Eosinophils promote immune responses that preserve parasitic nematode larvae (P3086)

We have shown that eosinophils protect, rather than attack Trichinella spiralis larvae during primary infection in the skeletal muscle. Accumulation of Th2 cells at sites of infection is also impaired in the absence of eosinophils. Here we further elucidated the mechanism underlying this effect. Intravenous infection with T. spiralis newborn larvae specifically and rapidly induced the recruitment of eosinophils to skeletal muscle. The presence of eosinophils only during the earliest stages of muscle infection was sufficient to support parasite growth and survival, suggesting that eosinophils are required to be present at the time newborn larvae first arrive in the muscle, when the local immune response is first engaged. Transfer of MHCII-/- eosinophils also supported parasite growth and survival, showing that antigen presentation by eosinophils is not required. Furthermore, the numbers of myeloid dendritic cells in cervical lymph nodes and skeletal muscles were reduced in eosinophil-ablated, infected mice and improved when eosinophils were restored. The reduction in myeloid dendritic cells correlated with decreased numbers of proliferating Th2 cells in cervical lymph nodes, indicating that eosinophils promote accumulation of myeloid dendritic cells, which may promote Th2 responses. Taken together, our findings suggest that eosinophils exert their influence at the very early stages of the immune response that preserves T. sprialis larvae.