High iNOS expression in macrophages in canine leishmaniasis is associated with low intracellular parasite burden

The expression of iNOS by macrophages in 33 dogs suffering from spontaneous leishmaniasis was analysed by immunohistochemistry in skin, liver and lymph nodes. A correlation study between the number of macrophages expressing iNOS and the number of macrophages containing leishmania amastigotes was carried out. Formalin-fixed paraffin-embedded tissue sections from the skin (28 cases), popliteal lymph nodes (8 cases) and liver (3 cases) of dogs of different age, sex and breed suffering from leishmaniasis were included in the study. Dogs were referred as positive for Leishmania spp by serology and the diagnosis was confirmed by demonstration of leishmania amastigotes within macrophages by histopathology. Tissue samples of skin (3 cases), popliteal lymph nodes (5 cases) and liver (3 cases) from dogs seronegative for leishmaniasis with no histopathological changes were included in the study as controls. The immunohistochemical study revealed that macrophages containing a high number of leishmania did not express iNOS. Correlation between the number of macrophages expressing iNOS and the number of macrophages containing leishmania amastigotes was assessed using the Spearman test. High expression of iNOS in macrophages was related with low number of leishmania amastigotes in macrophages in all cases (r=-0.47, p=0.002). These results suggest that iNOS expression by macrophages plays an important role during the control of Leishmania infection in dogs.