Assessing the cellular and humoral immune response in Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) infected with Leishmania infantum (Nicolle, 1908)

The aim of this study was to evaluate aspects of the innate cellular and humoral immune response by evaluating hemocyte dynamics, phagocytosis, phenoloxidase (PO) activity and nitric oxide (NO) production in Rhipicephalus sanguineus sensu lato (s.l.) (Acari: Ixodidae) infected with Leishmania infantum and to assess the persistence of parasites at time 0 and 1, 2, 5, and 7 days post-infection (dpi). The total and differential count of the five types of hemocytes circulating in the hemolymph of R. sanguineus s.l. females showed the average total number of hemocytes in the group infected with L. infantum to be significantly higher (p < 0.05) on the 1st and 2nd dpi compared to the control group. The hemocyte differential count showed that the average number of plasmatocytes and granulocytes increased significantly on the 1st, 2nd, and 5th dpi with L. infantum compared to the control group (p < 0.001). Phagocytosis assays revealed that plasmatocytes and granulocytes were able to perform phagocytosis of latex beads and L. infantum on the 1st and 2nd dpi, respectively. NO production was significantly increased (p < 0.001) on the 1st, 2nd, and 5th dpi with L. infantum and PO activity increased significantly (p < 0.05) only on the 5th dpi. L. infantum DNA was significantly increased (p < 0.001) on the 5th and 7th dpi compared to time 0. Although there are no studies describing the response of R. sanguineus s.l. to an infection with L. infantum, these results suggest that R. sanguineus s.l. activates the cellular and humoral immune response after infection with L. infantum. Further studies are however, needed to assess the impact of such a response on fighting infection.