Myeloid Differentiation Factor 88 Deficiency Research Articles

MyD88-dependent signaling in non-parenchymal cells promotes liver carcinogenesis.

In Western countries, a rising incidence of obesity and type 2 diabetes correlates with an increase of non-alcoholic steatohepatitis (NASH)-a major risk factor for liver cirrhosis and hepatocellular carcinoma (HCC). NASH is associated with chronic liver injury, triggering hepatocyte death and enhanced translocation of intestinal bacteria, leading to persistent liver inflammation through activation of Toll-like receptors and their adapter protein myeloid differentiation factor 88 (MyD88). Therefore, we investigated the role of MyD88 during progression from NASH to HCC using a mouse model of chronic liver injury (hepatocyte-specific deletion of nuclear factor κB essential modulator, Nemo; NemoΔhepa). NemoΔhepa; NemoΔhepa/MyD88-/- and NemoΔhepa/MyD88Δhepa were generated and the impact on liver disease progression was investigated. Ubiquitous MyD88 ablation (NemoΔhepa/MyD88-/-) aggravated the degree of liver damage, accompanied by an overall decrease in inflammation, whereas infiltrating macrophages and natural killer cells were elevated. At a later stage, MyD88 deficiency impaired HCC formation. In contrast, hepatocyte-specific MyD88 deletion (NemoΔhepa/MyD88Δhepa) did not affect disease progression. These results suggest that signaling of Toll-like receptors through MyD88 in non-parenchymal liver cells is required for carcinogenesis during chronic liver injury. Hence, blocking MyD88 signaling may offer a therapeutic option to prevent HCC formation in patients with NASH.

MyD88 controls airway epithelial Muc5ac expression during TLR activation conditions from agricultural organic dust exposure.

Inflammation from airborne microbes can overwhelm compensatory mucociliary clearance mechanisms, leading to mucous cell metaplasia. Toll-like receptor (TLR) activation via myeloid differentiation factor 88 (MyD88) signaling is central to pathogen responses. We have previously shown that agricultural organic dust extract (ODE), with abundant microbial component diversity, activates TLR-induced airway inflammation. With the use of an established model, C57BL/6J wild-type (WT) and global MyD88 knockout (KO) mice were treated with intranasal inhalation of ODE or saline, daily for 1 wk. ODE primarily increased mucin (Muc)5ac levels relative to Muc5b. Compared with ODE-challenged WT mice, ODE-challenged, MyD88-deficient mice demonstrated significantly increased Muc5ac immunostaining, protein levels by immunoblot, and expression by quantitative PCR. The enhanced Muc5ac levels in MyD88-deficient mice were not explained by differences in the differentiation program of airway secretory cells in naïve mice. Increased Muc5ac levels in MyD88-deficient mice were also not explained by augmented inflammation, IL-17A, or neutrophil elastase levels. Furthermore, the enhanced airway mucins in the MyD88-deficient mice were not due to defective secretion, as the mucin secretory capacity of MyD88-KO mice remained intact. Finally, ODE-induced Muc5ac levels were enhanced in MyD88-deficient airway epithelial cells in vitro. In conclusion, MyD88 deficiency enhances airway mucous cell metaplasia under environments with high TLR activation.

Innate immune adaptor TRIF deficiency accelerates disease progression of ALS mice with accumulation of aberrantly activated astrocytes

There is compelling evidence that glial-immune interactions contribute to the progression of neurodegenerative diseases. The adaptive immune response has been implicated in disease processes of amyotrophic lateral sclerosis (ALS), but it remains unknown if innate immune signaling also contributes to ALS progression. Here we report that deficiency of the innate immune adaptor TIR domain-containing adaptor inducing interferon-β (TRIF), which is essential for certain Toll-like receptor (TLR) signaling cascades, significantly shortens survival time and accelerates disease progression of ALS mice. While myeloid differentiation factor 88 (MyD88) is also a crucial adaptor for most TLR signaling pathways, MyD88 deficiency had only a marginal impact on disease course. Moreover, TRIF deficiency reduced the number of natural killer (NK), NK-T-lymphocytes, and CD8-T cells infiltrating into the spinal cord of ALS mice, but experimental modulation of these populations did not substantially influence survival time. Instead, we found that aberrantly activated astrocytes expressing Mac2, p62, and apoptotic markers were accumulated in the lesions of TRIF-deficient ALS mice, and that the number of aberrantly activated astrocytes was negatively correlated with survival time. These findings suggest that TRIF pathway plays an important role in protecting a microenvironment surrounding motor neurons by eliminating aberrantly activated astrocytes.

