Leishmania infantum-specific IFN-γ production in stimulated blood from dogs with clinical leishmaniosis at diagnosis and during treatment

There is limited data regarding Leishmania infantum specific T cell mediated immunity in naturally infected sick dogs at the time of diagnosis and during anti-Leishmania treatment. Our aim was to investigate the kinetics of L. infantum specific IFN-γ production in dogs with leishmaniosis at the time of diagnosis and during treatment and to correlate it with specific L. infantum antibodies, blood parasitemia and clinicopathological findings. Thirty-four dogs were diagnosed with leishmaniosis based on physical examination, routine laboratory tests and L. infantum-specific antibody levels by quantitative ELISA. Heparinized whole blood was stimulated with L. infantum soluble antigen (LSA) and concanavalin A (ConA) and incubated for 5days. IFN-γ concentration was evaluated in supernatants of stimulated blood using a commercial sandwich ELISA. Leishmania real-time PCR was also performed for assessing blood parasitemia. Dogs were treated with meglumine antimoniate and allopurinol. Sixteen dogs were classified as IFN-γ non-producers after LSA stimulation (mean±SD: 0±0pg/mL) and 18 dogs as IFN-γ producers (mean±SD: 2885.3±4436.1pg/mL) at the time of diagnosis (P<0.0001). IFN-γ non-producers were classified in a more severe clinical staging than IFN-γ producers that presented a mild to moderate clinical staging (P=0.03). In the IFN-γ non-producer group, production of IFN-γ after LSA stimulation was significantly increased during treatment especially at day 365 (P=0.018) together with clinical improvement when compared with day 0. In contrast, IFN-γ producers maintained their IFN-γ production after LSA stimulation and no statistically significant changes were found during treatment follow-up. At diagnosis, IFN-γ non-producers showed a significantly higher blood parasitemia versus IFN-γ -producers (P=0.005). IFN-γ non-producers drastically reduced blood parasitemia to minimum values at day 365 when compared with day 0 (P=0.017). No significant differences were found at day 365 in blood parasitemia of IFN-γ producers compared to pre-treatment. At diagnosis, L. infantum specific antibodies were higher in IFN-γ non-producers than IFN-γ producers (P=0.014). A marked reduction of antibody levels was found at day 365 when compared with day 0 in IFN-γ non-producers (P=0.005) and producers (P=0.001). These results demonstrate that IFN-γ concentration increases with long-term anti-Leishmania treatment together with clinical improvement in dogs that do not produce IFN-γ at diagnosis. Together with clinical recovery, reduction in blood parasitemia and L. infantum specific antibodies, tracking IFN-γ concentration could constitute an important prognostic tool for immune monitoring in CanL.