 was permanently activated. Meanwhile, p53, p21 and Gadd45γ gene expression, and caspase 3 activation, gradually increased in a time-dependent manner. In the late stage (day180–360), p53, p21 and Gadd45γ gene expression were significantly higher in infected mice; JNK and caspase 3 were activated. TUNEL analysis showed apoptosis of hepatocytes. No significant change in CyclinE, p53 mRNA and p-p38 expression were observed at any time.

Conclusions

Our data support the concept of a sequential activation of metabolic pathways which 1) would first favor parasitic, liver and immune cell proliferation and survival, and thus promote metacestode fertility and tolerance by the host, and 2) would then favor liver damage/apoptosis, impairment in protein synthesis and xenobiotic metabolism, as well as promote immune deficiency, and thus contribute to the dissemination of the protoscoleces after metacestode fertility has been acquired. These findings give a rational explanation to the clinical observations of hepatomegaly and of unexpected survival of AE patients after major hepatic resections, and of chronic liver injury, necrosis and of hepatic failure at an advanced stage and in experimental animals.

Time course of gene expression profiling in the liver of experimental mice infected with Echinococcus multilocularis

BACKGROUND

Alveolar echinococcosis (AE) is a severe chronic parasitic disease which behaves like a slow-growing liver cancer. Clinical observations suggest that the parasite, Echinococcus multilocularis (E. multilocularis) influences liver homeostasis and hepatic cell metabolism. However, this has never been analyzed during the time course of infection in the common model of secondary echinococcosis in experimental mice.

METHODOLOGY/PRINCIPAL FINDINGS

Gene expression profiles were assessed using DNA microarray analysis, 1, 2, 3 and 6 months after injection of E. multilocularis metacestode in the liver of susceptible mice. Data were collected at different time points to monitor the dynamic behavior of gene expression. 557 differentially expressed genes were identified at one or more time points, including 351 up-regulated and 228 down-regulated genes. Time-course analysis indicated, at the initial stage of E. multilocularis infection (month 1-2), that most of up-regulated pathways were related to immune processes and cell trafficking such as chemokine-, mitogen-activated protein kinase (MAPK) signaling, and down-regulated pathways were related to xenobiotic metabolism; at the middle stage (month 3), MAPK signaling pathway was maintained and peroxisome proliferator-activated receptor (PPAR) signaling pathway emerged; at the late stage (month 6), most of up-regulated pathways were related to PPAR signaling pathway, complement and coagulation cascades, while down-regulated pathways were related to metabolism of xenobiotics by cytochrome P450. Quantitative RT-PCR analysis of a random selection of 19 genes confirmed the reliability of the microarray data. Immunohistochemistry analysis showed that proliferating cell nuclear antigen (PCNA) was increased in the liver of E. multilocularis infected mice from 2 months to 6 months.

CONCLUSIONS

E. multilocularis metacestode definitely exerts a deep influence on liver homeostasis, by modifying a number of gene expression and metabolic pathways. It especially promotes hepatic cell proliferation, as evidenced by the increased PCNA constantly found in all the experimental time-points we studied and by an increased gene expression of key metabolic pathways.

Killer B lymphocytes: the evidence and the potential

Immune regulation plays a critical role in controlling potentially dangerous inflammation and maintaining health. The Fas ligand/Fas receptor axis has been studied extensively as a mechanism of killing T cells and other cells during infections, autoimmunity, and cancer. FasL expression has been primarily attributed to activated T cells and NK cells. Evidence has emerged that B lymphocytes can express FasL and other death-inducing ligands, and can mediate cell death under many circumstances. Among B cell subsets, the expression of both Fas ligand and IL-10 is highest on the CD5(+) B cell population, suggesting that CD5(+) B cells may have a specialized regulatory function. The relevance of killer B cells to normal immune regulation, disease pathogenesis, and inflammation is discussed.