General, but not myeloid or type II lung epithelial cell, myeloid differentiation factor 88 deficiency abrogates house dust mite induced allergic lung inflammation

Asthma is a highly prevalent chronic allergic inflammatory disease of the airways affecting people worldwide. House dust mite (HDM) is the most common allergen implicated in human allergic asthma. HDM-induced allergic responses are thought to depend upon activation of pathways involving Toll-like receptors and their adaptor protein myeloid differentiation factor 88 (MyD88). We sought here to determine the role of MyD88 in myeloid and type II lung epithelial cells in the development of asthma-like allergic disease using a mouse model. Repeated exposure to HDM caused allergic responses in control mice characterized by influx of eosinophils into the bronchoalveolar space and lung tissue, lung pathology and mucus production and protein leak into bronchoalveolar lavage fluid. All these responses were abrogated in mice with a general deficiency of MyD88 but unaltered in mice with MyD88 deficiency, specifically in myeloid or type II lung epithelial cells. We conclude that cells other than myeloid or type II lung epithelial cells are responsible for MyD88-dependent HDM-induced allergic airway inflammation.

Differential Effect of MyD88 Signal in Donor T Cells on Graft-versus-Leukemia Effect and Graft-versus-Host Disease after Experimental Allogeneic Stem Cell Transplantation.

Despite the presence of toll like receptor (TLR) expression in conventional TCRαβ T cells, the direct role of TLR signaling via myeloid differentiation factor 88 (MyD88) within T lymphocytes on graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) effect after allogeneic stem cell transplantation (allo-SCT) remains unknown. In the allo-SCT model of C57BL/6 (H-2b) → B6D2F1 (H-2b/d), recipients received transplants of wild type (WT) T-cell-depleted (TCD) bone marrow (BM) and splenic T cells from either WT or MyD88 deficient (MyD88KO) donors. Host-type (H-2d) P815 mastocytoma or L1210 leukemia cells were injected either subcutaneously or intravenously to generate a GVHD/GVL model. Allogeneic recipients of MyD88KO T cells demonstrated a greater tumor growth without attenuation of GVHD severity. Moreover, GVHD-induced GVL effect, caused by increasing the conditioning intensity was also not observed in the recipients of MyD88KO T cells. In vitro, the absence of MyD88 in T cells resulted in defective cytolytic activity to tumor targets with reduced ability to produce IFN-γ or granzyme B, which are known to critical for the GVL effect. However, donor T cell expansion with effector and memory T-cell differentiation were more enhanced in GVHD hosts of MyD88KO T cells. Recipients of MyD88KO T cells experienced greater expansion of Foxp3- and IL4-expressing T cells with reduced INF-γ producing T cells in the spleen and tumor-draining lymph nodes early after transplantation. Taken together, these results highlight a differential role for MyD88 deficiency on donor T-cells, with decreased GVL effect without attenuation of the GVHD severity after experimental allo-SCT.

Abstract 11888: MyD88 Expressed by Myeloid Cells is Essential for Angiotensin II-Induced Vascular Dysfunction, Inflammation and Arterial Hypertension

Background: Angiotensin II (ATII) causes hypertension and promotes infiltration of inflammatory cells into the vessel wall. Vascular superoxide formation and shear stress mediated inflammatory remodeling of conduit arteries was shown to be myeloid differentiation factor 88 (MyD88) dependent, but the exact mechanism are unknown. Objective: The goal of this study was to determine the mechanism, how MyD88 contributes to the development of ATII-induced vascular dysfunction and arterial hypertension. Methods and Results: MyD88 deficiency profoundly attenuated ATII-induced (1 mg/kg/d for 7 days) blood pressure increase (measured by radio telemetry) and vascular dysfunction (assessed by aortic ring relaxation studies). Additionally vascular superoxide levels as well as mRNA expression levels of VCAM-1, iNOS, Nox2 were decreased in ATII-infused MyD88 -/- mice compared to WT controls. Aortic flow cytometric analysis revealed that ATII-induced infiltration with CD11b + Ly6C high inflammatory monocytes was significantly dampened in MyD88 -/- mice. ATII led to an increased expression of inflammatory monocyte markers in blood and aorta, which was blocked in MyD88 -/- mice, indicating a role of MyD88 for myeloid cell differentiation. Additionally less IFN-gamma + NK cells were detected in the vessel wall of ATII-treated MyD88 -/- mice and aortic lysates showed reduced mRNA levels of several proinflammatory cytokines like IL-12 and IL-1beta. Bone marrow transfer experiments further revealed a protective effect of MyD88 deficiency in inflammatory cells represented by a reduction of vascular dysfunction and inflammation. Conclusion: We provide first evidence that MyD88 expressed by bone marrow-derived cells plays an essential role in ATII-induced vascular dysfunction and arterial hypertension. Our data indicate that MyD88 is important for cytokine production and might be required for ATII-induced differentiation of monocytes into an inflammatory phenotype.

