Lysophosphatidic Acid Receptor 1 Is Important for Intestinal Epithelial Barrier Function and Susceptibility to Colitis.

Intestinal epithelial cells form a barrier that is critical in protecting the host from the hostile luminal environment. Previously, we showed that lysophosphatidic acid (LPA) receptor 1 regulates proliferation of intestinal epithelial cells, such that the absence of LPA1 mitigates the epithelial wound healing process. This study provides evidence that LPA1 is important for the maintenance of epithelial barrier integrity. The epithelial permeability, determined by fluorescently labeled dextran flux and transepithelial resistance, is increased in the intestine of mice with global deletion of Lpar1, Lpar1-/- (Lpa1-/-). Serum liposaccharide level and bacteria loads in the intestinal mucosa and peripheral organs were elevated in Lpa1-/- mice. Decreased claudin-4, caudin-7, and E-cadherin expression in Lpa1-/- mice further suggested defective apical junction integrity in these mice. Regulation of LPA1 expression in Caco-2 cells modulated epithelial permeability and the expression levels of junctional proteins. The increased epithelial permeability in Lpa1-/- mice correlated with increased susceptibility to an experimental model of colitis. This resulted in more severe inflammation and increased mortality compared with control mice. Treatment of Caco-2 cells with tumor necrosis factor-α and interferon-γ significantly increased paracellular permeability, which was blocked by cotreatment with LPA, but not LPA1 knockdown cells. Similarly, orally given LPA blocked tumor necrosis factor-mediated intestinal barrier defect in mice. LPA1 plays a significant role in maintenance of epithelial barrier in the intestine via regulation of apical junction integrity.

IBD Serology and Disease Outcomes in African Americans With Crohn's Disease.

Backgrounds: Recent studies have identified the role of serologic markers in characterizing disease phenotype, location, complications, and severity among Northern Europeans (NE) with Crohn's disease (CD). However, very little is known about the role of serology in CD among African Americans (AA). Our study explored the relationship between serology and disease phenotype in AA with CD, while controlling for genetic ancestry. Methods: AAs with CD were enrolled as participants through multicenter collaborative efforts. Serological levels of IgA anti-Saccharomyces cervisiae antibody (ASCA), IgG ASCA, E. coli outermembrane porin C, anti-CBir1, and ANCA were measured using enzyme-linked immunosorbent assays. Genotyping was performed using Illumina immunochip technology; an admixture rate was calculated for each subject. Multiple imputation by chained equations was performed to account for data missing at random. Logistic regression was used to calculate adjusted odds ratio (OR) for associations between serological markers and both complicated disease and disease requiring surgery. Results: A total of 358 patients were included in the analysis. The majority of our patients had inflammatory, noncomplicated disease (58.4%), perianal disease (55.7%), and documented colonic inflammation (86.8%). On multivariable analysis, both IgG ASCA and OmpC were associated with complicated disease (OR, 2.67; 95% CI, 1.67-4.28; OR, 2.23; 95% CI, 1.41-3.53, respectively) and disease requiring surgery (OR, 2.51; 95% CI, 1.49-4.22; OR, 3.57; 95% CI, 2.12-6.00). NE admixture to the African genome did not have any associations or interactions in relation to clinical outcome. Conclusions: Our study comprises the largest cohort of AAs with CD. The utility of serological markers for the prognosis of CD in NE applies equally to AA populations.

Crohn's disease-associated Escherichia coli survive in macrophages by suppressing NFκB signaling.

BACKGROUND: Epidemiological and genetic studies suggest a role for enteric flora in the pathogenesis of Crohn's disease (CD). Crohn's disease-associated Escherichia coli (CDEC) is characterized by their ability to invade epithelial cells and survive and induce high concentration of TNF-α from infected macrophages. However, the molecular mechanisms of CDEC survival in infected macrophages are not completely understood. METHODS: Intracellular survival of CDEC strain LF82 isolated from inflamed ileum tissue, 13I isolated from inflamed colonic tissue, and control E. coli strains were tested in the murine macrophage cell line, J774A.1 by Gentamicin protection assay. Modulation of intracellular cell signaling pathways by the E. coli strains were assessed by western blot analysis and confocal microscopy. RESULTS: 13I demonstrated increased survival in macrophages with 2.6-fold higher intracellular bacteria compared with LF82, yet both strains induced comparable levels of TNF-α. LF82 and 13I differentially modulated key mitogen-activated protein kinase pathways during the acute phase of infection; LF82 activated all 3 mitogen-activated protein kinase pathways, whereas 13I activated ERK1/2 pathway but not p38 and JNK pathways. Both 13I and LF82 suppressed nuclear translocation of NFκB compared with noninvasive E. coli strains during the acute phase of infection. However, unlike noninvasive E. coli strains, 13I and LF82 infection resulted in chronic activation of NFκB during the later phase of infection. CONCLUSIONS: Our results showed that CDEC survive in macrophages by initially suppressing NFκB activation. However, persistence of bacterial within macrophages induces chronic activation of NFκB, which correlates with increased TNF-α secretion from infected macrophages.