Analysis of gene expression profiles in the liver and spleen of mice infected with Trypanosoma evansi by using a cDNA microarray

Trypanosoma evansi, the cause of the disease Surra in livestock, is the most widely geographically distributed pathogenic trypanosome occurring in Africa, South and Central America, and Asia, where it causes significant economic loss. Although many studies have described the histopathology induced in the organs of mice infected with T. evansi, few studies have been conducted on gene expression in these organs. Here we used complementary DNA microarray to analyze the gene expression profiles in the liver and spleen of mice infected with T. evansi (STIB 806) at the peak parasitemia (7 days after infection). A total of 14,000 sequences including full length and partial complementary DNAs representing novel, known, and control genes of mouse were analyzed. Results from GeneOntology annotation showed that 158 genes in the liver and 73 genes in the spleen were up-regulated in the infected mice and that 178 genes in the liver and 117 genes in the spleen of infected mice were down-regulated compared with control (non-infected) mice. Most of these genes are metabolism, transport, protein biosynthesis, transcription factors, and nucleic acid binding protein-related genes. The changes of some important genes, such as heat shock protein 70 and proliferating cell nuclear antigen, were confirmed by quantitative reverse transcriptase polymerase chain reaction and immunohistochemistry. TdT-mediated dUTP-digoxigenin nick end labeling analysis results revealed that extensive apoptosis occurred in the liver of infected mice at the peak of parasitemia. Our results provide a comprehensive profile of changes in gene expression in the liver and spleen of mice infected with T. evansi and may be helpful in understanding the pathogenesis of Surra at a molecular level.

Ozone inhalation induces exacerbation of eosinophilic airway inflammation and hyperresponsiveness in allergen-sensitized mice

BACKGROUND

Ozone (O(3)) exposure evokes asthma exacerbations by mechanisms that are poorly understood. We used a murine model to characterize the effects of O(3) on allergic airway inflammation and hyperresponsiveness and to identify factors that might contribute to the O(3)-induced exacerbation of asthma.

METHODS

BALB/c mice were sensitized and challenged with Aspergillus fumigatus (Af). A group of sensitized and challenged mice was exposed to 3.0 ppm of O(3) for 2 h and studied 12 h later (96 h after Af challenge). Naive mice and mice exposed to O(3) alone were used as controls. Bronchoalveolar lavage (BAL) cellular and cytokine content, lung function [enhanced pause (P(enh))], isometric force generation by tracheal rings and gene and protein expression of Fas and FasL were assessed. Apoptosis of eosinophils was quantified by FACS.

RESULTS

In sensitized mice allergen challenge induced a significant increase of P(enh) and contractile force in tracheal rings that peaked 24 h after challenge and resolved by 96 h. O(3) inhalation induced an exacerbation of airway hyperresponsiveness accompanied by recurrence of neutrophils and enhancement of eosinophils 96 h after allergen challenge. The combination of allergen and O(3) exposure inhibited Fas and FasL gene and protein expression and eosinophil apoptosis and increased interleukin-5 (IL-5), granulocyte-macrophage-colony stimulating factor (GM-CSF) and G-CSF protein levels.

CONCLUSIONS

O(3) affects airway responsiveness of allergen-primed airways indirectly by increasing viability of eosinophils and eosinophil-mediated pathological changes.

Trypanosoma cruzi infection beats the B-cell compartment favouring parasite establishment: can we strike first?

Trypanosoma cruzi, the causative agent of Chagas' disease, may sabotage humoral response by affecting B cells at the different stages of its development. The present review highlights the contributions of our laboratory in understanding how T. cruzi hinders B-cell generation and B-cell expansion limiting host defence and favouring its chronic establishment. We discuss how homoeostatic mechanisms can be triggered to control exacerbated B-cell proliferation that favour T. cruzi infection by eliminating parasite-specific B cells. Specific targeting of evasion mechanisms displayed in T. cruzi infection, as in vivo Fas/FasL blockade or Gal-3 expression inhibition, allowed us to modulate B-cell responses enhancing the anti-parasite humoral immune response. A comprehensive understanding of the biology of the B cell in health and disease is strictly required to devise immunointervention strategies aimed at enhancing protective immune responses during infections.