MyD88 Is Dispensable for Cerebral Amyloidosis and Neuroinflammation in APP/PS1 Transgenic Mice

Activated microglia are associated with amyloid plaques in transgenic mouse models of cerebral amyloidosis and in human Alzheimer disease; yet, their implication in Alzheimer disease pathogenesis remains unclear. It has been suggested that microglia play dual roles depending on the context of activation,contributing negatively to disease pathogenesis by secreting proinflammatory innate cytokines or performing a beneficial role via phagocytosis of amyloid beta (Aβ) deposits. Toll-like receptors, most of which signal through the adaptor protein myeloid differentiation factor 88 (MyD88), have been suggested as candidate Aβ innate pattern recognition receptors. It was recently reported that MyD88 deficiency reduced brain amyloid pathology and microglial activation. To assess a putative role of MyD88 in cerebral amyloidosis and glial activation in APPswe/PS1ΔE9 (APP/PS1) mice, we crossed MyD88-deficient (MyD88(-/-)) mice with APP/PS1 mice, interbred first filial offspring, and studied APP/PS1 MyD88(+/+), APP/PS1 MyD88(+/-), and APP/PS1 MyD88(-/-) cohorts. Biochemical analysis of detergent-soluble and detergent-insoluble Aβ1-40 or Aβ1-42 in brain homogenates did not reveal significant between-group differences. Furthermore, no significant differences were observed on amyloid plaque load or soluble fibrillar Aβ by quantitative immunohistochemical analysis. In addition, neither activated microglia nor astrocytes differed among the three groups. These data suggest that MyD88 signaling is dispensable for Aβ-induced glial activation and does not significantly affect the nature or extent of cerebral β-amyloidosis in APP/PS1 mice.

Relevance of the myeloid differentiation factor 88 (MyD88) on RANKL, OPG, and nod expressions induced by TLR and IL-1R signaling in bone marrow stromal cells.

The myeloid differentiation factor 88 (MyD88) plays a pivotal role in Toll-like receptor (TLR)- and interleukin-1 receptor (IL-1R)-induced osteoclastogenesis. We examined the role of MyD88 on p38 mitogen-activated protein kinase (MAPK) and nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) activation and nucleotide-binding oligomerization domain (Nod) induction by lipopolysaccharide (LPS) and IL-1 beta, and their effect on receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) production in bone marrow stromal cell (BMSC). RANKL, Nod1, Nod2, NF-κB, and p38 protein levels were determined by Western blot. Nod2 was stimulated with muramyl dipeptide (MDP) prior to TLR4 stimulation with LPS. MyD88 deficiency markedly inhibited RANKL expression after LPS stimulation and increased OPG messenger RNA (mRNA) production. Also, MyD88 was necessary for NF-κB and p38 MAPK activation. MDP alone did not induce RANKL and OPG expressions; however, when combined with LPS, their expressions were significantly increased (p < 0.05). Our results support that MyD88 signaling has a pivotal role in osteoclastogenesis thought NF-κB and p38 activation. Nod2 and especially Nod1 levels were influenced by MyD88.

Clinical Features and Outcome of Patients With IRAK-4 and MyD88 Deficiency

C Picard, H von Bernuth, P Ghandil. Medicine (Baltimore). 2010;89(6):403–425 To describe the clinical features and outcomes of patients with autosomal recessive defects in the interleukin 1 receptor-associated kinase 4 (IRAK-4) and the myeloid differentiation factor 88 (MyD88). The authors provided the cumulative data of 48 patients with IRAK-4 deficiency and 12 patients with MyD88 deficiency from 37 kindreds in 15 countries. The data for this report were collected on the basis of a detailed questionnaire filled out by the physician who cared for the enrolled patient. The leading threat to these patients was invasive pneumococcal disease, which was seen …

