Detection of serum antibodies and circulating antigens in a chimpanzee experimentally infected with Onchocerca volvulus

Abstract
The course of the humoral immune response was followed in a chimpanzee experimentally infected over 27 weeks with a total of 168 Onchocerca volvulus 3rd-stage larvae obtained from naturally infected wild-caught blackflies. Antibodies against an adult worm extract could be detected by ELISA from week 16 onwards (after the inoculation of 44 larvae). Peak antibody levels were observed between weeks 66 and 74 (about one year after the last larval injection). Thereafter, antibody levels markedly decreased but rose again after week 120. First microfilariae could be detected from week 124 onwards. Microfilarial counts remained low (not more than two microfilariae per skin snip) until the end of the observation period. High levels of IgM antibodies against adult O. volvulus antigens were detectable between weeks 26 and 80 by ELISA. Total IgE levels were found to be only marginally elevated during the course of the infection. Circulating parasite antigens were only detectable for a short time (weeks 34 to 44) of the prepatent period by immuno-radiometric assays (IRMAs) using monoclonal antibodies which were raised against O. gibsoni eggs. Competitive radio-immuno-assays detected host antibodies inhibiting binding of 125I-labelled monoclonal antibodies to parasite antigens from week 28 onwards. Host antibodies clearly interfere later in infection with the detection of circulating antigens.