Modulation of autoimmunity by treatment of an infectious disease

Chagas' heart disease (CHD), caused by the parasite Trypanosoma cruzi, is the most common form of myocarditis in Central America and South America. Some humans and experimental animals develop both humoral and cell-mediated cardiac-specific autoimmunity during infection. Benznidazole, a trypanocidal drug, is effective at reducing parasite load and decreasing the severity of myocarditis in acutely infected patients. We hypothesized that the magnitude of autoimmunity that develops following T. cruzi infection is directly proportional to the amount of damage caused by the parasite. To test this hypothesis, we used benznidazole to reduce the number of parasites in an experimental model of CHD and determined whether this treatment altered the autoimmune response. Infection of A/J mice with the Brazil strain of T. cruzi leads to the development of severe inflammation, fibrosis, necrosis, and parasitosis in the heart accompanied by vigorous cardiac myosin-specific delayed-type hypersensitivity (DTH) and antibody production at 21 days postinfection. Mice succumbed to infection within a month if left untreated. Treatment of infected mice with benznidazole eliminated mortality and decreased disease severity. Treatment also reduced cardiac myosin-specific DTH and antibody production. Reinfection of treated mice with a heart-derived, virulent strain of T. cruzi or immunization with myosin led to the redevelopment of myosin-specific autoimmune responses and inflammation. These results provide a direct link between the levels of T. cruzi and the presence of autoimmunity and suggest that elimination of the parasite may result in the reduction or elimination of autoimmunity in the chronic phase of infection.

BAFF and LPS cooperate to induce B cells to become susceptible to CD95/Fas-mediated cell death

Microorganisms with pathogen-associated molecular patterns (PAMP) activate B cells directly by binding to TLR and also indirectly by inducing APC to release cytokines such as BAFF that promote B cell survival. We found that murine B cells activated concomitantly with LPS (TLR-4 ligand) and BAFF are protected from spontaneous apoptosis, but are more susceptible to Fas/CD95-mediated cell death. This increased susceptibility to Fas-induced apoptosis is associated with a dramatic coordinated up-regulation of Fas/CD95 and IRF-4 expression through a mechanism mediated, at least in part, by inhibition of the MEK/ERK pathway. Up-regulation of Fas/CD95 by BAFF is restricted to B cells activated through TLR-4, but not through TLR-9, BCR or CD40. TLR ligands differ in the BAFF family receptors (R) they induce on B cells: BAFF-R is increased by the TLR4 ligand, LPS, but not by the TLR9 ligand, CpG-containing oligodeoxynucleotides, which, in contrast, strongly up-regulates transmembrane activator and CAML interactor (TACI). This suggests the up-regulation of Fas by BAFF is mediated by BAFF-R and not by TACI. Consistently, APRIL, which binds to TACI and B cell maturation antigen but not BAFF-R, did not enhance Fas expression on LPS-activated B cells. Increased susceptibility to Fas-mediated killing of B cells activated with LPS and BAFF may be a fail-safe mechanism to avoid overexpansion of nonspecific or autoreactive B cells.

Cytokines and chemokines shaping the B-cell compartment

The whole life of a B-cell from a stem cell to a mature plasma cell is governed, among other factors, by cytokines and growth factors in their microenvironment. Remarkable progress in the understanding of the mechanisms of cytokines action on the B-cell compartment was achieved by analysis of gene-targeted mice. The generation of mice deficient for individual cytokines or their receptors has shed light on the in vivo function of cytokines in B-cell responses. This review focuses on the role of cytokines in the development, maturation and differentiation of different B-cell subsets into antibody-secreting cells or memory B-cells.

Cross-talk between apoptosis and cytokines in the regulation of parasitic infection

Parasitic diseases have worldwide medical and economical impact. Host T lymphocytes and the cytokines they produce determine the outcome of parasitic infections. Programmed cell death by apoptosis is induced in the course of parasitic infections, and affects cytokine production by removing activated effector T and B cells. In addition, engulfment of apoptotic cells promotes the secretion of cytokines that regulate intracellular replication of protozoan parasites. In this review, we discuss how the cross-talk between apoptosis and cytokines regulates parasitic infection.

