Ivermectin-Induced Killing of Microfilariaein Vitroby Neutrophils Mediated by NO

Abstract

Rat neutrophil granulocytes isolated after intraperitoneal casein injection of the donors exhibit high cytotoxic efficacyin vitroagainst microfilariae ofLitomosoides cariniiin the presence of ivermectin. Optimum effects of 80–90% killing of microfilariae were obtained with 100 ng ivermectin per milliliter and a microfilariae:cell ratio of 1:100. Spleen cells killed approximately 30% of the microfilariae under these conditions. Cytotoxic effects were independent of any adherence of the cell to the larvae. In contrast to the effects of spleen cells, cytotoxicity of neutrophils was completely abrogated when cells and targets were separated by a membrane impermeable for the cells, suggesting a very short-living mediator in the latter case. Correspondingly, cytotoxic effects of neutrophils were completely inhibited by the addition of the arginine analoguesNG-monomethyl-l-arginine andl-canavanine, indicating the involvement of reactive nitrogen intermediates. The nitric oxide scavenger hemoglobin also protected the microfilariae. Several compounds which are known to interfere with reactive oxygen intermediates were ineffective. An excess of ferrous ions in the medium in the presence of a reducing agent significantly reduced the cytotoxic efficacy of neutrophils.