Interstitial cells in the primate gastrointestinal tract

Kit immunohistochemistry and confocal reconstructions have provided detailed 3-dimensional images of ICC networks throughout the gastrointestinal (GI) tract. Morphological criteria have been used to establish that different classes of ICC exist within the GI tract and physiological studies have shown that these classes have distinct physiological roles in GI motility. Structural studies have focused predominately on rodent models and less information is available on whether similar classes of ICC exist within the GI tracts of humans or non-human primates. Using Kit immunohistochemistry and confocal imaging, we examined the 3-dimensional structure of ICC throughout the GI tract of cynomolgus monkeys. Whole or flat mounts and cryostat sections were used to examine ICC networks in the lower esophageal sphincter (LES), stomach, small intestine and colon. Anti-histamine antibodies were used to distinguish ICC from mast cells in the lamina propria. Kit labeling identified complex networks of ICC populations throughout the non-human primate GI tract that have structural characteristics similar to that described for ICC populations in rodent models. ICC-MY formed anastomosing networks in the myenteric plexus region. ICC-IM were interposed between smooth muscle cells in the stomach and colon and were concentrated within the deep muscular plexus (ICC-DMP) of the intestine. ICC-SEP were found in septal regions of the antrum that separated circular muscle bundles. Spindle-shaped histamine⁺ mast cells were found in the lamina propria throughout the GI tract. Since similar sub-populations of ICC exist within the GI tract of primates and rodents and the use of rodents to study the functional roles of different classes of ICC is warranted.     

Telocytes are the physiological counterpart of inflammatory fibroid polyps and PDGFRA‐mutant GISTs

PDGFRA mutations in the gastrointestinal (GI) tract can cause GI stromal tumour (GIST) and inflammatory fibroid polyp (IFP). Hitherto no cell type has been identified as a physiological counterpart of the latter, while interstitial Cajal cells (ICC) are considered the precursor of the former. However, ICC hyperplasia (ICCH), which strongly supports the ICC role in GIST pathogenesis, has been identified in germline KIT‐mutant settings but not in PDGFRA‐mutant ones, challenging the precursor role of ICC for PDGFRA‐driven GISTs. Telocytes are a recently described interstitial cell type, CD34+/PDGFRA+. Formerly considered fibroblasts, they are found in many organs, including the GI tract where they are thought to be involved in neurotransmission. Alongside IFPs and gastric GISTs, GI wall “fibrosis” has been reported in germline PDGFRA‐mutants. Taking the opportunity offered by its presence in a germline PDGFRA‐mutant individual, we demonstrate that this lesion is sustained by hyperplastic telocytes, constituting the PDGFRA‐mutant counterpart of germline KIT mutation‐associated ICCH. Moreover, our findings support a pathogenetic relationship between telocyte hyperplasia and both IFPs and PDGFRA‐mutant GISTs. We propose the term “telocytoma” for defining IFP, as it conveys both the pathogenetic (neoplastic) and histotypic (“telocytary”) essence of this tumour, unlike IFP, which rather evokes an inflammatory‐hyperplastic lesion.     

Alterations of the interstitial cells of Cajal and the microstructure of the gastrointestinal tract in KIT distal kinase mutant mice

The development and maintenance of interstitial cells of Cajal (ICC) are closely associated with SCF/KIT signal activity. In this study, we evaluate the distribution of ICC in KIT distal kinase domain mutant mice (Wads) and determine whether the loss-of-function mutations in KIT easily lead to gastrointestinal (GI) disorders. ICC were examined by anti-KIT immunohistochemistry and western blotting. The GI microstructure of wild-type (WT) and Wads mice in normal intestines and incomplete intestinal obstruction was evaluated by hematoxylin and eosin staining. The results in Wads^m/m mice were as follows. Myenteric ICC were obviously decreased in the stomach and colon and were totally absent in the small intestine. Intramuscular ICC were nearly absent in the stomach and irregularly distributed in the colon. Moreover, the smooth muscle thickness of the small intestine was increased 1.3-fold in Wads^m/m, compared to WT and Wads^m/+ mice and the diameter of the intestinal lumen was also enlarged in Wads^m/m mice. When constructing an incomplete intestinal obstruction model, the extent of distention involved was greater in Wads mice (1.6-fold in Wads^m/+ mice and 1.8-fold in Wads^m/m mice vs. WT mice). Meanwhile, the intestinal lumen expansion and decrease in ICC were more pronounced in Wads mice than in WT mice. Our results suggest that the KIT distal kinase domain mutation leads to an ICC loss in a subtype and location-specific pattern in Wads^m/m mice. The injury of the KIT signaling in mutant mice results in more serious pathological manifestations after being exposed to pathogenic factors.     

