Induction of Sd(a)-sialomucin and sulfated H-sulfomucin in mouse small intestinal mucosa by infection with parasitic helminth.

Mucin is a major component of mucus on gastrointestinal mucosa. Mucin alteration in the host is considered to be the principal event for expulsion of intestinal helminths. However, it is unclear what mucin alterations are induced by various helminth infections. In this study, the alterations of mouse small intestinal mucin after infection with two nematodes, Nippostrongylus brasiliensis and Heligmosomoides polygyrus, which parasitize the jejunal epithelium, and a cestode, Vampirolepis nana, which parasitizes the ileal epithelium, were examined biochemically and histologically using two anti-mucin monoclonal antibodies (mAbs), HCM31 and PGM34, which recognize Sd(a) antigen, NeuAcα2-3(GalNAcß1-4)Galß1-4GlcNAcß-, and sulphated H type 2 antigen, Fucα1-2Galß1-4GlcNAc(6SO3H)ß-, respectively. The goblet cell mucins that reacted with HCM31 increased conspicuously on the jejunal mucosa concurrently with expulsion of N. brasiliensis. Increased levels of HCM31-reactive mucins were observed in the jejunal mucosa after H. polygyrus infection, despite the ongoing parasitism. Goblet cell mucins that reacted with PGM34 increased on the ileal mucosa during V. nana parasitism. Small intestinal goblet cells reacting with the two mAbs were not observed in non-infected mice, although sialomucins and sulfomucins were abundantly present. Additionally, the number of ileal goblet cells that reacted with the two mAbs was increased at the time of expulsion of heterophyid trematode. These results indicate that the type of specific acidic mucins expressed after infection varies among species of intestinal helminth, and, furthermore, that the relationship with worm expulsion is also different.

Entamoeba histolytica exacerbates epithelial tight junction permeability and proinflammatory responses in Muc2(-/-) mice.

Human mucin-2 (MUC-2) is the first line of innate host defense in preventing pathogen-induced epithelial injury. Entamoeba histolytica (Eh) colonizes the mucus layer by binding of the parasite's surface galactose lectin to galactose and N-acetyl-d-galactosamine residues on colonic MUC-2, preventing parasite contact-dependent cytolysis of epithelial cells. We quantified early innate responses to Eh in wild-type and MUC-2-deficient mice (Muc2(-/-)) using closed colonic loops. Eh infection in wild-type but not Muc2(-/-) mice induced a time-dependent increase in (3)H-labeled mucin and nonmucin glycoprotein secretions. Immunohistochemical staining revealed intense MUC-2 secretion, which formed a thick, protective mucus plug overlying the surface epithelium, entrapping Eh. In Muc2(-/-) mice, Eh induced a pronounced time-dependent secretory exudate with increased gross pathology scores and serum albumin leakage. Colonic pathology, secretory responses, and increased proinflammatory cytokine secretions of TNF-α, IFN-γ, and IL-13 correlated with altered expression of the tight junction proteins claudin-2, occludin, and ZO-1. We identified the putative Eh virulence factor that elicits the proinflammatory responses and alters tight junction permeability as Eh cysteine protease A5 (EhCP-A5). The present findings demonstrate that colonic mucins confer both luminal and epithelial barrier functions and that, in the absence of MUC-2, mice are more susceptible to Eh-induced secretory and proinflammatory responses mediated by EhCP-A5.

Quantitative analyses of genes associated with mucin synthesis of broiler chickens with induced necrotic enteritis.

Clostridial infection of the intestine can result in necrotic enteritis (NE), compromising production and health of poultry. Mucins play a major role in protecting the intestinal epithelium from infection. The relative roles of different mucins in gut pathology following bacterial challenge are unclear. This study was designed to quantify the expression of mucin and mucin-related genes, using intestinal samples from an NE challenge trial where birds were fed diets with or without in-feed antimicrobials. A method for quantifying mucin gene expression was established using a suite of reference genes to normalize expression data. This method was then used to quantify the expression of 11 candidate genes involved in mucin, inflammatory cytokine, or growth factor biosynthesis (IL-18, KGF, TLR4, TFF2, TNF-α, MUC2, MUC4, MUC5ac, MUC5b, MUC13, and MUC16). The only genes that were differentially expressed in the intestine among treatment groups were MUC2, MUC13, and MUC5ac. Expression of MUC2 and MUC13 was depressed by co-challenge with Eimeria spp. and Clostridium perfringens. Antimicrobial treatment prevented an NE-induced decrease in MUC2 expression but did not affect MUC13. The expression of MUC5ac was elevated in birds challenged with Eimeria spp./C. perfringens compared with unchallenged controls and antimicrobial treatment. Changes to MUC gene expression in challenged birds is most likely a consequence of severe necrosis of the jejunal mucosa.