The role of bacteria in the pathogenesis of ulcerative colitis.

Factors implicated in the pathophysiology of ulcerative colitis (UC) are an abnormal immune response, defect in intestinal epithelial barrier function, and gut microbiota. Currently, it is unclear whether specific bacterial strains are responsible for the induction of intestinal inflammation, but increased bacterial tissue invasion has been described in affected UC patients. Further, a quantitative and qualitative microbial imbalance in UC, defined as dysbiosis, has been characterized by an increase in Rhodococcus spp., Shigella spp., and Escherichia spp., but a decrease in certain Bacteroides spp.. More specifically, Campylobacter spp., Enterobacteriae, and enterohepatic Helicobacter were more prevalent in tissue sample from UC patients subjected to molecular detection methods, but not controls. In addition, serologic testing identified Fusobacterim varium as a potential contributor to the intestinal inflammation in UC. Interestingly, in-situ hybridization studies have shown anti-inflammatory Lactobacillus spp. and Pediococcus spp. were absent in samples from subjects affected by UC. Therefore, dysbiosis is a factor in the pathogenesis of UC.

Development of a unique small molecule modulator of CXCR4.

BACKGROUND: Metastasis, the spread and growth of tumor cells to distant organ sites, represents the most devastating attribute and plays a major role in the morbidity and mortality of cancer. Inflammation is crucial for malignant tumor transformation and survival. Thus, blocking inflammation is expected to serve as an effective cancer treatment. Among anti-inflammation therapies, chemokine modulation is now beginning to emerge from the pipeline. CXC chemokine receptor-4 (CXCR4) and its ligand stromal cell-derived factor-1 (CXCL12) interaction and the resulting cell signaling cascade have emerged as highly relevant targets since they play pleiotropic roles in metastatic progression. The unique function of CXCR4 is to promote the homing of tumor cells to their microenvironment at the distant organ sites. METHODOLOGY/PRINCIPAL FINDINGS: We describe the actions of N,N'-(1,4-phenylenebis(methylene))dipyrimidin-2-amine (designated MSX-122), a novel small molecule and partial CXCR4 antagonist with properties quite unlike that of any other reported CXCR4 antagonists, which was prepared in a single chemical step using a reductive amination reaction. Its specificity toward CXCR4 was tested in a binding affinity assay and a ligand competition assay using (18)F-labeled MSX-122. The potency of the compound was determined in two functional assays, Matrigel invasion assay and cAMP modulation. The therapeutic potential of MSX-122 was evaluated in three different murine models for inflammation including an experimental colitis, carrageenan induced paw edema, and bleomycin induced lung fibrosis and three different animal models for metastasis including breast cancer micrometastasis in lung, head and neck cancer metastasis in lung, and uveal melanoma micrometastasis in liver in which CXCR4 was reported to play crucial roles. CONCLUSIONS/SIGNIFICANCE: We developed a novel small molecule, MSX-122, that is a partial CXCR4 antagonist without mobilizing stem cells, which can be safer for long-term blockade of metastasis than other reported CXCR4 antagonists.

Bacterial induction of proinflammatory cytokines in inflammatory bowel disease.

