Relationship between parasitic load and Th1 lymphocytes in skin’s biopsies of dogs with leishmaniasis

Abstract

Visceral leishmaniasis (VL) is a severe chronic systemic disease caused by Leishmania donovani or L. infantum. Several studies have shown that susceptibility to VL is related to high levels of circulating antibodies and a depression of the immunity mediated by Th1 cells, mainly with decreased production of interferon (IFN-γ) and interleukin-12 (IL-12). Like human leishmaniasis, active canine VL is characterized by polyclonal activation of B-cells and specific immune suppression. Canine patients with reactive serological diagnosis to Leishmania sp were selected and samples were taken for direct parasitological examination and skin biopsies of the pinna for the immune-histochemistry technique, in order to detect Th1 lymphocytes in relation to parasitic amount. In samples of animals without symptoms and high parasite load, the number of Th1 lymphocytes did not exceed 4 cells per field, while in the samples with moderate and low parasite loads, the number of Th1 lymphocytes exceeded 8 cells per field of higher magnification, reaching up to 10. In animals with symptoms, it was observed that in samples with moderate and high parasite loads, the number of Th1 lymphocytes did not exceed 5 cells, while the samples with low parasitic amount exceeded 8 cells per field of higher magnification. It is concluded that the presence or absence of symptoms in canines with VL does not depend on the parasitic amount found in skin biopsies. On the other hand, it was observed that the high parasitic amount is related to immune suppression mediated by Th1 lymphocytes, while in animals with high immunological response, the number of parasites is low.