Intestinal epithelial tuft cell induction is negated by a murine helminth and its secreted products.

Helminth parasites are adept manipulators of the immune system, using multiple strategies to evade the host type 2 response. In the intestinal niche, the epithelium is crucial for initiating type 2 immunity via tuft cells, which together with goblet cells expand dramatically in response to the type 2 cytokines IL-4 and IL-13. However, it is not known whether helminths modulate these epithelial cell populations. In vitro, using small intestinal organoids, we found that excretory/secretory products (HpES) from Heligmosomoides polygyrus blocked the effects of IL-4/13, inhibiting tuft and goblet cell gene expression and expansion, and inducing spheroid growth characteristic of fetal epithelium and homeostatic repair. Similar outcomes were seen in organoids exposed to parasite larvae. In vivo, H. polygyrus infection inhibited tuft cell responses to heterologous Nippostrongylus brasiliensis infection or succinate, and HpES also reduced succinate-stimulated tuft cell expansion. Our results demonstrate that helminth parasites reshape their intestinal environment in a novel strategy for undermining the host protective response.

Mucin gene deficiency in mice impairs host resistance to an enteric parasitic infection.

BACKGROUND & AIMS: Hyperplasia of mucin-secreting intestinal goblet cells accompanies a number of enteric infections, including infections by nematode parasites. Nevertheless, the precise role of mucins in host defense in nematode infection is not known. We investigated the role of the mucin (Muc2) in worm expulsion and host immunity in a model of nematode infection. METHODS: Resistant (BALB/c, C57BL/6), susceptible (AKR), and Muc2-deficient mouse strains were infected with the nematode, Trichuris muris, and worm expulsion, energy status of the whipworms, changes in mucus/mucins, and inflammatory and immune responses were investigated after infection. RESULTS: The increase in Muc2 production, observed exclusively in resistant mice, correlated with worm expulsion. Moreover, expulsion of the worms from the intestine was significantly delayed in the Muc2-deficient mice. Although a marked impairment in the development of periodic acid Schiff (PAS)-stained intestinal goblet cells was observed in Muc2-deficient mice, as infection progressed a significant increase in the number of PAS-positive goblet cells was observed in these mice. Surprisingly, an increase in Muc5ac, a mucin normally expressed in the airways and stomach, was observed after infection of only the resistant animals. Overall, the mucus barrier in the resistant mice was less permeable than that of susceptible mice. Furthermore, the worms isolated from the resistant mice had a lower energy status. CONCLUSIONS: Mucins are an important component of innate defense in enteric infection; this is the first demonstration of the important functional contribution of mucins to host protection from nematode infection.

Changes in the mucosal barrier during acute and chronic Trichuris muris infection.

The intestinal mucosal barrier, part of the innate immune defence, is responsive to the external environment and changes in response to infection. There is disparate evidence for the epithelial and goblet cell products within the intrinsic barrier being part of a response to resolve infection. We comprehensively analysed the changes of mucosal glycoconjugates during acute and chronic infection by utilising the Trichuris muris (T. muris) model. Transcription factors, atonal homolog 1 (Math-1) and SAM pointed domain containing ETS transcription factor (Spdef) were activated during acute infection, which promoted stem cell fate towards a secretory cell phenotype. The thickness of the intermediate barrier, the carbohydrate-rich glycocalyx, composed of cell surface mucins increased with exposure to T. muris, with an increase in Muc4, Muc13 and Muc17. Overall, hypersecretion of glycoproteins into the extrinsic barrier (mediated by IL-13) via the gamma amino-butyric acid-α3 receptor (GABA-α3), was observed during acute infection. Furthermore, altered glycosylation was observed during acute and chronic infection; mucins were more highly charged during acute infection than during chronic infection. This study readdresses the changes within the mucosal barrier, in particular in the cell surface and secreted mucins during acute and chronic nematode infection.

Host Protective Mechanisms to Intestinal Amebiasis.

