Downloaded from www.microbiologyresearch.org by IP: 54.90.167.105 On: Tue, 10 May 2016 21:31:31 Journal of Medical Microbiology (2004), 53, 741–748 DOI 10.1099/jmm.0.45657-0 45657 & 2004 SGM Printed in Great Britain 741 Correspondence Jacques R. Nicoli, jnicoli@icb.ufmg.br Received 2 March 2004 Accepted 27 April 2004 Influence of normal microbiota on some aspects of the immune response during experimental infection with Trypanosoma cruzi in mice Rinaldo Duarte, 1 Andre ´ ia M. Silva, 1 Leda Q. Vieira, 2 Luiz Carlos C. Afonso 3 and Jacques R. Nicoli 1 1, 2 Departamento de Microbiologia 1 and Departamento de Bioquı ´mica-Imunologia 2 , Instituto de Cie ˆ ncias Biolo ´ gicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil 3 Departamento de Cie ˆ ncias Biolo ´ gicas, ICEB/NUPEB, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil To study the influence of normal associated microbiota on systemic immunological responses during experimental Chagas’ disease, germ-free and conventional NIH Swiss mice were infected with Y strain of Trypanosoma cruzi. Although no statistical differences in mortality and parasitaemia were found, conventional mice showed IFN-ª, TNF-Æ and NO production (P , 0 . 05) by spleen cell cultures and higher blood levels of immunoglobulins of the IgG2a isotype (P , 0 . 05) when compared to their germ-free counterparts. Moreover, higher levels of IgG1 were also found in conventional animals. On the other hand, no differences in IL10 production were found between germ-free and conventional mice after infection (P , 0 . 05). Interestingly, spleen cell cultures from non-infected germ-free mice spontaneously produced higher levels of IL10 than cultures from conventional mice. Moreover, cultures from non-infected germ-free mice responded to T. cruzi antigens with IFN-ª production, contrary to cultures from conventional animals. In conclusion, the presence of the normal microbiota skews the immune response towards production of inflammatory cytokines during experimental infection with T. cruzi in mice. However, the increase in production of cytokines that is linked to resistance to this parasite did not alter the outcome of infection significantly, probably due to high virulence of the Y strain. INTRODUCTION From the early days of life, human beings are associated with a very large and complex microbiota that, by its size, should be considered as a functionally active organ, the full potential of which remains to be elucidated (Berg, 1996). In healthy hosts, the presence of this microbiota has a very large impact on various aspects of function and metabolism such as metabolic rate, gastrointestinal function, specific and quan- titative aspects of immune function and the many aspects of biochemical homeostasis. Presently available data also in- dicate that this normal microbiota almost always has a profound influence on host–parasite relationships. As an example, it is well known that the presence of intestinal microbiota is essential for the pathogenicity of some proto- zoa and helminthes such as Entamoeba histolytica (Phillips & Wolfe, 1959), Nippostrongylus brasiliensis (Wescott & Todd, 1964), Nematospiroides dubius (Wescott, 1968), Trichinella spiralis (Przyjalkowski & Wescott, 1969), Eimeria tenella (Visco & Burns, 1972), Ascaridia galli (Johnson & Reid, 1973), Trichuris suis (Rutter & Beer, 1975), Eimeria falci- formes (Owen, 1975), Eimeria ovinoidalis (Gouet et al., 1984) and Giardia duodenalis (Torres et al., 2000). In contrast, this microbiota can reduce the pathological consequences of other infectious diseases as described for experimental infections with Trypanosoma cruzi (Silva et al., 1987), Cryptococcus neoformans (Salkowski et al., 1987), Strongy- loides venezuelensis (Martins et al., 2000) and almost all enteropathogenic bacteria (Clostridium difficile, Clostridium perfringens, Escherichia coli, Pseudomonas aeruginosa, Salmo- nella typhimurium, Shigella flexneri, Vibrio cholerae) (Wilson, 1995). Experimental infections with Raillietina cesticillus (Reid & Botero, 1967) and Isospora suis (Harleman & Meyer, 1984) are two of the very few cases where the normal microbiota has no influence on the course of a disease. T. cruzi is the causative agent of Chagas’ disease in man and the protozoa determines a systemic infection that is con- trolled, although not completely eliminated, by T-cell- dependent immune responses. Control of parasitism in the acute phase of infection is critically dependent on intracellu- Abbreviations: LPS, lipopolysaccharide; tGPI mucin, T. cruzi glycophosphatidylinositol-anchored mucin-like glycoconjugates.