Neutrophils engage the kallikrein-kinin system to open up the endothelial barrier in acute inflammation.

Neutrophil recruitment and plasma exudation are key elements in the immune response to injury or infection. Activated neutrophils stimulate opening of the endothelial barrier; however, the underlying mechanisms have remained largely unknown. In this study, we identified a pivotal role of the proinflammatory kallikrein-kinin system and consequent formation of bradykinin in neutrophil-evoked vascular leak. In mouse and hamster models of acute inflammation, inhibitors of bradykinin generation, and signaling markedly reduced plasma exudation in response to chemoattractant activation of neutrophils. The neutrophil-driven leak was likewise suppressed in mice deficient in either the bradykinin B2 receptor or factor XII (initiator of the kallikrein-kinin system). In human endothelial cell monolayers, material secreted from activated neutrophils induced cytoskeletal rearrangement, leading to paracellular gap formation in a bradykinin-dependent manner. As a mechanistic basis, we found that a neutrophil-derived heparin-binding protein (HBP/azurocidin) displaced the bradykinin precursor high-molecular-weight kininogen from endothelial cells, thereby enabling proteolytic processing of kininogen into bradykinin by neutrophil and plasma proteases. These data provide novel insight into the signaling pathway by which neutrophils open up the endothelial barrier and identify the kallikrein-kinin system as a target for therapeutic interventions in acute inflammatory reactions.-Kenne, E., Rasmuson, J., Renné, T., Vieira, M. L., Müller-Esterl, W., Herwald, H., Lindbom, L. Neutrophils engage the kallikrein-kinin system to open up the endothelial barrier in acute inflammation.

Mast cells increase vascular permeability by heparin-initiated bradykinin formation in vivo.

Activated mast cells trigger edema in allergic and inflammatory disease. We report a paracrine mechanism by which mast cell-released heparin increases vascular permeability in vivo. Heparin activated the protease factor XII, which initiates bradykinin formation in plasma. Targeting factor XII or kinin B2 receptors abolished heparin-triggered leukocyte-endothelium adhesion and interfered with a mast cell-driven drop in blood pressure in rodents. Intravital laser scanning microscopy and tracer measurements showed heparin-driven fluid extravasation in mouse skin microvessels. Ablation of factor XII or kinin B2 receptors abolished heparin-induced skin edema and protected mice from allergen-activated mast cell-driven leakage. In contrast, heparin and activated mast cells induced excessive edema in mice deficient in the major inhibitor of factor XII, C1 esterase inhibitor. Allergen exposure triggered edema attacks in hereditary angioedema patients, lacking C1 esterase inhibitor. The data indicate that heparin-initiated bradykinin formation plays a fundamental role in mast cell-mediated diseases.

The F-BAR protein NOSTRIN participates in FGF signal transduction and vascular development.

F-BAR proteins are multivalent adaptors that link plasma membrane and cytoskeleton and coordinate cellular processes such as membrane protrusion and migration. Yet, little is known about the function of F-BAR proteins in vivo. Here we report, that the F-BAR protein NOSTRIN is necessary for proper vascular development in zebrafish and postnatal retinal angiogenesis in mice. The loss of NOSTRIN impacts on the migration of endothelial tip cells and leads to a reduction of tip cell filopodia number and length. NOSTRIN forms a complex with the GTPase Rac1 and its exchange factor Sos1 and overexpression of NOSTRIN in cells induces Rac1 activation. Furthermore, NOSTRIN is required for fibroblast growth factor 2 dependent activation of Rac1 in primary endothelial cells and the angiogenic response to fibroblast growth factor 2 in the in vivo matrigel plug assay. We propose a novel regulatory circuit, in which NOSTRIN assembles a signalling complex containing FGFR1, Rac1 and Sos1 thereby facilitating the activation of Rac1 in endothelial cells during developmental angiogenesis.

NOSTRINbeta--a shortened NOSTRIN variant with a role in transcriptional regulation.