It has become increasingly clear that inflammatory bowel disease (IBD) develops on the background of genetic defects in the host, conveying an increased susceptibility to an environmental antigen or antigens. The environmental factor implicated in the pathophysiology of gut inflammation, which is undergoing increased scrutiny, is the intestinal flora. The intestinal flora as a whole and specific bacteria and their products have been found to trigger cytokine expression in various cell types. Consistently, multiple bacterial strains were found to induce tumor necrosis factor alpha (TNF-α) and interleukin-8 (IL-8) in macrophage and epithelial cell systems, respectively, in particular in Crohn's disease. Interestingly, various cell types from patients with IBD display an increased susceptibility to specific bacterial products, including flagellin, pili, and lipopolysaccharides. It remains to be determined whether additional effector proteins regulate cytokine expression and the aberrant mucosal immune response in IBD.

The role of lymphostatin/EHEC factor for adherence-1 in the pathogenesis of gram negative infection.

Lymphostatin/EHEC factor for adherence-1 is a novel large toxin represented in various Gram negative bacteria, highly associated with the development of infectious diarrhea and hemolytic uremic syndrome. In vitro and in vivo experiments identified lymphostatin/EFA-1 as a toxin with a central role in the pathogenesis of Gram negative bacteria, responsible for bacterial adhesion, intestinal colonization, immunosuppression, and disruption of gut epithelial barrier function.

Prohibitin inhibits tumor necrosis factor alpha-induced nuclear factor-kappa B nuclear translocation via the novel mechanism of decreasing importin alpha3 expression.

Expression of prohibitin 1 (PHB), a multifunctional protein in the cell, is decreased during inflammatory bowel disease (IBD). Little is known regarding the regulation and role of PHB during intestinal inflammation. We examined the effect of tumor necrosis factor alpha (TNF-alpha), a cytokine that plays a central role in the pathogenesis of IBD, on PHB expression and the effect of sustained PHB expression on TNF-alpha activation of nuclear factor-kappa B (NF-kappaB) and epithelial barrier dysfunction, two hallmarks of intestinal inflammation. We show that TNF-alpha decreased PHB protein and mRNA abundance in intestinal epithelial cells in vitro and in colon mucosa in vivo. Sustained expression of prohibitin in intestinal epithelial cells in vitro and in vivo (prohibitin transgenic mice, PHB TG) resulted in a marked decrease in TNF-alpha-induced nuclear translocation of the NF-kappaB protein p65, NF-kappaB/DNA binding, and NF-kappaB-mediated transcriptional activation despite robust IkappaB-alpha phosphorylation and degradation and increased cytosolic p65. Cells overexpressing PHB were protected from TNF-alpha-induced increased epithelial permeability. Expression of importin alpha3, a protein involved in p50/p65 nuclear import, was decreased in cells overexpressing PHB and in colon mucosa of PHB TG mice. Restoration of importin alpha3 levels sustained NF-kappaB activation by TNF-alpha during PHB transfection. These results suggest that PHB inhibits NF-kappaB nuclear translocation via a novel mechanism involving alteration of importin alpha3 levels. TNF-alpha decreases PHB expression in intestinal epithelial cells and restoration of PHB expression in these cells can protect against the deleterious effects of TNF-alpha and NF-kappaB on barrier function.

The bacterial virulence factor lymphostatin compromises intestinal epithelial barrier function by modulating rho GTPases.

Lymphocyte inhibitory factor A (lifA) in Citrobacter rodentium encodes the large toxin lymphostatin, which contains two enzymatic motifs associated with bacterial pathogenesis, a glucosyltransferase and a protease. Our aim was to determine the effects of each lymphostatin motif on intestinal epithelial-barrier function. In-frame mutations of C. rodentium lifA glucosyltransferase (CrGlM21) and protease (CrPrM5) were generated by homologous recombination. Infection of both model intestinal epithelial monolayers and mice with C. rodentium wild type resulted in compromised epithelial barrier function and mislocalization of key intercellular junction proteins in the tight junction and adherens junction. In contrast, CrGlM21 was impaired in its ability to reduce barrier function and influenced the tight junction proteins ZO-1 and occludin. CrPrM5 demonstrated decreased effects on the adherens junction proteins beta-catenin and E-cadherin. Analysis of the mechanisms revealed that C. rodentium wild type differentially influenced Rho GTPase activation, suppressed Cdc42 activation, and induced Rho GTPase activation. CrGlM21 lost its suppressive effects on Cdc42 activation, whereas CrPrM5 was unable to activate Rho signaling. Rescue experiments using constitutively active Cdc42 or C3 exotoxin to inhibit Rho GTPase supported a role of Rho GTPases in the epithelial barrier compromise induced by C. rodentium. Taken together, our results suggest that lymphostatin is a bacterial virulence factor that contributes to the disruption of intestinal epithelial-barrier function via the modulation of Rho GTPase activities.

