The Pglyrp1-Regulated Microbiome Enhances Experimental Allergic Asthma.

Changes in intestinal or respiratory microbiomes in infants correlate with increased incidence of asthma, but the causative role of microbiome in the susceptibility to asthma and the host genes that regulate these changes in microbiome are mostly unknown. In this study, we show that decreased responsiveness to allergic asthma in Pglyrp1 -/- mice (lacking bactericidal peptidoglycan recognition protein 1) could be transferred to germ-free wild-type mice by colonization of mothers and newborns with microbiota from Pglyrp1 -/- mice. These colonized mice had decreased airway resistance and fewer inflammatory cells, less severe histopathology, and lower levels of IgE and proallergic cytokines and chemokines in the lungs. This microbiome-dependent decreased responsiveness to asthma was most pronounced in colonized germ-free BALB/c mice (genetically predisposed to asthma), only partially evident in outbred germ-free Swiss Webster mice, and marginal in conventional BALB/c mice following depletion of microbiome with antibiotics. Mice with a low asthmatic response colonized with microbiota from Pglyrp1 -/- mice had increased abundance of Bacteroidetes and decreased abundance of Firmicutes, Tenericutes, Deferribacteres, and Spirochaetes in the feces and increased abundance of Pasteurella in the oropharynx. These changes in bacterial abundance in the feces and oropharynx correlated with lower asthmatic responses in the lungs. Thus, our results show that Pglyrp1 enhances allergic asthmatic responses primarily through its effect on the host intestinal microbiome and identify several bacteria that may increase or decrease sensitivity to asthma. This effect of microbiome is strong in asthma-prone BALB/c mice and weak in asthma-resistant outbred mice and requires germ-free conditions before colonization with microbiota from Pglyrp1 -/- mice.

Bactericidal peptidoglycan recognition protein induces oxidative stress in Escherichia coli through a block in respiratory chain and increase in central carbon catabolism.

Mammalian Peptidoglycan Recognition Proteins (PGRPs) kill both Gram-positive and Gram-negative bacteria through simultaneous induction of oxidative, thiol and metal stress responses in bacteria. However, metabolic pathways through which PGRPs induce these bactericidal stress responses are unknown. We screened Keio collection of Escherichia coli deletion mutants and revealed that deleting genes for respiratory chain flavoproteins or for tricarboxylic acid (TCA) cycle resulted in increased resistance of E. coli to PGRP killing. PGRP-induced killing depended on the production of hydrogen peroxide, which required increased supply of NADH for respiratory chain oxidoreductases from central carbon catabolism (glycolysis and TCA cycle), and was controlled by cAMP-Crp. Bactericidal PGRP induced a rapid decrease in respiration, which suggested that the main source of increased production of hydrogen peroxide was a block in respiratory chain and diversion of electrons from NADH oxidoreductases to oxygen. CpxRA two-component system was a negative regulator of PGRP-induced oxidative stress. By contrast, PGRP-induced thiol stress (depletion of thiols) and metal stress (increase in intracellular free Zn2+ through influx of extracellular Zn2+ ) were mostly independent of oxidative stress. Thus, manipulating pathways that induce oxidative, thiol and metal stress in bacteria could be a useful strategy to design new approaches to antibacterial therapy.

How innate immunity proteins kill bacteria and why they are not prone to resistance.

Recent advances on antibacterial activity of peptidoglycan recognition proteins (PGRPs) offer some insight into how innate immunity has retained its antimicrobial effectiveness for millions of years with no frequent emergence of resistant strains. First, PGRP can bind to multiple components of bacterial envelope (peptidoglycan, lipoteichoic acid, and lipopolysaccharide). Second, PGRP simultaneously induces oxidative, thiol, and metal stress responses in bacteria, which individually are bacteriostatic, but in combination are bactericidal. Third, PGRP induces oxidative, thiol, and metal stress responses in bacteria through three independent pathways. Fourth, antibacterial effects of PGRP are enhanced by other innate immune responses. Thus, emergence of PGRP resistance is prevented by bacteriostatic effect and independence of each PGRP-induced stress response, as PGRP resistance would require simultaneous acquisition of three separate mechanisms disabling the induction of all three stress responses. By contrast, each antibiotic has one primary target and one primary antibacterial mechanism, and for this reason resistance to antibiotics can be generated by inhibition of this primary mechanism. Manipulating bacterial metabolic responses can enhance bacterial killing by antibiotics and elimination of antibiotic-tolerant bacteria, but such manipulations do not overcome genetically encoded antibiotic resistance. Pathogens cause infections by evading, inhibiting, or subverting host immune responses.

