Intestinal macrophages: unique effector cells of the innate immune system

Blockade of complement activation product C5a activity using specific antibody attenuates intestinal damage in trinitrobenzene sulfonic acid induced model of colitis

Complement represents a chief component of innate immunity in host defense. However, excessive complement activation has been involved in the pathogenesis of inflammatory diseases. In this study, we investigated the contribution of complement to intestinal pathology of patients and rodents with inflammatory bowel disease. The expression of complement effectors (C3a and C3) was increased remarkably in inflamed colons of IBD patients compared with those of normal counterparts. In accordance with this, the sustained activation of complement in serum and colon (including elevated C3a and C5a levels, enhanced hemolytic activity, downregulated expression of C5a receptors) was observed, following the establishment of 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis, which peaked at 24 h. Mice pretreated with neutralizing anti-C5a antibodies (-2, 0, and 2 days after TNBS instillation) had significantly reduced weight loss and improved macroscopic/microscopic scores, comparable to the efficacy of prednisolone treatment. Strikingly, treatment with anti-C5a at 24 h after TNBS instillation showed remarkable therapeutic effects, whereas prednisolone did not. The efficacy of anti-C5a administration was associated with decreased release of proinflammatory chemokines and cytokines, inhibition of infiltration of neutrophils into colons, and enhanced Th2 response. These findings suggest a disease-promoting role of complement, particular C5a, in the pathology of TNBS-induced colitis in mice, indicating possible therapeutic potentials for C5a-specific antibody in IBD.

Targeting the innate immune system in pediatric inflammatory bowel disease

The pathogenesis of inflammatory bowel disease (IBD) is complex and involves both innate and adaptive immune responses. This article addresses, in a selective and speculative fashion, the topic of how the various components of the intestinal innate immune system can be manipulated for the purpose of developing new therapeutic approaches. These various components include: agents that stimulate mucosal innate immune responses, such as food components and the gut microbiota; cells that directly respond to these stimuli, including epithelial cells, macrophages and dendritic cells; and molecules that mediate innate immune responses, such as Toll-like receptors and protein kinases. Downregulation of excessive innate immune responses makes therapeutic sense in both pediatric and adult IBD. However, because IBD is complex and characteristically chronic, major alterations of adaptive immunity are also involved in the mediation of inflammation. Thus, novel and truly effective approaches to treat IBD will undoubtedly require intervening in the innate as well as the adaptive branches of the mucosal immunity.

Interplay between inflammation, immune system and neuronal pathways: effect on gastrointestinal motility

Sepsis is a systemic inflammatory response representing the leading cause of death in critically ill patients, mostly due to multiple organ failure. The gastrointestinal tract plays a pivotal role in the pathogenesis of sepsis-induced multiple organ failure through intestinal barrier dysfunction, bacterial translocation and ileus. In this review we address the role of the gastrointestinal tract, the mediators, cell types and transduction pathways involved, based on experimental data obtained from models of inflammation-induced ileus and (preliminary) clinical data. The complex interplay within the gastrointestinal wall between mast cells, residential macrophages and glial cells on the one hand, and neurons and smooth muscle cells on the other hand, involves intracellular signaling pathways, Toll-like receptors and a plethora of neuroactive substances such as nitric oxide, prostaglandins, cytokines, chemokines, growth factors, tryptases and hormones. Multidirectional signaling between the different components in the gastrointestinal wall, the spinal cord and central nervous system impacts inflammation and its consequences. We propose that novel therapeutic strategies should target inflammation on the one hand and gastrointestinal motility, gastrointestinal sensitivity and even pain signaling on the other hand, for instance by impeding afferent neuronal signaling, by activation of the vagal anti-inflammatory pathway or by the use of pharmacological agents such as ghrelin and ghrelin agonists or drugs interfering with the endocannabinoid system.

Commensal microbiota induce LPS hyporesponsiveness in colonic macrophages via the production of IL-10

Several subsets of innate immune cells, all with unique properties, reside within the intestinal lamina propria. However, compared with intestinal dendritic cells (DCs), intestinal macrophages are less well characterized. In this study, we examined the properties of macrophages in the colonic lamina propria (LMφ). Colonic DCs (LDC) showed LPS-induced production of IL-12p40. In contrast, LMφ showed constitutive IL-10 production and unresponsiveness to LPS in terms of inflammatory cytokine production. Comparison of the gene expression profiles between LMφ and LDC revealed that LMφ preferentially expressed IL-10-related genes. LMφ obtained from mice lacking IL-10 or Stat3 showed hyperproduction of tumour necrosis factor (TNF)-α and IL-6 in response to LPS. IL-10 production in the large intestine was mainly induced by LMφ and regulatory T cells and was dependent on the presence of commensal microbiota. Accordingly, LMφ from germ-free mice showed less production of IL-10 and increased levels of LPS-induced TNF-α and IL-6 production. Taken together, these results demonstrate that the activity of LMφ to produce pro-inflammatory cytokines is negatively regulated through commensal microbiota-dependent IL-10 production in the large intestine.

The role of the macrophage in sentinel responses in intestinal immunity

PURPOSE OF REVIEW

The purpose of this review is to highlight macrophages as central mediators of intestinal immune homeostasis and inflammation.

RECENT FINDINGS

We review recent developments elucidating distinct phenotypic adaptations in intestinal macrophages that determine their functional role in a microbe-rich environment. The involvement of intestinal macrophages in the pathogenesis of inflammatory bowel disease is also discussed.

SUMMARY

Intestinal macrophages represent the largest pool of tissue macrophages in the human body and a critical interface with the enteric microbiota. In normal physiology, luminal microbes breach the intestinal epithelial barrier and gain access to the lamina propria. Bacteria are efficiently phagocytosed by macrophages strategically located underneath the epithelium. The importance of functional adaptations of macrophages to perform their role in this unique environment is best illustrated by failure of these mechanisms during the development of chronic inflammatory bowel diseases. Compared with monocytes or macrophages from any other organ, intestinal macrophages express different phenotypic markers, efficiently eradicate intracellular bacteria, but do not mount potent inflammatory responses. Converging human genetic and functional findings suggest that dysregulation of macrophage-specific immune responses against an otherwise harmless enteric microbiota are key factors in the pathogenesis of inflammatory bowel disease.

Norwalk virus does not replicate in human macrophages or dendritic cells derived from the peripheral blood of susceptible humans

Human noroviruses are difficult to study due to the lack of an efficient in vitro cell culture system or small animal model. Murine norovirus replicates in murine macrophages (MPhi) and dendritic cells (DCs), raising the possibility that human NoVs might replicate in such human cell types. To test this hypothesis, we evaluated DCs and MPhi derived from monocyte subsets and CD11c(+) DCs isolated from peripheral blood mononuclear cells of individuals susceptible to Norwalk virus (NV) infection. These cells were exposed to NV and replication was evaluated by immunofluorescence and by quantitative RT-PCR. A few PBMC-derived DCs expressed NV proteins. However, NV RNA did not increase in any of the cells tested. These results demonstrate that NV does not replicate in human CD11c(+) DCs, monocyte-derived DCs and MPhi, but abortive infection may occur in a few DCs. These results suggest that NV tropism is distinct from that of murine noroviruses.

