Macrophage-nematode interaction in vivo: Nippostrongylus brasiliensis infective larvae in the peritoneum of unsensitized rats.

ABSTRACT

Infective larvae of Nippostrongylus brasiliensis injected into the peritoneum of non-immune rats become coated with several layers of host macrophages. Cell-coated larvae remain free in the peritoneum or attach to the omentum, while other larvae attach to the omentum without becoming coated. All larvae, whether coated or not, die, become pigmented and break into fragments. Ultrastructural observations revealed a progressive disintegration of the soft tissues of the immobilized larvae, characterized by autolytic changes and accumulation of pigment with histochemical characteristics of lipofuscin. The cuticle remains intact and excludes Trypan blue during the entire autolytic process, thus demonstrating that macrophage secretions do not participate in the disintegration process. When larval enzymes are inactivated by heat treatment and the larvae are injected i.p., no autolysis occurs and the internal organs remain recognizable. These larvae become coated over their entire length with several layers of macrophages and are progressively phagocytized by macrophages clustering at both ends. Different modes of nematode disintegration within the rodent host involving macrophages are discussed.