The Th2 immune response in chronic schistosomiasis is associated with the development of periportal fibrosis. However, little is known about the phenotype and activation status of T cells in the process. Objective. To evaluate the profile of T cells in schistosomiasis patients with periportal fibrosis. Methods. It was a cross-sectional study, conducted in the village of Agua Preta, Bahia, Brazil, which included 37 subjects with periportal fibrosis determined by ultrasound. Peripheral blood mononuclear cells were obtained by the Ficcol-hypaque gradient and the frequency of T cells expressing the surface markers CD28, CD69, CD25, and CTLA-4 was determined by flow cytometry. Results. The frequency of CD4+CD28+ T lymphocytes was higher in individuals with moderate to severe fibrosis compared to patients with incipient fibrosis. We did not observe any significant difference in the frequency of CD4+ T cells expressing CD69 among groups of individuals. There was also no significant difference in the frequency of CD8+ T cells expressing CD28 or CD69 among the studied groups. Individuals with moderate to severe fibrosis presented a lower frequency of CD8+ T cells, CD4+CD25high T cells, and CD4+CTLA-4+ T cells when compared to patients without fibrosis or incipient fibrosis. The frequency of CD4+CD25low cells did not differ between groups. Conclusion. The high frequency of activated T cells coinciding with a low frequency of putative Treg cells may account for the development of periportal fibrosis in human schistosomiasis. 1. Introduction Schistosomiasis is a parasitic disease which accounts for the second place in terms of socioeconomic and public health burden in tropical and subtropical areas. It is a chronic and debilitating disease caused by parasites of the genus Schistosoma. About 200 million people are affected worldwide, and close to 800 million are at the risk of infection [1]. Liver pathology results from the host immune response to antigens from the eggs that become trapped in the portal venous system. The granulomas formed around the eggs act as barriers which prevent the dispersion of egg antigens of S. mansoni. However, about 5% of infected individuals evolve to periportal fibrosis which is associated with the morbidity and mortality described in chronic schistosomiasis [2–4]. Studies have evaluated the cytokine response associated with granuloma formation and development of periportal fibrosis due to schistosomiasis, both in experimental models and in vitro models of granuloma or tissue biopsies [5–7]. There are, however, few studies evaluating
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