Inflammatory bowel disease: Established and evolving considerations on its etiopathogenesis and therapy

Modern studies of inflammatory bowel disease (IBD) pathogenesis have been pursued for about four decades, a period of time where the pace of progress has been steadily increasing. This progress has occurred in parallel with and is largely due to developments in multiple basic scientific disciplines that range from population and social studies, genetics, microbiology, immunology, biochemistry, cellular and molecular biology, and DNA engineering. From this cumulative and constantly expanding knowledge base the fundamental pillars of IBD pathogenesis appear to have been identified and consolidated during the last couple of decades. Presently there is a general consensus among basic IBD investigators that both Crohn's disease (CD) and ulcerative colitis (UC) are the result of the combined effects of four basic components: global changes in the environment, the input of multiple genetic variations, alterations in the intestinal microbiota, and aberrations of innate and adaptive immune responses. There is also agreement on the conclusion that none of these four components can by itself trigger or maintain intestinal inflammation. A combination of various factors, and most likely of all four factors, is probably needed to bring about CD or UC in individual patients, but each patient or set of patients seems to have a different combination of alterations leading to the disease. This would imply that different causes and diverse mechanisms underlie IBD, and this could also explain why every patient displays his or her own clinical manifestations and a personalized response to therapy, and requires tailored approaches with different medications. While we are becoming increasingly aware of the importance of this individual variability, we have only a superficial notion of the reasons why this occurs, as hinted by the uniqueness of the genetic background and of the gut flora in each person. So, we are apparently facing the paradox of having to deal with the tremendous complexity of the mechanisms responsible for chronic intestinal inflammation in the setting of each patient's individuality in the response to this biological complexity. This obviously poses considerable challenges to reaching a full understanding of IBD pathogenesis, but being aware of the difficulties is the first step in finding answers to them.

Well-controlled proinflammatory cytokine responses of Peyer's patch cells to probiotic Lactobacillus casei

SUMMARY

In order to clarify the probiotic features of immunomodulation, cytokine production by murine spleen and Peyer's patch (PP) cells was examined in response to probiotic and pathogenic bacteria. In spleen cells, probiotic Lactobacillus casei induced interleukin (IL)-12 production by CD11b(+) cells more strongly than pathogenic Gram-positive and Gram-negative bacteria and effectively promoted the development of T helper (Th) type 1 cells followed by high levels of secretion of interferon (IFN)-gamma. Although the levels of IL-12 secreted by PP cells in response to L. casei were lower in comparison with spleen cells, Th1 cells developed as a result of this low-level induction of IL-12. However, IFN-gamma secretion by the L. casei-induced Th1 cells stimulated with a specific antigen was down-regulated in PP cells. Development of IL-17-producing Th17 cells was efficiently induced in PP cells by antigen stimulation. Lactobacillus casei slightly, but significantly, inhibited the antigen-induced secretion of IL-17 without a decrease in the proportion of Th17 cells. No bacteria tested induced the development of IL-10-producing, transforming growth factor-beta-producing or Foxp3-expressing regulatory T cells, thus suggesting that certain probiotics might regulate proinflammatory responses through as yet unidentified mechanisms in PP cells. These data show probiotic L. casei to have considerable potential to induce IL-12 production and promote Th1 cell development, but the secretion of proinflammatory cytokines such as IL-12 and IL-17 may be well controlled in PP cells.

Inflammation anergy in human intestinal macrophages is due to Smad-induced IkappaBalpha expression and NF-kappaB inactivation

Human intestinal macrophages contribute to tissue homeostasis in noninflamed mucosa through profound down-regulation of pro-inflammatory cytokine release. Here, we show that this down-regulation extends to Toll-like receptor (TLR)-induced cytokine release, as intestinal macrophages expressed TLR3-TLR9 but did not release cytokines in response to TLR-specific ligands. Likely contributing to this unique functional profile, intestinal macrophages expressed markedly down-regulated adapter proteins MyD88 and Toll interleukin receptor 1 domain-containing adapter-inducing interferon beta, which together mediate all TLR MyD88-dependent and -independent NF-kappaB signaling, did not phosphorylate NF-kappaB p65 or Smad-induced IkappaBalpha, and did not translocate NF-kappaB into the nucleus. Importantly, transforming growth factor-beta released from intestinal extracellular matrix (stroma) induced identical down-regulation in the NF-kappaB signaling and function of blood monocytes, the exclusive source of intestinal macrophages. Our findings implicate stromal transforming growth factor-beta-induced dysregulation of NF-kappaB proteins and Smad signaling in the differentiation of pro-inflammatory blood monocytes into noninflammatory intestinal macrophages.

Securing the immune tightrope: mononuclear phagocytes in the intestinal lamina propria

The intestinal landscape comprises the host's own tissue and immune cells, as well as a diverse intestinal microbiota. Intricate regulatory mechanisms have evolved to maintain peaceful coexistence at this site, the breakdown of which can result in devastating inflammatory bowel diseases (IBDs). Mononuclear phagocytes promote both innate and adaptive immune responses in the gut and, as such, are essential for the maintenance of intestinal homeostasis. Here, we review the origins and functions of the mononuclear phagocytes found in the intestinal lamina propria, highlighting the problems that have arisen from their classification. Understanding these cells in their physiological context will be important for developing new therapies for IBDs.

A review of metabolic staging in severely injured patients

An interpretation of the metabolic response to injury in patients with severe accidental or surgical trauma is made. In the last century, various authors attributed a meaning to the post-traumatic inflammatory response by using teleological arguments. Their interpretations of this response, not only facilitates integrating the knowledge, but also the flow from the bench to the bedside, which is the main objective of modern translational research. The goal of the current review is to correlate the metabolic changes with the three phenotypes -ischemia-reperfusion, leukocytic and angiogenic- that the patients express during the evolution of the systemic inflammatory response. The sequence in the expression of multiple metabolic systems that becomes progressively more elaborate and complex in severe injured patients urges for more detailed knowledge in order to establish the most adequate metabolic support according to the evolutive phase. Thus, clinicians must employ different treatment strategies based on the different metabolic phases when caring for this challenging patient population. Perhaps, the best therapeutic option would be to favor early hypometabolism during the ischemia-reperfusion phase, to boost the antienzymatic metabolism and to reduce hypermetabolism during the leukocytic phase through the early administration of enteral nutrition and the modulation of the acute phase response. Lastly, the early epithelial regeneration of the injured organs and tissues by means of an oxidative metabolism would reduce the fibrotic sequelae in these severely injured patients.

The macrophage in HIV-1 infection: from activation to deactivation?