Germline mutations of KIT in gastrointestinal stromal tumor (GIST) and mastocytosis

Somatic mutations of KIT are frequently found in mastocytosis and gastrointestinal stromal tumor (GIST), while germline mutations of KIT are rare, and only found in few cases of familial GIST and mastocytosis. Although ligand-independent activation is the common feature of KIT mutations, the phenotypes mediated by various germline KIT mutations are different. Germline KIT mutations affect different tissues such as interstitial cells of Cajal (ICC), mast cells or melanocytes, and thereby lead to GIST, mastocytosis, or abnormal pigmentation. In this review, we summarize germline KIT mutations in familial mastocytosis and GIST and discuss the possible cellular context dependent transforming activity of KIT mutations.     

LIX1 regulates YAP activity and controls gastrointestinal cancer cell plasticity

Gastrointestinal stromal tumours (GISTs), the most common mesenchymal neoplasm of the gastrointestinal tract, result from deregulated proliferation of transformed KIT‐positive interstitial cells of Cajal that share mesenchymal progenitors with smooth muscle cells. Despite the identification of selective KIT inhibitors, primary resistance and relapse remain a major concern. Moreover, most patients develop resistance partly through reactivation of KIT and its downstream signalling pathways. We previously identified the Limb Expression 1 (LIX1) gene as a unique marker of digestive mesenchyme immaturity. We also demonstrated that LIX1 regulates mesenchymal progenitor proliferation and differentiation by controlling the Hippo effector YAP1, which is constitutively activated in many sarcomas. Therefore, we wanted to determine LIX1 role in GIST development. We found that LIX1 is strongly up‐regulated in GIST samples and this is associated with unfavourable prognosis. Moreover, LIX1 controls GIST cell proliferation in vitro and in vivo. Upon LIX1 inactivation in GIST cells, YAP1/TAZ activity is reduced, KIT (the GIST signature) is down‐regulated, and cells acquire smooth muscle lineage features. Our data highlight LIX1 role in digestive mesenchyme‐derived cell‐fate decisions and identify this novel regulator as a target for drug design for GIST treatment by influencing its differentiation status.     

Roles of Interleukin-9 in the Growth and Cholecystokinin-Induced Intracellular Calcium Signaling of Cultured Interstitial Cells of Cajal

Interstitial cells of Cajal (ICC) are pacemaker cells in the gastrointestinal (GI) tract and loss of ICC is associated with many GI motility disorders. Previous studies have shown that ICC have the capacity to regenerate or restore, and several growth factors are critical to their growth, maintenance or regeneration. The present study aimed to investigate the roles of interleukin-9 (IL-9) in the growth, maintenance and pacemaker functions of cultured ICC. Here, we report that IL-9 promotes proliferation of ICC, and culturing ICC with IL-9 enhances cholecystokinin-8-induced Ca²⁺ transients, which is probably caused by facilitating maintenance of ICC functions under culture condition. We also show co-localizations of cholecystokinin-1 receptor and IL-9 receptor with c-kit by double-immunohistochemical labeling. In conclusion, IL-9 can promote ICC growth and help maintain ICC functions; IL-9 probably performs its functions via IL-9 receptors on ICC.     

Biological and clinical review of stromal tumors in the gastrointestinal tract

Submucosal tumors of the gastrointestinal tract (GI tract) mainly consist of gastrointestinal mesenchymal tumors (GIMTs) that are distributed in the GI tract from the esophagus through the rectum. GIMTs include myogenic tumors, neurogenic tumors and gastrointestinal stromal tumors (GISTs). The term "GIST" is now preferentially used for the tumors that express CD34 and KIT. GIMTs are composed of spindle or epithelioid cells, and 20% to 30% show malignant behavior, including peritoneal dissemination and hematogenous metastasis. KIT expression and mutations in the c-kit gene are found only in GISTs, but not in myogenic or neurogenic tumors. Mutation in the c-kit gene is associated with aggressive features and poor prognosis, and malignant GISTs frequently have mutations in the c-kit gene. The clinicopathological features of GISTs with or without c-kit mutations are markedly different. Therefore, GIMTs may be divided into four major categories based on histochemical and genetic data: myogenic tumors; neurogenic tumors; GISTs with c-kit mutation; and GISTs without c-kit mutation. The origin of GISTs is not fully understood. However, phenotypical resemblance to the interstitial cells of Cajal (ICCs) and gain-of-function mutations in the c-kit gene may suggest origin from ICCs and/or multipotential mesenchymal cells that differentiate into ICCs.     