Gene expression profiles in response to Fas stimulation in Trypanosoma cruzi-infected host cells

To determine the molecular mechanism by which apoptosis is inhibited in Trypanosoma cruzi-infected host cells, we used human cDNA apoptosis chips to compare the gene expression profiles in response with 'death ligands target' (Fas) stimulation in infected and uninfected cells. Of the 164 apoptosis-related genes examined, 20, including those encoding both pro- and anti-apoptotic proteins, were highly up-regulated in the infected group. Genes encoding caspases and apoptosis inhibitors were optimally expressed 10-30 min after induction of apoptosis, whereas genes involved in transcriptional regulation and cell proliferation were up-regulated after 2-24 h. These results suggest that host anti-apoptotic gene(s) may play a crucial role in the inhibition of Fas-mediated apoptosis in T. cruzi-infected cells.

Trypanosome apoptotic factor mediates apoptosis in human brain vascular endothelial cells

Human African trypanosomiasis (HAT, sleeping sickness) is a devastating disease caused by infection with Trypanosoma brucei ssp. These hemoflagellates invade the central nervous system (CNS) and induce meningo-encephalitis, neuronal demyelination, blood-brain-barrier (BBB) dysfunction, peri-vascular infiltration, astrocytosis and apoptosis. The molecular basis of these manifestations is unclear. We previously reported T. brucei-induced apoptosis in cerebella and brain-stem nuclei in mice at peak parasitemia. Here, we identify and characterize a trypanosome apoptotic factor (TAF) expressed by T. brucei that mediates apoptosis in mouse-brain and human-brain vascular endothelial cells (HBVEC). Molecular, biochemical and apoptotic assays, coupled with surface enhanced laser desorption ionization (SELDI), and protein database analyses were utilized to show that TAF is a soluble, non-serum, parasite-derived, heat-labile protein that causes DNA laddering and apoptosis in HBVEC. Protein-chip assay analysis of the SELDI spectrum of infected mouse serum and procyclic culture supernatants revealed a single major peak at 8652.7 Da. Further database analysis indicated that the TAF may be a procyclin or procyclin derivative. A synthetic 27 mer peptide (ProEP2-1), corresponding to a region common to EP procyclins (EP2-1), induced apoptosis in HBVEC and in cerebella of mice similar to that induced in T. brucei-infected mice. Western blot analysis utilizing an anti-procyclin monoclonal antibody (mAb) revealed that TAF is present in infected but not uninfected brain tissue lysates. Furthermore, this mAb blocked T. brucei- and ProEP2-1-induced apoptosis in HBVEC in vitro. We conclude that T. brucei TAF or its derivative(s) play a major role in the apoptosis associated with HAT pathology.

Galectin-3 Mediates IL-4-Induced Survival and Differentiation of B Cells: Functional Cross-Talk and Implications during Trypanosoma cruzi Infection

The role of transcription factors in B cell survival and differentiation has been delineated during the last years. However, little is known about the intermediate signals and the intracellular pathways that control these events. In this study, we provide evidence both in vitro and in vivo, showing that galectin-3 (Gal-3), a beta-galactoside-binding protein, is a critical mediator of B cell differentiation and survival. Although Gal-3 is not expressed in resting B cells from normal mice, its expression is markedly induced after activation with stimuli such as IL-4 and CD40 cross-linking. These signals promote survival and block the final differentiation of these cells, thus allowing the rising of a memory B cell phenotype. In addition, Gal-3 is expressed in B cells from Trypanosoma cruzi-infected mice, which received signals for activation and differentiation in vivo. By using an antisense strategy, we determined that Gal-3 is a critical signal mediating the effects of IL-4 on B cell fate. Blockade of intracellular Gal-3 in vitro abrogated IL-4-induced survival of activated B cells, favoring the differentiation toward a plasma cell pathway. Moreover, B cells with restrained endogenous Gal-3 expression failed to down-regulate the Blimp-1 transcription factor after IL-4 stimulation. Finally, inhibition of Gal-3 in vivo skewed the balance toward plasma cell differentiation, which resulted in increased Ig production and parasite clearance during T. cruzi infection. Thus, the present study provides evidence of a novel role for Gal-3 as an intracellular mediator of B cell survival and a checkpoint in IL-4-induced B cell commitment toward a memory phenotype.