HUMORAL AND CELL-MEDIATED-IMMUNITY IN NATURAL AND EXPERIMENTAL CANINELEISHMANIASIS

This paper describes immunological and clinicopathological findings in dogs naturally and experimentally infected with progressive visceral leishmaniasis. Eight dogs were intravenously inoculated with 5 X 10(7) stationary phase promastigotes of Leishmania infantum (LEM 2002, ZMON -1). A further eight naturally infected dogs were diagnosed by parasit ological and serological methods and selected according to their clini cal and immunological condition. Clinical, hematological, pathological and parasitological examinations, including parasite burden and distr ibution, were included in the study. Antibody production was estimated by means of enzyme-linked immunosorbent assay and immunofluorescence assay techniques; the cellular immune response was studied by means of the skin test and the lymphocyte proliferation test. Experimentally i nfected dogs developed a chronic and progressive disease with the same clinical signs shown by naturally infected dogs. Both naturally and e xperimentally infected dogs developed the same histopathological react ion, but to differing degrees. Parasite burden and distribution were r elated to the extent of lesions, and were consequently less pronounced in experimentally infected dogs. The main feature of the immune respo nse in experimental and natural infection was the lack of specific T-c ell response to leishmanial antigen. Non-specific responses to mitogen s were normal (i.e. as compared with healthy dogs) throughout the expe rimental infection, but were partially suppressed (65.3%) in naturally infected animals. A remarkable humoral response was evident in both n atural and experimental infection: IgG-isotype antibodies were detecte d in experimental infection at 50-70 days post infection, and their pr oduction increased during the course of the infection. However, high t iters were observed only in naturally infected dogs.