We recently observed that a novel, shortened variant of eNOS trafficking inducer (NOSTRIN) is expressed in cirrhotic liver. This shortened variant (NOSTRINbeta) lacks the first 78 amino acids of full-length NOSTRIN (NOSTRINalpha) and thus a substantial part of its F-BAR domain. In contrast to NOSTRINalpha, NOSTRINbeta mainly localizes to the cell nucleus. In this study, we show that nuclear import of NOSTRINbeta depends on two nuclear localization signals (aa 32-36: KKRK and aa 57-61: KAKKK). Each of the sequences is independently functional, but both are required to sustain nuclear localization of NOSTRINbeta. Export of NOSTRINbeta from the nucleus is facilitated by a CRM1-dependent mechanism relying on the nuclear export sequence LELEKERIQL (aa 135-145). Unlike NOSTRINbeta, the full-length variant NOSTRINalpha was conspicuously absent from the nucleus. This is most likely because of the fact that its N-terminal F-BAR domain, which is truncated in NOSTRINbeta, facilitates association with cellular membranes. NOSTRINbeta directly binds to the 5'-regulatory region of the NOSTRIN gene (bp -200 to -1), and overexpression of NOSTRINbeta strongly decreases transcription of a reporter gene under control of this DNA region. Taken together, our results suggest that nuclear NOSTRINbeta may negatively regulate transcription of the NOSTRIN gene.

Nitric oxide-independent vasodilator rescues heme-oxidized soluble guanylate cyclase from proteasomal degradation.

Nitric oxide (NO) is an essential vasodilator. In vascular diseases, oxidative stress attenuates NO signaling by both chemical scavenging of free NO and oxidation and downregulation of its major intracellular receptor, the alphabeta heterodimeric heme-containing soluble guanylate cyclase (sGC). Oxidation can also induce loss of the heme of sGC, as well as the responsiveness of sGC to NO. sGC activators such as BAY 58-2667 bind to oxidized/heme-free sGC and reactivate the enzyme to exert disease-specific vasodilation. Here, we show that oxidation-induced downregulation of sGC protein extends to isolated blood vessels. Mechanistically, degradation was triggered through sGC ubiquitination and proteasomal degradation. The heme-binding site ligand BAY 58-2667 prevented sGC ubiquitination and stabilized both alpha and beta subunits. Collectively, our data establish oxidation-ubiquitination of sGC as a modulator of NO/cGMP signaling and point to a new mechanism of action for sGC activating vasodilators by stabilizing their receptor, oxidized/heme-free sGC.

Activation of mammalian target of rapamycin controls the loss of TCRzeta in lupus T cells through HRES-1/Rab4-regulated lysosomal degradation.

Persistent mitochondrial hyperpolarization (MHP) and enhanced calcium fluxing underlie aberrant T cell activation and death pathway selection in systemic lupus erythematosus. Treatment with rapamycin, which effectively controls disease activity, normalizes CD3/CD28-induced calcium fluxing but fails to influence MHP, suggesting that altered calcium fluxing is downstream or independent of mitochondrial dysfunction. In this article, we show that activity of the mammalian target of rapamycin (mTOR), which is a sensor of the mitochondrial transmembrane potential, is increased in lupus T cells. Activation of mTOR was inducible by NO, a key trigger of MHP, which in turn enhanced the expression of HRES-1/Rab4, a small GTPase that regulates recycling of surface receptors through early endosomes. Expression of HRES-1/Rab4 was increased in CD4(+) lupus T cells, and in accordance with its dominant impact on the endocytic recycling of CD4, it was inversely correlated with diminished CD4 expression. HRES-1/Rab4 overexpression was also inversely correlated with diminished TCRzeta protein levels. Pull-down studies revealed a direct interaction of HRES-1/Rab4 with CD4 and TCRzeta. Importantly, the deficiency of the TCRzeta chain and of Lck and the compensatory up-regulation of FcepsilonRIgamma and Syk, which mediate enhanced calcium fluxing in lupus T cells, were reversed in patients treated with rapamcyin in vivo. Knockdown of HRES-1/Rab4 by small interfering RNA and inhibitors of lysosomal function augmented TCRzeta protein levels in vitro. The results suggest that activation of mTOR causes the loss of TCRzeta in lupus T cells through HRES-1/Rab4-dependent lysosomal degradation.

Neutrophil-derived proteinase 3 induces kallikrein-independent release of a novel vasoactive kinin.

