Pathogenesis of Crohn's disease: multifocal gastrointestinal infarction

In a prospective study, specimens of resected small and large intestine from fifteen patients with Crohn's disease were prepared by heparin-saline vascular perfusion, followed by either resin casting of the mesenteric vascular supply and tissue maceration or glutaraldehyde perfusion-fixation, resin casting, and tissue clearance. The specimens were examined by macrophotography, histopathology, and either scanning or transmission electronmicroscopy. A pathogenetic sequence of events in Crohn's disease was seen--vascular injury, focal arteritis, fibrin deposition, arterial occlusion mainly at the level of the muscularis propria, followed by tissue infarction or neovascularisation. These features were confined to segments of intestine affected by Crohn's disease and did not occur in normal bowel. The findings suggest that Crohn's disease is mediated by multifocal gastrointestinal infarction. This pathogenetic process is compatible with many of the clinical features of Crohn's disease, and its recognition has important implications for the identification of the primary cause of the illness and advances in clinical management.

Colonization of gastrointestinal tracts of chicks by Campylobacter jejuni

Bacterial enumeration and histologic examination of organs and tissues of 8-day-old chicks 7 days after peroral inoculation with Campylobacter jejuni revealed that the organism colonized primarily the lower gastrointestinal tract. The principal sites of localization were the ceca, large intestine, and cloaca, where densely packed cells of C. jejuni were observed in mucus within crypts. Examination of C. jejuni-colonized crypts by transmission electron microscopy revealed that the campylobacters freely pervaded the lumina of crypts without attachment to crypt microvilli. Understanding the mechanism of colonization may lead to approaches that will reduce the incidence of C. jejuni carriage by poultry.

Endogenous expression of type II cGMP-dependent protein kinase mRNA and protein in rat intestine. Implications for cystic fibrosis transmembrane conductance regulator

Certain pathogenic bacteria produce a family of heat stable enterotoxins (STa) which activate intestinal guanylyl cyclases, increase cGMP, and elicit life-threatening secretory diarrhea. The intracellular effector of cGMP actions has not been clarified. Recently we cloned the cDNA for a rat intestinal type II cGMP dependent protein kinase (cGK II) which is highly enriched in intestinal mucosa. Here we show that cGK II mRNA and protein are restricted to the intestinal segments from the duodenum to the proximal colon, with the highest amounts of cGK II protein in duodenum and jejunum. cGK II mRNA and protein decreased along the villus to crypt axis in the small intestine, whereas substantial amounts of both were found in the crypts of cecum. In intestinal epithelia, cGK II was specifically localized in the apical membrane, a major site of ion transport regulation. In contrast to cGK II, cGK I was localized in smooth muscle cells of the villus lamina propria. Short circuit current (ISC), a measure of Cl- secretion, was increased to a similar extent by STa and by 8-Br-cGMP, a selective activator of cGK, except in distal colon and in monolayers of T84 human colon carcinoma cells in which cGK II was not detected. In human and mouse intestine, the cyclic nucleotide-regulated Cl- conductance can be exclusively accounted for by the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel. Viewed collectively, the data suggest that cGK II is the mediator of STa and cGMP effects on Cl- transport in intestinal-epithelia.

Intestinal microflora and digestive toxicity of irinotecan in mice

PURPOSE

Delayed diarrhea is the most important side effect of irinotecan. The aim of this study was to investigate the role of intestinal microflora on the induction of systemic and intestinal toxicity and diarrhea, studying germ-free and holoxenic mice i.p. injected with irinotecan.

EXPERIMENTAL DESIGN

To evaluate the lethal dose, starting with 100 mg/kg/4 d, we treated the holoxenic mice with 100, 80, and 60 mg/kg/4 d and germ-free mice with 60, 80, 100, and 150 mg/kg/4 d. We recorded the percentage of dead animals, diarrhea, and the epithelial damage to the jejunum, ileum, cecum, and colon at optical and scanning electron microscopy.