Physiology and pathophysiology of the interstitial cell of Cajal: from bench to bedside. I. Functional development and plasticity of interstitial cells of Cajal networks

Interstitial cells of Cajal (ICC) are the pacemaker cells in gastrointestinal (GI) muscles. They also mediate or transduce inputs from enteric motor nerves to the smooth muscle syncytium. What is known about functional roles of ICC comes from developmental studies based on the discovery that ICC express c-kit. Functional development of ICC networks depends on signaling via the Kit receptor pathway. Immunohistochemical studies using Kit antibodies have expanded our knowledge about the ICC phenotype, the structure of ICC networks, the interactions of ICC with other cells within the tunica muscularis, and the loss of ICC in some motility disorders. Manipulating Kit signaling with reagents to block the receptor or downstream signaling pathways or by using mutant mice in which Kit or its ligand, stem cell factor, are defective has allowed novel studies of the development of these cells within the tunica muscularis and also allowed the study of specific functions of different classes of ICC in several regions of the GI tract. This article examines the role of ICC in GI motility, focusing on the functional development and maintenance of ICC networks in the GI tract and the phenotypic changes that can occur when the Kit signaling pathway is disrupted.     

Role of Interstitial Cells of Cajal and their relationship with the enteric nervous system.

The term 'Interstitial cells of Cajal' (ICC) designates several groups of mesenchymal cells present along the gastro-intestinal tract (GI), in close association with smooth muscle cells and elements of the enteric nervous system (ENS). For years, transmission electron microscopy (TEM) has been the only reliable tool to study ICC. Whilst TEM remains the golden standard for identification of ICC, the observation that the tyrosine kinase receptor c-kit plays a crucial role in their development recently resulted in numerous immunohistochemical studies and also led to a better characterization of their roles. ICC form extensive networks of electrically coupled cells and certain groups of ICC are currently regarded as the source of the spontaneous slow waves of the gut musculature (pacemaker cells). Other ICC appear to be involved in the transduction of the relaxation of smooth muscle triggered by nitric oxide. Abnormal distribution of ICC has been reported in several human diseases and abnormal functioning of ICC might actually be involved in many disorders of GI transit. This review addresses (1) the morphology and relationships of ICC along the GI tract in man and mouse, mainly based on data from immunohistochemistry and confocal microscopy, (2) the emerging role of ICC in the pathophysiology of human diseases, like infantile hypertrophic pyloric stenosis (a common disorder with a dysfunction of the pyloric sphincter), Hirschsprung's disease (aganglion-osis coli) and intestinal pseudo-obstruction, (3) developmental issues, (4) recent reports suggesting a possible link between ICC and gastrointestinal stromal tumors.     

Inhibition of KIT-Glycosylation by 2-Deoxyglucose Abrogates KIT-Signaling and Combination with ABT-263 Synergistically Induces Apoptosis in Gastrointestinal Stromal Tumor

Positron emission tomography (PET) with ¹⁸F-fluorodeoxyglucose (FDG) is frequently used for visualizing gastrointestinal stromal tumors (GIST), which are highly glucose-avid tumors. Dramatic metabolic responses following imatinib treatment indicate a high, KIT-dependent glucose turnover which has been particularly helpful for predicting tumor response to imatinib. The glucose analogue 2-deoxyglucose (2DG) inhibits glucose metabolism in cancer cells that depend on aerobic glycolysis for ATP production. We show that 2DG inhibits proliferation in both imatinib-sensitive and imatinib-resistant GIST cell lines at levels that can be achieved clinically. KIT-negative GIST48B have 3-14-fold higher IC50 levels than KIT-positive GIST cells indicating that oncogenic KIT may sensitize cells to 2DG. GIST sensitivity to 2DG is increased in low-glucose media (110mg/dl). 2DG leads to dose- and glucose dependent inhibition of KIT glycosylation with resultant reduction of membrane-bound KIT, inhibition of KIT-phosphorylation and inactivation of KIT-dependent signaling intermediates. In contrast to imatinib, 2DG caused ER-stress and elicited the unfolded protein response (UPR). Mannose but not pyruvate rescued GIST cells from 2DG-induced growth arrest, suggesting that loss of KIT integrity is the predominant effect of 2DG in GIST. Additive anti-tumoral effects were seen with imatinib and BH3-mimetics. Our data provide the first evidence that modulation of the glucose-metabolism by 2DG may have a disease-specific effect and may be therapeutically useful in GIST.     