MyD88 Deficiency Attenuates Angiotensin II-Induced Abdominal Aortic Aneurysm Formation Independent of Signaling Through Toll-Like Receptors 2 and 4

The purpose of this study was to determine whether myeloid differentiation factor 88 (MyD88) and its related Toll-like receptors (TLRs) 2 and 4 contributed to the development of angiotensin II (AngII)-induced abdominal aortic aneurysms (AAAs) and atherosclerosis. AngII was infused into either apoE(-/-) or LDL receptor (LDLR)(-/-) male mice that were either MyD88(+/+) or (-/-). MyD88 deficiency profoundly reduced AngII-induced AAAs and atherosclerosis in both strains. To define whether deficiency of specific TLRs had similar effects, AngII was infused into LDLR(-/-) mice that were also deficient in either TLR2 or TLR4. TLR2 deficiency had no effect on AAA development but inhibited atherosclerosis. In contrast, TLR4 deficiency attenuated both AAAs and atherosclerosis. To resolve whether MyD88 and TLR4 exerted their effects through cells of hematopoietic lineage, LDLR(-/-) mice were lethally irradiated and repopulated with bone marrow-derived cells from either MyD88 or TLR4 strains. MyD88 deficiency in bone marrow-derived cells profoundly reduced both AngII-induced AAAs and atherosclerosis. However, TLR4 deficiency in bone marrow-derived cells had no effect on either pathology. These studies demonstrate that MyD88 deficiency in leukocytes profoundly reduces AngII-induced AAAs and atherosclerosis via mechanisms independent of either TLR2 or TLR4.

Myeloid differentiation factor 88-deficient bone marrow cells improve Alzheimer’s disease-related symptoms and pathology

Alzheimer's disease is characterized by extracellular deposits of amyloid β peptide in the brain. Increasing evidence suggests that amyloid β peptide injures neurons both directly and indirectly by triggering neurotoxic innate immune responses. Myeloid differentiation factor 88 is the key signalling molecule downstream to most innate immune receptors crucial in inflammatory activation. For this reason, we investigated the effects of myeloid differentiation factor 88-deficient bone marrow cells on Alzheimer's disease-related symptoms and pathology by establishing bone marrow chimeric amyloid β peptide precursor transgenic mice, in which bone marrow cells differentiate into microglia and are recruited to amyloid β peptide deposits. We observed that myeloid differentiation factor 88-deficient bone marrow reconstruction reduced both inflammatory activation and amyloid β peptide burden in the brain. In addition, synaptophysin, a marker of neuronal integrity, was preserved and the expression of neuronal plasticity-related genes, ARC and NMDA-R1, was increased. Thus, myeloid differentiation factor 88-deficient microglia significantly improved the cognitive function of amyloid β peptide precursor protein transgenic mice. Myeloid differentiation factor 88-deficiency enhanced amyloid β peptide phagocytosis by microglia/macrophages and blunted toxic inflammatory activation. Both the expression of amyloid β peptide precursor protein and amyloid β peptide degrading enzymes and also the efflux of amyloid β peptide from brain parenchyma were unaffected by myeloid differentiation factor 88-deficient microglia. By contrast, the activity of β-secretase was increased. β-Secretase is expressed primarily in neurons, with relatively little expression in astrocytes and microglia. Therefore, microglial replenishment with myeloid differentiation factor 88-deficient bone marrow cells might improve cognitive functions in Alzheimer's disease mouse models by enhancing amyloid β peptide phagocytosis and reducing inflammatory activation. These results could offer a new therapeutic option that might delay the progression of Alzheimer's disease.

Nucleotide-binding oligomerization domain 2 and Toll-like receptor 2 function independently in a murine model of arthritis triggered by intraarticular peptidoglycan

