Amastigotes of Leshmania mexicana amazonensis appeared healthy and well preserved within the parasitophorous vacuoles of macrophages during the infection of a susceptible (Balb/c) or a relatively resistant (A/J) inbred strain of mice. Immunofluorescence showed the presence of leishmanial antigens within infected macrophages and in their external membranes similar for both strains. When the amastigotes were found extracellularly or within polymorphonuclear neutrophils or eosinophils, marked ultrastructural degenerative changes were observed in them. Such necrotic alterations were seen frequently in the resistant mice and rarely in the susceptible ones. Thus, necrosis of parasitized macrophages appeared as a major mechanism through which the resistant host eliminates the parasites from the lesions. It may be considered as a histological marker of resistance in leishmaniasis and represents a prominent component of the delayed-type immunological mechanism occurring in resistant hosts.
Experimental cutaneous leishmaniasis; Balb/c and A/J mice; Leishmania mexicana amazonensis; Fibrinoid tissue necrosis; Caseous tissue necrosis; Purulent tissue necrosis