In vitroproduction and characterization of excretory/secretory products of Onchocerca volvulus

Onchocerca volvulusexcretory/secretory products (ESP) free of host contaminants are often needed for immunologic and biochemical studies. Since prolonged in vitrosurvival of O. volvulusin culture requires the presence of human serum, as a supplement, it was necessary to investigate other culture medium supplements in which pure ESP could be generated. Thus heat-inactivated normal rabbit serum, fetal calf serum and the synthetic serum substitute Ultroser-G were tested for their abilities to sustain O. volvulusadult females and nodular microfilariae in vitroand their abilities to promote the synthesis and release of ESP. Using [35S]-methionine as the radioactive precursor, O. volvulusnodular microfilariae and adult females were shown to actively synthesize and release excretory/secretory proteins with increasing efficiency in human serum, rabbit serum, Ultroser-G and fetal calf serum. Analysis of the ESP by SDS-PAGE revealed that at least 30 polypeptides in the 7-174 kDa range were continuously released. About 14 of these components were immunogenic to the human host as shown by immunoprecipitation. Prominent antigenic polypeptides were those with relative molecular weights of 13, 16, 33, 68 and 170. Rabbit serum, fetal calf serum and Ultroser-G could therefore, conveniently replace human serum in cultures of O. volvulusnodular microfilariae and adult females.