Localized Leishmania lymphadenitis. Immunohistochemical studies.

Tissues from 10 patients with localized leishmania lymphadenitis were stained by immunoperoxidase technique for leishmanian antigens, immunoglobulins (Ig), complement, components, alpha 1-antitrypsin, and fibrin and by routine and chloroacetate esterase techniques. Lymph nodes with leishmania lymphadenitis showed a granulomatous process with a varying degree of necrosis, leishmanian amastigotes, abundant plasma cells, and focal fibrosis. Leishmanian antigens stained by rabbit anti-Leishmania tropica antiserum was detected in lymph nodes with granulomatous lymphadenitis (eight cases examined) and in a skin lesion but not in a lymph node showing only nonspecific hyperplasia. Positive antigen staining was seen in leishmanian amastigotes, granulomata, and (in three cases) vascular smooth muscles. Dominant plasma cell classes were IgG and IgE. Macrophages and granulomata stained positively for IgG and IgE (but not for IgM or IgA), faintly for C3, and strongly for alpha 1-antitrypsin. Mast cells were few. IgG and IgE may be involved in a specific way in this condition; formation of immune complexes with leishmanian antigens leads to immunologically mediated lysis of the host macrophages. This finding is important for the understanding of the pathogenesis of leishmania lymphadenitis and for effective elimination of the parasites.