Blau syndrome is an autoinflammatory disease resulting from mutations in the NOD2 gene, wherein granulomatous arthritis, uveitis, and dermatitis develop. The mechanisms by which aberrant NOD2 causes joint inflammation are poorly understood. Indeed, very few studies have addressed the function of nucleotide-binding oligomerization domain 2 (NOD-2) in the joint. This study was undertaken to investigate NOD-2 function in an experimental model of arthritis and to explore the potential interplay between Toll-like receptor 2 (TLR-2) and NOD-2 in joint inflammation. Mice deficient in TLR-2, myeloid differentiation factor 88 (MyD88), or NOD-2 and their wild-type controls were given an intraarticular injection of muramyl dipeptide (MDP), peptidoglycan (PG; a metabolite of which is MDP), or palmitoyl-3-cysteine-serine-lysine-4 (Pam(3)CSK(4)), a synthetic TLR-2 agonist. Joint inflammation was assessed by near-infrared fluorescence imaging and histologic analysis. Locally administered PG resulted in joint inflammation, which was markedly reduced in mice deficient in either TLR-2 or the TLR signaling mediator MyD88. In addition to TLR-2 signaling events, NOD-2 mediated joint inflammation, as evidenced by the fact that mice deficient in NOD-2 showed significantly reduced PG-induced arthritis. TLR-2 or MyD88 deficiency did not influence arthritis induced by the specific NOD-2 agonist MDP. In addition, NOD-2 deficiency did not alter the TLR-2-dependent joint inflammation elicited by the synthetic TLR-2 agonist Pam(3)CSK(4). Whereas NOD-2 and TLR-2 are both critical for the development of PG-induced arthritis, they appear to elicit inflammation independently of each other. Our findings indicate that NOD-2 plays an inflammatory role in arthritis.

Bone marrow-derived immune cells mediate sensitization to liver injury in a myeloid differentiation factor 88-dependent fashion.

Toll-like receptors (TLRs) expressed on both immune cells and hepatocytes recognize microbial danger signals and regulate immune responses. Previous studies showed that TLR9 and TLR2 mediate Propionibacterium acnes-induced sensitization to lipopolysaccharide-triggered acute liver injury in mice. Ligand-specific activation of TLR2 and TLR9 are dependent on the common TLR adaptor, myeloid differentiation factor 88 (MyD88). Here, we dissected the role of MyD88 in parenchymal and bone marrow (BM)-derived cells in liver sensitization. Using chimeric mice with green fluorescent protein-expressing BM cells, we identified that P. acnes-induced liver inflammatory foci are of BM origin. Chimeras with MyD88-deficient BM showed no inflammatory foci after P. acnes or TLR2+TLR9 challenge, suggesting that recruitment of inflammatory cells to the liver required MyD88 expression in BM-derived cells. Further, selective MyD88 deficiency in parenchymal cells in mice with wild-type BM failed to prevent inflammatory cell infiltration. These results demonstrate that MyD88 in immune cells rather than in liver parenchymal cells plays an important role in inflammatory cell recruitment and liver injury.

The critical role of toll-like receptor (TLR) 4 in alcoholic liver disease is independent of the common TLR adapter MyD88.

The Toll-like receptor 4 (TLR4) that recognizes endotoxin, a trigger of inflammation in alcoholic liver disease (ALD), activates two signaling pathways utilizing different adapter molecules: the common TLR adapter, myeloid differentiation factor 88 (MyD88), or Toll/interleukin immune-response-domain-containing adaptor inducing interferon (IFN)-beta. The MyD88 pathway induces proinflammatory cytokine activation, a critical mediator of ALD. Here we evaluated the role of MyD88 in alcohol-induced liver injury in wild-type, TLR2-deficient, TLR4-deficient, or MyD88-deficient (knockout [KO]) mice after administration of the Lieber-De-Carli diet (4.5% volume/volume ethanol) or an isocaloric liquid control diet for 5 weeks. Alcohol feeding resulted in a significant increase in serum alanine aminotransferase levels, liver steatosis and triglyceride levels suggesting liver damage in WT, TLR2-KO, and MyD88-KO but not in TLR4-KO mice. Expression of inflammatory mediators (tumor necrosis factor-alpha and interleukin-6) and TLR4 coreceptors (CD14 and MD2) was significantly higher in livers of alcohol-fed WT, TLR2-KO, or MyD88-KO, but not in TLR4-KO mice, compared to controls. Reactive oxygen radicals produced by cytochrome P450 and the nicotinamide adenine dinucleotide phosphate complexes contribute to alcoholic liver damage. Alcohol feeding-induced expression and activation of cytochrome P450 and the nicotinamide adenine dinucleotide phosphate complex were prevented by TLR4-deficiency but not by MyD88-deficiency. Liver expression of interferon regulatory factor 3 (IRF3), a MyD88-independent signaling molecule, was not affected by chronic alcohol treatment in whole livers of WT mice or in any of the KO mice. However, the induction of IRF7, an IRF3-inducible gene, was found in Kupffer cells of alcohol-fed WT mice. Alcohol feeding also induced nuclear factor-kappaB activation in a TLR4-dependent MyD88-independent manner. While TLR4 deficiency was protective, MyD88 deficiency failed to prevent alcohol-induced liver damage and inflammation. These results suggest that the common TLR adapter, MyD88, is dispensable in TLR4-mediated liver injury in ALD.

