Butyrate: Connecting the gut-lung axis to the management of pulmonary disorders.

Short-chain fatty acids (SCFAs) are metabolites released by bacterial components of the microbiota. These molecules have a wide range of effects in the microbiota itself, but also in host cells in which they are known for contributing to the regulation of cell metabolism, barrier function, and immunological responses. Recent studies indicate that these molecules are important players in the gut-lung axis and highlight the possibility of using strategies that alter their intestinal production to prevent or treat distinct lung inflammatory diseases. Here, we review the effects of the SCFA butyrate and its derivatives in vitro and in vivo on murine models of respiratory disorders, besides discussing the potential therapeutic use of butyrate and the other SCFAs in lung diseases.

Natterin-Induced Neutrophilia Is Dependent on cGAS/STING Activation via Type I IFN Signaling Pathway.

Natterin is a potent pro-inflammatory fish molecule, inducing local and systemic IL-1ß/IL-1R1-dependent neutrophilia mediated by non-canonical NLRP6 and NLRC4 inflammasome activation in mice, independent of NLRP3. In this work, we investigated whether Natterin activates mitochondrial damage, resulting in self-DNA leaks into the cytosol, and whether the DNA sensor cGAS and STING pathway participate in triggering the innate immune response. Employing a peritonitis mouse model, we found that the deficiency of the tlr2/tlr4, myd88 and trif results in decreased neutrophil influx to peritoneal cavities of mice, indicative that in addition to MyD88, TRIF contributes to neutrophilia triggered by TLR4 engagement by Natterin. Next, we demonstrated that gpcr91 deficiency in mice abolished the neutrophil recruitment after Natterin injection, but mice pre-treated with 2-deoxy-d-glucose that blocks glycolysis presented similar infiltration than WT Natterin-injected mice. In addition, we observed that, compared with the WT Natterin-injected mice, DPI and cyclosporin A treated mice had a lower number of neutrophils in the peritoneal exudate. The levels of dsDNA in the supernatant of the peritoneal exudate and processed IL-33 in the supernatant of the peritoneal exudate or cytoplasmic supernatant of the peritoneal cell lysate of WT Natterin-injected mice were several folds higher than those of the control mice. The recruitment of neutrophils to peritoneal cavity 2 h post-Natterin injection was intensely impaired in ifnar KO mice and partially in il-28r KO mice, but not in ifnγr KO mice. Finally, using cgas KO, sting KO, or irf3 KO mice we found that recruitment of neutrophils to peritoneal cavities was virtually abolished in response to Natterin. These findings reveal cytosolic DNA sensors as critical regulators for Natterin-induced neutrophilia.

Natterin-induced neutrophilia is dependent on cGAS/STING activation via type i IFN signaling pathway

Natterin is a potent pro-inflammatory fish molecule, inducing local and systemic IL-1β/IL-1R1-dependent neutrophilia mediated by non-canonical NLRP6 and NLRC4 inflammasome activation in mice, independent of NLRP3. In this work, we investigated whether Natterin activates mitochondrial damage, resulting in self-DNA leaks into the cytosol, and whether the DNA sensor cGAS and STING pathway participate in triggering the innate immune response. Employing a peritonitis mouse model, we found that the deficiency of the tlr2/tlr4, myd88 and trif results in decreased neutrophil influx to peritoneal cavities of mice, indicative that in addition to MyD88, TRIF contributes to neutrophilia triggered by TLR4 engagement by Natterin. Next, we demonstrated that gpcr91 deficiency in mice abolished the neutrophil recruitment after Natterin injection, but mice pre-treated with 2-deoxy-d-glucose that blocks glycolysis presented similar infiltration than WT Natterin-injected mice. In addition, we observed that, compared with the WT Natterin-injected mice, DPI and cyclosporin A treated mice had a lower number of neutrophils in the peritoneal exudate. The levels of dsDNA in the supernatant of the peritoneal exudate and processed IL-33 in the supernatant of the peritoneal exudate or cytoplasmic supernatant of the peritoneal cell lysate of WT Natterin-injected mice were several folds higher than those of the control mice. The recruitment of neutrophils to peritoneal cavity 2 h post-Natterin injection was intensely impaired in ifnar KO mice and partially in il-28r KO mice, but not in ifnγr KO mice. Finally, using cgas KO, sting KO, or irf3 KO mice we found that recruitment of neutrophils to peritoneal cavities was virtually abolished in response to Natterin. These findings reveal cytosolic DNA sensors as critical regulators for Natterin-induced neutrophilia.

