Depletion of FoxP3(+) Tregs improves control of larval Echinococcus multilocularis infection by promoting co-stimulation and Th1/17 immunity

Introduction: The growth potential of the tumor-like Echinococcus multilocularis metacestode (causing alveolar echinococcosis, AE) is directly linked to the nature/function of the periparasitic host immune-mediated processes. Previous studies had shown that regulatory T cells (Tregs) become gradually up-regulated in the course of both chronic human and murine AE. Thus we now tackled the role of FoxP3(+) Tregs and FoxP3(+)-Treg-regulated immune response in contributing to the control of this helminthic infection. Methods: The infection outcome in E. multilocularis-infected DEREG mice was measured upon determining parasite load (wet weight of parasitic metacestode tissue). Flow cytometry and qRT-PCR were used to assess Treg, Th17-, Th1-, Th2-type immune responses and antigen presenting cell activation. Results: We showed that E. multilocularis-infected DEREG-mice treated with DT (as compared to infected control DEREG-mice without DT application) exhibited a significantly lower parasite load, associated with a persisting capacity of co-stimulation, and an increased Th1/Th17-polarization. Conclusions: FoxP3(+) Tregs appear as one of the key players in immune regulatory processes favoring (i) metacestode survival by inhibiting the maturation potential of co-stimulatory activity and (ii) T cell exhaustion (suppressing Th1/Th17-type immune responses). We showed as well that prospectively, targeting FoxP3(+) Tregs could be an option to develop an immunotherapy against AE.