[Show abstract][Hide abstract] ABSTRACT: Background:
Our previous studies have demonstrated that B cells in human inflammatory bowel disease (IBD) are highly activated and produce copious amounts of chemokines. Here, we showed that B cells produce eotaxin-1, a selective chemokine for acute eosinophilia. Increased levels of activated eosinophils have been found in the intestinal mucosa in patients with IBD, but their role(s) and the regulation of their migration patterns remain poorly defined.
To determine how B-cell secretion of eotaxin-1 influences eosinophil activation and migration, we performed immunoepidemiological approaches coupled with in vitro studies. B cells and eosinophils from patients with Crohn's disease and ulcerative colitis were isolated, and responses to Toll-like receptor ligands (TLR) were measured and assessed for the relationship with clinical disease.
Eotaxin-1 from recirculating B cells, and TLR ligands, regulated eosinophil homing mechanisms in IBD. B cells stimulated with hypo-acylated lipopolysaccharide (LPS) produced copious amounts of eotaxin-1, which influenced eosinophil activation profiles in the bloodstream. We also found that hexa-acylated LPS, such Escherichia coli LPS, directly activated TLR2-expressing and TLR4-expressing eosinophils from patients with IBD to express a different repertoire of mucosal homing receptors, namely CCR9 and CCR10. Whereas B-cell production of eotaxin-1 was correlated with reduced disease activity, eosinophil activation by hexa-acylated LPS was associated with increased disease activity.
These results suggest that systemic TLR ligands influence eosinophil migration patterns, both directly and indirectly, through B cells. Our report uncovers unexpected mechanisms of cross talk between certain immune cells that shed new light on IBD immunology.
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to characterize the relationship between adipose tissue phenotype and depot-specific microvascular function in fat.
In 30 obese subjects (age 42±11 years, body mass index 46±11 kg/m(2)) undergoing bariatric surgery, we intraoperatively collected visceral and subcutaneous adipose tissue and characterized depot-specific adipose phenotypes. We assessed vasomotor function of the adipose microvasculature using videomicroscopy of small arterioles (75-250 μm) isolated from different fat compartments. Endothelium-dependent, acetylcholine-mediated vasodilation was severely impaired in visceral arterioles, compared to the subcutaneous depot (P<0.001 by ANOVA). Nonendothelium dependent responses to papaverine and nitroprusside were similar. Endothelial nitric oxide synthase inhibition with N(ω)-nitro-l-arginine methyl ester reduced subcutaneous vasodilation but had no effect on severely blunted visceral arteriolar responses. Visceral fat exhibited greater expression of proinflammatory, oxidative stress-related, hypoxia-induced, and proangiogenic genes; increased activated macrophage populations; and had a higher capacity for cytokine production ex vivo.
Our findings provide clinical evidence that the visceral microenvironment may be intrinsically toxic to arterial health providing a potential mechanism by which visceral adiposity burden is linked to atherosclerotic vascular disease. Our findings also support the evolving concept that both adipose tissue quality and quantity may play significant roles in shaping cardiovascular phenotypes in human obesity.
[Show abstract][Hide abstract] ABSTRACT: Resistance to schistosomiasis is associated with increased levels of serum parasite-specific IgE. IgE exerts its functions through its cellular receptors, FcεRI and FcεRII/CD23; however, its functional significance in humans requires further characterization. We previously reported that increased levels of CD23(+) B cells correlate with resistance to schistosomiasis in hyperexposed populations and sought to define their potential function and relationship with IgE. We found that CD23(+) B cells are a heterogeneous cell population with functional and phenotypic differences. Circulating CD23(+) B cells are uniquely activated in schistosomiasis and express the CD23b isoform and CXCR5, the homing receptor for lymphoid follicles. High CXCR5 expression by CD23(+) B cells was associated with the capacity to home to the cognate ligand CXCL13. CD23-bound IgE cross-linking increased surface expression of CXCR5, suggesting that CD23(+) B cells home directly into the lymphoid follicles upon antigen capture. As human schistosomiasis is an intravascular parasitic infection associated with a high antigenic burden in the blood, circulating CD23(+) B cells may play a role in the capture and shuttling of antigens directly to splenic follicles, highlighting a new role for circulating B cells. This function likely plays an important role in the development of protective immunity to infection with schistosomes.