Krüppel-like factor 5 mediates transmissible murine colonic hyperplasia caused by Citrobacter rodentium infection.

BACKGROUND & AIMS: Krüppel-like factor 5 (KLF5) is a transcription factor that is highly expressed in proliferating crypt cells of the intestinal epithelium. KLF5 has a pro-proliferative effect in vitro and is induced by mitogenic and stress stimuli. To determine whether KLF5 is involved in mediating proliferative responses to intestinal stressors in vivo, we examined its function in a mouse model of transmissible murine colonic hyperplasia triggered by colonization of the mouse colon by the bacteria Citrobacter rodentium. METHODS: Heterozygous Klf5 knockout (Klf5(+/-)) mice were generated from embryonic stem cells carrying an insertional disruption of the Klf5 gene. Klf5(+/-) mice or wild-type (WT) littermates were infected with C rodentium by oral gavage. At various time points postinfection, mice were killed and distal colons were harvested. Colonic crypt heights were determined morphometrically from sections stained with H&E. Frozen tissues were stained by immunofluorescence using antibodies against Klf5 and the proliferation marker, Ki67, to determine Klf5 expression and numbers of proliferating cells per crypt. RESULTS: Infection of WT mice with C rodentium resulted in a 2-fold increase in colonic crypt heights at 14 days postinfection and was accompanied by a 1.7-fold increase in Klf5 expression. Infection of Klf5(+/-) mice showed an attenuated induction of Klf5 expression, and hyperproliferative responses to C rodentium were reduced in the Klf5(+/-) animals as compared with WT littermates. CONCLUSION: Our study shows that Klf5 is a key mediator of crypt cell proliferation in the colon in response to pathogenic bacterial infection.

Detectable serum flagellin and lipopolysaccharide and upregulated anti-flagellin and lipopolysaccharide immunoglobulins in human short bowel syndrome.

Gut barrier dysfunction may occur in short bowel syndrome (SBS). We hypothesized that systemic exposure to flagellin and lipopolysaccharide (LPS) in SBS might regulate specific immune responses. We analyzed serial serum samples obtained from parenteral nutrition (PN)-dependent patients with SBS versus non-SBS control serum. Serum from 23 adult SBS patients was obtained at baseline and 4, 8, 12, 16, 20, and 24 wk in a trial of modified diet with or without growth hormone. Control serum was obtained from 48 healthy adults and 37 adults requiring PN during critical illness. Serum flagellin was detected by an ELISA recognizing an array of gram-negative flagellins, and LPS was detected by limulus assay. Serum flagellin- and LPS-specific immunoglobulin levels (IgM, IgA, and IgG) were determined by ELISA. Serum flagellin and LPS were undetectable in control subjects. In contrast, serum flagellin, LPS, or both were detected in 14 SBS patients (61%) during one or more time points [flagellin alone, 5/23 (22%); LPS alone, 6/23 (26%); or flagellin + LPS, 3/23 (13%)]. Flagellin-specific serum IgM, IgA, and IgG levels were markedly increased in SBS patients compared with both control populations and remained elevated during the 6-mo study period. LPS-specific IgA was significantly higher in SBS patients compared with healthy controls; LPS-specific IgM, IgA, and IgG levels each decreased over time in association with PN weaning. We conclude that adults with PN-dependent SBS are systemically exposed to flagellin and LPS, presumably from the gut lumen. This likely regulates innate and adaptive immune responses to these specific bacterial products.

Invasive Escherichia coli are a feature of Crohn's disease.

