Immune suppression in advanced chronic fascioliasis: an experimental study in a rat model.

Chronicity and Th2 immune responses are features of helminth infections in humans. The liver fluke promotes its own survival through several strategies to down-regulate the immune response of the host during the early phase of infection. However, there is no evidence that this modulation occurs much later. The immune response in advanced chronic fascioliasis was analyzed in an experimental rat model at 20 weeks after infection. Cytokine quantification in infected rat serum revealed basal levels. The predominant immunoglobulin (Ig) isotype was IgG1. Flow cytometry analysis of T cell (CD3(+), CD4(+), and CD8a(+)), B cell (CD45R(+)), and macrophage (CD11b(+)) populations in spleens showed no significant differences between infected and control rats. Mononuclear cell proliferation in the spleen in response to T and B mitogens was strongly inhibited in infected versus control rats. During early chronic infection, there is a predominance of a Th2 response, which decreases in advanced chronic infection characterized by a persistent immune suppression.