Onchocerca volvulus: In vitro killing of microfilaria by neutrophils and eosinophils from experimentally infected chimpanzees

Peripheral blood leukocytes from chimpanzees experimentally infected with third stage larvae, or with nodular microfilaria (mf) of Onchocerca volvulus, were evaluated for their ability to kill nodular mf in vitro. Inoculation of chimpanzees with third stage larvae, and prospective follow up, permitted each animal to be classified as patent, infected but not patent, or post-patent. Neither lymphocytes nor monocytes significantly adhered to, immobilized, or killed mf. However, neutrophils or eosinophils killed mf effectively in the presence of immune serum. Neutrophil and eosinophil enriched cell preparations from control animals were able to kill mf with serum from infected animals, but to a significantly lesser degree than when both cells and serum were taken from infected animals. Chimpanzees inoculated with mf showed a progressive increase in cellular killing of mf after a second inoculation which surpassed that seen with animals inoculated with third stage larvae. Antibody-mediated killing of mf by neutrophils and eosinophils may be important in the termination of patency in this infection.