The kinin-forming pathway is activated on endothelial cells and neutrophils when high-molecular weight kininogen (HK) is cleaved by plasma kallikrein liberating bradykinin, a potent mediator of inflammation. Kinins are released during inflammatory conditions such as vasculitis, associated with neutrophil influx around blood vessels. Some patients with vasculitis have elevated plasma levels of neutrophil-derived proteinase 3 (PR3) and anti-PR3 Abs. This study investigated if neutrophil-derived PR3 could induce activation of the kinin pathway. PR3 incubated with HK, or a synthetic peptide derived from HK, induced breakdown and release of a novel tridecapeptide termed PR3-kinin, NH(2)-MKRPPGFSPFRSS-COOH, consisting of bradykinin with two additional amino acids on each terminus. The reaction was specific and inhibited by anti-PR3 and alpha(1)-antitrypsin. Recombinant wild-type PR3 incubated with HK induced HK breakdown, whereas mutated PR3, lacking enzymatic activity, did not. PR3-kinin bound to and activated human kinin B(1) receptors, but did not bind to B(2) receptors, expressed by transfected HEK293 cells in vitro. In human plasma PR3-kinin was further processed to the B(2) receptor agonist bradykinin. PR3-kinin exerted a hypotensive effect in vivo through both B(1) and B(2) receptors as demonstrated using wild-type and B(1) overexpressing rats as well as wild-type and B(2) receptor knockout mice. Neutrophil extracts from vasculitis patients and healthy controls contained comparable amounts of PR3 and induced HK proteolysis, an effect that was abolished when PR3 was immunoadsorbed. Neutrophil-derived PR3 can proteolyze HK and liberate PR3-kinin, thereby initiating kallikrein-independent activation of the kinin pathway.

Streptococcal inhibitor of complement-mediated lysis (SIC): an anti-inflammatory virulence determinant.

Since the late 1980s, a worldwide increase of severe Streptococcus pyogenes infections has been associated with strains of the M1 serotype, strains which all secrete the streptococcal inhibitor of complement-mediated lysis (SIC). Previous work has shown that SIC blocks complement-mediated haemolysis, inhibits the activity of antibacterial peptides and has affinity for the human plasma proteins clusterin and histidine-rich glycoprotein; the latter is a member of the cystatin protein family. The present work demonstrates that SIC binds to cystatin C, high-molecular-mass kininogen (HK) and low-molecular-mass kininogen, which are additional members of this protein family. The binding sites in HK are located in the cystatin-like domain D3 and the endothelial cell-binding domain D5. Immobilization of HK to cellular structures plays a central role in activation of the human contact system. SIC was found to inhibit the binding of HK to endothelial cells, and to reduce contact activation as measured by prolonged blood clotting time and impaired release of bradykinin. These results suggest that SIC modifies host defence systems, which may contribute to the virulence of S. pyogenes strains of the M1 serotype.

Postnatal expression of V2 vasopressin receptor splice variants in the rat cerebellum.

The V(2) vasopressin receptor gene contains an alternative splice site in exon-3, which leads to the generation of two splice variants (V(2a) and V(2b)) first identified in the kidney. The open reading frame of the alternatively spliced V(2b) transcript encodes a truncated receptor, showing the same amino acid sequence as the canonical V(2a) receptor up to the sixth transmembrane segment, but displaying a distinct sequence to the corresponding seventh transmembrane segment and C-terminal domain relative to the V(2a) receptor. Here, we demonstrate the postnatal expression of V(2a) and V(2b) variants in the rat cerebellum. Most importantly, we showed by in situ hybridization and immunocytochemistry that both V(2) splice variants were preferentially expressed in Purkinje cells, from early to late postnatal development. In addition, both variants were transiently expressed in the neuroblastic external granule cells and Bergmann fibers. These results indicate that the cellular distributions of both splice variants are developmentally regulated, and suggest that the transient expression of the V(2) receptor is involved in the mechanisms of cerebellar cytodifferentiation by AVP. Finally, transfected CHO-K1 expressing similar amounts of both V(2) splice variants, as that found in the cerebellum, showed a significant reduction in the surface expression of V(2a) receptors, suggesting that the differential expression of the V(2) splice variants regulates the vasopressin signaling in the cerebellum.

Targeting the heme-oxidized nitric oxide receptor for selective vasodilatation of diseased blood vessels.

