Influence of indigenous microbiota on experimental toxoplasmosis in conventional and germ-free mice.

Toxoplasmosis represents one of the most common zoonoses worldwide. Its agent, Toxoplasma gondii, causes a severe innate pro-inflammatory response. The indigenous intestinal microbiota promotes host animal homoeostasis and may protect the host against pathogens. Germ-free (GF) animals provide an important tool for the study of interactions between host and microbiota. In this study, we assessed the role of indigenous microorganisms in disease development utilizing a murine toxoplasmosis model, which includes conventional (CV) and GF NIH Swiss mice. CV and GF mice orally inoculated with T. gondii had similar survival curves. However, disease developed differently in the two animal groups. In CV mice, intestinal permeability increased and levels of intestinal pro-inflammatory cytokines were altered. In GF animals, there were discrete epithelial degenerative changes and mucosal oedema, but the liver and lungs displayed significant lesions. We conclude that, despite similar survival curves, CV animals succumb to an exaggerated inflammatory response, whereas GF mice fail to produce an adequate systemic response.

Evaluation of mucositis induced by irinotecan after microbial colonization in germ-free mice.

Mucositis is one of the most debilitating side effects of chemotherapy and some previous studies suggest a role for indigenous microbiota in the course of this pathology. Therefore, the aim of our study was to evaluate the differences in phenotype between germ-free (GF) and conventional (CV) mice, and the role of ß-glucuronidase-producing bacteria in the development of irinotecan treatment in a murine model. After mucositis induction, CV mice showed a significant increase in all inflammatory parameters when compared to GF mice. CV animals also showed more lesions of the intestinal epithelium, coherent with their higher intestinal permeability. The conventionalization of GF animals reversed their phenotype to that found in CV mice. In addition, gnotobiotic mice monoassociated with an Escherichia coli strain producing ß-glucuronidase showed an increased permeability when compared to gnotobiotic mice monoassociated with an E. coli strain deleted for the gene encoding ß-glucuronidase, but these did not show any differences in the influx of neutrophils, eosinophils or histological characteristics. Our data confirmed that components of the gut microbiota are involved in the signs of mucositis. Nevertheless, other mechanisms than this enzyme are involved in the irinotecan treatment, since the monoassociation was not able to restore the entire phenotype observed in the CV animals with irinotecan treatment in our murine model.

Mast cells are crucial in the resistance against Toxoplasma gondii oral infection.

During oral infection, mucosal immunity assumes a predominant role. Here, we addressed the role of mast cells (MCs), which are mainly located in mucosa during oral infection with Toxoplasma gondii, using MC-deficient (W/W(v) ) mice. We show that in the absence of MCs the resistance of W/W(v) mice to oral infection was considerably reduced. W/W(v) mice uniformly succumbed within 15 days of infection after administration of cysts of the ME49 strain of T. gondii. The rapid lethality of T. gondii in W/W(v) mice correlated with a delayed Th1-cell response, since IFN-γ and IL-12 levels peaked in the later phase of the infection. In vitro, BM-derived MCs were able to recognize parasite lysate in a MyD88-dependent way, reaffirming the role of this TLR adapter in immune responses to T. gondii. The importance of MCs in vivo was confirmed when W/W(v) mice reconstituted with BM-derived MCs from control mice retrieved an early strong Th1-cell response and specially a significant IL-12 production. In conclusion, MCs play an important role for the development of a protective immune response during oral infection with T. gondii.

Apoptosis in Helicobacter pylori gastritis is related to cagA status.

BACKGROUND: Helicobacter pylori infection increases gastric epithelial cell apoptosis; however, the influence of cagA status is still controversial. We aimed to investigate if cagA status is related to apoptosis in H. pylori gastritis at different anatomic sites of the gastric mucosa. MATERIALS AND METHODS: We studied by immunohistochemistry (streptavidin-biotin method) pro-apoptotic (Bax and Bak) and antiapoptotic (Bcl-2 and Bcl-x) proteins expression, scored from 0 to 4, in gastric biopsies, at the antrum (lesser and greater curvatures), incisura, and corpus (greater curvature) from 50 patients with H. pylori gastritis (22 males, 28 females, median age 40 years) and eight non-infected patients (6 males, median age 39.6 years). H. pylori and cagA status were determined by polymerase chain reaction. RESULTS: Apoptotic proteins were expressed in a granular pattern, in the cytoplasm of foveolar cells; Bax and Bak expression was higher than Bcl-2 and Bcl-x in most cases and was significantly higher in patients infected by cagA-positive strains than in those infected by cagA-negative strains (p = .001). Bak expression was higher at the lesser curvature (antrum and incisura) than in the other regions (p = .002) and was correlated with atrophy. Anti-apoptotic proteins were significantly more expressed at the antral lesser curvature than in the other regions of the stomach (Bcl-2: p = .02; Bcl-x: p < .001). CONCLUSIONS: Infection with cagA-positive strains is significantly associated with overexpression of pro-apoptotic proteins in the gastric mucosa, mainly at the antral lesser curvature, which may have a role on atrophy development. Anti-apoptotic proteins were also overexpressed at the lesser curvature, which may occur to keep epithelial cell turnover or might be related to malignant transformation.