Peptidoglycan recognition proteins kill bacteria by inducing oxidative, thiol, and metal stress.

Mammalian Peptidoglycan Recognition Proteins (PGRPs) are a family of evolutionary conserved bactericidal innate immunity proteins, but the mechanism through which they kill bacteria is unclear. We previously proposed that PGRPs are bactericidal due to induction of reactive oxygen species (ROS), a mechanism of killing that was also postulated, and later refuted, for several bactericidal antibiotics. Here, using whole genome expression arrays, qRT-PCR, and biochemical tests we show that in both Escherichia coli and Bacillus subtilis PGRPs induce a transcriptomic signature characteristic of oxidative stress, as well as correlated biochemical changes. However, induction of ROS was required, but not sufficient for PGRP killing. PGRPs also induced depletion of intracellular thiols and increased cytosolic concentrations of zinc and copper, as evidenced by transcriptome changes and supported by direct measurements. Depletion of thiols and elevated concentrations of metals were also required, but by themselves not sufficient, for bacterial killing. Chemical treatment studies demonstrated that efficient bacterial killing can be recapitulated only by the simultaneous addition of agents leading to production of ROS, depletion of thiols, and elevation of intracellular metal concentrations. These results identify a novel mechanism of bacterial killing by innate immunity proteins, which depends on synergistic effect of oxidative, thiol, and metal stress and differs from bacterial killing by antibiotics. These results offer potential targets for developing new antibacterial agents that would kill antibiotic-resistant bacteria.

Peptidoglycan recognition protein 3 and Nod2 synergistically protect mice from dextran sodium sulfate-induced colitis.

Aberrant immune response and changes in the gut microflora are the main causes of inflammatory bowel disease (IBD). Peptidoglycan recognition proteins (Pglyrp1, Pglyrp2, Pglyrp3, and Pglyrp4) are bactericidal innate immunity proteins that maintain normal gut microbiome, protect against experimental colitis, and are associated with IBD in humans. Nucleotide-binding oligomerization domain 2 (Nod2) is an intracellular bacterial sensor and may be required for maintaining normal gut microbiome. Mutations in Nod2 are strongly associated with Crohn's disease, but the causative mechanism is not understood, and the role of Nod2 in ulcerative colitis is not known. Because IBD is likely caused by variable multiple mutations in different individuals, in this study, we examined the combined role of Pglyrp3 and Nod2 in the development of experimental colitis in mice. We demonstrate that a combined deficiency of Pglyrp3 and Nod2 results in higher sensitivity to dextran sodium sulfate-induced colitis compared with a single deficiency. Pglyrp3(-/-)Nod2(-/-) mice had decreased survival and higher loss of body weight, increased intestinal bleeding, higher apoptosis of colonic mucosa, elevated expression of cytokines and chemokines, altered gut microbiome, and increased levels of ATP in the colon. Increased sensitivity to dextran sodium sulfate-induced colitis in Pglyrp3(-/-)Nod2(-/-) mice depended on increased apoptosis of intestinal epithelium, changed gut microflora, and elevated ATP. Pglyrp3 deficiency contributed colitis-predisposing intestinal microflora and increased intestinal ATP, whereas Nod2 deficiency contributed higher apoptosis and responsiveness to increased level of ATP. In summary, Pglyrp3 and Nod2 are both required for maintaining gut homeostasis and protection against colitis, but their protective mechanisms differ.

Peptidoglycan recognition protein 1 enhances experimental asthma by promoting Th2 and Th17 and limiting regulatory T cell and plasmacytoid dendritic cell responses.