ROS are a risk factor of several cardiovascular disorders and interfere with NO/soluble guanylyl cyclase/cyclic GMP (NO/sGC/cGMP) signaling through scavenging of NO and formation of the strong oxidant peroxynitrite. Increased oxidative stress affects the heme-containing NO receptor sGC by both decreasing its expression levels and impairing NO-induced activation, making vasodilator therapy with NO donors less effective. Here we show in vivo that oxidative stress and related vascular disease states, including human diabetes mellitus, led to an sGC that was indistinguishable from the in vitro oxidized/heme-free enzyme. This sGC variant represents what we believe to be a novel cGMP signaling entity that is unresponsive to NO and prone to degradation. Whereas high-affinity ligands for the unoccupied heme pocket of sGC such as zinc-protoporphyrin IX and the novel NO-independent sGC activator 4-[((4-carboxybutyl){2-[(4-phenethylbenzyl)oxy]phenethyl}amino) methyl [benzoic]acid (BAY 58-2667) stabilized the enzyme, only the latter activated the NO-insensitive sGC variant. Importantly, in isolated cells, in blood vessels, and in vivo, BAY 58-2667 was more effective and potentiated under pathophysiological and oxidative stress conditions. This therapeutic principle preferentially dilates diseased versus normal blood vessels and may have far-reaching implications for the currently investigated clinical use of BAY 58-2667 as a unique diagnostic tool and highly innovative vascular therapy.

Bradykinin B2 Receptors of dendritic cells, acting as sensors of kinins proteolytically released by Trypanosoma cruzi, are critical for the development of protective type-1 responses.

Although the concept that dendritic cells (DCs) recognize pathogens through the engagement of Toll-like receptors is widely accepted, we recently suggested that immature DCs might sense kinin-releasing strains of Trypanosoma cruzi through the triggering of G-protein-coupled bradykinin B2 receptors (B2R). Here we report that C57BL/6.B2R-/- mice infected intraperitoneally with T. cruzi display higher parasitemia and mortality rates as compared to B2R+/+ mice. qRT-PCR revealed a 5-fold increase in T. cruzi DNA (14 d post-infection [p.i.]) in B2R-/- heart, while spleen parasitism was negligible in both mice strains. Analysis of recall responses (14 d p.i.) showed high and comparable frequencies of IFN-gamma-producing CD4+ and CD8+ T cells in the spleen of B2R-/- and wild-type mice. However, production of IFN-gamma by effector T cells isolated from B2R-/- heart was significantly reduced as compared with wild-type mice. As the infection continued, wild-type mice presented IFN-gamma-producing (CD4+CD44+ and CD8+CD44+) T cells both in the spleen and heart while B2R-/- mice showed negligible frequencies of such activated T cells. Furthermore, the collapse of type-1 immune responses in B2R-/- mice was linked to upregulated secretion of IL-17 and TNF-alpha by antigen-responsive CD4+ T cells. In vitro analysis of tissue culture trypomastigote interaction with splenic CD11c+ DCs indicated that DC maturation (IL-12, CD40, and CD86) is controlled by the kinin/B2R pathway. Further, systemic injection of trypomastigotes induced IL-12 production by CD11c+ DCs isolated from B2R+/+ spleen, but not by DCs from B2R-/- mice. Notably, adoptive transfer of B2R+/+ CD11c+ DCs (intravenously) into B2R-/- mice rendered them resistant to acute challenge, rescued development of type-1 immunity, and repressed TH17 responses. Collectively, our results demonstrate that activation of B2R, a DC sensor of endogenous maturation signals, is critically required for development of acquired resistance to T. cruzi infection.

Translocation of endothelial nitric-oxide synthase involves a ternary complex with caveolin-1 and NOSTRIN.

Recently, we characterized a novel endothelial nitric-oxide synthase (eNOS)-interacting protein, NOSTRIN (for eNOS-trafficking inducer), which decreases eNOS activity upon overexpression and induces translocation of eNOS away from the plasma membrane. Here, we show that NOSTRIN directly binds to caveolin-1, a well-established inhibitor of eNOS. Because this interaction occurs between the N terminus of caveolin (positions 1-61) and the central domain of NOSTRIN (positions 323-434), it allows for independent binding of each of the two proteins to eNOS. Consistently, we were able to demonstrate the existence of a ternary complex of NOSTRIN, eNOS, and caveolin-1 in Chinese hamster ovary (CHO)-eNOS cells. In human umbilical vein endothelial cells (HUVECs), the ternary complex assembles at the plasma membrane upon confluence or thrombin stimulation. In CHO-eNOS cells, NOSTRIN-mediated translocation of eNOS involves caveolin in a process most likely representing caveolar trafficking. Accordingly, trafficking of NOSTRIN/eNOS/caveolin is affected by altering the state of actin filaments or cholesterol levels in the plasma membrane. During caveolar trafficking, NOSTRIN functions as an adaptor to recruit mediators such as dynamin-2 essential for membrane fission. We propose that a ternary complex between NOSTRIN, caveolin-1, and eNOS mediates translocation of eNOS, with important implications for the activity and availability of eNOS in the cell.