The protozoan parasite Entamoeba histolytica is the causative agent of amebiasis, an infection that manifests as colitis and, in some cases, liver abscess. A better understanding of host protective factors is key to developing an effective remedy. Recently, significant advances have been made in understanding the mechanisms of MUC2 production by goblet cells upon amebic infection, regulation of antimicrobial peptide production by Paneth cells, the interaction of commensal microbiota with immune stimulation, and host genetics in conferring protection from amebiasis. In addition to host pathways that may serve as potential therapeutic targets, significant progress has also been made with respect to development of a vaccine against amebiasis. Here, we aim to highlight the current understanding and knowledge gaps critically.

Tumor suppressor p53 regulates intestinal type 2 immunity.

The role of p53 in tumor suppression has been extensively studied and well-established. However, the role of p53 in parasitic infections and the intestinal type 2 immunity is unclear. Here, we report that p53 is crucial for intestinal type 2 immunity in response to the infection of parasites, such as Tritrichomonas muris and Nippostrongylus brasiliensis. Mechanistically, p53 plays a critical role in the activation of the tuft cell-IL-25-type 2 innate lymphoid cell circuit, partly via transcriptional regulation of Lrmp in tuft cells. Lrmp modulates Ca2+ influx and IL-25 release, which are critical triggers of type 2 innate lymphoid cell response. Our results thus reveal a previously unrecognized function of p53 in regulating intestinal type 2 immunity to protect against parasitic infections, highlighting the role of p53 as a guardian of immune integrity.

TFF3 interacts with LINGO2 to regulate EGFR activation for protection against colitis and gastrointestinal helminths.

Intestinal epithelial cells (IEC) have important functions in nutrient absorption, barrier integrity, regeneration, pathogen-sensing, and mucus secretion. Goblet cells are a specialized cell type of IEC that secrete Trefoil factor 3 (TFF3) to regulate mucus viscosity and wound healing, but whether TFF3-responsiveness requires a receptor is unclear. Here, we show that leucine rich repeat receptor and nogo-interacting protein 2 (LINGO2) is essential for TFF3-mediated functions. LINGO2 immunoprecipitates with TFF3, co-localizes with TFF3 on the cell membrane of IEC, and allows TFF3 to block apoptosis. We further show that TFF3-LINGO2 interactions disrupt EGFR-LINGO2 complexes resulting in enhanced EGFR signaling. Excessive basal EGFR activation in Lingo2 deficient mice increases disease severity during colitis and augments immunity against helminth infection. Conversely, TFF3 deficiency reduces helminth immunity. Thus, TFF3-LINGO2 interactions de-repress inhibitory LINGO2-EGFR complexes, allowing TFF3 to drive wound healing and immunity.

IL-4/IL-13 independent goblet cell hyperplasia in experimental helminth infections.

BACKGROUND: Intestinal mucus production by hyperplasic goblet cells is a striking pathological feature of many parasitic helminth infections and is related to intestinal protection and worm expulsion. Induction of goblet cell hyperplasia is associated with TH2 immune responses, which in helminth infections are controlled primarily by IL-13, and also IL-4. In the study presented here we examine the goblet cell hyperplasic response to three experimental parasitic helminth infections; namely Nippostrongylus brasiliensis, Syphacia obvelata and Schistosoma mansoni. RESULTS: As expected N. brasiliensis infection induced a strong goblet cell hyperplasia dependent on IL-4/IL-13/IL-4Ralpha expression. In contrast, and despite previously published transiently elevated IL-4/IL-13 levels, S. obvelata infections did not increase goblet cell hyperplasia in the colon. Furthermore, induction of goblet cell hyperplasia in response to S. mansoni eggs traversing the intestine was equivalent between BALB/c, IL-4/IL-13-/- and IL-4Ralpha-/- mice. CONCLUSION: Together these data demonstrate that intestinal goblet cell hyperplasia can be independent of TH2 immune responses associated with parasitic helminth infections.

Innate immune response mechanisms in the intestinal epithelium: potential roles for mast cells and goblet cells in the expulsion of adult Trichinella spiralis.

SUMMARYGastrointestinal infection with the nematode Trichinella spiralis is accompanied by a rapid and reversible expansion of the mucosal mast cell and goblet cell populations in the intestinal epithelium, which is associated with the release of their mediators into the gut lumen. Both goblet cell and mast cell hyperplasia are highly dependent on mucosal T-cells and augmented by the cytokines IL-4 and IL-13. However, the contribution of both mast and goblet cells, and the mediators they produce, to the expulsion of the adults of T. spiralis is only beginning to be elucidated through studies predominantly employing T. spiralis-mouse models. In the present article, we review the factors proposed to control T. spiralis-induced mucosal mast cell (MMC) and goblet cell differentiation in the small intestine, and focus on some key MMC and goblet cell effector molecules which may contribute to the expulsion of adult worms and/or inhibition of larval development.