Asthma is a common inflammatory disease involving cross-talk between innate and adaptive immunity. We reveal that antibacterial innate immunity protein, peptidoglycan recognition protein (Pglyrp)1, is involved in the development of allergic asthma. Pglyrp1(-/-) mice developed less severe asthma than wild-type (WT) mice following sensitization with house dust mite (allergen) (HDM). HDM-sensitized Pglyrp1(-/-) mice, compared with WT mice, had diminished bronchial hyperresponsiveness (lung airway resistance); numbers of eosinophils, neutrophils, lymphocytes, and macrophages in bronchoalveolar lavage fluid and lungs; inflammatory cell infiltrates in the lungs around bronchi, bronchioles, and pulmonary arteries and veins; lung remodeling (mucin-producing goblet cell hyperplasia and metaplasia and smooth muscle hypertrophy and fibrosis); levels of IgE, eotaxins, IL-4, IL-5, and IL-17 in the lungs; and numbers of Th2 and Th17 cells and expression of their marker genes in the lungs. The mechanism underlying this decreased sensitivity of Pglyrp1(-/-) mice to asthma was increased generation and activation of CD8α(+)ß(+) and CD8α(+)ß(-) plasmacytoid dendritic cells (pDC) and increased recruitment and activity of regulatory T (Treg) cells in the lungs. In vivo depletion of pDC in HDM-sensitized Pglyrp1(-/-) mice reversed the low responsive asthma phenotype of Pglyrp1(-/-) mice to resemble the more severe WT phenotype. Thus, Pglyrp1(-/-) mice efficiently control allergic asthma by upregulating pDC and Treg cells in the lungs, whereas in WT mice, Pglyrp1 is proinflammatory and decreases pDC and Treg cells and increases proasthmatic Th2 and Th17 responses. Blocking Pglyrp1 or enhancing pDC in the lungs may be beneficial for prevention and treatment of asthma.

Peptidoglycan recognition protein Pglyrp2 protects mice from psoriasis-like skin inflammation by promoting regulatory T cells and limiting Th17 responses.

Skin protects the body from the environment and is an important component of the innate and adaptive immune systems. Psoriasis is a frequent inflammatory skin disease of unknown cause determined by multigenic predisposition, environmental factors, and aberrant immune response. Peptidoglycan recognition proteins (Pglyrps) are expressed in the skin, and we report in this article that they modulate sensitivity in an experimentally induced mouse model of psoriasis. We demonstrate that Pglyrp2(-/-) mice (but not Pglyrp3(-/-) and Pglyrp4(-/-) mice) are more sensitive to the development of 12-O-tetradecanoylphorbol 13-acetate-induced psoriasis-like inflammation, whereas Pglyrp1(-/-) mice are less sensitive. The mechanism underlying this increased sensitivity of Pglyrp2(-/-) mice to 12-O-tetradecanoylphorbol 13-acetate-induced psoriasis-like inflammation is reduced recruitment of regulatory T cells to the skin and enhanced production and activation of Th17 cells in the skin in Pglyrp2(-/-) mice, which results in more severe inflammation and keratinocyte proliferation. Thus, in wild type mice, Pglyrp2 limits overactivation of Th17 cells by promoting accumulation of regulatory T cells at the site of inflammation, which protects the skin from the exaggerated inflammatory response.

Respiratory chain components are required for peptidoglycan recognition protein-induced thiol depletion and killing in Bacillus subtilis and Escherichia coli.

Mammalian peptidoglycan recognition proteins (PGRPs or PGLYRPs) kill bacteria through induction of synergistic oxidative, thiol, and metal stress. Tn-seq screening of Bacillus subtilis transposon insertion library revealed that mutants in the shikimate pathway of chorismate synthesis had high survival following PGLYRP4 treatment. Deletion mutants for these genes had decreased amounts of menaquinone (MK), increased resistance to killing, and attenuated depletion of thiols following PGLYRP4 treatment. These effects were reversed by MK or reproduced by inhibiting MK synthesis. Deletion of cytochrome aa3-600 or NADH dehydrogenase (NDH) genes also increased B. subtilis resistance to PGLYRP4-induced killing and attenuated thiol depletion. PGLYRP4 treatment also inhibited B. subtilis respiration. Similarly in Escherichia coli, deletion of ubiquinone (UQ) synthesis, formate dehydrogenases (FDH), NDH-1, or cytochrome bd-I genes attenuated PGLYRP4-induced thiol depletion. PGLYRP4-induced low level of cytoplasmic membrane depolarization in B. subtilis and E. coli was likely not responsible for thiol depletion. Thus, our results show that the respiratory electron transport chain components, cytochrome aa3-600, MK, and NDH in B. subtilis, and cytochrome bd-I, UQ, FDH-O, and NDH-1 in E. coli, are required for both PGLYRP4-induced killing and thiol depletion and indicate conservation of the PGLYRP4-induced thiol depletion and killing mechanisms in Gram-positive and Gram-negative bacteria.

Bacterial Peptidoglycan as a Driver of Chronic Brain Inflammation.