RESULTS

Germ-free mice were more resistant to irinotecan than the holoxenic group. The lethal dose was between 60 and 80 mg of irinotecan for holoxenic mice and > or =150 mg for the germ-free. The intestinal damage score was higher in holoxenic than germ-free mice at 100 mg and equally diffuse in the small and large bowel. The damage in germ-free mice was less severe (8 of 40 samples) prevailing in the ileum. The differences were significant for all sites (jejunum, P < 0.001; ileum, P = 0.012; cecum, P = 0.001; colon, P < 0.001). No damage was found in germ-free mice at 60 mg. Diarrhea was present in all 100 and 80 mg holoxenic mice and in 19 of 20 cases at 60 mg whereas it was absent in 60 mg or sporadic in 80 and 100 mg germ-free mice.

CONCLUSIONS

The intestinal microflora plays a key role in the intestinal toxicity of irinotecan.

Activated mast cells infiltrate in close proximity to enteric nerves in diarrhea-predominant irritable bowel syndrome

Mast cells (MC) may be one factor influencing the response of visceral afferent nerves to mechanical and chemical stimuli. The aim of this study was to evaluate the degree of infiltration and activity of colonic MC in irritable bowel syndrome (IBS). Biopsy specimens were obtained from the cecum and rectum of 14 diarrhea predominant IBS and 14 normal controls. Electron microscopy was used to determine the number of intact and degranulated colonic MC and to quantify these separately according to the distance between MC and enteric nerves. An increased number of MC in both cecum and rectum in the IBS group in comparison with the control group was demonstrated (p<0.05). Activated MC in close proximity to enteric nerves were significantly increased in both cecum and rectum of the IBS group compared to control group (p<0.005). In addition, activated MC were significantly increased in close proximity to the nerves compared to those in the remote area in both cecum and rectum of the IBS group (p<0.0001). MC were significantly increased and activated in both cecum and rectum of the IBS group compared to controls. MC may play a role in the gut sensory hypersensitivity of IBS.

Pathogenicity of human and porcine intestinal spirochetes in one-day-old specific-pathogen-free chicks: an animal model of intestinal spirochetosis

One-day-old chicks were infected orally with two strains of weakly hemolytic spirochetes isolated from a human and a pig with intestinal spirochetosis. These spirochetosis both colonized birds, attached end-on to their cecal enterocytes, induced watery diarrhea, and significantly depressed growth rates. Cultures of Serpulina innocens failed to colonize the chicks.

Mechanisms of association of Candida albicans with intestinal mucosa

The association of Candida albicans with gastrointestinal (GI) mucosal surfaces was studied in vitro and in vivo. The caecal mucosal surfaces from antibiotic-treated and untreated control mice challenged orally with C. albicans revealed that large numbers of C. albicans were associated with the intestinal epithelium of antibiotic-treated mice but not with that of the control mice that possessed an indigenous wall-associated bacterial flora. Moreover, Candida cells only penetrated deep into the mucosa of animals in which the ecology of the intestinal microflora had been disrupted. In mice given antibiotics, C. albicans was associated with the mucosa of all areas of the GI tract; the caecal mucosa had the most associated Candida, whereas the stomach and small intestine had very few associated yeasts. Further examination of caecal mucosa from antibiotic-treated mice showed that C. albicans associated with the mucosa by at least five distinct mechanisms. These included: adhesion to epithelium, adhesion to mucus, co-adhesion to adherent fungi, co-adhesion to adherent bacteria, and entrapment in the mucous gel overlying the epithelium. The cell-surface hydrophobicity of C. albicans also was examined and found not to play a role in Candida adhesion to intestinal mucosa. The predominant association mechanisms appeared to be entrapment in the mucous gel, and adhesion to mucus and the epithelium. The ecological and pathological significance of co-adhesion by C. albicans to attached organisms is unclear but it may be important in the initiation of mucosal lesions.