Molecular basis of carrageenan-induced cytokines production in macrophages.

BACKGROUND: Low molecular weight carrageenan (Cg) is a seaweed-derived sulfated polysaccharide widely used as inflammatory stimulus in preclinical studies. However, the molecular mechanisms of Cg-induced inflammation are not fully elucidated. The present study aimed to investigate the molecular basis involved in Cg-induced macrophages activation and cytokines production. METHODS: Primary culture of mouse peritoneal macrophages were stimulated with Kappa Cg. The supernatant and cell lysate were used for ELISA, western blotting, immunofluorescence. Cg-induced mouse colitis was also developed. RESULTS: Here we show that Cg activates peritoneal macrophages to produce pro-inflammatory cytokines such as TNF and IL-1ß. While Cg-induced TNF production/secretion depends on TLR4/MyD88 signaling, the production of pro-IL-1ß relies on TLR4/TRIF/SYK/reactive oxygen species (ROS) signaling pathway. The maturation of pro-IL1ß into IL-1ß is dependent on canonical NLRP3 inflammasome activation via Pannexin-1/P2X7/K+ efflux signaling. In vivo, Cg-induced colitis was reduced in mice in the absence of NLRP3 inflammasome components. CONCLUSIONS: In conclusion, we unravel a critical role of the NLRP3 inflammasome in Cg-induced pro-inflammatory cytokines production and colitis, which is an important discovery on the pro-inflammatory properties of this sulfated polysaccharide for pre-clinical studies. Video abstract Carrageenan (Cg) is one the most used flogistic stimulus in preclinical studies. Nevertheless, the molecular basis of Cg-induced inflammation is not totally elucidated. Herein, Lopes et al. unraveled the molecular basis for Cg-induced macrophages production of biological active IL-1ß. The Cg-stimulated macrophages produces pro-IL-1ß depends on TLR4/TRIF/Syk/ROS, whereas its processing into mature IL-1ß is dependent on the canonical NLRP3 inflammasome.

MEK5/ERK5 signaling mediates IL-4-induced M2 macrophage differentiation through regulation of c-Myc expression.

Macrophages are highly plastic cells, responding to diverse environmental stimuli to acquire different functional phenotypes. Signaling through MAPKs has been reported to regulate the differentiation of macrophages, but the role of ERK5 in IL-4-mediated M2 macrophage differentiation is still unclear. Here, we showed that the ERK5 signaling pathway plays a critical role in IL-4-induced M2 macrophage differentiation. Pharmacologic inhibition of MEK5, an upstream activator of ERK5, markedly reduced the expression of classical M2 markers, such as Arg-1, Ym-1, and Fizz-1, as well as the production of M2-related chemokines and cytokines, CCL22, CCL17, and IGF-1 in IL-4-stimulated macrophages. Moreover, pharmacologic inhibition of ERK5 also decreased the expression of several M2 markers induced by IL-4. In accordance, myeloid cell-specific Erk5 depletion (Erk5∆mye ), using LysMcre /Erk5f/f mice, confirmed the involvement of ERK5 in IL-4-induced M2 polarization. Mechanistically, the inhibition of ERK5 did not affect STAT3 or STAT6 phosphorylation, suggesting that ERK5 signaling regulates M2 differentiation in a STAT3 and STAT6-independent manner. However, genetic deficiency or pharmacologic inhibition of the MEK5/ERK5 pathway reduced the expression of c-Myc in IL-4-activated macrophages, which is a critical transcription factor involved in M2 differentiation. Our study thus suggests that the MEK5/ERK5 signaling pathway is crucial in IL-4-induced M2 macrophage differentiation through the induction of c-Myc expression.