Evaluation of the mucosal inflammatory responses to equine cyathostomins in response to anthelmintic treatment.

Members of Cyathostominae are pervasive parasites of equids that can cause larval cyathostominosis, a potentially life-threatening disease that occurs when a multitude of encysted larvae synchronously excyst from the wall of the large intestine. Moxidectin and fenbendazole are the two current labeled drugs that target the encysted larval stages; however, there is limited knowledge of the local inflammatory response to the larvae and to the two treatments in clinically healthy horses. This study is the first to evaluate the local inflammatory response to cyathostomin larvae and to larvicidal treatment at 2 and 5 weeks post treatment. Thirty-six ponies with naturally acquired cyathostomin infections were randomly allocated into 3 groups: Group 1, fenbendazole at 10 mg/kg for 5 days, Group 2, a single dose of moxidectin at 0.4 mg/kg, and Group 3, untreated controls. Tissue samples from the cecum and dorsal and ventral colons were used for histopathological and immunohistochemical evaluation. Tissues were stained with routine hematoxylin and eosin (H&E) for light microscopy and immunohistochemically for MAC387, CD20, and CD3 for differentiation of activated macrophages, B cells, and T cells, respectively. Semiquantitative scores were assigned for all inflammatory cell types and fibrous connective tissue. Larvae observed by light microscopy were enumerated and classified by stage. Mucosal ulcerations and submucosal granulomas were also enumerated. Mean macrophage scores were higher in the moxidectin group than the fenbendazole group (p = 0.0185) and the control group had a higher activated macrophage score than both treatment groups (p = 0.0104, p = 0.0004). T lymphocyte scores were higher in the moxidectin group when compared to the control group (p = 0.0069). Goblet cell hyperplasia scores were elevated at 5 weeks post treatment compared to 2 weeks post treatment (p = 0.0047) and were elevated in the ventral colon compared to the dorsal colon (p = 0.0301). Eosinophil scores were elevated surrounding degenerative larvae when compared to intact larvae (p = 0.0001). Mucosal ulcerations were found only in the control group at 2 weeks post treatment. This study found subtle inflammatory differences between treatment groups but provided new information about goblet cells and eosinophils in relation to encysted cyathostomin larvae.

Altered expression of goblet cell- and mucin glycosylation-related genes in the intestinal epithelium during infection with the nematode Nippostrongylus brasiliensis in rat.

Intestinal nematode infection induces marked goblet cell hyperplasia and mucus secretion, but the mechanisms of regulation of the changes still remain to be elucidated. In the present study, epithelial cells were isolated from the rat small intestine at various times after Nippostrongylus brasiliensis infection, and the levels of expression of goblet cell- and mucin glycosylation-related genes were estimated by semi-quantitative reverse transcription (RT)-PCR. Among the genes investigated, mucin core peptide (MUC) 2, sialyltransferase (Siat) 4c and trefoil factor family (TFF) 3 were upregulated as early as 2-4 days post-infection, suggesting that they are associated with an early innate protective response. Seven days post-infection and thereafter, when the nematodes reached maturity, significant upregulation of MUC3, MUC4, resistin-like molecule beta (Relmbeta) and 3O-sulfotransferase (3ST)1 was observed, while 3ST2 expression levels increased after the majority of the worms were expelled from the intestine. Similar alterations of glycosylation-related gene expression were also observed in mast-cell-deficient Ws/Ws rats, suggesting that mast cells in the epithelium are not relevant to the upregulation of these genes. The present finding that the expression level of each goblet cell- or glycosylation-related gene was altered differently during the time course of infection indicates the progression of sequential qualitative changes in the mucus layer after infection.

Conditional IL-4/IL-13-deficient mice reveal a critical role of innate immune cells for protective immunity against gastrointestinal helminths.