Hesperidin depolarizes the pacemaker potentials through 5-HT4 receptor in murine small intestinal interstitial cells of Cajal

ABSTRACT

Hesperidin, a citrus flavonoid, can exert numerous beneficial effects on human health. Interstitial cells of Cajal (ICC) are pacemaker cells in the gastrointestinal (GI) tract. In the present study, we investigated potential effects of hesperidin on pacemaker potential of ICC in murine small intestine and GI motility. A whole-cell patch-clamp configuration was used to record pacemaker potential in ICC, and GI motility was investigated in vivo by recording gastric emptying (GE) and intestinal transit rate (ITR). Hesperidin depolarized pacemaker potentials of ICC in a dose-dependent manner. Pre-treatment with methoctramine or 4-DAMP did not inhibit hesperidin-induced pacemaker potential depolarization. Neither a 5-HT₃ receptor antagonist (Y25130) nor a 5-HT₇ receptor antagonist (SB269970) reduced the effect of hesperidin on ICC pacemaker potential, whereas the 5-HT₄ receptor antagonist RS39604 was found to inhibit this effect. In the presence of GDP–β–S, hesperidin-induced pacemaker potential depolarization was inhibited. Moreover, in the presence of U73122 and calphostin C, hesperidin did not depolarize pacemaker potentials. Furthermore, hesperidin accelerated GE and ITR in vivo. These results imply that hesperidin depolarized ICC pacemaker potential via 5-HT₄ receptors, G protein, and PLC/PKC dependent pathways and that it increased GI motility. Therefore, hesperidin may be a promising novel drug to regulate GI motility.     

Neurotensin receptor 1 is expressed in gastrointestinal stromal tumors but not in interstitial cells of Cajal

Gastrointestinal stromal tumors (GIST) are thought to derive from the interstitial cells of Cajal (ICC) or an ICC precursor. Oncogenic mutations of the KIT or PDGFRA receptor tyrosine kinases are present in the majority of GIST, leading to ligand-independent activation of the intracellular signal transduction pathways. We previously investigated the gene expression profile in the murine Kit(K641E) GIST model and identified Ntsr1 mRNA, encoding the Neurotensin receptor 1, amongst the upregulated genes. Here we characterized Ntsr1 mRNA and protein expression in the murine Kit(K641E) GIST model and in tissue microarrays of human GIST. Ntsr1 mRNA upregulation in Kit(K641E) animals was confirmed by quantitative PCR. Ntsr1 immunoreactivity was not detected in the Kit positive ICC of WT mice, but was present in the Kit positive hyperplasia of Kit(K641E) mice. In the normal human gut, NTSR1 immunoreactivity was detected in myenteric neurons but not in KIT positive ICC. Two independent tissue microarrays, including a total of 97 GIST, revealed NTSR1 immunoreactivity in all specimens, including the KIT negative GIST with PDGFRA mutation. NTSR1 immunoreactivity exhibited nuclear, cytoplasmic or mixed patterns, which might relate to variable levels of NTSR1 activation. As studies using radio-labeled NTSR1 ligand analogues for whole body tumor imaging and for targeted therapeutic interventions have already been reported, this study opens new perspectives for similar approaches in GIST.     