CD3+ Macrophages Deliver Proinflammatory Cytokines by a CD3- and Transmembrane TNF-Dependent Pathway and Are Increased at the BCG-Infection Site.

Macrophages are essential cells of the innate immune response against microbial infections, and they have the ability to adapt under both pro- and anti-inflammatory conditions and develop different functions. A growing body of evidence regarding a novel macrophage subpopulation that expresses CD3 has recently emerged. Here, we explain that human circulating monocytes can be differentiated into CD3+TCRαß+ and CD3+TCRαß- macrophages. Both cell subpopulations express on their cell surface HLA family molecules, but only the CD3+TCRαß+ macrophage subpopulation co-express CD1 family molecules and transmembrane TNF (tmTNF). CD3+TCRαß+ macrophages secrete IL-1ß, IL-6 IP-10, and MCP-1 by both tmTNF- and CD3-dependent pathways, while CD3+TCRαß- macrophages specifically produce IFN-γ, TNF, and MIP-1ß by a CD3-dependent pathway. In this study, we also used a mouse model of BCG-induced pleurisy and demonstrated that CD3+ myeloid cells (TCRαß+ and TCRαß- cells) are increased at the infection sites during the acute phase (2 weeks post-infection). Interestingly, cell increment was mediated by tmTNF, and the soluble form of TNF was dispensable. BCG-infection also induced the expression of TNF receptor 2 on CD3+ myeloid cells, which increased after BCG-infection, suggesting that the tmTNF/TNFRs axis plays an important role in the presence or function of these cells in tuberculosis.

Liver Immune Cells Release Type 1 Interferon Due to DNA Sensing and Amplify Liver Injury from Acetaminophen Overdose.

Hepatocytes may rupture after a drug overdose, and their intracellular contents act as damage-associated molecular patterns (DAMPs) that lead to additional leukocyte infiltration, amplifying the original injury. Necrosis-derived DNA can be recognized as a DAMP, activating liver non-parenchymal cells (NPCs). We hypothesized that NPCs react to DNA by releasing interferon (IFN)-1, which amplifies acetaminophen (APAP)-triggered liver necrosis. We orally overdosed different knockout mouse strains to investigate the pathways involved in DNA-mediated amplification of APAP-induced necrosis. Mice were imaged under intravital confocal microscopy to estimate injury progression, and hepatocytes and liver NPCs were differentially isolated for gene expression assays. Flow cytometry (FACS) using a fluorescent reporter mouse estimated the interferon-beta production by liver leukocytes under different injury conditions. We also treated mice with DNase to investigate the role of necrosis DNA signaling in IFN-1 production. Hepatocytes released a large amount of DNA after APAP overdose, which was not primarily sensed by these cells. However, liver NPCs promptly sensed such environmental disturbances and activated several DNA sensing pathways. Liver NPCs synthesized and released IFN-1, which was associated with concomitant hepatocyte necrosis. Ablation of IFN-1 recognition in interferon α/ß receptor (IFNAR-/-) mice delayed APAP-mediated liver necrosis and dampened IFN-1 sensing pathways. We demonstrated a novel loop involving DNA recognition by hepatic NPCs and additional IFN-1 mediated hepatocyte death.

IL-33 signalling in liver immune cells enhances drug-induced liver injury and inflammation.