Electron microscope studies of experimental Entamoeba histolytica infection in the guinea pig. I. Penetration of the intestinal epithelium by trophozoites

Germ-free guinea pigs were inoculated intracecally with Entamoeba histolytica and the enteric flora derived from a human patient with acute amebic colitis. Aanimals were killed at post-inoculation intervals of 7 to 12 days. The mode of penetration of cecal epithelium by the ameba was examined by light and electron microscopy. The following sequence was reconstructed from numerous individual observations. When the amebae were in moderately close proximity to the brush, border, the microvilli became shortened, irregular, and sometimes disappeared. Dense material was observed between the amebae and microvilli. When the ameba was very close to the epithelium the apical portion of epithelial cytoplasm projected into the lumen contacting the organism, thus becoming detached from adjoining cells. This produced spaces between epithelial cells through which amebae invaded interepithelial spaces. Initially the ameba penetrated the interglandular epithelium. Later, it penetrated equally the glandular and interglandular epithelium barrier. There were marked alterations of cytoplasmic components of epithelial cells. Polymorphonuclear leukocytes migrated into the epithelium filling these spaces; these often showed a variety of degenerative processes. Amebae, utilizing their pseudopodia, moved further through the intercellular spaces and reached the lamina propria.

Anatomy of the rabbit cecum

The anatomy of the rabbit cecum was investigated using macroscopic dissections, vascular injections, dried total specimens, light microscopy, and scanning and electron microscopy. The morphology of the three portions of the cecum (ampulla coli, corpus ceci and appendix vermiformis) is described. For comparison, the proximal colon, ileum and sacculus rotundus were also investigated. The thickness of the different layers of the intestinal wall of each area was measured. The arterial supply and mesenteries of the cecum were also studied. The rabbit cecum represents structurally a highly developed organ.

The morphology of the attachment and probable feeding site of the nematode Trichuris muris (Schrank, 1788) Hall, 1916

The 'tunnel' within which the nematode Trichuris muris is contained was examined by light, scanning, and transmission electron microscopy. The amount of worm covered by the tunnel varied with age. Young larval worms were completely embedded in the host's intestinal mucosa whereas older larvae and adults had part, if not all, of the posterior region protruding into the lumen. All worms were found to have heads embedded in the tissue and in no cases were whole worms found free in the lumen.The 'tunnel' was shown to be a syncytial protoplasmic mass with recognizable cellular elements such as nuclei, lipid droplets, mitrochondria, and mucous droplets anteriorly whereas more distal to the head these elements became increasingly scarce and degenerated. The syncytium is bordered apically, laterally, and basally by cell membrane. The basal lamina can be identified beneath the basal membrane of the syncytium indicating that syncytium formation occurs in the epithelial sheet only and does not extend into the lamina propria. Evidence suggests that the nematode initially induces a syncytium about its head, feeds on the syncytial cytoplasm, and then moves on to initiate extension of the syncytium. The result of this movement is a 'tunnel' snaking across the caecum and colon.

Effect of probiotics on intestinal mucosal immunity and ultrastructure of cecal tonsils of chickens