Crohn's disease (CD) and ulcerative colitis (UC) are idiopathic inflammatory conditions of the gut. Our goal was to investigate if invasive Escherichia coli strains were present in patients with inflammatory bowel disease (IBD). Bacterial strains were isolated from biopsy material obtained from normal controls, and patients with a clinical diagnosis of CD and UC. Invasive bacteria were characterized by gentamicin protection assay and biochemical profiling (Api-20E). Strains were characterized by induction of cytokine expression in epithelial and macrophage cell cultures, measurement of epithelial barrier function, and confocal microscopy. Of all invasive bacterial strains in CD 98.9% were identified as E. coli as opposed to 42.1% in UC and 2.1% in normal controls. Epithelial invasion in vitro was significantly higher for CD-associated E. coli (8.4%, +/-5.5 of initial inoculum (I/O)) in comparison to UC (2.5%, +/-0.4 I/O), but highest for strains from inflamed CD tissue (11.3%, +/-4.3 I/O). Both, CD and UC E. coli strains induced high mean TNF-alpha expression in macrophage cell lines (2604.8 pg/10(5) cells, +/-447.4; 2,402.6 pg/10(5) cells, +/-476.3, respectively), but concentrations were significantly higher for isolates from inflamed CD tissue (3071.3 pg/10(5) cells, +/-226.0). Invasive E. coli from IBD tissue induced similar concentrations of interleukin (IL)-8 in epithelial cell cultures, but strains from inflamed CD tissue induced significantly less epithelial IL-8 (674.1 pg/10(5) cells, +/-58.0 vs 920.5 pg/10(5) cells, +/-94.6). IBD-associated E. coli strains significantly decreased transepithelial resistance, induced disorganization of F-actin and displacement of ZO-1, and E-cadherin from the apical junctional complex (AJC). In comparison to normal controls and UC, E. coli are more prevalent in CD, are highly invasive, and do not encode for known effector proteins. E. coli strains from IBD patients regulate cytokine expression and epithelial barrier function, two pathological features of IBD.

Are plasma citrulline and glutamine biomarkers of intestinal absorptive function in patients with short bowel syndrome?

Sensitive biomarkers for intestinal absorptive function would be clinically useful in short bowel syndrome (SBS). Citrulline (Cit) is a product of the metabolism of glutamine (Gln) and derived amino acids by enterocytes. Cit is produced almost exclusively by the gut, which is also a major site of Gln metabolism. The goals of this study were to examine whether plasma Cit and Gln concentrations are biomarkers of residual small intestinal length and nutrient absorptive functions in adult SBS patients followed prospectively. We studied 24 stable adults with severe SBS receiving chronic parenteral nutrition (PN) in a double-blind, randomized trial of individualized dietary modification +/- recombinant human growth hormone (GH). During a baseline week, intestinal absorption studies (% absorption of fluid, kcal, nitrogen, fat, carbohydrate, sodium, phosphorus, and magnesium) were performed and concomitant plasma Cit and Gln concentrations determined. Individualized dietary modification and treatment with subcutaneous injection of placebo (n = 9) or GH (0.1 mg/kg daily x 21 days, then 3 times/week; n = 15) were then begun. PN weaning was initiated after week 4 and continued as tolerated for 24 weeks. Repeat plasma amino acid determination and nutrient absorption studies were performed at weeks 4 and 12. Residual small bowel length at baseline was positively correlated with baseline plasma Cit (r = 0.467; p = .028). However, no significant correlations between absolute Cit or Gln concentrations and the percent absorption of nutrient substrates at any time point were observed. Similarly, no correlation between the change in Cit or GLN concentration and the change in % nutrient absorption was observed (baseline vs weeks 4 and 12, respectively). By weeks 12 and 24, 7 and 13 subjects were weaned completely from PN, respectively. However, baseline plasma Cit or Gln did not predict PN weaning at these time points. We concluded that plasma Cit (but not Gln) concentrations appeared to be an indicator of small intestinal length in adult SBS. However, neither plasma Cit nor Gln was a biomarker for intestinal absorptive function in this cohort of patients with SBS.

Prohibitin protects against oxidative stress in intestinal epithelial cells.

Prohibitin (PHB) is an evolutionarily conserved and ubiquitously expressed protein whose expression or function in intestinal diseases is not known. In this study, we examined the expression and role of PHB in oxidative stress associated with inflammatory bowel disease. Our results show that PHB primarily localizes to the mitochondria in intestinal epithelial cells. Its expression is down-regulated during active human Crohn's disease, experimental colitis in vivo, and oxidative stress in vitro. PHB overexpression increases the expression of glutathione-S-transferase pi and protects from oxidant-induced depletion of glutathione. Finally, PHB overexpression decreases accumulation of reactive oxygen metabolites, as well as increased permeability induced by oxidative stress in intestinal epithelial cells. Together, these results suggest that PHB constitutes a previously unrecognized cellular defense against oxidant injury. Thus, strategies to modulate PHB levels may constitute a novel therapeutic approach for intestinal inflammatory diseases, wherein oxidative stress plays a critical role in tissue injury and inflammation.