OBJECTIVE AND DESIGN: The aim of this study was to investigate the contribution of IL-33/ST2 axis in the onset and progression of acute liver injury using a mice model of drug-induced liver injury (DILI). MATERIAL AND TREATMENTS: DILI was induced by overdose administration of acetaminophen (APAP) by oral gavage in wild-type BALB/c, ST2-deficient mice and in different bone marrow chimeras. Neutrophils were depleted by anti-Ly6G and macrophages with clodronate liposomes (CLL). METHODS: Blood and liver were collected for biochemical, immunologic and genetic analyses. Mice were imaged by confocal intravital microscopy and liver non-parenchymal cells and hepatocytes were isolated for flow cytometry, genetic and immunofluorescence studies. RESULTS: Acetaminophen overdose caused a massive necrosis and accumulation of immune cells within the liver, concomitantly with IL-33 and chemokine release. Liver non-parenchymal cells were the major sensors for IL-33, and amongst them, neutrophils were the major players in amplification of the inflammatory response triggered by IL-33/ST2 signalling pathway. CONCLUSION: Blockage of IL-33/ST2 axis reduces APAP-mediated organ injury by dampening liver chemokine release and activation of resident and infiltrating liver non-parenchymal cells.

Stingray venom activates IL-33 producing cardiomyocytes, but not mast cell, to promote acute neutrophil-mediated injury.

One of the hallmarks of acute inflammation is neutrophil infiltration of tissues. We investigated molecular mechanisms implicated in acute neutrophilic inflammation induced by the venom of a freshwater stingray (Potamotrygon cf. henlei) in mice. Ray venom induced early mobilization of neutrophil in the microvasculature of cremaster mice and infiltration of the peritoneal cavity 2 hours after injury, in a dose-response manner. IL-1ß, IL-6, TNF-α, and KC were produced. The neutrophilic infiltration did not occur in mice with ST2 receptor and MyD88 adapters neutralized, or in those with PI3K and p38 MAPK signaling blocked. Drastic reduction of neutrophil infiltration to peritoneal cavities was observed in ST2-/-, TLR2/TLR4-/-, MyD88-/-, TRIF-/- and IL-17A-/- mice, and a partial reduction was observed in IL-18R-/- mice. Mast cell Kit W(sh)/W(sh)-, AHR-, NLRP3-, ICE-, IL-1ß-, P2RX7-, CD39-, IL-17RA-, and TBX21 KO mice retain the ability to induce neutrophilia in peritoneal cavity after ray venom injection. IL-6 and TNF-α alone were insufficient for promote neutrophilia in the absence of ST2 signaling. Finally, abundant production of IL-33 by cardiomyocytes was observed. These results refine our understanding of the importance of the IL-33/ST2 axis and IL-33-producing cardiomyocytes in the early acute neutrophilia induced by freshwater stingray venoms.

Neutrophils releasing IL-17A into NETs are essential to plasma cell differentiation in inflamed tissue dependent on IL-1R.

Interleukin (IL) 17A in chronic inflammation is also produced by innate immune cells as neutrophils. Mice with chronic humoral response induced by venom of Thalassophryne nattereri (VTn) proved to be a good tool for evaluating the impact of IL-17A on the development of long-lived plasma cells in the inflamed peritoneal cavity. Here, we report that VTn induces IL-17A production by neutrophils accumulating in the peritoneal cavity and triggers the extrusion of IL-17A along with neutrophil extracellular traps (NETs). Neutrophil depletion reduced the number of IL17A-producing cells in VTn-immunized mice and blocked the differentiation of long-lived plasma cells. Specific antibody production and survival of long-lived plasma cells was ablated in VTn-immunized mice deficient in CD4, while CD28 signaling had the opposite effect on differentiation of long-lived plasma cells. Further, maturation of long-lived plasma cells in inflamed peritoneal cavity was IL-1R1 and COX-2 dependent. Finally, when both the Raf-MEK-ERK pathway and the IL-17A or IL-1R1 activities were blocked, neutrophils were unable to promote the differentiation of memory B cells into long-lived plasma cells, confirming the essential role of neutrophils and IL-17A along with NETs in an IL-1/IL-1R-dependent manner as the novel helping partner for plasma cell differentiation in chronically inflamed tissues.