Expression of endogenous nuclear bradykinin B2 receptors mediating signaling in immediate early gene activation.

Bradykinin (BK) represents a pro-inflammatory mediator that partakes in many inflammatory diseases. The mechanism of action of BK is thought to be primarily mediated by specific cell surface membrane B2 receptors (B2Rs). Some evidence has suggested, however, the existence of an intracellular/nuclear B2R population. Whether these receptors are functional and contribute to BK signaling remains to be determined. In this study, by mean of Western blotting, 3D-confocal microscopy, receptor autoradiography and radioligand binding analysis, we showed that plasma membrane and highly purified nuclei from isolated rat hepatocytes contain specific B2R that bind BK. The results depicting B2R nuclear expression in isolated nuclear organelles were reproduced in situ on hepatic sections by immunogold labeling and transmission electron microscopy. Functional tests on single nuclei, by means of confocal microscopy and the calcium-sensitive probe fluo-4AM, showed that BK induces concentration-dependent transitory mobilization of nucleoplasmic calcium; these responses were blocked by B2R antagonist HOE 140, not by the B1R antagonist R954 and, were also found in wild-type C57/Bl6 mice, but not in B2R-KO mice. In isolated nuclei, BK elicited activation/phosphorylation of Akt, acetylation of histone H3 and ensuing pro-inflammatory iNOS gene induction as determined by Western blot and RT-PCR. ChIP assay confirmed binding of acetylated-histone H3 complexes, but not B2R, to promoter region of iNOS gene suggesting that B2R-mediated gene expression is bridged with accessory downstream effectors. This study discloses a previously undescribed mechanism in BK-induced transcriptional events, via intracrine B2R-mediated signaling, occurring in rat autologous hepatic cells.

Cell cycle-regulated inactivation of endothelial NO synthase through NOSIP-dependent targeting to the cytoskeleton.

Nitric oxide (NO) plays a key role in vascular function, cell proliferation, and apoptosis. Proper subcellular localization of endothelial NO synthase (eNOS) is crucial for its activity; however, the role of eNOS trafficking for NO biosynthesis remains to be defined. Overexpression of NOS-interacting protein (NOSIP) induces translocation of eNOS from the plasma membrane to intracellular compartments, thereby impairing NO production. Here we report that endogenous NOSIP reduces the enzymatic capacity of eNOS, specifically in the G(2) phase of the cell cycle by targeting eNOS to the actin cytoskeleton. This regulation is critically dependent on the nucleocytoplasmic shuttling of NOSIP and its cytoplasmic accumulation in the G(2) phase. The predominant nuclear localization of NOSIP depends on a bipartite nuclear localization sequence (NLS) mediating interaction with importin alpha. Mutational destruction of the NLS abolishes nuclear import and interaction with importin alpha. Nuclear export is insensitive to leptomycin B and hence different from the CRM1-dependent default mechanism. Inhibition of NOSIP expression by RNA interference completely abolishes G(2)-specific cytoskeletal association and inhibition of eNOS. These findings describe a novel cell cycle-dependent modulation of endogenous NO levels that are critical to the cell cycle-related actions of NO such as apoptosis or cell proliferation.

The serum protein alpha 2-Heremans-Schmid glycoprotein/fetuin-A is a systemically acting inhibitor of ectopic calcification.