Peptidoglycan (PGN) is a cell wall component of both Gram-positive and Gram-negative bacteria. Signature fragments of PGN are proinflammatory through engagement of pattern recognition receptors (PRR) on resident tissue cells and circulating leukocytes. Despite its abundance in the gut microbiota, there is limited recognition that PGN could contribute to chronic neuroinflammation. This review highlights current insights into the roles of PGN as a determinant of brain inflammation, notably in multiple sclerosis (MS) and its experimental autoimmune encephalomyelitis (EAE) models. Recent studies demonstrate PGN in blood of healthy adult humans. PGN amplifies autoimmune pathology via activation of innate immune cells. Novel uptake routes through (altered) gut mucosa by myeloid leukocyte subsets promote PGN transport to the brain.

Nod2 protects mice from inflammation and obesity-dependent liver cancer.

Nod2 is a pattern recognition receptor that modulates host innate immune responses and protects from inflammation, steatosis, and obesity. Obesity and inflammation are risk factors for hepatocellular carcinoma, however, the role of Nod2 in obesity-dependent hepatic tumorigenesis is not known. Here we tested the hypothesis that Nod2 protects from high fat diet (HFD)-dependent hepatic cancer. We used an obesity-dependent hepatic tumor model. WT and Nod2-/- mice were treated with the carcinogen dimethylbenz[a]anthracene (DMBA) and maintained on HFD. Nod2-/- mice treated with DMBA and maintained on HFD gain significantly more weight and develop more liver tumors than similarly treated WT mice. Livers of Nod2-/- tumorigenic mice had increased expression of genes involved in cell proliferation, immune responses, and cholesterol biosynthesis, increased infiltration of neutrophils, inflammatory monocytes, and T cells, and increased activation of STAT3 and ERK during the later stages of tumorigenesis. Bioinformatic analyses of genes with differential expression predicted an increase in cancer, immune, and cholesterol biosynthesis pathways. In summary, we have identified a novel role for Nod2 and demonstrate that Nod2 protects from HFD-dependent liver malignancy and this protection is accompanied by decreased cell proliferation, inflammation, steroid biosynthesis, neutrophils and macrophages infiltration, and STAT3 and MAPK signaling in the liver.

Formate dehydrogenase, ubiquinone, and cytochrome bd-I are required for peptidoglycan recognition protein-induced oxidative stress and killing in Escherichia coli.

Mammalian Peptidoglycan Recognition Proteins (PGRPs) kill bacteria through induction of synergistic oxidative, thiol, and metal stress. PGRPs induce oxidative stress in bacteria through a block in the respiratory chain, which results in decreased respiration and incomplete reduction of oxygen (O2) to hydrogen peroxide (H2O2). In this study we identify the site of PGRP-induced generation of H2O2 in Escherichia coli. Tn-seq screening of E. coli Tn10 insertion library revealed that mutants in formate dehydrogenase (FDH) genes had the highest survival following PGRP treatment. Mutants lacking functional FDH-O had abolished PGRP-induced H2O2 production and the highest resistance to PGRP-induced killing, and formate enhanced PGRP-induced killing and H2O2 production in an FDH-dependent manner. Mutants in ubiquinone synthesis (but not menaquinone and demethylmenaquinone) and cytochrome bd-I (but not cytochromes bo3 and bd-II) also had completely abolished PGRP-induced H2O2 production and high resistance to PGRP-induced killing. Because electrons in the respiratory chain flow from dehydrogenases' substrates through quinones and then cytochromes to O2, these results imply that the site of PGRP-induced incomplete reduction of O2 to H2O2 is downstream from dehydrogenases and ubiquinone at the level of cytochrome bd-I, which results in oxidative stress. These results reveal several essential steps in PGRP-induced bacterial killing.

Peptidoglycan recognition protein-S (PGRP-S) is upregulated by NF-kappaB.

Cerebral ischemia triggers inflammation and apoptosis, and the transcription factor NF-kappaB is a key regulator of both events. Here, we report on the induction of the peptidoglycan recognition protein-S (PGRP-S) in a mouse model of cerebral ischemia. Upregulation was reduced if the NF-kappaB subunit RelA was conditionally deleted in the brain. Regulation of PGRP-S transcription by RelA was confirmed in vitro. Cotransfection of a RelA expression plasmid stimulated the expression of a PGRP-S luciferase fusion gene. Mutation of two NF-kappaB response elements in the PGRP-S promoter disrupted stimulation by RelA. To investigate the function of PGRP-S in cerebral ischemia, we subjected PGRP-S(-/-) mice to cerebral ischemia. However, there was no difference in the infarct size in PGRP-S-deficient mice compared to controls. In summary, the data show that PGRP-S is induced in cerebral ischemia by RelA, but its role in ischemia is unclear.