Tumor Necrosis Factor and Its Receptors Are Crucial to Control Mycobacterium bovis Bacillus Calmette-Guerin Pleural Infection in a Murine Model.

Tumor necrosis factor (TNF) is crucial to control Mycobacterium tuberculosis infection, which remains a leading cause of morbidity and mortality worldwide. TNF blockade compromises host immunity and may cause reactivation of latent infection, resulting in overt pulmonary, pleural, and extrapulmonary tuberculosis. Herein, we investigate the roles of TNF and TNF receptors in the control of Mycobacterium bovis bacillus Calmette-Guerin (BCG) pleural infection in a murine model. As controls, wild-type mice and those with a defective CCR5, a receptor that is crucial for control of viral infection but not for tuberculosis, were used. BCG-induced pleural infection was uncontrolled and progressive in absence of TNF or TNF receptor 1 (TNFR1)/TNFR2 (TNFR1R2) with increased inflammatory cell recruitment and bacterial load in the pleural cavity, and heightened levels of pleural and serum proinflammatory cytokines and chemokines, compared to wild-type control mice. The visceral pleura was thickened with chronic inflammation, which was prominent in TNF(-/-) and TNFR1R2(-/-) mice. The parietal pleural of TNF(-/-) and TNFR1R2(-/-) mice exhibited abundant inflammatory nodules containing mycobacteria, and these mice developed nonresolving inflammation and succumbed from disseminated BCG infection. By contrast, CCR5(-/-) mice survived and controlled pleural BCG infection as wild-type control mice. In conclusion, BCG-induced pleurisy was uncontrolled in the absence of TNF or TNF receptors with exacerbated inflammatory response, impaired bacterial clearance, and defective mesothelium repair, suggesting a critical role of TNF to control mycobacterial pleurisy.

Differential TLR2 downstream signaling regulates lipid metabolism and cytokine production triggered by Mycobacterium bovis BCG infection.

The nuclear receptor PPARγ acts as a key modulator of lipid metabolism, inflammation and pathogenesis in BCG-infected macrophages. However, the molecular mechanisms involved in PPARγ expression and functions during infection are not completely understood. Here, we investigate signaling pathways triggered by TLR2, the involvement of co-receptors and lipid rafts in the mechanism of PPARγ expression, lipid body formation and cytokine synthesis in macrophages during BCG infection. BCG induces NF-κB activation and increased PPARγ expression in a TLR2-dependent manner. Furthermore, BCG-triggered increase of lipid body biogenesis was inhibited by the PPARγ antagonist GW9662, but not by the NF-κB inhibitor JSH-23. In contrast, KC/CXCL1 production was largely dependent on NF-κB but not on PPARγ. BCG infection induced increased expression of CD36 in macrophages in vitro. Moreover, CD36 co-immunoprecipitates with TLR2 in BCG-infected macrophages, suggesting its interaction with TLR2 in BCG signaling. Pretreatment with CD36 neutralizing antibodies significantly inhibited PPARγ expression, lipid body formation and PGE2 production induced by BCG. Involvement of CD36 in lipid body formation was further confirmed by decreased BCG-induced lipid body formation in CD36 deficient macrophages. Similarly, CD14 and CD11b/CD18 blockage also inhibited BCG-induced lipid body formation, whereas TNF-α synthesis was not affected. Disruption of rafts recapitulates the latter result, inhibiting lipid body formation, but not TNF-α synthesis in BCG-infected macrophages. In conclusion, our results suggest that CD36-TLR2 cooperation and signaling compartmentalization within rafts, divert host response signaling through PPARγ-dependent and NF-κB-independent pathways, leading to increased macrophage lipid accumulation and down-modulation of macrophage response.

IL-22 modulates IL-17A production and controls inflammation and tissue damage in experimental dengue infection.