Ectopic calcification is a frequent complication of many degenerative diseases. Here we identify the serum protein alpha2-Heremans-Schmid glycoprotein (Ahsg, also known as fetuin-A) as an important inhibitor of ectopic calcification acting on the systemic level. Ahsg-deficient mice are phenotypically normal, but develop severe calcification of various organs on a mineral and vitamin D-rich diet and on a normal diet when the deficiency is combined with a DBA/2 genetic background. This phenotype is not associated with apparent changes in calcium and phosphate homeostasis, but with a decreased inhibitory activity of the Ahsg-deficient extracellular fluid on mineral formation. The same underlying principle may contribute to many calcifying disorders including calciphylaxis, a syndrome of severe systemic calcification in patients with chronic renal failure. Taken together, our data demonstrate a critical role of Ahsg as an inhibitor of unwanted mineralization and provide a novel therapeutic concept to prevent ectopic calcification accompanying various diseases.

Subcellular targeting and trafficking of nitric oxide synthases.

Unlike most other endogenous messengers that are deposited in vesicles, processed on demand and/or secreted in a regulated fashion, NO (nitric oxide) is a highly active molecule that readily diffuses through cell membranes and thus cannot be stored inside the producing cell. Rather, its signalling capacity must be controlled at the levels of biosynthesis and local availability. The importance of temporal and spatial control of NO production is highlighted by the finding that differential localization of NO synthases in cardiomyocytes translates into distinct effects of NO in the heart. Thus NO synthases belong to the most tightly controlled enzymes, being regulated at transcriptional and translational levels, through co- and post-translational modifications, by substrate availability and not least via specific sorting to subcellular compartments, where they are in close proximity to their target proteins. Considerable efforts have been made to elucidate the molecular mechanisms that underlie the intracellular targeting and trafficking of NO synthases, to ultimately understand the cellular pathways controlling the formation and function of this powerful signalling molecule. In the present review, we discuss the mechanisms and triggers for subcellular routing and dynamic redistribution of NO synthases and the ensuing consequences for NO production and action.

FCH/Cdc15 domain determines distinct subcellular localization of NOSTRIN.

NOSTRIN, an NO synthase binding protein, belongs to the PCH family of proteins, exposing a typical domain structure. While its SH3 domain and the C-terminal coiled-coil region cc2 have been studied earlier, the function of the N-terminal half comprising a Cdc15 domain with an FCH (Fes/CIP homology) region followed by a coiled-coil stretch cc1 is unknown. Here, we show that the FCH region is necessary and sufficient for membrane association of NOSTRIN, whereas the Cdc15 domain further specifies subcellular distribution of the protein. Thus, the FCH region and the Cdc15 domain fulfill complementary functions in subcellular targeting of NOSTRIN.

Interplay between parasite cysteine proteases and the host kinin system modulates microvascular leakage and macrophage infection by promastigotes of the Leishmania donovani complex.

Kinins, the vasoactive peptides proteolytically liberated from kininogens, were recently recognized as signals alerting the innate immune system. Here we demonstrate that Leishmania donovani and Leishmania chagasi, two etiological agents of visceral leishmaniasis (VL), activate the kinin system. Intravital microscopy in the hamster cheek pouch showed that topically applied promastigotes induced macromolecular leakage (FITC-dextran) through postcapillary venules. Peaking at 15 min, the parasite-induced leakage was drastically enhanced by captopril (Cap), an inhibitor of angiotensin-converting enzyme (ACE), a kinin-degrading metallopeptidase. The enhanced microvascular responses were cancelled by HOE-140, an antagonist of the B2 bradykinin receptor (B2R), or by pre-treatment of promastigotes with the irreversible cysteine proteinase inhibitor N-methylpiperazine-urea-Phe-homoPhe-vinylsulfone-benzene (N-Pip-hF-VSPh). In agreement with the above-mentioned data, the promastigotes vigorously induced edema in the paw of Cap-treated J129 mice, but not Cap-B2R-/- mice. Analysis of parasite-induced breakdown of high molecular weight kininogens (HK), combined with active site-affinity-labeling with biotin-N-Pip-hF-VSPh, identified 35-40 kDa proteins as kinin-releasing cysteine peptidases. We then checked if macrophage infectivity was influenced by interplay between these kinin-releasing parasite proteases, kininogens, and kinin-degrading peptidases (i.e. ACE). Our studies revealed that full-fledged B2R engagement resulted in vigorous increase of L. chagasi uptake by resident macrophages. Evidence that inflammatory macrophages treated with HOE-140 became highly susceptible to amastigote outgrowth, assessed 72 h after initial macrophage interaction, further suggests that the kinin/B2R activation pathway may critically modulate inflammation and innate immunity in visceral leishmaniasis.