Macrophages play a crucial role in innate and adaptative immunity in response to microorganisms and are an important cellular target during HIV-1 infection. Recently, the heterogeneity of the macrophage population has been highlighted. Classically activated or type 1 macrophages (M1) induced in particular by IFN-γ display a pro-inflammatory profile. The alternatively activated or type 2 macrophages (M2) induced by Th-2 cytokines, such as IL-4 and IL-13 express anti-inflammatory and tissue repair properties. Finally IL-10 has been described as the prototypic cytokine involved in the deactivation of macrophages (dM). Since the capacity of macrophages to support productive HIV-1 infection is known to be modulated by cytokines, this review shows how modulation of macrophage activation by cytokines impacts the capacity to support productive HIV-1 infection. Based on the activation status of macrophages we propose a model starting with M1 classically activated macrophages with accelerated formation of viral reservoirs in a context of Th1 and proinflammatory cytokines. Then IL-4/IL-13 alternatively activated M2 macrophages will enter into the game that will stop the expansion of the HIV-1 reservoir. Finally IL-10 deactivation of macrophages will lead to immune failure observed at the very late stages of the HIV-1 disease.

Immune responses to gut microbiota-commensals and pathogens

The mammalian alimentary tract harbors hundreds of species of commensal microorganisms that intimately interact with the host immune system. Within the gut, the immune system actively reacts with potentially pathogenic microbes, while simultaneously remaining ignorant towards the vast majority of non-pathogenic microbiota. The disruption of this delicate balance results in inflammatory bowel diseases. In this review, we describe the recent advances in our understanding of how host-microbiota interactions shape the immune system and how they affect the responses against pathogenic bacteria.

Activated macrophages in the tumour microenvironment-dancing to the tune of TLR and NF-kappaB

A large number of variables have been identified which appear to influence macrophage phenotype within the tumour microenvironment. These include reciprocal chemical and physical interactions with tumour cells and with non-malignant cells of the tumour microenvironment, tissue oxygen tension, and the origin and prior experience of the particular macrophage population. In this review we outline the key evidence for these influences and consider how macrophage phenotype is acquired and the relevance of the TLR-NF-kappaB pathway.

Induction and cellular expression of tartrate resistant acid phosphatase during dextran sodium sulphate induced colitis in rats

The aim of this study was to investigate the cellular and molecular expression of tartrate resistant acid phosphatase (TRAP) as a marker of activated macrophages in macrophage dependent dextran sulphate sodium (DSS)-induced colitis in rats. In normal colon, TRAP+/CX(3)CR(1)+ macrophages were located in the upper part of the lamina propria. In the early stage (day 1-3) of acute colitis prior to histopathological changes, induction of the cytokines TNFalpha, IL-12 and IFN gamma occurred concomitant with increased mRNA and enzyme activity of TRAP along with a slight increase of TRAP immunolabelling in macrophages of the upper lamina propria, suggesting induction of TRAP in resident macrophages. Among these cytokines, TNFalpha up-regulated TRAP expression in the RAW 264.7 monocyte/macrophage cell line. In a later phase (day 7) with fulminant colitis, a massive infiltration of macrophages including recruited TRAP+/CCR2+ cells was observed also in the lower part of the lamina propria as well as in the submuscular layer. Additionally, differentiated cellular expression of pro- and mature TRAP also suggest that mucosal macrophages in the lower part of lamina propria bordering the sub-mucosa provide a source of replenishment of macrophages situated in the upper lamina propria. In conclusion, induction of TRAP provides an early sign of macrophage responsiveness in DSS induced colitis.

Increased number and activation of colonic macrophages in pediatric patients with untreated Crohn's disease

BACKGROUND

Pediatric inflammatory bowel disease (IBD) may be phenotypically different from adult IBD. In IBD lesions, macrophages are overactivated, suggesting involvement of innate immunity in the pathogenesis. Here, mucosal macrophages were studied in selected untreated pediatric patients compared with adults from a population-based Norwegian cohort of IBD patients. Age-matched non-IBD controls were also included.

METHODS

Untreated children (<18 years) and adults (> or =18 years) were included at diagnosis with colonic and ileal biopsies. Controls were symptomatic non-IBD patients with histologically normal gut. Frozen mucosal sections were examined by immunohistochemistry for cellular expression of the pan-macrophage marker CD68 and the costimulatory molecule CD40. Two-color immunofluorescence staining in situ was performed to identify CD40(+) macrophages.

RESULTS

Non-IBD adults had significantly higher mucosal density of colonic CD68(+) macrophages than non-IBD children. In pediatric Crohn's disease (CD), macrophages were significantly increased in the colon (but not in the ileum) compared with controls. Their mucosal density in pediatric CD was significantly higher than in pediatric ulcerative colitis. The number of CD40(+) (activated) macrophages was significantly elevated in both histologically inflamed and uninflamed colon and ileum of IBD children.

CONCLUSIONS

Histologically normal colon mucosa contains fewer macrophages in children than in adults. However, in colon of children with untreated CD the mucosal macrophage density is increased. Activated mucosal macrophages are increased in untreated pediatric IBD regardless of inflammatory grade. Such upregulated innate mucosal immune activation may contribute to the colonic phenotype of childhood CD.

Lansoprazole, a Proton Pump Inhibitor, Suppresses Production of Tumor Necrosis Factor-alpha and Interleukin-1beta Induced by Lipopolysaccharide and Helicobacter Pylori Bacterial Components in Human Monocytic Cells via Inhibition of Activation of Nuclear Factor-kappaB and Extracellular Signal-Regulated Kinase

Pathogenic bacterial components play critical roles in initiation of gastrointestinal inflammation via activation of intracellular signaling pathways which induce proinflammatory cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-1β. Lansoprazole (LANSO), a proton pump inhibitor, has been widely used for the treatment of peptic ulcers and reflux esophagitis due to its potent acid-suppressive effect. It has also been reported to have anti-inflammatory effects. In this study we investigated the effects of LANSO on the production of TNF-α and IL-1β induced by lipopolysaccharide (LPS) and Helicobacter pylori water-soluble extract (HpWE) in the human monocytic cell line (THP-1). LANSO (100 µM) significantly reduced mRNA expression and production of TNF-α and IL-1β by THP-1 cells stimulated by LPS and HpWE. LANSO inhibited phosphorylation and degradation of inhibitory factor κB-α (IκB-α) and phosphorylation of extracellular signal-regulated kinase (ERK) induced by LPS and HpWE in THP-1 cells. These findings suggest that LANSO exerts anti-inflammatory effects by suppressing induction of TNF-α and IL-1β via inhibition of nuclear factor (NF)-κB and ERK activation.