Approximately one-third of the world population is infected with gastrointestinal helminths. Studies in mouse models have demonstrated that the cytokines interleukin (IL)-4 and IL-13 are essential for worm expulsion, but the critical cellular source of these cytokines is poorly defined. Here, we compared the immune response to Nippostrongylus brasiliensis in wild-type, T cell-specific IL-4/IL-13-deficient and general IL-4/IL-13-deficient mice. We show that T cell-derived IL-4/IL-13 promoted T helper 2 (Th2) polarization in a paracrine manner, differentiation of alternatively activated macrophages, and tissue recruitment of innate effector cells. However, innate IL-4/IL-13 played the critical role for induction of goblet cell hyperplasia and secretion of effector molecules like Mucin5ac and RELMß in the small intestine. Surprisingly, T cell-specific IL-4/IL-13-deficient and wild-type mice cleared the parasite with comparable efficiency, whereas IL-4/IL-13-deficient mice showed impaired expulsion. These findings demonstrate that IL-4/IL-13 produced by cells of the innate immune system is required and sufficient to initiate effective type 2 immune responses resulting in protective immunity against N. brasiliensis.

Inflammatory responses in the intestinal mucosa of gerbils and hamsters experimentally infected with the adult stage of Taenia solium.

The inflammatory response in gerbils and hamsters harbouring experimental infections with Taenia solium adult parasites as well as worm burden and duration of infections were examined. For this purpose, non-suppressed or immunosuppressed rodents were infected with eight cysticerci and necropsied at different times up to 35 days post-infection. Cells in the mucosa surrounding the implantation site of T. solium scolices (duodenum-jejunum) and in ileum were counted in stained sections. A competitive enzyme linked immunosorbent assay was used to determine histamine concentration in intestinal fluid. In non-suppressed hosts, an inflammatory reaction developed with scarce macrophages, a slight increase of plasma cells, lymphocytes and fibroblasts, a moderate increase of eosinophils and neutrophils, and high numbers of goblet and mast cells. Goblet cells began to increase at 6 days post-infection and peaked at 13 days post-infection with a four-fold increase with respect to the control group. Mast cells only increased in gerbils starting at 9 days post-infection with an eight-fold increase when cells peaked between 11 and 19 days post-infection. Histamine concentration in intestinal fluid of gerbils had a similar behaviour to mast cells. Minimal increase of mast cells was seen in hamsters. The recovery of tapeworms was inversely related to the number of both cell types, which decreased when tapeworms were eliminated. Infections lasted up to 25 days in gerbils and up to 46 days in hamsters. Worms measured only 1-2 cm in gerbils and up to 40 cm in hamsters. When gerbils were suppressed with the steroid methyl predinisolone, tapeworms could be recovered up to 35 days post-infection and tapeworms measured up to 22 cm, a minor increase of goblet and mast cells was observed and histamine concentration was similar to that in non-infected animals. Our results suggest that expulsion of T. solium in gerbils and hamsters may be related to the increase of goblet cells and mast cells, but these cells may have different roles in each rodent model of taeniosis.

Local and systemic immune responses to Echinococcus granulosus in experimentally infected dogs.

Local and systemic immune responses were studied in six dogs experimentally infected with the dog/sheep tapeworm Echinococcus granulosus. All dogs developed similar IgG antibody response to parasite antigens. In contrast, IgE and IgA responses differed widely. No relationship between IgA responses and parasite burden at the end of the infection were observed. Further, clear differences in the anti-parasite IgA response in serum as compared with specific IgA forming cells in mesenteric lymph nodes were observed within the same dog. An inverse association of anti-parasite IgE and parasite load seemed to be present, with the strongest IgE response in the one dog that had no worms in the intestine at the end of the experiment. No differences were observed in the numbers of intestinal mast cells and goblet cells among all infected dogs. However, the dog with no detectable parasite load had a marked reduction of detected mast cells in the submuscular and muscular layer of the mucosa. Our data give new insight into the immune response of dogs during E. granulosus infection and provide information that may be useful for the rational design of vaccines for the control of hydatid disease.

Ileal mucosal mast cell, eosinophil, and goblet cell populations during Hymenolepis diminuta infection of the rat.