Infection and immunity 06/2011; 79(9):3770-7. DOI:10.1128/IAI.05094-11 · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Schistosomiasis is caused by parasitic trematodes. Individuals can accumulate hundreds of intravascular worms, which secrete a myriad of antigenic molecules into the bloodstream. Some of these molecules suppress immunity to microbial Toll-like receptor (TLR) ligands, such as lipopolysaccharides, which may increase host susceptibility to coinfecting pathogens. We show that schistosomiasis is associated with extremely high levels of endotoxemia as well as high mobility group 1, an endogenous inflammatory TLR ligand, in the absence of other coinfected pathogens. Circulating B cells express surface TLR2 and TLR4, reflecting systemic exposure to microbial ligands. Bacterial translocation may occur with schistosomal egg movement from the vascular to the gut and other routes, such as the skin during infection. Our report suggests that immunosuppressive schistosome antigens may have evolved to curb inflammatory responses to the high antigenic burden of translocated bacteria products and endogenous TLR ligands that arise during parasite exposure and inflammation.
The American journal of tropical medicine and hygiene 02/2011; 84(2):321-4. DOI:10.4269/ajtmh.2011.10-0397 · 2.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Human peripheral blood BCRμ(+) B cells express high levels of CD23 and circulate preloaded with IgE. The Ag specificity of CD23-bound IgE presumably differs from the BCR and likely reflects the Ag-specific mix of free serum IgE. CD23-bound IgE is thought to enhance B cell Ag presentation to T cells raising the question of how a B cell might respond when presented with a broad mix of Ags and CD23-bound IgE specificities. We recently reported that an increase in CD23(+) B cells is associated with the development of resistance to schistosomiasis, highlighting the potential importance of CD23-bound IgE in mediating immunity. We sought to determine the relationship between BCR and CD23-bound IgE-mediated B cell activation in the context of schistosomiasis. We found that crude schistosome Ags downregulate basal B cell activation levels in individuals hyperexposed to infectious worms. Schistosome-specific IgE from resistant, occupationally exposed Kenyans recovered responses of B cells to schistosome Ag. Furthermore, cross-linking of CD23 overrode intracellular signals mediated via the BCR, illustrating its critical and dominating role in B cell activation. These results suggest that CD23-bound IgE augments and dominates recall responses through naive B cells.
The Journal of Immunology 01/2011; 186(2):1060-7. DOI:10.4049/jimmunol.1002709 · 4.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bacteria have a central, although poorly understood, role in inflammatory bowel disease (IBD). Host-bacteria interactions primarily take place in the gastrointestinal tract, but cells may also encounter translocated bacteria in the bloodstream. IBD is associated with activated, circulating Toll-like receptor (TLR)2 and TLR4-expressing B cells suggesting that blood-borne microbial TLR ligands modulate B cell responses.
Serum levels of lipopolysaccharide (LPS)/endotoxin and high mobility group box 1 (HMGB1), an endogenous TLR ligand, were quantified in Crohn's disease (CD) and ulcerative colitis (UC). Responses of purified B cells to LPS and HMGB1 were correlated with levels of systemic TLR ligands and clinical parameters of disease.
While IBD patients have increased levels of blood LPS, the net effect of endotoxemia has unexpected characteristics illustrating that LPS has both pro- and antiinflammatory roles through TLR4+ B cells. Experimental treatment of B cells demonstrates that the antiinflammatory effect of LPS is due to its hypo-acylation of lipid A suggesting an increased prevalence of systemic, hypo-acylated LPS in CD. In contrast, high levels of LPS are associated with disease activity in UC. HMGB1 activates B cells through TLR2 and CD36. Serum levels of HMGB1 correlate with spontaneous IL-8 production by B cells suggesting that blood-borne TLR2 ligands increase B-cell activation in vivo.
Systemic TLR ligands modulate B cells towards either proinflammatory or antiinflammatory activity depending on the predominant ligand(s). Further, the circulating B cell may represent an important proxy for quantifying the LPS lipid A acylation burden in patients with IBD.
[Show abstract][Hide abstract] ABSTRACT: There is a need for developing vaccines that elicit mucosal immunity. Although oral or nasal vaccination methods would be ideal, current strategies have yielded mixed success. Toll-like receptor 2 (TLR2) ligands are effective adjuvants and are currently used in the Haemophilus influenzae type B vaccine. Induction of humoral immunity in the mucosa is critical for effective vaccination; thus, we sought to determine the effects of TLR2 ligands on human mucosal B cell differentiation. We demonstrate that TLR2 ligands induce CCR9 and CCR10 expression by circulating B cells and increased chemotaxis to cognate chemokines CCL25 and CCL28 suggesting that TLR2 induces B cell homing to the gastrointestinal tract. TLR2 stimulation of B cells also induced J chain and IgA production demonstrating the induction of mucosal-like antibody secreting cells. These observations suggest that vaccines containing TLR2-ligands as adjuvants could induce mucosal B cell immunity even when delivered in a non-mucosal manner.