Intestinal macrophages: differentiation and involvement in intestinal immunopathologies

Intestinal macrophages, preferentially located in the subepithelial lamina propria, represent the largest pool of tissue macrophages in humans. As an adaptation to the local antigen- and bacteria-rich environment, intestinal macrophages exhibit several distinct phenotypic and functional characteristics. Notably, microbe-associated molecular pattern receptors, including the lipopolysaccharide (LPS) receptors CD14 and TLR4, and also the Fc receptors for IgA and IgG are absent on most intestinal macrophages under homeostatic conditions. Moreover, while macrophages in the intestinal mucosa are refractory to the induction of proinflammatory cytokine secretion, they still display potent phagocytic activity. These adaptations allow intestinal macrophages to comply with their main task, i.e., the efficient removal of microbes while maintaining local tissue homeostasis. In this paper, we review recent findings on the functional differentiation of monocyte subsets into distinct macrophage populations and on the phenotypic and functional adaptations that have evolved in intestinal macrophages in response to their antigen-rich environment. Furthermore, the involvement of intestinal macrophages in the pathogenesis of celiac disease and inflammatory bowel diseases is discussed.

Regulatory mechanisms of immune responses to intestinal bacteria

The intestinal mucosa allows the residence of trillions of bacteria with which it interacts dynamically. To establish and maintain a mutually beneficial relationship, the mucosal immune system must enforce tolerance toward the vast non-pathogenic microbiota while simultaneously remaining reactive to potentially pathogenic microbes; the disruption of this delicate balance results in inflammatory bowel diseases. In this review, we describe advances in our understanding of regulatory mechanisms of the innate immune system and how these shape adaptive immune systems during steady-state and inflammatory processes in the intestinal mucosa.

Macrophages in vaginal but not intestinal mucosa are monocyte-like and permissive to human immunodeficiency virus type 1 infection

Mucosal surfaces play a major role in human immunodeficiency virus type 1 (HIV-1) transmission and pathogenesis, and yet the role of lamina propria macrophages in mucosal HIV-1 infection has received little investigative attention. We report here that vaginal and intestinal macrophages display distinct phenotype and HIV-1 permissiveness profiles. Vaginal macrophages expressed the innate response receptors CD14, CD89, CD16, CD32, and CD64 and the HIV-1 receptor/coreceptors CD4, CCR5, and CXCR4, similar to monocytes. Consistent with this phenotype, green fluorescent protein-tagged R5 HIV-1 entered macrophages in explanted vaginal mucosa as early as 30 min after inoculation of virus onto the epithelium, and purified vaginal macrophages supported substantial levels of HIV-1 replication by a panel of highly macrophage-tropic R5 viruses. In sharp contrast, intestinal macrophages expressed no detectable, or very low levels of, innate response receptors and HIV-1 receptor/coreceptors and did not support HIV-1 replication, although virus occasionally entered macrophages in intestinal tissue explants. Thus, vaginal, but not intestinal, macrophages are monocyte-like and permissive to R5 HIV-1 after the virus has translocated across the epithelium. These findings suggest that genital and gut macrophages have different roles in mucosal HIV-1 pathogenesis and that vaginal macrophages play a previously underappreciated but potentially important role in mucosal HIV-1 infection in the female genital tract.

Detection of galectin-3 in patients with inflammatory bowel diseases: new serum marker of active forms of IBD?

OBJECTIVE

It is an open question whether multifunctional galectin-3 can be a serum marker in inflammatory bowel disease.

METHODS

Western blots and commercial ELISA detected and quantitated the lectin immunocytochemistry using double labeling localized it in tissue sections.

RESULTS

Serum concentrations were significantly increased in specimen of patients with active and remission-stage ulcerative colitis and Crohn's disease, associated with emerging positivity of CD14(+) cells.

CONCLUSION

Enhanced concentration of galectin-3 in serum reflects presence of disease and points to its involvement in the pathogenesis.

Inhibition of cyclin-dependent kinases by olomoucine and roscovitine reduces lipopolysaccharide-induced inflammatory responses via down-regulation of nuclear factor kappaB

OBJECTIVES

Initiation and maintenance of pro-inflammatory reactions elicited by bacterial lipopolysaccharide and/or cytokines in the macrophage lineage have been reported to play a crucial role in acute and chronic pathogenic effects. Whether pro-inflammatory responses triggered by lipopolysaccharide in growth arrested cells differ from those in proliferating cells remains unanswered.

MATERIALS AND METHODS

Olomoucine and roscovitine are cyclin-dependent kinase (CDK) inhibitors that prevent progression through the cell cycle. After treatment with CDK inhibitors, expression of pro-inflammatory genes was analysed by reverse transcriptase-polymerase chain reaction. Protein levels of inducible nitric oxide synthase (iNOS) and nuclear factor kappaB (NF-kappaB) were determined by Western blotting. Promoter activity of iNOS was measured by the luciferase activity assay.

RESULTS

In this study we have demonstrated that both olomoucine and roscovitine inhibit cell proliferation and diminish nitric oxide production and cytokine gene expression, in lipopolysaccharide-stimulated murine RAW264.7 macrophages. In addition, olomoucine reduces iNOS promoter activity and alleviates NF-kappaB transcription activation. After co-transfection with E2F1 interference RNA, suppression of lipopolysaccharide-mediated iNOS promoter activity and NF-kappaB activation was observed. Furthermore, we demonstrated that olomoucine-induced growth arrested cells reduce expression of the p65 subunit of NF-kappaB.

CONCLUSIONS

The findings of this study suggest that inhibition of cell-cycle progression is capable of reducing pro-inflammatory responses via down-regulation of NF-kappaB.

Suppression of experimental colitis in mice by CD11c+ dendritic cells

BACKGROUND

The innate immune system serves a critical role in homeostasis of the gastrointestinal (GI) tract. Both macrophages (MØs) and dendritic cells (DCs) have been shown to have pathogenic roles in animal models of inflammatory bowel disease. However, studies by several labs have established that resident MØs and DCs within the normal GI tract maintain an immunosuppressive phenotype compared to that seen in other peripheral sites. Recent studies by our lab demonstrated that the depletion of both MØs and DCs before the initiation of dextran sodium sulfate (DSS)-induced colitis resulted in exacerbation of disease, partly caused by increased neutrophil influx.

METHODS/RESULTS

In this current report, DSS-induced colitis was shown to be significantly more severe when DCs were selectively depleted in mice as indicated by changes in weight loss, stool consistency, rectal bleeding, and histopathology. In contrast to enhanced colitis in MØ/DC-depleted mice, which was associated with increased neutrophil influx, increased colitis in DC-depleted mice was not associated with an increase in neutrophils in the colon, as shown by CXCL1 chemokine levels and myeloperoxidase (MPO) activity. However, increased IL-6 gene and protein expression in colon tissues correlated positively with increased colitis severity in DC-depleted mice compared to colitis in DC-intact mice.

CONCLUSIONS

This study demonstrates that resident DCs can suppress the severity of acute DSS colitis and that regulation of IL-6 production may contribute to DC-mediated control of intestinal inflammation.

