The role of the macrophage in cutaneous leishmaniasis

The investigation of the role of the macrophage in cutaneous leishmaniasis has been prompted by observations of the clinical behaviour of the infection. In contrast to the self-healing oriental sore, chronic leishmaniasis is characterized by persistent lesions and leishmania recidiva by lesions that flare up locally long after clinical healing. In both clinical types, the parasite is thought to be maintained inside the macrophages. It will be shown that the normal macrophages of mice and guinea-pigs are parasitized by L. tropica; the parasite is not killed by the macrophages but it multiplies within these cells. Incubation of the macrophages with rabbit or human anti-Leishmania sera on the other hand, leads to the attachment of specific immunoglobulins to the macrophage cell surface and consequently to the prevention of parasitization by L. tropica under the experimental conditions. The parasite appears to be immobilized at the macrophage cell surface. Normal rabbit or human sera did not interfere with parasitization. It is postulated that the parasite specifically immobilized at the cell surface might possibly be better exposed to and affected by the immune response than intracellular parasites. Furthermore, infected parasitized macrophages contribute to the immune response by processing soluble antigens from the intracellular parasites and presenting them on their surfaces, as seen by the greater affinity (higher dilution) of anti-Leishmania antibody for the cell membrane of infected macrophages than for normal macrophages.