Methylprednisolone acetate induces, and Delta 7-dafachronic acid suppresses, Strongyloides stercoralis hyperinfection in NSG mice

Strongyloides stercoralis hyperinfection causes high mortality rates in humans, and, while hyperinfection can be induced by immunosuppressive glucocorticoids, the pathogenesis remains unknown. Since immunocompetent mice are resistant to infection with S. stercoralis, we hypothesized that NSG mice, which have a reduced innate immune response and lack adaptive immunity, would be susceptible to the infection and develop hyperinfection. Interestingly, despite the presence of large numbers of adult and first-stage larvae in S. stercoralis-infected NSG mice, no hyperinfection was observed even when the mice were treated with a monoclonal antibody to eliminate residual granulocyte activity. NSG mice were then infected with third-stage larvae and treated for 6 wk with methylprednisolone acetate (MPA), a synthetic glucocorticoid. MPA treatment of infected mice resulted in 50% mortality and caused a significant >10-fold increase in the number of parasitic female worms compared with infected untreated mice. In addition, autoinfective third-stage larvae, which initiate hyperinfection, were found in high numbers in MPA-treated, but not untreated, mice. Remarkably, treatment with Delta 7-dafachronic acid, an agonist of the parasite nuclear receptor Ss-DAF-12, significantly reduced the worm burden in MPA-treated mice undergoing hyperinfection with S. stercoralis. Overall, this study provides a useful mouse model for S. stercoralis autoinfection and suggests a therapeutic strategy for treating lethal hyperinfection.