Evidence for dendritic cell-dependent CD4(+) T helper-1 type responses to commensal bacteria in normal human intestinal lamina propria

Reactivity of lamina propria (LP) T cells to commensal bacteria has been demonstrated in animal models of inflammatory bowel disease (IBD) and in humans with IBD, but few studies have evaluated the function of such cells in normal individuals. LP mononuclear cells (LPMC) were disaggregated from healthy human intestinal tissue and cultured with heat-killed commensal and pathogenic bacteria. CD3(+)CD4(+) IFN-gamma-producing (Th1) cells reactive to commensal bacteria were demonstrated at frequencies ranging from 0.05 to 2.28% in LPMC. Bacteria-specific Th1 responses were inhibited by anti-HLA-DR antibodies and chloroquine exposure, were enriched in LP relative to peripheral blood, and expressed effector memory cell markers. Bacteria-specific CD4(+) T cell proliferation in vitro was dependent on the presence of LP dendritic cells (DCs), which produced pro-inflammatory cytokines upon bacterial exposure. These results suggest that bacteria-reactive DCs and CD4(+) T cells in normal LP have substantial pro-inflammatory potential that is revealed upon disaggregation in vitro.

Macrophage phenotype as a determinant of biologic scaffold remodeling

Macrophage phenotype can be characterized as proinflammatory (M1) or immunomodulatory and tissue remodeling (M2). The present study used a rat model to determine the macrophage phenotype at the site of implantation of two biologic scaffolds that were derived from porcine small intestinal submucosa (SIS) and that differed mainly according to their method of processing: the Restore device (SIS) and the CuffPatch device (carbodiimide crosslinked form of porcine-derived SIS (CDI-SIS)). An autologous tissue graft was used as a control implant. Immunohistologic methods were used to identify macrophage surface markers CD68 (pan macrophages), CD80 and CCR7 (M1 profile), and CD163 (M2 profile) during the remodeling process. All graft sites were characterized by the dense population of CD68+ mononuclear cells present during the first 4 weeks. The SIS device elicited a predominantly CD163+ response (M2 profile, p < 0.001) and showed constructive remodeling at 16 weeks. The CDI-SIS device showed a predominately CD80+ and CCR7+ response (M1 profile, p < 0.03), and at 16 weeks was characterized by chronic inflammation. The autologous tissue graft showed a predominately CD163+ response (M2) at 1 week, with a dual M1/M2 population (CD80+, CCR7+, and CD163+) by 2 and 4 weeks and moderately well organized connective tissue by 16 weeks. The processing methods used during the manufacturing of a biologic scaffold can have a profound influence upon the macrophage phenotype profile and downstream remodeling events. Routine histologic examination alone is inadequate to determine the phenotype of mononuclear cells that participate in the host response to the scaffold.

In vitro differentiation of human monocytes into dendritic cells by peptic-tryptic digest of gliadin is independent of genetic predisposition and the presence of celiac disease

INTRODUCTION

This study was done to further reveal the role of the innate immune system in celiac disease.

METHODS

Dendritic cells were matured from venous blood of patients with active or treated celiac disease and DQ2-DQ8-positive or negative controls. Dendritic cells were treated with a peptic-tryptic digest of gliadin (500 microg/ml) and their activation was analyzed by fluorescent-activated cell sorting analysis, cytokine secretion, and their ability to elicit T cell proliferation.

RESULTS AND DISCUSSION

Gliadin upregulated interleukin (IL)-6, IL-8, and IL-12 (p40) secretion in dendritic cells and induced strong expression of the maturation markers human leukocyte antigen (HLA)-DR, CD25, CD83, and CD86 of all subjects irrespective of their genotype or the presence of disease, whereas the digest of bovine serum albumin showed no effect. However, gliadin-stimulated dendritic cells from active celiac showed enhanced stimulation of autologous T cells compared to the other groups.

CONCLUSION

Further research should be aimed at identifying the mechanisms that control inflammation in healthy individuals.

Nod2-dependent Th2 polarization of antigen-specific immunity

While a number of microbial-associated molecular patterns have been known for decades to act as adjuvants, the mechanisms and the signaling pathways underlying their action have remained elusive. Here, we examined the unfolding of the adaptive immune response induced by Nod2 in vivo upon activation by its specific ligand, muramyl dipeptide, a component of peptidoglycan. Our findings demonstrate that this bacterial sensor triggers a potent Ag-specific immune response with a Th2-type polarization profile, characterized by the induction of IL-4 and IL-5 by T cells and IgG1 Ab responses. Nod2 was also found to be critical for the induction of both Th1- and Th2-type responses following costimulation with TLR agonists. Importantly, the synergistic responses to Nod2 and TLR agonists seen in vivo were recapitulated by dendritic cells in vitro, suggesting that these cells likely play a central role in the integration of Nod2- and TLR-dependent signals for driving the adaptive immune response. Taken together, our results identify Nod2 as a critical mediator of microbial-induced potentiation and polarization of Ag-dependent immunity. Moreover, these findings affect our understanding of Crohn's diseases pathogenesis, where lack of Nod2-dependent Th2 signaling in a subset of these patients might explain heightened Th1-mediated inflammation at the level of the intestinal mucosa.

Th2 cytokine-induced alterations in intestinal smooth muscle function depend on alternatively activated macrophages

BACKGROUND & AIMS

Enteric nematode infection induces a strong type 2 T helper cell (Th2) cytokine response characterized by increased infiltration of various immune cells, including macrophages. The role of these immune cells in host defense against nematode infection remains poorly defined. The present study investigated the role of macrophages and the arginase pathway in nematode-induced changes in intestinal smooth muscle function and worm expulsion.

METHODS

Mice were infected with Nippostrongylus brasiliensis and treated with clodronate-containing liposome to deplete macrophages or given S-(2-boronoethyl)-I-cysteine in drinking water to inhibit arginase activity. Segments of intestinal smooth muscle were suspended in organ baths to determine responses to acetylcholine, 5-hydroxytryptamine, or nerve stimulation. The phenotype of macrophages was monitored by measuring mRNA expression of the specific molecular markers by real-time polymerase chain reaction or viewed by immunofluorescence staining.

RESULTS

Infection increased the infiltration of macrophages and up-regulation alternatively activated macrophage markers by a mechanism dependent on interleukin-4 (IL-4) or interleukin-13 (IL-13) activation of signal transducer and activator of transcription 6. Elimination of alternatively activated macrophages blocked smooth muscle hypercontractility and the increased smooth muscle thickness, and impaired worm expulsion. In addition, specific inhibition of arginase activity interfered with smooth muscle contractility, but only partially affected the protective immunity of the host.

CONCLUSIONS

These data show that the phenotype of macrophages is determined by the local immune environment and that alternatively activated macrophages play a major role in the effects of Th2 cytokines, IL-4 and IL-13, on intestinal smooth muscle function.

Dendritic cells in intestinal immune regulation

A breakdown in intestinal homeostasis can result in chronic inflammatory diseases of the gut including inflammatory bowel disease, coeliac disease and allergy. Dendritic cells, through their ability to orchestrate protective immunity and immune tolerance in the host, have a key role in shaping the intestinal immune response. The mechanisms through which dendritic cells can respond to environmental cues in the intestine and select appropriate immune responses have until recently been poorly understood. Here, we review recent work that is beginning to identify factors responsible for intestinal conditioning of dendritic-cell function and the subsequent decision between tolerance and immunity in the intestine.

