Immunological and histological study of T- and B-lymphocyte activity in canine visceral leishmaniosis.

Lymphocyte activity during canine leishmaniosis was studied by histological and immunological methods in experimental and natural infections. Eight dogs were inoculated with 5 x 10(7) promastigotes of Leishmania infantum, LEM 75, zimodeme MON-1, and maintained for 110 days post-infection. Another eight dogs with advanced natural infection were identified by parasitological and serological methods. Three techniques were used: the lymphocyte transformation test (LTT) to study T-cell activity, immunofluorescence assay and enzyme-linked immunosorbent assay to measure antibody production (B-cell activity), and methyl green-pyronin staining to assess tissue responses of lymphocytes. There was a noticeable B-cell response, reflected both histologically and immunologically. High percentages of activated lymphocytes and plasma cells were evident in lymphoid organs and production of specific antibodies was seen throughout the infection. LTT results showed a T-cell unresponsiveness during canine leishmaniosis. These same immunohistological features were observed, although to different degrees, in both experimental and natural infections.