A Balancing Act: PGRPs Preserve and Protect.

How does the immune system maintain a balance between preserving a beneficial microbiome and protecting against pathogens while also inducing effective, yet not damaging, responses? In this issue of Cell Host & Microbe, Charroux et al. (2018) reveal that, in Drosophila, this task is performed by three isoforms of PGRP-LB, a peptidoglycan-hydrolyzing amidase.

Author Correction: Nod2 and Nod2-regulated microbiota protect BALB/c mice from diet-induced obesity and metabolic dysfunction.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

Nod2 and Nod2-regulated microbiota protect BALB/c mice from diet-induced obesity and metabolic dysfunction.

Genetics plays a central role in susceptibility to obesity and metabolic diseases. BALB/c mice are known to be resistant to high fat diet (HFD)-induced obesity, however the genetic cause remains unknown. We report that deletion of the innate immunity antibacterial gene Nod2 abolishes this resistance, as Nod2 -/- BALB/c mice developed HFD-dependent obesity and hallmark features of metabolic syndrome. Nod2 -/- HFD mice developed hyperlipidemia, hyperglycemia, glucose intolerance, increased adiposity, and steatosis, with large lipid droplets in their hepatocytes. These changes were accompanied by increased expression of immune genes in adipose tissue and differential expression of genes for lipid metabolism, signaling, stress, transport, cell cycle, and development in both adipose tissue and liver. Nod2 -/- HFD mice exhibited changes in the composition of the gut microbiota and long-term treatment with antibiotics abolished diet-dependent weight gain in Nod2 -/- mice, but not in wild type mice. Furthermore, microbiota from Nod2 -/- HFD mice transferred sensitivity to weight gain, steatosis, and hyperglycemia to wild type germ free mice. In summary, we have identified a novel role for Nod2 in obesity and demonstrate that Nod2 and Nod2-regulated microbiota protect BALB/c mice from diet-induced obesity and metabolic dysfunction.

Identification of serum N-acetylmuramoyl-l-alanine amidase as liver peptidoglycan recognition protein 2.

N-acetylmuramoyl-l-alanine amidase (NAMLAA) hydrolyzes bacterial peptidoglycan and is present in human serum. A peptidoglycan-recognition protein 2 (PGLYRP2) is expressed in human liver and has N-acetylmuramoyl-l-alanine amidase activity. Here, we determined the amino acid sequences of human serum NAMLAA and liver PGLYRP2 and tested the hypothesis that serum NAMLAA and PGLYRP2 are the same protein. Liver PGLYRP2 and serum NAMLAA had the same mass determined by mass spectrometry and polyacrylamide gel electrophoresis, and both proteins and recombinant PGLYRP2 reacted with polyclonal anti-NAMLAA and anti-PGLYRP2 antibodies, and with monoclonal anti-NAMLAA antibodies. Digestion of serum NAMLAA with trypsin, chymotrypsin, or trypsin plus V8 protease, or with CNBr yielded, respectively, 37, 40, and 3 overlapping peptides that matched 100% and covered 81% of the deduced amino acid sequence of mature PGLYRP2. These peptides overlapped all exon-intron junctions indicating no alternative splice forms. Digestion of liver PGLYRP2 with trypsin yielded 23 peptides that matched 100% and covered 44% of the deduced amino acid sequence of mature PGLYRP2. Serum NAMLAA had a C398-C404 disulfide, partial phosphorylation of S218, and deamidation of N253 and N301. These results indicate that serum NAMLAA and liver PGLYRP2 are the same protein encoded by the pglyrp2 gene.

Pglyrp-Regulated Gut Microflora Prevotella falsenii, Parabacteroides distasonis and Bacteroides eggerthii Enhance and Alistipes finegoldii Attenuates Colitis in Mice.