Induction of pro-inflammatory programs in enteroendocrine cells by the Toll-like receptor agonists flagellin and bacterial LPS

Enteroendocrine cells are hormone-secreting cells spread along the intestinal epithelium. Their principal function is to promote the digestion of food. However, little is known about other functions that these cells may play, since they are difficult to study as a whole endocrine organ due to their diffuse localization. It is known that the intestinal epithelial barrier is actively involved in the host defense against pathogen invasion. Here we applied gene expression profiling to characterize the response of the human LCC-18 enteroendocrine cell line to physiological and pathological stimuli mimicked by fatty acids (FAs), flagellin and LPS exposure. We observed that these cells participate in an innate immune reaction to pathogens through the expression of pro-inflammatory factors (i.e. CXCL1 and 3 and IL-32) that we could validate by molecular and proteomic approach. Interestingly, IL-32 has been recently found over-expressed in the inflamed mucosa of patients affected by inflammatory bowel disease. This is very important because modifications of enteroendocrine cells during intestinal inflammation have been so far considered as secondary effects of the inflammatory status rather than due to direct pathogen/enteroendocrine cell interaction. As expected, FAs exposure up-regulates pro-differentiative genes and the production of cholecystokinin but it does not enhance the expression of pro-inflammatory genes. The present observations enlighten a new aspect of the cross talk between immune and endocrine system and suggest enteroendocrine cells as important contributors of inflammatory processes occurring in the gut in response to pathogen exposure and direct enhancers of the inflammatory status associated with human inflammatory bowel disease.

TRPM2-mediated Ca2+influx induces chemokine production in monocytes that aggravates inflammatory neutrophil infiltration

Reactive oxygen species (ROS) induce chemokines responsible for the recruitment of inflammatory cells to sites of injury or infection. Here we show that the plasma membrane Ca(2+)-permeable channel TRPM2 controls ROS-induced chemokine production in monocytes. In human U937 monocytes, hydrogen peroxide (H(2)O(2)) evokes Ca(2+) influx through TRPM2 to activate Ca(2+)-dependent tyrosine kinase Pyk2 and amplify Erk signaling via Ras GTPase. This elicits nuclear translocation of nuclear factor-kappaB essential for the production of the chemokine interleukin-8 (CXCL8). In monocytes from Trpm2-deficient mice, H(2)O(2)-induced Ca(2+) influx and production of the macrophage inflammatory protein-2 (CXCL2), the mouse CXCL8 functional homolog, were impaired. In the dextran sulfate sodium-induced colitis inflammation model, CXCL2 expression, neutrophil infiltration and ulceration were attenuated by Trpm2 disruption. Thus, TRPM2 Ca(2+) influx controls the ROS-induced signaling cascade responsible for chemokine production, which aggravates inflammation. We propose functional inhibition of TRPM2 channels as a new therapeutic strategy for treating inflammatory diseases.

The mucosal immune system at the gastrointestinal barrier

The immune system faces a considerable challenge in its efforts to maintain tissue homeostasis in the intestinal mucosa. It is constantly confronted with a large array of antigens, and has to prevent the dissemination and proliferation of potentially harmful agents while sparing the vital structures of the intestine from immune-mediated destruction. Complex interactions between the highly adapted effector cells and mechanisms of the innate and adaptive immune system generally prevent the luminal microflora from penetrating the intestinal mucosa and from spreading systemically. Non-haematopoietic cells critically contribute to the maintenance of local tissue homeostasis in an antigen-rich environment by producing protective factors (e.g. production of mucus by goblet cells, or secretion of microbicidal defensins by Paneth cells) and also through interactions with the adaptive and innate immune system (such as the production of chemotactic factors that lead to the selective recruitment of immune cell subsets). The complexity of the regulatory mechanisms that control the local immune response to luminal antigens is also reflected in the observation that mutations in immunologically relevant genes often lead to the development of uncontrolled inflammatory reactions in the microbially colonized intestine of experimental animals.

Mucosal immunity and HIV/AIDS vaccines. Report of an International Workshop, 28-30 October 2007

In October 2007, a joint ANRS-NIH workshop was held on “Mucosal immunity and HIV/AIDS vaccines” in Veyrier-du-Lac, France. Goal of the meeting was to discuss recent developments in the understanding of viral entry and dissemination at mucosal surfaces, rationale for designing vaccines to elicit mucosal immune responses by various routes of immunization, and the types of immune responses elicited. Lessons were drawn from existing vaccines against viral mucosal infections, from the recent failure of the Merck Ad5/HIV vaccine and from attempts at mucosal immunization against SIV. This report summarizes the main concepts and conclusions that came out of the meeting.

Coexpression of myofibroblast and macrophage markers: novel evidence for an in vivo plasticity of chorioamniotic mesodermal cells of the human placenta

Human chorioamniotic membranes generate temporary but large mucosal surfaces. Due to lack of fetal vessels, macrophages represent the only subset of immunocytes of fetal origin available in the chorioamniotic mesodermal layer. This layer contains two distinct groups of cells: the fibroblasts/myofibroblasts and the macrophages; however, the relative contribution of these two cell populations has been a point of contention. In addressing various discrepancies, we hypothesized that cells in the chorioamniotic mesodermal layer have plasticity. Immunophenotyping of these cells using a panel of antibodies (CD14, CD68, CD163, HLA-DR, type I procollagen, alpha-smooth muscle actin, desmin, vimentin) revealed coexpression of both myofibroblast and macrophage markers. The proportion of CD14+ macrophages was higher in inflamed chorioamniotic membranes (P<0.05). Cells immunoreactive to the macrophage markers showed nuclear expression of PU.1, a hematopoietic cell-specific transcription factor. Furthermore, treatment with proinflammatory cytokines (IL-1beta and TNFalpha) or Toll-like receptor-4 overexpression upregulated PU.1 mRNA expression in chorioamniotic mesodermal cells. Overexpression of PU.1 in chorionic mesodermal cells increased the expression of CD14 mRNA and protein. A reporter gene assay and chromatin immunoprecipitation demonstrated binding of PU.1 to the CD14 promoter region. This study reports that chorioamniotic mesodermal cells display plasticity ranging from overt transformation of fibroblast/myofibroblast to macrophages, and that PU.1 plays a role in macrophage differentiation. Chorioamniotic mesodermal cells are another novel example of phenotypic switching between fibroblast/myofibroblast and macrophage. The findings reported herein suggest that the plasticity of mesodermal cells is an effective mechanism of the chorioamniotic membranes to manage several biological needs, such as mucosal immune defense and the maintenance/disruption of physical integrity, with a limited pool of cells.

