Abstract:
Leishmania spp. infect several vertebrate hosts, including humans. The diseases caused by this protozoan, leishmaniasis, can present different clinical manifestations, from localized skin lesions that heal spontaneously, to disseminated skin lesions, mucocutaneous form of the disease, and visceral leishmaniasis, the most severe form that can lead to death if left untreated. The dissemination and homing of infected cells containing Leishmania are crucial for the parasite's survival in the host and the establishment of the lesions. However, the understanding of the mechanisms underlying host cell adhesion and migration during infection by this protozoan remains limited. Therefore, this study aimed to evaluate the migration of human monocytes, macrophages, and dendritic cells in Leishmania infection, and the mechanisms involved in this process. Human host cells from healthy donors were obtained, infected with different isolates of Leishmania, and subjected to directional and random migration using a transwell system and real-time tracking, respectively. We also assessed the formation of adhesion complexes by immunostaining p-FAK and p-paxillin. Additionally, we investigated actin dynamics by analyzing the expression of Rac1, Rho-A, Cdc42, and phalloidin staining in these cells, as well as the formation of podosomes by immunostaining vinculin. Finally, we investigated the role of the AKT/PI3K signaling pathway in the migration of host cells infected by these parasites, through the analysis of protein expression by western blot, and the effect of inhibition of this pathway on the migration of infected host cells. Our results showed a reduction in the two-dimensional migration of human monocytes and macrophages infected with L. amazonensis, L. braziliensis, or L. infantum, associated with a decrease in the formation of adhesion complexes, podosomes, and actin dynamics in these cells. However, we observed an increase in the migration of dendritic cells infected by L. infantum or Leishmania isolates from patients with the disseminated or diffuse form of the disease. Additionally, we observed that the increase in migration in these cells is associated with an increase in the formation of adhesion complexes, podosomes, actin dynamics, and CCR7 expression. Finally, we observed that Leishmania infection induces activation of the AKT/PI3K pathway. Taken together, our data point to a role of dendritic cells, but not macrophages and monocytes, in the dissemination of Leishmania parasites in the vertebrate host.