The stem cell growth factor receptor KIT is not expressed on interstitial cells in bladder

The mast/stem cell growth factor receptor KIT has long been assumed to be a specific marker for interstitial cells of Cajal (ICC) in the bladder, with possible druggable perspectives. However, several authors have challenged the presence of KIT⁺ ICC in recent years. The aim of this study was therefore to attempt to clarify the conflicting reports on KIT expression in the bladder of human beings, rat, mouse and guinea pig and to elucidate the possible role of antibody‐related issues and interspecies differences in this matter. Fresh samples were obtained from human, rat, mouse and guinea pig cystectomies and processed for single/double immunohistochemistry/immunofluorescence. Specific antibodies against KIT, mast cell tryptase (MCT), anoctamin‐1 (ANO1) and vimentin were used to characterize the cell types expressing KIT. Gut (jejunum) tissue was used as an external antibody control. Our results revealed KIT expression on mast cells but not on ICC in human, rat, mouse and guinea pig bladder. Parallel immunohistochemistry showed KIT expression on ICC in human, rat, mouse and guinea pig gut, which confirmed the selectivity of the KIT antibody clones. In conclusion, we have shown that KIT⁺ cells in human, rat, mouse and guinea pig bladder are mast cells and not ICC. The present report is important as it opposes the idea that KIT⁺ ICC are present in bladder. In this perspective, functional concepts of KIT⁺ ICC being involved in sensory and/or motor aspects of bladder physiology should be revised.     

Kit K641E oncogene up-regulates Sprouty homolog 4 and Trophoblast glycoprotein in interstitial cells of Cajal in a murine model of gastrointestinal stromal tumours

Gastrointestinal stromal tumours (GIST) are thought to derive from the interstitial cells of Cajal (ICC) or an ICC precursor. Oncogenic mutations of the receptor tyrosine kinase KIT are present in most GIST. KIT K642E was originally identified in sporadic GIST and later found in the germ line of a familial GIST cohort. A mouse model harbouring a germline Kit K641E mutant was created to model familial GIST. The expression profile was investigated in the gastric antrum of the Kit ^K641E murine GIST model by microarray, quantitative PCR and immunofluorescence. Gja1/Cx43 , Gpc6 , Gpr133 , Pacrg , Pde3a , Prkar2b , Prkcq/Pkce , Rasd2 , Spry4 and Tpbg/5T4 were found to be up-regulated. The proteins encoded by Gja1/Cx43 , Pde3a , Prkcq/Pkce were localized in Kit-ir ICC in wild-type and Kit ^K641E animals while Spry4 and Tpbg/5T4 were detected in Kit-ir cells only in Kit ^K641E, but not in Kit ^WT/WT animals. Most up-regulated genes in this mouse model belong to the gene expression profile of human GIST but also to the profile of normal Kit⁺ ICC in the mouse small intestine. Spry4 and Tpbg/5T4 may represent candidates for targeted therapeutic approaches in GIST with oncogenic KIT mutations.     

Relationship between interstitial cells of Cajal, fibroblast-like cells and inhibitory motor nerves in the internal anal sphincter

Interstitial cells of Cajal (ICC) have been shown to participate in nitrergic neurotransmission in various regions of the gastrointestinal (GI) tract. Recently, fibroblast-like cells, which are positive for platelet-derived growth factor receptor ?? (PDGFR??⁺), have been suggested to participate additionally in inhibitory neurotransmission in the GI tract. The distribution of ICC and PDGFR??⁺ cell populations and their relationship to inhibitory nerves within the mouse internal anal sphincter (IAS) are unknown. Immunohistochemical techniques and confocal microscopy were therefore used to examine the density and arrangement of ICC, PDGFR??⁺ cells and neuronal nitric-oxide-synthase-positive (nNOS⁺) nerve fibers in the IAS of wild-type (WT) and W/W ^v mice. Of the total tissue volume within the IAS circular muscle layer, 18% consisted in highly branched PDGFR??⁺ cells (PDGFR??⁺-IM). Other populations of PDGFR??⁺ cells were observed within the submucosa and along the serosal and myenteric surfaces. Spindle-shaped intramuscular ICC (ICC-IM) were present in the WT mouse IAS but were largely absent from the W/W ^v IAS. The ICC-IM volume (5% of tissue volume) in the WT mouse IAS was significantly smaller than that of PDGFR??⁺-IM. Stellate-shaped submucosal ICC (ICC-SM) were observed in the WT and W/W ^v IAS. Minimum surface distance analysis revealed that nNOS⁺ nerve fibers were closely aligned with both ICC-IM and PDGFR??⁺-IM. An even closer association was seen between ICC-IM and PDGFR??⁺-IM. Thus, a close morphological arrangement exists between inhibitory motor neurons, ICC-IM and PDGFR??⁺-IM suggesting that some functional interaction occurs between them contributing to inhibitory neurotransmission in the IAS.     