Gene-centric association mapping of chromosome 3p implicates MST1 in IBD pathogenesis

Association mapping and candidate gene studies within inflammatory bowel diseases (IBD) linkage regions, as well as genome-wide association studies in Crohn's disease (CD) have led to the discovery of multiple risk genes, but these explain only a fraction of the genetic susceptibility observed in IBD. We have thus been pursuing a region on chromosome 3p21-22 showing linkage to CD and ulcerative colitis (UC) using a gene-centric association mapping approach. We identified 12 functional candidate genes by searching for literature cocitations with relevant keywords and for gene expression patterns consistent with immune/intestinal function. We then performed an association study composed of a screening phase, where tagging single nucleotide polymorphisms (SNPs) were evaluated in 1,020 IBD patients, and an independent replication phase in 745 IBD patients. These analyses identified and replicated significant association with IBD for four SNPs within a 1.2 Mb linkage disequilibrium region. We then identified a non-synonymous coding variant (rs3197999, R689C) in the macrophage-stimulating 1 (MST1) gene (P-value 3.62 x 10(-6)) that accounts for the association signal, and shows association with both CD and UC. MST1 encodes macrophage-stimulating protein (MSP), a protein regulating the innate immune responses to bacterial ligands. R689C is predicted to interfere with MSP binding to its receptor, suggesting a role for this gene in the pathogenesis of IBD.

Phenotypic characterisation of intestinal dendritic cells in sheep

The present study was undertaken to identify dendritic cells (DCs) in the ileum and rectum of lambs and adult sheep. The distribution of these cells in four different intestinal compartments, i.e. lamina propria, lymphoid follicles, domes and interfollicular areas was assessed, and the presence of these cells in lambs and adult sheep was compared. Specimens were examined by using a number of potential DC markers (CD11c, CD205, MHC class II (MHCII), CD1b and CD209) in immunohistochemical and multicolour immunofluorescent procedures. The ovine ileal and rectal mucosa contain many CD11c+/CD205+ cells with a dendritic morphology, and the majority of these cells co-expressed MHCII. These double-positive cells were also labelled with the CD209 antibody in the lamina propria and interfollicular regions. Only very few cells expressed CD1b. In conclusion, a major DC population in ileum and rectum of sheep co-expressed the CD11c, CD205 and MHCII molecules. The CD209 antibody appeared to be a novel marker for a subpopulation of ovine intestinal DCs.

HIV infection and the gastrointestinal immune system

There has recently been a resurgence of interest in the gastrointestinal pathology observed in patients infected with HIV. The gastrointestinal tract is a major site of HIV replication, which results in massive depletion of lamina propria CD4 T cells during acute infection. Highly active antiretroviral therapy leads to incomplete suppression of viral replication and substantially delayed and only partial restoration of gastrointestinal CD4 T cells. The gastrointestinal pathology associated with HIV infection comprises significant enteropathy with increased levels of inflammation and decreased levels of mucosal repair and regeneration. Assessment of gut mucosal immune system has provided novel directions for therapeutic interventions that modify the consequences of acute HIV infection.

Innate immune recognition at the epithelial barrier drives adaptive immunity: APCs take the back seat

Innate immune recognition of microbe-associated molecular patterns by multiple families of pattern-recognition molecules such as Toll-like receptors and Nod-like receptors instructs the innate and adaptive immune system to protect the host from pathogens while also acting to establish a beneficial mutualism with commensal organisms. Although this task has been thought to be performed mainly by specialized antigen-presenting cells such as dendritic cells, recent observations point to the idea that innate immune recognition by stromal cells has important implications for the regulation of mucosal homeostasis as well as for the initiation of innate and adaptive immunity.

TREM-1--expressing intestinal macrophages crucially amplify chronic inflammation in experimental colitis and inflammatory bowel diseases

Triggering receptor expressed on myeloid cells-1 (TREM-1) potently amplifies acute inflammatory responses by enhancing degranulation and secretion of proinflammatory mediators. Here we demonstrate that TREM-1 is also crucially involved in chronic inflammatory bowel diseases (IBD). Myeloid cells of the normal intestine generally lack TREM-1 expression. In experimental mouse models of colitis and in patients with IBD, however, TREM-1 expression in the intestine was upregulated and correlated with disease activity. TREM-1 significantly enhanced the secretion of relevant proinflammatory mediators in intestinal macrophages from IBD patients. Blocking TREM-1 by the administration of an antagonistic peptide substantially attenuated clinical course and histopathological alterations in experimental mouse models of colitis. This effect was also seen when the antagonistic peptide was administered only after the first appearance of clinical signs of colitis. Hence, TREM-1-mediated amplification of inflammation contributes not only to the exacerbation of acute inflammatory disorders but also to the perpetuation of chronic inflammatory disorders. Furthermore, interfering with TREM-1 engagement leads to the simultaneous reduction of production and secretion of a variety of pro-inflammatory mediators such as TNF, IL-6, IL-8 (CXCL8), MCP-1 (CCL2), and IL-1beta. Therefore, TREM-1 may also represent an attractive target for the treatment of chronic inflammatory disorders.

Expression of Toll-like receptor 2 (TLR2), TLR4, and CD14 in biopsy samples of patients with inflammatory bowel diseases: upregulated expression of TLR2 in terminal ileum of patients with ulcerative colitis

Dysregulation of innate and adaptive intestinal immune responses to bacterial microbiota is supposed to be involved in pathogenetic mechanisms of inflammatory bowel diseases (IBDs). We investigated expression of Toll-like receptor 2 (TLR2), TLR4, and their transmembrane coreceptor CD14 in biopsy samples from patients with IBD and in non-inflamed gut mucosa from controls. Small intestine and colon samples were obtained by colonoscopy from patients with Crohn's disease (CD), ulcerative colitis (UC), and controls. Immunohistochemical analysis of cryostat sections using polyclonal and monoclonal antibodies specific for TLR2, TLR4, and CD14 showed a significant increase in TLR2 expression in the terminal ileum of patients with inactive and active UC against controls. Significant upregulation of TLR4 expression relative to controls was found in the terminal ileum and rectum of UC patients in remission and in the terminal ileum of CD patients with active disease. CD14 expression was upregulated in the terminal ileum of CD patients in remission and with active disease, in the cecum of UC patients in remission and with active disease, and in rectum of UC patients with active disease. Hence, dysregulation of TLR2, TLR4, and CD14 expression in different parts of the intestinal mucosa may be crucial in IBD pathogenesis.

Inflammation: a way to understanding the evolution of portal hypertension

BACKGROUND

Portal hypertension is a clinical syndrome that manifests as ascites, portosystemic encephalopathy and variceal hemorrhage, and these alterations often lead to death.

HYPOTHESIS

Splanchnic and/or systemic responses to portal hypertension could have pathophysiological mechanisms similar to those involved in the post-traumatic inflammatory response.The splanchnic and systemic impairments produced throughout the evolution of experimental prehepatic portal hypertension could be considered to have an inflammatory origin. In portal vein ligated rats, portal hypertensive enteropathy, hepatic steatosis and portal hypertensive encephalopathy show phenotypes during their development that can be considered inflammatory, such as: ischemia-reperfusion (vasodilatory response), infiltration by inflammatory cells (mast cells) and bacteria (intestinal translocation of endotoxins and bacteria) and lastly, angiogenesis. Similar inflammatory phenotypes, worsened by chronic liver disease (with anti-oxidant and anti-enzymatic ability reduction) characterize the evolution of portal hypertension and its complications (hepatorenal syndrome, ascites and esophageal variceal hemorrhage) in humans.