The population dynamics in the enteric connective tissues of eosinophils, mucosal mast cells (MMC), and in the mucosal epithelium of goblet cells were examined morphometrically in fixed ileal tissue of outbred Sprague Dawley rats during the first 32 days of infection with the tapeworm Hymenolepis diminuta. MMC and eosinophils were present in the lamina propria and submucosa; however, only eosinophils were also present in the muscularis externa. Eosinophilic infiltrate was first observed in the lamina propria at 15 days postinfection (dpi) and the numbers of eosinophils remained elevated through 32 dpi. Initial mucosal mastocytosis was detected on 6 dpi and MMC numbers continued to rise over the study period without reaching a plateau. Goblet cell hyperplasia occurred only at 32 dpi. In contrast to some intestinal nematode infections where these same 3 cell types are associated with the host's expulsion responses, H. diminuta is not lost by a rapid host response in the outbred Sprague Dawley rat strain used in these experiments. We suggest that either the induction of hyperplasia of these host effector cells in ileum tissue during H. diminuta infection is not capable of triggering parasite rejection mechanisms, or the function of the induced hyperplasia is necessary for some as yet unassociated physiological or tissue architecture change in the host's intestine.

A new role for mucins in immunity: insights from gastrointestinal nematode infection.

The body's mucosal surfaces are protected from pathogens and physical and chemical attack by the gel-like extracellular matrix, mucus. The framework of this barrier is provided by polymeric, gel-forming mucins. These enormous O-linked glycoproteins are synthesised, stored and secreted by goblet cells that are also the source of other protective factors. Immune regulation of goblet cells during the course of infection impacts on mucin production and properties and ultimately upon barrier function. The barrier function of mucins in protection of the host is well accepted as an important aspect of innate defence. However, it is becoming increasingly clear that mucins have a much more direct role in combating pathogens and parasites and are an important part of the coordinated immune response to infection. Of particular relevance to this review is the finding that mucins are essential anti-parasitic effector molecules. The current understanding of the roles of these multifunctional glycoproteins, and other goblet cell products, in mucosal defence against intestinal dwelling nematodes is discussed.

The goblet cell is the cellular source of the anti-microbial angiogenin 4 in the large intestine post Trichuris muris infection.

BACKGROUND: Mouse angiogenin 4 (Ang4) has previously been described as a Paneth cell-derived antimicrobial peptide important in epithelial host defence in the small intestine. However, a source for Ang4 in the large intestine, which is devoid of Paneth cells, has not been defined. METHODOLOGY/PRINCIPAL FINDINGS: Analysis was performed on Ang4 expression in colonic tissue by qPCR and immunohistochemistry following infection with the large intestine dwelling helminth parasite Trichuris muris. This demonstrated an increase in expression of the peptide following infection of resistant BALB/c mice. Further, histological analysis of colonic tissue revealed the cellular source of this Ang4 to be goblet cells. To elucidate the mechanism of Ang4 expression immunohistochemistry and qPCR for Ang4 was performed on colonic tissue from T. muris infected mouse mutants. Experiments comparing C3H/HeN and C3H/HeJ mice, which have a natural inactivating mutation of TLR4, revealed that Ang4 expression is TLR4 independent. Subsequent experiments with IL-13 and IL-4 receptor alpha deficient mice demonstrated that goblet cell expression of Ang4 is controlled either directly or indirectly by IL-13. CONCLUSIONS: The cellular source of mouse Ang4 in the colon following T. muris infection is the goblet cell and expression is under the control of IL-13.

Goblet cells: are they an unspecific barrier against Giardia intestinalis or a gate?

Giardiosis is one of the major intestinal parasitic diseases of human beings as well as wild and domesticated animals. Several protective mechanisms against infection have been described. However, specific information about relationship between giardiosis and the increased proliferation of goblet cells (GC) in patients infected with Giardia intestinalis (Syn. G. duodenalis, G. lamblia) is scarce. In this work, we compare and quantify the number of GC, and have inferred their metabolic state in the small intestine of dogs parasitized with Giardia intestinalis compared to dogs without parasites. Small intestine segments were processed using routine methods for histology and electron microscopy; areas and cells were screened with an Axiovision Ver. 4.0 system. Data were analyzed by ANOVA and comparison of averages. Parasitized dogs showed higher GC numbers than nonparasitized ones. Averages were: 20+/-0.81 GC/25 microm(2) with independent mucin granules and 11+/-1.53 GC/25 microm(2) that were expelling mucus, compared to 11+/-0.94 GC/25 microm(2) and 1+/-0.27 GC/25 microm(2), respectively, in nonparasitized dogs (Tukey, p<0.001). The increases in GC number seem to be an unspecific defensive mechanism against Giardia trophozoites. However, we found some evidence supporting that GC hyperplasia could be a prejudicial to epithelial barrier that gives rise to gates allowing for Giardia-tissue invasion.