Kinetics of Foxp3-expressing regulatory cells in experimental Toxocara canis infection

Foxp3-expressing cells have recently been recognized as a cornerstone for the homeostasis of the immune system, and as key cells in many infectious diseases. Moreover, they have been found to contribute to the regulation of parasite-induced immunopathology in many parasitic infections. However, their role in Toxocara-induced immunopathology has not yet been investigated. The aim of this study is to assess the kinetics of Foxp3-expressing regulatory cells during the course of experimental infection by Toxocara canis (T. canis). Foxp3+ cells were identified in the liver by immunohistochemistry, and splenic Foxp3 gene expression was evaluated. We found significantly progressive increase in Foxp3-expressing cell counts in the liver starting from 5 weeks p.i. These cells were detected within and around Toxocara-induced granulomas as well as in isolated inflammatory foci in the portal tracts or within the hepatic parenchyma. Likewise, expression of Foxp3 mRNA in the spleen significantly increased at 5 and 16 weeks p.i. Furthermore, immunization of mice with Toxocara excretory-secretory antigen prior to experimental infection caused earlier mobilization and recruitment of Foxp3+ cells to the liver and enhanced splenic expression of Foxp3 transcripts. These results suggest a potential role of Foxp3-expressing regulatory cells in the evolution of the immunopathological events during infection by T. canis.