Growth hormone favorably affects bone turnover and bone mineral density in patients with short bowel syndrome undergoing intestinal rehabilitation.

BACKGROUND: Patients with short bowel syndrome (SBS) have a high prevalence of metabolic bone disease due to nutrient malabsorption and potential effects of parenteral nutrition (PN). Human growth hormone (hGH) has been shown in some studies to have anabolic effects on bone, but hGH effects on bone in patients with SBS are unknown. METHODS: Adults with PN-dependent SBS underwent a 7-day period of baseline studies while receiving usual oral diet and PN and then began receiving modified diets designed to improve nutrient absorption and daily oral calcium/vitamin D supplements (1500 mg elemental calcium and 600 IU vitamin D, respectively). Subjects were randomized to receive in a double-blind manner either subcutaneous (sc) saline placebo as the control or hGH (0.1 mg/kg/d for 3 weeks, then 0.1 mg/kg 3 days a week for 8 subsequent weeks). Open-label hGH was given from week 13 to week 24 in subjects who required PN after completion of the 12-week double-blind phase. Markers of bone turnover (serum osteocalcin and urinary N-telopeptide [NTX]), vitamin D nutriture (serum calcium, 25-hydroxyvitamin D [25-OH D] and parathyroid hormone [PTH] concentrations), and intestinal calcium absorption were measured at baseline and at weeks 4 and 12. Dual x-ray absorptiometry (DXA) of the hip and spine was performed to determine bone mineral density (BMD) at baseline and weeks 12 and 24. RESULTS: The majority of subjects in each group exhibited evidence of vitamin D deficiency at baseline (25-OH D levels<30 ng/mL; 78% and 79% of control and hGH-treated subjects, respectively). Subjects treated with hGH demonstrated a significant increase from baseline in serum osteocalcin levels at 12 weeks (+62%; p<.05). The levels of NTX were increased over time in the hGH-treated group; however, this did not reach statistical significance. Both NTX and osteocalcin remained unchanged in control subjects. BMD of the spine and total hip was unchanged in subjects treated with placebo or hGH at 24 weeks. However, femoral neck BMD was slightly but significantly decreased in the placebo group at this time point but remained unchanged from baseline in the hGH-treated subjects. CONCLUSIONS: hGH therapy significantly increased markers of bone turnover during the initial 3 months of therapy and stabilized femoral neck bone mass over a 6-month period in patients with severe SBS undergoing intestinal rehabilitation.

hPepT1 mediates bacterial tripeptide fMLP uptake in human monocytes.

Here, we examined hPepT1 expression in the monocytic cell line, KG-1. Reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that hPepT1 is expressed in KG-1 cells, while cDNA cloning and direct sequencing confirmed the sequence of KG-1 hPepT1 (accession number, AY634368). Immunoblotting of cell lysates from KG-1 cells or macrophages isolated from human peripheral blood revealed a approximately 100 kDa immunoreactive band mainly present in the membrane fraction. Uptake experiments showed that the transport of 20 microM radiolabeled Gly-Sarcosine ([14C]Gly-Sar) in KG-1 cells was Na+, Cl- dependent and disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS)-sensitive. In addition, hPepT1 activity was likely to be coupled to a Na+/H+ exchanger, as evidenced by the fact that [14C]Gly-Sar uptake was not affected by the absence of Na+ when cells were incubated at low pH (5.2). Interestingly, hPepT1-mediated transport was reduced in KG-1 cells incubated at low pH as it was also observed in nonpolarized Caco2-BBE cells. This pattern of pH-dependence is due to a disruption of the driving force of hPepT1-mediated transport events. This was supported by our finding that nonpolarized cells, Caco2-BBE cells and KG-1 cells, have an increased permeability to H+ when compared to polarized Caco2-BBE cells. Finally, we showed that hPepT1 is responsible for transporting fMLP into undifferentiated and differentiated (macrophage-like) KG-1 cells. Together, these results show that hPepT1 is expressed in nonpolarized immune cells, such as macrophages, where the transporter functions best at the physiological pH 7.2. Furthermore, we provide evidence for hPepT1-mediated fMLP transport, which might constitute a novel immune cell activation pathway during intestinal inflammation.