Distribution of the intermediate filament nestin in the muscularis propria of the human gastrointestinal tract

The intermediate filament nestin is expressed in neural stem cells, neuroectodermal tumors and various adult tissues. In the gastrointestinal (GI) tract, nestin has been reported in glial cells. Recently, nestin has been reported in interstitial cells of Cajal (ICC) and in gastrointestinal stromal tumors, thought to derive from ICC. Here we investigated nestin immunoreactivity (-ir) in the normal human GI tract, with emphasis on Kit-ir ICC. Two different antibodies specific for human nestin and multicolor high-resolution confocal microscopy were used on material from our human GI tissue collection. The staining pattern of both nestin antibodies was similar. In labeled cells, nestin-ir appeared filamentous. Most intramuscular ICC in antrum and all myenteric ICC (ICC-MP) in small intestine were nestin-ir, while nestin-ir was not detected in deep muscular plexus ICC. In the colon, some - but not all - ICC-MP and most ICC in the circular musculature were nestin-ir while nestin-ir was not detected in ICC in the longitudinal musculature and in the submuscular plexus. In addition, many Kit-negative cells were nestin-ir in all regions. Neurons and smooth muscle cells were consistently nestin negative, while most S100-ir glial cells were nestin-ir. In addition, nestin-ir was also present in some CD34-ir fibroblast-like cells, in endothelium and in other cell types in the mucosa and serosa. In conclusion, nestin-ir is abundantly present in the normal human GI tract. Among a number of cell types, several, but not all, subpopulations of Kit-ir ICC were nestin-ir. The functional significance of nestin in the GI tract remains obscure.     

Autophagy is involved in endogenous and NVP-AUY922-induced KIT degradation in gastrointestinal stromal tumors

Gastrointestinal stromal tumor (GIST) is a prototype of mutant KIT oncogene-driven tumor. Prolonged tyrosine kinase inhibitor (TKI) treatment may result in a resistant phenotype through acquired secondary KIT mutation. Heat shock protein 90 (HSP90AA1) is a chaperone protein responsible for protein maturation and stability, and KIT is a known client protein of HSP90AA1. Inhibition of HSP90AA1 has been shown to destabilize KIT protein by enhancing its degradation via the proteasome-dependent pathway. In this study, we demonstrated that NVP-AUY922 (AUY922), a new class of HSP90AA1 inhibitor, is effective in inhibiting the growth of GIST cells expressing mutant KIT protein, the imatinib-sensitive GIST882 and imatinib-resistant GIST48 cells. The growth inhibition was accompanied with a sustained reduction of both total and phosphorylated KIT proteins and the induction of apoptosis in both cell lines. Surprisingly, AUY922-induced KIT reduction could be partially reversed by pharmacological inhibition of either autophagy or proteasome degradation pathway. The blockade of autophagy alone led to the accumulation of the KIT protein, highlighting the role of autophagy in endogenous KIT turnover. The involvement of autophagy in endogenous and AUY922-induced KIT protein turnover was further confirmed by the colocalization of KIT with MAP1LC3B-, acridine orange- or SQSTM1-labeled autophagosome, and by the accumulation of KIT in GIST cells by silencing either BECN1 or ATG5 to disrupt autophagosome activity. Therefore, the results not only highlight the potential application of AUY922 for the treatment of KIT-expressing GISTs, but also provide the first evidence for the involvement of autophagy in endogenous and HSP90AA1 inhibitor-induced KIT degradation.     

Gastrointestinal inoculation of Sporothrix schenckii in mice

Antibiotic-decontaminated and untreated conventional mice were inoculated intragastrically with 10⁷ viable cells of Sporothrix schenckii to compare the incidence of gastrointestinal (GI) colonization. In control mice, S. schenckii was completely eliminated from the GI tract by 12 h post-inoculation. Antibiotictreated mice also failed to become colonized with this fungus, however, higher population levels of Sporothrix cells remained in the GI tract for a longer period of time before being eliminated. The ability of S. schenckii to disseminate from the lumen of the bowel to infect other organs was also tested. Results indicate that the gastrointestinal tract is not a portal of entry into the host for S. schenckii.