Invasion of enterocytes by pathogenic microbes evokes both innate and adaptive immune responses, and microbial pathogens have developed strategies to overcome the initial host immune defense. ␤-Defensins are potentially important endogenous antibiotic-like effectors of innate immunity expressed by intestinal epithelia. In this study, the interplay between the enteric protozoan parasite Cryptosporidium parvum and host epithelial ␤-defensin expression was investigated. Using human and murine models of infection, we demonstrated that C. parvum infection differentially regulates ␤-defensin gene expression. Downregulation of murine ␤-defensin-1 mRNA and protein was observed in both in vitro and in vivo models of infection. Infection of the human colonic HT29 cell line with the parasite resulted in differential effects on various members of the defensin gene family. Partial reduction in human ␤-defensin-1 (hBD-1), induction of hBD-2, and no effect on hBD-3 gene expression was observed. Recombinant hBD-1 and hBD-2 peptides exhibited significant antimicrobial activity against C. parvum sporozoites in vitro. These findings demonstrate that C. parvum infection of enterocytes may affect the expression of various defensins in different ways and suggest that the overall outcome of the effect of antimicrobial peptides on early survival of the parasite may be complex.

The microsporidian Encephalitozoon intestinalis develops within intestinal epithelial cells (enterocytes) and is an important opportunistic diarrhoeal pathogen associated with AIDS. Little is known about the protective immune response against the parasite although in mice IFN-gamma is involved and is required to prevent dissemination of the infection to other organs. The present study was designed to establish a suitable short-term in vitro culture technique for E. intestinalis that would enable studies of the role of cytokines such as IFN-gamma in the effector phase of immunity. Encephalitozoon intestinalis reproduced considerably better in the murine enterocyte cell line CMT-93 than in the three human enterocyte cell lines Caco-2, HT29 and HCT-8. Treatment of CMT-93 cells with IFN-gamma significantly reduced parasite reproduction in a dose- and time-dependent manner. IFN-gamma also inhibited development of the parasite in Caco-2 cells. Neither production of NO nor Fe deprivation appeared to be involved in IFN-gamma-mediated parasite killing. However studies suggested that tryptophan catabolism by indoleamine 2,3-dioxygenase played an important part in inactivation of E. intestinalis.

Schistosoma mansoni liver fibrosis is a complicated multicellular process involving numerous cytokines, chemokines, and growth factors. Transforming growth factor beta 1 (TGF-1) and interleukin (IL)-13 have been identified as critical pro-fibrotic mediators in many studies. IL-17A was linked to enhanced TGF- and IL-13-induced pathologies. This case-control study aimed to explore the effect of IL-17A on TGF- and IL-13-induced liver fibrosis during experimentally schistosomiasis mansoni infection. A total of 40 laboratory-bred female C57BL/6 mice were divided into four equal groups (G), G1 non-infected, G2 infected wild type (WT), G3 infected/anti-IL-17 monoclonal antibodies (mAb) and G4 treated mice. Mice were infected percutaneously with 40±5 cercariae per mouse. Neutralizing IL-17 mAb was administered to G3 intraperitoneally 3 weeks after infection and then every third day until 2 days before sacrification; mice of G4 were treated with a single dose of praziquantel. Serum levels of TGF-, IL-13, IL-17A, and proinflammatory cytokines were measured by ELISA. Liver granulomas were identified by hematoxylin-eosin stain and measured by an ocular micrometer. There was a significantly increased serum concentration of TGF-, IL-13, and IL-17A in infected WT mice (P<0.01), but praziquantel treatment reduced cytokine levels (P<0.03). Neutralization of IL-17A activity remarkably reduced serum concentrations of TGF- and IL-13 (P <0.03) resulting in improved liver functions and reduced granuloma size. Secretion of IL-IL-6 and TNF-were markedly enhanced by infection, however, mice that received anti-mouse IL-17 mAb displayed fewer inflammatory mediators (P<0.03). In conclusion, IL-17A might contribute to the progress of liver fibrosis by enhancing the profibrotic effect of TGF- and IL-13 in mice infected with S. mansoni.

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