Dysbiosis is a hallmark of inflammatory bowel disease (IBD), but it is unclear which specific intestinal bacteria predispose to and which protect from IBD and how they are regulated. Peptidoglycan recognition proteins (Pglyrps) are antibacterial, participate in maintaining intestinal microflora, and modulate inflammatory responses. Mice deficient in any one of the four Pglyrp genes are more sensitive to dextran sulfate sodium (DSS)-induced colitis, and stools from Pglyrp-deficient mice transferred to wild type (WT) germ-free mice predispose them to much more severe colitis than stools from WT mice. However, the identities of these Pglyrp-regulated bacteria that predispose Pglyrp-deficient mice to colitis or protect WT mice from colitis are not known. Here we identified significant changes in ß-diversity of stool bacteria in Pglyrp-deficient mice compared with WT mice. The most consistent changes in microbiome in all Pglyrp-deficient mice were in Bacteroidales, from which we selected four species, two with increased abundance (Prevotella falsenii and Parabacteroides distasonis) and two with decreased abundance (Bacteroides eggerthii and Alistipes finegoldii). We then gavaged WT mice with stock type strains of these species to test the hypothesis that they predispose to or protect from DSS-induced colitis. P. falsenii, P. distasonis, and B. eggerthii all enhanced DSS-induced colitis in both WT mice with otherwise undisturbed intestinal microflora and in WT mice with antibiotic-depleted intestinal microflora. By contrast, A. finegoldii (which is the most abundant species in WT mice) attenuated DSS-induced colitis both in WT mice with otherwise undisturbed intestinal microflora and in WT mice with antibiotic-depleted intestinal microflora, similar to the colitis protective effect of the entire normal microflora. These results identify P. falsenii, P. distasonis, and B. eggerthii as colitis-promoting species and A. finegoldii as colitis-protective species.

Peptidoglycan recognition in innate immunity.

The innate immune system recognizes micro-organisms through a series of pattern recognition receptors that are highly conserved in evolution. Peptidoglycan (PGN) is a unique and essential component of the cell wall of virtually all bacteria, is not present in eukaryotes, and is an excellent target for the innate immune system. Indeed, higher eukaryotes, including mammals, have several PGN recognition molecules, including CD14, Toll-like receptor 2 (TLR2), nucleotide oligomerization domain (Nod)-containing proteins, a family of peptidoglycan recognition proteins (PGRPs), and PGN-lytic enzymes (lysozyme and amidase). These molecules induce host responses to micro-organisms, degrade PGN, or have direct antimicrobial effects.

Peptidoglycan recognition proteins (PGRPs).

Innate immune system recognizes microorganisms through a series of pattern recognition receptors that are highly conserved in evolution. Peptidoglycan recognition proteins (PGRPs) are pattern recognition molecules that are conserved from insects to mammals and recognize bacteria and their unique cell wall component, peptidoglycan (PGN). Drosophila, mosquito, and mammals have families of 13, 7, and 4 PGRP genes, respectively, and some of these genes are alternatively spliced. PGRPs are differentially expressed in various cells and tissues, their expression is often upregulated by bacteria, and they mediate host responses to bacterial infections. Insect PGRPs have four known effector functions that are unique for insects: activation of prophenoloxidase cascade, activation of Toll receptor, activation of Imd pathway, and induction of phagocytosis. One function, amidase activity, is shared by some insect and mammalian PGRPs, whereas antibacterial activity of some mammalian PGRPs is unique for mammals.

Genetic Association of Peptidoglycan Recognition Protein Variants with Inflammatory Bowel Disease.

Inflammatory bowel disease (IBD) is a common disease, includes Crohn's disease (CD) and ulcerative colitis (UC), and is determined by altered gut bacterial populations and aberrant host immune response. Peptidoglycan recognition proteins (PGLYRP) are innate immunity bactericidal proteins expressed in the intestine. In mice, PGLYRPs modulate bacterial populations in the gut and sensitivity to experimentally induced UC. The role of PGLYRPs in humans with CD and/or UC has not been previously investigated. Here we tested the hypothesis that genetic variants in PGLYRP1, PGLYRP2, PGLYRP3 and PGLYRP4 genes associate with CD and/or UC and with gender and/or age of onset of disease in the patient population. We sequenced all PGLYRP exons in 372 CD patients, 77 UC patients, 265 population controls, 210 familial CD controls, and 24 familial UC controls, identified all polymorphisms in these populations, and analyzed the variants for significant association with CD and UC. We identified 16 polymorphisms in the four PGLYRP genes that significantly associated with CD, UC, and/or subgroups of patient populations. Of the 16, 5 significantly associated with both CD and UC, 6 with CD, and 5 with UC. 12 significant variants result in amino acid substitutions and based on structural modeling several of these missense variants may have structural and/or functional consequences for PGLYRP proteins. Our data demonstrate that genetic variants in PGLYRP genes associate with CD and UC and may provide a novel insight into the mechanism of pathogenesis of IBD.