Nondevelopment of Wuchereria bancrofti in nude (congenitally athymic) mice

Infective larvae of Wuchereria bancrofti (Nematoda: Filarioidea) were harvested from Aedes aegypti mosquitoes fed in vitro on microfilaremic blood of Haitian volunteers. Larvae were inoculated either into the subcutaneous tissue (SC) or peritoneal cavity (IP) of congenitally athymic (nude) mice, C3H/HeN (nu/nu). Initially 15 male and two female mice received larval doses from 38-180, and necropsy was done between 11 and 75 days post-inoculation. No worms were found at necropsy. Four additional male mice given 75 larvae each were also injected daily with 0.3 ml of normal human serum, but again no worms were recovered at necropsy on days 13 through 17. Given the severe nature of the nude immunodeficiency, it seems unlikely that the total failure of W. bancrofti to develop in nude mice results from a T cell-dependent immune response. Perhaps either non-immune mechanisms actively destroy larvae or the mouse lacks a factor(s) essential for parasite development, but not found in human serum. In any case, the thymic independence of resistance to W. bancrofti is clearly unlike that shown to the related filaria, Brugia pahangi.