Histological spectrum of cutaneous leishmaniasis due to Leishmania tropica.

Skin biopsies from 117 cases of acute and 23 cases of lupoid leishmaniasis were studied. Of the 117 acute cases, anergic macrophage response were seen in 44, diffuse necrosis in 9 and focalized necrosis in 11 biopsies; the remaining 53 biopsies showed scanty or no parasites with a few to abundant epithelioid cells probably representing post necrotic changes before complete healing of the lesions. The 23 biopsies of lupoid leishmaniasis showed rather well organized epithelioid granulomata surrounded by lymphocytes, inconspicuous plasma cells, no amastigotes and no necrosis. Lupoid cases showed strong delayed hypersensitivity with leishmanin and low serum antibody titres. It appears that the lesions of urban cutaneous leishmaniasis spend a long time in the anergic phase. Partial destruction of parasites by activated macrophages together with gradual elevation of antibody levels prepares the appropriate antigen-antibody ratio for optimum development of necrosis at PI3 leading to effective elimination of parasites. Plasma cells appear to be important in the induction of necrosis and inhibition of epithelioid granulomata. A significant inverse relationship has been found between plasma cells and epitheloid cells. The delayed hypersensitivity observed in lupoid leishmaniasis is probably the result of a poor humoral response evidenced by inconspicuous plasma cells and low serum antibody titres.