Human in vitro immune reactions to animal filariids.

Infective third stage larvae of animal filariids Brugia pahangi and Breinlia booliati incubated in vitro in the presence of normal human peripheral leucocytes and sera from human filariasis subjects resulted in decrease in motility, cell adherence, and formation of precipitates around the larvae. Strongest immune reactions were seen with sera from amicrofilaraemic symptomatic subjects, normal exposed individuals, and patients with tropical pulmonary eosinophilia syndrome (TPE). Weaker reactions were observed with sera from patients with elephantiasis. In all cases, reactivity to B. pahangi larvae was considerably higher than against B. booliati. Sera from microfilaraemic patients and unexposed control subjects were nonreactive. The implication of these human in vitro immune reactions against filarial parasites of animal origin is discussed in the context of the hypothesis of "zooprophylaxis" previously suggested by other workers.