CONCLUSION

Low-grade inflammation, related to prehepatic portal hypertension, switches to high-grade inflammation with the development of severe and life-threatening complications when associated with chronic liver disease.

Cytomegalovirus blocks intestinal stroma-induced down-regulation of macrophage HIV-1 infection

Intestinal macrophages, unlike macrophages from other tissues, do not support HIV-1 infection or produce proinflammatory cytokines. In vitro studies suggest this unique, functional phenotype is a result of the exposure of newly recruited blood monocytes to intestinal stromal products. However, in AIDS-related CMV colitis, mucosal macrophages express HIV-1 and proinflammatory cytokines. Therefore, we investigated the mechanism by which CMV confers permissiveness to HIV-1 and cytokine production on intestinal macrophages. We show that intestinal stroma-conditioned media (S-CM) down-regulated monocyte-derived macrophage infection by HIV-1 (pseudotyped with YU2 envelope or vesicular stomatitis virus glycoprotein) and production of TNF-alpha, but preinfection of the cells with CMV reversed this down-regulation, enhancing HIV-1 infection, p24 production, and TNF-alpha release. The ability of CMV to reverse S-CM down-regulation of macrophage HIV-1 infection was blocked by anti-TNF-alpha antibodies and over-ridden by exogenous TNF-alpha. Immunohistochemical analysis of monocyte-derived macrophages exposed to CMV and HIV-1 (YU2 pseudotype) revealed that the cells infrequently contained CMV and HIV-1 viral proteins. In addition, analysis of colon tissue sections from HIV-1-infected patients with CMV colitis showed that some macrophage-like cells contained CMV and TNF-alpha proteins, others contained HIV-1 and TNF-alpha proteins, but cells infrequently contained CMV and HIV-1 proteins. These results indicate that CMV blocks stromal product inhibition of HIV-1 infection in macrophages, and this inhibition is mediated, at least in part, by CMV-induced TNF-alpha acting in trans to enhance HIV-1 infection.

Lactic acid bacterial colonization and human rotavirus infection influence distribution and frequencies of monocytes/macrophages and dendritic cells in neonatal gnotobiotic pigs

Despite accumulating knowledge of porcine macrophages and dendritic cells (DCs) from in vitro studies, information regarding monocytes/macrophages and DCs in lymphoid tissues of enteric pathogen-infected neonatal animals in vivo is limited. In this study we evaluated the influence of commensal bacterial [two strains of lactic acid bacteria (LAB), Lactobacillus acidophilus and L. reuteri] colonization and rotavirus infection on distribution and frequencies of monocytes/macrophages and conventional DCs (cDCs) in ileum, spleen and blood. Gnotobiotic pigs were inoculated with LAB and virulent Wa strain human rotavirus (HRV) (LAB+HRV+), HRV only (LAB−HRV+), LAB only (LAB+HRV−) or mock (LAB−HRV−). The cDCs were characterized as SWC3⁺CD11R1⁺, whereas monocytes/macrophages were identified as SWC3⁺CD11R1⁻ by flow cytometry in the gnotobiotic pigs at 10 days of age. Infection with HRV alone activated/recruited significantly more monocytes/macrophages to the intestine than LAB colonization and 56% versus 28% of these cells expressed CD14. Colonization with LAB alone also significantly increased the frequencies of monocytes/macrophages and cDCs and the CD14 expression on monocytes/macrophages in ileum and spleen compared to the controls. LAB colonization plus HRV infection significantly reduced macrophage and cDC frequencies in spleen compared to LAB colonization or HRV infection alone, suggesting that LAB colonization down-regulated HRV− infection-induced monocyte/macrophage activation/recruitment at the systemic lymphoid tissue. These results illustrated the distribution of porcine monocytes/macrophages and cDCs and the frequencies of CD14 expression on these cells in intestinal and systemic lymphoid tissues in the early stage of immune responses to intestinal colonization by LAB versus infection by an enteric pathogen HRV and will facilitate further in vivo studies on functional characterization of these immune cells in neonates.

Intestinal innate immunity and the pathogenesis of Salmonella enteritis

Acute gastroenteritis caused by Salmonella typhimurium infection is a clinical problem with significant public health impact. The availability of several experimental models of this condition has allowed detailed investigation of the cellular and molecular interactions involved in its pathogenesis. Such studies have shed light on the roles played by bacterial virulence factors and host innate immune mechanisms in the development of intestinal inflammation.

Unravelling the pathogenesis of inflammatory bowel disease

Recently, substantial advances in the understanding of the molecular pathogenesis of inflammatory bowel disease (IBD) have been made owing to three related lines of investigation. First, IBD has been found to be the most tractable of complex disorders for discovering susceptibility genes, and these have shown the importance of epithelial barrier function, and innate and adaptive immunity in disease pathogenesis. Second, efforts directed towards the identification of environmental factors implicate commensal bacteria (or their products), rather than conventional pathogens, as drivers of dysregulated immunity and IBD. Third, murine models, which exhibit many of the features of ulcerative colitis and seem to be bacteria-driven, have helped unravel the pathogenesis/mucosal immunopathology of IBD.

Lack of CD47 on nonhematopoietic cells induces split macrophage tolerance to CD47null cells

Macrophages recognize CD47 as a marker of "self" and phagocytose CD47(null) hematopoietic cells. Using CD47 chimera models, here, we show that the phagocytic activity of macrophages against CD47(null) hematopoietic cells is conferred by CD47 expression on nonhematopoietic cells, and this "education" process is hematopoietic cell-independent. Macrophages in the chimeras where nonhematopoietic cells express CD47 phagocytose CD47(null) cells, whereas those in the chimeras lacking CD47 on nonhematopoietic cells are tolerant to CD47(null) cells. However, macrophages in the latter chimeras retain phagocytic activity against CD47(null) RBCs, demonstrating a split macrophage tolerance to CD47(null) hematopoietic cells. The findings highlight the potential importance of nonhematopoietic cells in the regulation of macrophage function, and suggest a previously uncharacterized mechanism of macrophage tolerance.

Immunologic and molecular mechanisms in inflammatory bowel disease

Molecular and immunologic mechanisms underlying inflammation in inflammatory bowel disease (IBD) are largely unknown. Recent studies have helped better characterize genetic and environmental factors associated with colitis. Discoveries of genetic variants have confirmed that IBD is a bacteria and cytokine-driven pathologic immune response. Data have demonstrated that certain T cell subsets are important in executing the inflammatory cascade. Insufficient regulatory cell activity or modulatory cytokine production results in unrestrained inflammation. Biologic agents that block inflammatory cytokines (anti-TNFalpha antibodies) have been used successfully to treat IBD. Recent advances have also identified mucosal regulatory pathways.