Sixty chickens were randomly divided into two groups to determine the effect of oral administration of probiotics on the intestinal mucosal immune response and ultrastructure of cecal tonsils. The first group (control) was fed with a basic diet without antibiotic or probiotics. The second group was fed with the same diet as the control, except they received drinking water with probiotics (4 x 10(9) cfu per chicken and day) from posthatch to day 3 of age. The probiotic preparation was composed of Bacillus subtilis Bs964, Candida utilis BKM-Y74 and Lactobacillus acidophilus LH1F. Intestinal fluid, Peyer's Patch and cecal tonsils were taken at day 1, 4, 7, 10 and 18 after administration of probiotics. The results showed: (i) Compared to the control, probiotics enhanced the content of following items: immunglobulin (Ig)A in the intestinal fluid at day 7 (p < 0.01), the IgG-forming cells at day 10 (p < 0.05), IgM-forming cells in the Peyer's Patch at day 7 (p < 0.05), IgA-forming cells at day 7-10 (p < 0.05), IgG-forming cells at day 7 (p < 0.05) and IgM-forming cells in cecal tonsils diffuse area at day 4-7 (p < 0.05). (ii) T lymphocytes in cecal tonsils were enhanced at day 7 (p < 0.01) after orally fed with probiotics. (iii) The density of microvilli and length of cecal tonsils increased after probiotics were administrated at day 3. With chicken ageing, the efficiency of probiotics would decrease. These results suggested that probiotics enhance intestinal mucosal immunity of chicken at the early age.

Intestinal microbial flora after feeding phytohemagglutinin lectins (Phaseolus vulgaris) to rats

Incorporation of purified phytohemagglutinin (PHA) lectins derived from red kidney beans (Phaseolus vulgaris) in the diet of weanling rats will cause growth failure, malabsorption of nutrients, and bacterial overgrowth in the small intestine. These effects are not caused by feeding a similar quantity of PHA to germfree rats. To define the morphological and bacterial changes on the mucosal surfaces of the jejunum, ileum, and cecum in greater detail, we pair fed two groups of weanling rats isocaloric, isonitrogenous diets with or without 0.5% PHA protein. On the jejunal surfaces of control rats, the mucous layer was a confluent covering with sparsely scattered bacteria and protozoa. In PHA-treated rats, the mucous layer was thin and discontinuous, and the microvillous surface of the tissue was extensively populated by bacterial cells of two distinct morphotypes--a gram-negative rod and a gram-positive coccobacillus. In all PHA-treated animals, these bacteria formed adherent monospecific or mixed adherent microcolonies on the tissue surface. Tissue damage was observed in PHA-exposed jejunal tissue as evidenced by vesiculation of the microvillous plasma membrane and by damage to the brush border membrane. On the ileal surfaces of control rats, there was a thick mucous layer within which small numbers of bacteria and protozoa were seen. Segmented filamentous bacteria were anchored in the tissue surface. In PHA-treated rats, the ileal surface was only incompletely covered by a mucous layer, and the overlying mucosal surface was extensively covered by large numbers of protozoan cells (predominantly Hexamita muris). Most of the ileal surfaces not covered by the mucous layer were occupied and virtually occluded by an overgrowth of these protozoan cells with occasional cells of Giardia muris and the tissue-associated segmented bacillus. In the ceca of control rats, the mucosa was incompletely covered by a discontinuous mucous layer and colonized by an unnamed Spirillum sp., other bacteria, and occasional protozoa. The cecal surfaces of PHA-treated rats retained most of their incomplete overlying mucous layer, which was heavily colonized by the same type of Spirillum sp. seen in untreated animals; intestinal crypts were colonized. These descriptive morphological studies demonstrate that exposure to purified PHA in the diet caused characteristic changes in the microbial ecology of the small intestine. The changes in microbial flora contributed to the malabsorption of nutrients in the small intestines of PHA-fed animals.

The effect of diet on microfaunal population and function in the caecum of a subterranean naked mole-rat, Heterocephalus glaber