Dengue virus (DENV), a mosquito-borne flavivirus, is a public health problem in many tropical countries. IL-22 and IL-17A are key cytokines in several infectious and inflammatory diseases. We have assessed the contribution of IL-22 and IL-17A in the pathogenesis of experimental dengue infection using a mouse-adapted DENV serotype 2 strain (P23085) that causes a disease that resembles severe dengue in humans. We show that IL-22 and IL-17A are produced upon DENV-2 infection in immune-competent mice. Infected IL-22(-/-) mice had increased lethality, neutrophil accumulation and pro-inflammatory cytokines in tissues, notably IL-17A. Viral load was increased in spleen and liver of infected IL-22(-/-) mice. There was also more severe liver injury, as seen by increased transaminases levels and tissue histopathology. γδ T cells and NK cells are sources of IL-17A and IL-22, respectively, in liver and spleen. We also show that DENV-infected HepG2 cells treated with rhIL-22 had reduced cell death and decreased IL-6 production. IL-17RA(-/-) mice were protected upon infection and IL-17A-neutralizing-Ab-treatment partially reversed the phenotype observed in IL-22(-/-) -infected mice. We suggest that disrupting the balance between IL-22 and IL-17A levels may represent an important strategy to reduce inflammation and tissue injury associated with severe dengue infection.

GM-CSF priming drives bone marrow-derived macrophages to a pro-inflammatory pattern and downmodulates PGE2 in response to TLR2 ligands.

In response to pathogen recognition by Toll-like receptors (TLRs) on their cell surface, macrophages release lipid mediators and cytokines that are widely distributed throughout the body and play essential roles in host responses. Granulocyte macrophage colony-stimulating factor (GM-CSF) is important for the immune response during infections to improve the clearance of microorganisms. In this study, we examined the release of mediators in response to TLR2 ligands by bone marrow-derived macrophages (BMDMs) primed with GM-CSF. We demonstrated that when stimulated with TLR2 ligands, non-primed BMDMs preferentially produced PGE(2) in greater amounts than LTB(4). However, GM-CSF priming shifted the release of lipid mediators by BMDMs, resulting in a significant decrease of PGE(2) production in response to the same stimuli. The decrease of PGE(2) production from primed BMDMs was accompanied by a decrease in PGE-synthase mRNA expression and an increase in TNF-α and nitric oxide (NO) production. Moreover, some GM-CSF effects were potentiated by the addition of IFN-γ. Using a variety of TLR2 ligands, we established that PGE(2) release by GM-CSF-primed BMDMs was dependent on TLR2 co-receptors (TLR1, TLR6), CD14, MyD88 and the nuclear translocation of NFκB but was not dependent on peroxisome proliferator-activated receptor-γ (PPAR-γ) activation. Indeed, GM-CSF priming enhanced TLR2, TLR4 and MyD88 mRNA expression and phospho-IκBα formation. These findings demonstrate that GM-CSF drives BMDMs to present a profile relevant to the host during infections.

NLRP3 inflammasome-mediated neutrophil recruitment and hypernociception depend on leukotriene B(4) in a murine model of gout.

