Abstract
Regulatory T (Treg) cells are important in the regulation of immune response, but the exact regulation of Treg-cell function in vivo is still not well known. In the present study, we investigated the functional activity of CD4(+) CD25(+) Treg cells as well as the frequency and number of CD4(+) CD25(+) FoxP3(+) Treg cells in the spleens of experimentally infected mice with a tissue-migrating parasite, sparganum (plerocercoid of Spirometra mansoni) for 3 weeks. The results demonstrated fluctuations in the Treg-cell function during the parasite infection, being up-regulated at day 3, down-regulated until day 14, and thereafter up-regulated again at day 21. We also investigated the cytokine-producing capability of the splenocytes to study the pattern of immune response of the mice to the parasite. The results showed decreased capabilities of interleukin-2 (IL-2), interferon-γ (IFN-γ) and IL-17α production, whereas IL-4-producing and IL-10-producing capabilities were increased along with the parasitic infection. Meanwhile, IL-6-producing capability was increased to reach a peak at week 2, and thereafter was decreased to the baseline level. As a regulatory mechanism, we found that Treg-cell function was attenuated in the presence of the crude extracts of sparganum, but was enhanced in the presence of the excretory-secretory products, suggesting that sparganum products were involved in the triggering and regulation of immune response in the acute and chronic phases, respectively. Results show that Treg cells are central in the immune homeostasis in vivo that is maintained by host-parasite interactions during the parasitic infection.