The effect of dietary fibre and starch content on digestibility, microfaunal population and caecal function was investigated in a subterranean mole-rat, Heterocephalus glaber (Rodentia). Mole-rats were fed on a diet of either sweet potato (neutral-detergent fibre (NDF) 65 g/kg dry matter (DM), starch 638 g/kg DM) or carrot (NDF 157 g/kg DM, starch 258.7 g/kg DM) for 4 weeks. Daily intake and faecal output were monitored. Thereafter caecal microfaunal population, density and function were assessed using light and scanning electron microscopy and by measuring both gas and short chain fatty acid (SCFA) production. A 2.4-fold increase in fibre and 2.5-fold decrease in starch content resulted in a decrease in caecal DM content (390 g/kg). A concomitant dramatic decline (by 93%) in ciliate protozoa with a corresponding 2-fold increase in bacteria also accompanied this change in diet. Fermentative efficiency as indicated by gas production was 2.6 times greater on a carrot diet than on sweet potato. Microbial fermentation resulted in higher SCFA concentrations on the carrot diet, with a 42% reduction in SCFA concentration on the sweet potato diet. Here, SCFA contributed 5.1% of daily energy expenditure and this increased 5.0-fold on the carrot diet. Caecal micro-organism function, therefore, played an important role in the nutritional physiology of these naked mole-rats, and enabled maximum utilization of the food substrate.

The endocrine pancreas of spontaneously diabetic db/db mice: microangiopathy as revealed by transmission electron microscopy

Abnormalities in ultrastructures of islet capillaries were detected in db/db mice, with the visual inspection and morphometry of electron micrographs. The observed changes are: (1) capillary scarcity; (2) increase in the mean and diversity of capillary size; (3) pericapillary edema and fibrosis; (4) hypertrophy of the pericyte and abundance therein of actin-like microfilaments; and (5) luminal irregularity. Changes (2), (3) and (4) are conceived to indicate hyperperfusion, capillary hypertension and secondary vascular response. In particular, such pericyte changes were found to be shared by other organs whose capillaries are susceptible to diabetic complications.

Neuromuscular structures specific to the submucosal border of the human colonic circular muscle layer

The circular muscle layer of the human caecum and ascending colon is clearly subdivided into two portions: an outer one which includes the bulk of the circular muscle layer, and an inner one made up of only six to eight rows of cells. In the right transverse colon no demarcation can be observed, but a difference exists between the innermost and the outermost cells, since those of the two innermost rows possess some peculiarities with regard to the sarcoplasmic reticulum, glycogen particles, caveolae, and intercellular junctions. In the left part of the colon, the circular muscle layer is also divided into two portions. In fact, the innermost smooth muscle cells still possess peculiar morphologies, progressively increase in number, and become separate from each other making up a superficial muscle network. A fibrous lamella, along and inside which a ganglionated nerve plexus runs, is strictly apposed to the submucosal border of the circular muscle layer of the entire colonic length. A second nerve plexus runs between the two portions of the circular muscle layer. Both these plexuses are accompanied by interstitial cells of Cajal in the right colon only. The peculiar organization of the entire submucosal border of the human colonic circular muscle layer distinguishes it from other parts of the gut and probably represents a structural basis for control of human colonic motility. The presence of putative pacemaker cells (interstitial cells and peculiar smooth muscle cells) indicates that the inner border of human colonic circular muscle layer possesses pacemaking activities. Moreover, the interstitial cell--smooth muscle cell ratio differs depending on the colonic level; two main regions can be identified: the right and the left colon. Consequently, we might expect regional variation in pacemaking.

Gap junctions of the muscles of the small and large intestine

The distribution of gap junctions (nexuses) in various parts of the small and large intestines of the guinea-pig was studied using the freeze-fracture technique and in thin sections. The percentage area of smooth muscle cell surface occupied by gap junctions varies from 0.50% in the circular muscle of the duodenum to zero in the longitudinal muscle of the ileum. In the circular muscle of the jejunum and ileum the area occupied by nexuses is 0.22% (or about 11 micrometers 2 per cell). The sizes of junctions range from less than 0.01 micrometer 2 to 0.20 micrometer 2, with two-thirds of them being smaller than 0.05 micrometer 2. In the colon, gap junctions are rare, very small and confined to the circular muscle layer. Even the smallest aggregates of intramembrane particles correspond to areas of close apposition between the membranes of adjacent cells; it is therefore justified to interpret them as being gap junctions. Some gap junctions are formed between a smooth muscle cell and an interstitial cell. Gap junctions are not found in the longitudinal muscle of the small intestine; this is in sharp contrast to the abundance of gap junctions in the adjacent circular layer. In the small intestine of cats and rabbits, gap junctions are abundant in the circular muscle layer, whereas they are very small in size and very few in number in the longitudinal muscle layer.