OBJECTIVE: Deposition of monosodium urate monohydrate (MSU) crystals in the joints promotes an intense inflammatory response and joint dysfunction. This study evaluated the role of the NLRP3 inflammasome and 5-lipoxygenase (5-LOX)-derived leukotriene B(4) (LTB(4) ) in driving tissue inflammation and hypernociception in a murine model of gout. METHODS: Gout was induced by injecting MSU crystals into the joints of mice. Wild-type mice and mice deficient in NLRP3, ASC, caspase 1, interleukin-1ß (IL-1ß), IL-1 receptor type I (IL-1RI), IL-18R, myeloid differentiation factor 88 (MyD88), or 5-LOX were used. Evaluations were performed to assess neutrophil influx, LTB(4) activity, cytokine (IL-1ß, CXCL1) production (by enzyme-linked immunosorbent assay), synovial microvasculature cell adhesion (by intravital microscopy), and hypernociception. Cleaved caspase 1 and production of reactive oxygen species (ROS) were analyzed in macrophages by Western blotting and fluorometric assay, respectively. RESULTS: Injection of MSU crystals into the knee joints of mice induced neutrophil influx and neutrophil-dependent hypernociception. MSU crystal-induced neutrophil influx was CXCR2-dependent and relied on the induction of CXCL1 in an NLRP3/ASC/caspase 1/IL-1ß/MyD88-dependent manner. LTB(4) was produced rapidly after injection of MSU crystals, and this was necessary for caspase 1-dependent IL-1ß production and consequent release of CXCR2-acting chemokines in vivo. In vitro, macrophages produced LTB(4) after MSU crystal injection, and LTB(4) was relevant in the MSU crystal-induced maturation of IL-1ß. Mechanistically, LTB(4) drove MSU crystal-induced production of ROS and ROS-dependent activation of the NLRP3 inflammasome. CONCLUSION: These results reveal the role of the NLRP3 inflammasome in mediating MSU crystal-induced inflammation and dysfunction of the joints, and highlight a previously unrecognized role of LTB(4) in driving NLRP3 inflammasome activation in response to MSU crystals, both in vitro and in vivo.

Platelet-activating factor receptor is essential for the development of experimental cerebral malaria.

Cerebral malaria is a severe form of the disease that may result, in part, from an overt inflammatory response during infection by Plasmodium falciparum. The understanding of the pathogenesis of cerebral malaria may aid in the development of better therapeutic strategies for patients. The immune response in cerebral malaria involves elevation of circulating levels of cytokines and chemokines associated with leukocyte accumulation and breakdown of the blood-brain barrier in the central nervous system. Platelet-activating factor (PAF) is a mediator of inflammation shown to orchestrate inflammatory processes, including recruitment of leukocytes and increase of vascular permeability. Using mice lacking the PAF receptor (PAFR(-/-)), we investigated the relevance of this molecule for the outcome and the neuroinflammatory process triggered by P. berghei ANKA, an experimental model of cerebral malaria. In PAFR(-/-) mice, lethality was markedly delayed and brain inflammation was significantly reduced, as demonstrated by histology, accumulation, and activation of CD8(+) T cells, changes in vascular permeability and activation of caspase-3 on endothelial cells and leukocytes. Similarly, treatment with the PAFR antagonist UK-74,505 delayed lethality. Taken together, the results suggest that PAFR signaling is crucial for the development of experimental cerebral malaria. Mechanistically, PAFR activation is crucial for the cascade of events leading to changes in vascular permeability, accumulation, and activation of CD8(+) T cells and apoptosis of leukocytes and endothelial cells.

TLR2-dependent mast cell activation contributes to the control of Mycobacterium tuberculosis infection.

Mast Cells (MCs) express toll-like receptor 2 (TLR2), a receptor known to be triggered by several major mycobacterial ligands and involved in resistance against Mycobacterium tuberculosis (MTB) infection. This study investigated whether adoptive transfer of TLR2 positive MCs (TLR2(+/+)) corrects the increased susceptibility of TLR2(-/-) mice to MTB infection. TLR2(-/-) mice displayed increased mycobacterial burden, diminished myeloid cell recruitment and proinflammatory cytokine production accompanied by defective granuloma formation. The reconstitution of these mice with TLR2(+/+) MCs, but not TLR2(-/-), confers better control of the infection, promotes the normalization of myeloid cell recruitment associated with reestablishment of the granuloma formation. In addition, adoptive transfer of TLR2(+/+) MC to TLR2(-/-) mice resulted in regulation of the pulmonary levels of IL-beta, IL-6, TNF-alpha, enhanced Th1 response and activated CD8(+) T cell homing to the lungs. Our results suggest that activation of MCs via TLR2 is required to compensate the defect in protective immunity and inability of TLR2(-/-) mice to control MTB infection.