Double-stranded RNAs from the Helminth Parasite Schistosoma Activate TLR3 in Dendritic Cells

Stimulation of dendritic cells (DCs) by the egg stage of the helminth parasite Schistosoma mansoni activates a signaling pathway resulting in type I interferon (IFN) and IFN-stimulated gene (ISG) expression. Here, we demonstrate that S. mansoni eggs disjointedly activate myeloid differentiation factor 88 (MyD88)-dependent and MyD88-independent pathways in DCs. Inflammatory cytokine expression and NF-kappa B activation in DCs from MyD88-deficient mice were impaired, whereas signaling transducer activator of transcription (STAT) 1(Tyr701) phosphorylation and ISG expression were intact in MyD88 or Toll-like receptor (TLR)4-deficient counterparts. Accordingly, we analyzed distinct TLR members for their ability to respond to schistosome eggs and established that TLR3 resulted in the activation of NF-kappa B and the positive regulatory domain III-I site from IFN-beta promoter. Unexpectedly, egg-derived RNA possessed RNase A-resistant and RNase III-sensitive structures capable of triggering TLR3 activation, suggesting the involvement of double-stranded (ds) structures. Moreover, DCs from TLR3-deficient mice displayed a complete loss of signaling transducer activator of transcription 1 phosphorylation and ISG expression in response to egg-derived dsRNA. Finally, TLR3-deficient DCs showed a reduced response to schistosome eggs relative to wild-type cells. Collectively, our data suggest for the first time that dsRNA from a non-viral pathogen may act as an inducer of the innate immune system through TLR3.

MyD88 is required for mounting a robust host immune response to Streptococcus pneumoniae in the CNS.

Myeloid differentiation factor 88 (MyD88) is an essential intracellular signal transducer in Toll-like receptor (TLR) and interleukin (IL)-1 receptor family member-mediated cell activation. In order to characterize the role of MyD88 in pneumococcal meningitis we used gene-targeted mice lacking functional MyD88 expression. At 24 h after intracisternal infection, MyD88- deficient mice displayed a markedly diminished inflammatory host response in the CNS, as evidenced by reduced CSF pleocytosis and expression of cytokines, chemokines and complement factors. The reduced CNS inflammation was paralleled by a marked reduction in the prognostic relevant CNS complications, such as brain oedema formation. Nevertheless, MyD88 deficiency was associated with a worsening of disease which seemed to be attributable to severe bacteraemia. This notion was supported by the unexpected observation that infected MyD88-deficient mice displayed enhanced mRNA expression of inflammatory mediators [such as the proinflammatory cytokine tumour necrosis factor alpha (TNF-alpha) and the CXC chemokine macrophage inflammatory protein (MIP-2)] in the lung and consequently increased cell influx in the bronchoalveolar lavage fluid, compared with infected wild-type mice. Thus, the present study demonstrated for the first time an important role of MyD88 in immune activation to bacterial pathogens within the CNS. The role played by MyD88 in mounting an immune response to Streptococcus pneumoniae, however, seems to be dependent on the anatomical compartment involved.

Cutting edge: myeloid differentiation factor 88 deficiency improves resistance against sepsis caused by polymicrobial infection.

Toll-like receptors (TLRs) are important for the activation of innate immune cells upon encounter of microbial pathogens. The present study investigated the potential roles of TLR2, TLR4, and the signaling protein myeloid differentiation factor 88 (MyD88) in polymicrobial septic peritonitis. Whereas both TLR2 and TLR4 were dispensable for host defense against septic peritonitis, MyD88-deficient mice were protected in this infection model. Recruitment of neutrophils to the septic focus and bacterial clearance were normal in MyD88-deficient mice. In contrast, the systemic inflammatory response was strongly attenuated in the absence of MyD88. Surprisingly, MyD88 deficiency did not alter cytokine and chemokine production in spleen, but markedly reduced the inflammatory response in liver and lung. Production of monocyte chemoattractant protein-1 and macrophage-inflammatory protein-1alpha was entirely independent of MyD88. These results imply a central role of MyD88 for the systemic immune pathology of polymicrobial sepsis and show that cytokine production in spleen and induction of certain chemokines are MyD88 independent.