Morphology of experimental antibiotic-associated enterocolitis in the hamster: a model for human pseudomembranous colitis and antibiotic-associated diarrhoea

The morphology of antibiotic-associated enterocolitis in the hamster is described and compared with human antibiotic-associated pseudomembranous colitis. It is shown to be a caecal disease with proliferative mucosal changes and in this respect unlike the human counterpart. The bacteriology and toxicology, however, are identical. In addition, mucosal changes are described in animals on antibiotics but without established enterocolitis. As a result we suggest that there may be a spectrum of human disease ranging from mild antibiotic-associated diarrhoea to established pseudomembranous colitis. Therefore, despite the morphological variation, the hamster remains a good model for investigating the pathogenesis of pseudomembranous colitis and antibiotic-associated enteropathy in general.

Prevention of Clostridium difficile-induced experimental pseudomembranous colitis by Saccharomyces boulardii: a scanning electron microscopic and microbiological study

The ability of Saccharomyces boulardii to protect mice against intestinal pathology caused by toxinogenic Clostridium difficile was studied. Different regions of the intestine of experimental mice were prepared for observation by scanning electron microscopy or homogenized for C. difficile enumeration and quantification of toxin A by enzyme immunoassay and toxin B by cytotoxicity. The test group was treated for 6 d with an S. boulardii suspension in drinking water and challenged with C. difficule on day 4. The three control groups were: axenic mice, mice treated with only S. boulardii and mice only challenged with C. difficile. The results showed that: (i) 70% of the mice infected by C. difficile survived when treated with S. boulardii; (ii) the C. difficile-induced lesions on the small and large intestinal mucosa were absent or markedly less severe in S. boulardii-treated mice; and (iii) there was no decrease in the number of C. difficile but rather a reduction in the amount of toxins A and B in S. boulardii-treated mice.

Light microscopic and ultrastructural changes in the ceca of chicks inoculated with human and canine Serpulina pilosicoli

Light microscopic and ultrastructural changes were observed in chicks challenged with North American Serpulina pilosicoli, a weakly beta-hemolytic intestinal spirochete (WBHIS) associated with human and canine intestinal spirochetosis. Chicks in control groups received trypticase soy broth or canine Serpulina innocens. The birds were necropsied at weekly intervals, and the ceca were processed for bacteriologic and pathologic examinations. No WBHIS were isolated from the ceca of chicks in the control groups, but WBHIS with genotypes similar to the parent isolates were isolated from the ceca of chicks inoculated with human and canine S. pilosicoli. Gross examination revealed no significant changes in the ceca of chicks at any time post-inoculation. Light microscopic examination revealed no spirochetal attachment in the ceca of chicks in control groups. In contrast, focal to diffuse thickening of the brush border of the surface epithelium along with dilation of the crypt lumina and mild focal lamina propria heterophil infiltration were present in the ceca of chicks inoculated with human and canine S. pilosicoli. Scanning electron microscopic examination revealed focal to confluent spirochetal attachment mainly in the furrow region at the periphery of the crypt units. Transmission electron microscopic examination revealed spirochetes attached to the brush border of the cecal epithelium, causing effacement of the microvilli and disruption of the terminal web microfilaments. The cecal epithelium of chicks inoculated with the canine S. pilosicoli also had caplike elevations of the apical membrane at the point of attachment of the spirochetes together with large numbers of vesicles in the cytoplasm immediately beneath the terminal web and evidence of spirochetal invasion beyond the mucosal barrier. The changes observed suggested that the mechanism of attachment of human and canine S. pilosicoli to the cecal epithelium of chicks was analogous to but different from that described previously for other attaching and effacing gastroenteric bacterical pathogens of human beings and animals.