[Show abstract][Hide abstract] ABSTRACT: Toll-like receptor 4 (TLR4) is an innate immune receptor that is constitutively and inducibly activated in monocytes. Although TLR4 is expressed at very low levels on human B cells from healthy individuals, recent reports showed that TLR4 expression and function is elevated in B cells from inflammatory disease patients. New data showed that TLR4 expression on B cells is increased upon stimulation through surface Igμ and CD40 in combination with IL-4. In contrast, monocyte stimulation through CD40 and IL-4 receptors decreased TLR4 surface expression. Analysis of molecular signatures of TLR4 activation in stimulated B cells suggested that TLR4 is regulated by different mechanisms in B cells compared to monocytes. PU.1 and interferon regulatory factor association with the TLR4 promoter are sufficient for TLR4 transcription, but are not sufficient for surface TLR4 expression on B cells. In contrast, the PU.1/IRF combination is sufficient for surface TLR4 expression on monocytes. These data identify mechanisms that can activate B cell TLR4 expression in inflammatory disease patients, and demonstrate that B cells have additional layers of TLR4 regulation absent in monocytes.
[Show abstract][Hide abstract] ABSTRACT: Chronic systemic inflammation links periodontal disease and diabetes to increased incidence of serious comorbidities. Activation of TLRs, particularly TLR2 and TLR4, promotes chronic systemic inflammation. Human B cells have been generally thought to lack these TLRs. However, recent work showed that an increased percentage of circulating B cells from inflammatory disease patients express TLR2 and TLR4, and that TLR engagement on B cells resulted in unexpected changes in gene expression. New data show that B cells from inflammatory disease patients secrete multiple cytokines in response to different classes of TLR ligands. Furthermore, the B cell response to combinations of TLR ligands is cytokine- and ligand-specific. Some cytokines (IL-1beta and IL-10) are predominantly regulated by TLR4, but others (IL-8 and TNF-alpha) are predominantly regulated by TLR2, due in part to TLR-dictated changes in transcription factor/promoter association. TLR2 and TLR9 also regulate B cell TLR4 expression, demonstrating that TLR cross-talk controls B cell responses at multiple levels. Parallel examination of B cells from periodontal disease and diabetes patients suggested that outcomes of TLR cross-talk are influenced by disease pathology. We conclude that disease-associated alteration of B cell TLR responses specifically regulates cytokine production and may influence chronic inflammation.
The Journal of Immunology 11/2009; 183(11):7461-70. DOI:10.4049/jimmunol.0901517 · 4.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: IBD is characterized by a chronic, dysregulated immune response to intestinal bacteria. Past work has focused on the role of T cells and myeloid cells in mediating chronic gastrointestinal and systemic inflammation. Here, we show that circulating and tissue B cells from CD patients demonstrate elevated basal levels of activation. CD patient B cells express surface TLR2, spontaneously secrete high levels of IL-8, and contain increased ex vivo levels of phosphorylated signaling proteins. CD clinical activity correlates directly with B cell expression of IL-8 and TLR2, suggesting a positive relationship between these B cell inflammatory mediators and disease pathogenesis. In contrast, B cells from UC patients express TLR2 but generally do not demonstrate spontaneous IL-8 secretion; however, significant IL-8 production is inducible via TLR2 stimulation. Furthermore, UC clinical activity correlates inversely with levels of circulating TLR2+ B cells, which is opposite to the association observed in CD. In conclusion, TLR2+ B cells are associated with clinical measures of disease activity and differentially associated with CD- and UC-specific patterns of inflammatory mediators, suggesting a formerly unappreciated role of B cells in the pathogenesis of IBD.
[Show abstract][Hide abstract] ABSTRACT: IgE plays a critical role in hypersensitivity reactions such as asthma and allergy as well as poorly defined roles in immunity to parasitic helminth infections. The quantity of antigen-specific IgE is thought to affect the intensity of the allergic reaction as well as the perceived level of resistance to parasitic worms. Because most somatic IgE is bound by its receptors, FcεRI and FcεRII, and increased expression of IgE receptors also change with cellular activation status, the serum concentration of IgE may not necessarily reflect levels of systemic IgE. Accurate measures of IgE would help to define the bona fide role of this molecule in immunity. Furthermore, improved indicators of systemic antigen-specific IgE could better predict the risk for severe allergic responses. In this report, we demonstrate a simple method for measuring cell-bound IgE in whole blood using basic flow cytometry. This method demonstrates that, in general, cell-bound IgE correlates well with serum levels of IgE. However, discordance in serum and cell-bound IgE levels in some individuals illustrates the inadequacy of using serum levels of IgE as a systemic indicator and validates the need to assay both cell-bound and free IgE.