Attaching and effacing lesions caused by Escherichia coli O157:H7 in experimentally inoculated neonatal lambs

Four 6-day-old conventionally reared lambs were inoculated orally with a total of 10(9) cfu comprising equal numbers of four enterohaemorrhagic Escherichia coli (EHEC) O157:H7 strains. All animals remained clinically normal. Tissues were sampled under terminal anaesthesia at 12, 36, 60 and 84 h post inoculation (hpi). EHEC O157:H7 was cultured from most gastrointestinal tract sites. Small, sparse attaching and effacing (AE) lesions were found in the caecum at 12 and 36 hpi and in the terminal colon and rectum at 84 hpi. Organisms in the lesions were labelled specifically by an O157 antiserum. The results indicate that the well-characterised mechanisms for intimate attachment encoded by the locus for enterocyte effacement (LEE) of EHEC O157:H7 may contribute to the initial events, at least, of colonisation of sheep.

Mucosal damage mediated by clostridial toxin in experimental clindamycin-associated colitis

A toxin produced by Clostridium difficile has been implicated in the pathogenesis of antibiotic-associated colitis in humans and experimental animals. This study was undertaken in order to define the sequential evolution of caecal mucosal lesions in the hamster and to relate those lesions directly to the clostridial toxin. Sterile filtrates from a culture of C. difficile and from caecal contents of clindamycin-treated hamsters were studied with respect to their effects on the caecal mucosa and on cultured cell monolayers. The toxic filtrates both produced cellular swelling in vitro, and appeared to have a similar cytotoxic effect on caecal epithelial cells in vivo. Cellular damage was followed by extensive epithelial desquamation and the evolution of an acute pseudomembranous typhlitis. The pathogenetic sequence produced by the filtrates was identical with that previously described after direct clindamycin treatment. These findings demonstrate that intraluminal clostridial toxin can mediate development of the characteristic antibiotic-associated mucosal lesions.

Murine peptidoglycan recognition proteins PglyrpIalpha and PglyrpIbeta are encoded in the epidermal differentiation complex and are expressed in epidermal and hematopoietic tissues

Peptidoglycan recognition proteins (PGRPs or PGLYRPs) are pattern recognition molecules that are found in insects and mammals and are critical for innate immune responses. PGRPs bind peptidoglycan, a ubiquitous component of bacterial cell walls, and are involved in killing bacteria, degrading peptidoglycan, and initiating host defense reactions. Relatively little is known about the four mammalian PGRPs. In this article, we report the sequences of mouse PglyrpIalpha and PglyrpIbeta and provide details of their expression in wild-type mouse tissues. PglyrpIalpha and PglyrpIbeta are encoded within the epidermal differentiation complex on mouse chromosome 3F. Both genes are expressed in epidermal and hematopoietic tissues. PglyrpIbeta is expressed in each of 16 tissues tested, while PglyrpIalpha expression is limited to fewer tissues, including the lung and spleen as well as several tissues of the digestive system. Both proteins are expressed in epithelial cells throughout the gut, and immunohistochemical staining shows expression in salivary glands, the squamous epithelium of the stomach, and the villi of the jejunum. Immunohistochemical staining further shows expression of both PglyrpIalpha and PglyrpIbeta in macrophages in the spleen. PglyrpIalpha is not expressed in resting RAW264.7 macrophage-like cells, but is induced by stimulation with lipopolysaccharide. PglyrpIbeta is constitutively expressed in RAW264.7 cells and is unaffected by lipopolysaccharide or peptidoglycan stimulation. Computational and experimental data suggest that these proteins are secreted. This work provides a step toward understanding the roles of PglyrpIalpha and PglyrpIbeta in host defense and chronic inflammatory conditions induced by bacteria or their components.