Leishmania amazonensis induces mast cells to release DNA extracellular traps

Leishmaniasis is a group of neglected diseases caused by a protozoan of the genus Leishmania, which is transmitted by female sandflies. The sandflies inject promastigotes into the skin, interacting with different innate immune cells, such as the resident mast cells. Upon contact with Leishmania, these cells phagocytose the parasite, degranulate, and release various inflammatory mediators that influence the host's immune response. Our group demonstrated that L. major and L. amazonensis promastigotes induce murine mast cells to release DNA extracellular traps (DETs). These traps comprise chromatin associated with different proteins, which may trap and kill microorganisms and influence the host's immune response.  The present study aimed to investigate whether the human mast cell line HMC-1 could release DETs when stimulated by L. amazonensis promastigotes and to evaluate the pathways involved in the process using pharmacological inhibitors. Thus, HMC-1 was pre-treated with the following inhibitors: BAPTA, nafamostat, NAC, DPI, and GSK484 for 30 min and then stimulated with the promastigotes in a ratio 5 parasites: 1 HMC-1 for 2 h, 37^oC. DETs were quantified by Picogreen and the characteristic morphology of these structures visualized by microscopy. Our findings reveal that HMC-1 releases DETs induced by these promastigotes, dependent upon calcium and serine protease, which is probably tryptase but independent of reactive oxygen species and peptidyl arginine deiminase. These results demonstrated that the human HMC-1 cell line releases DETs upon interaction with Leishmania promastigotes and may be used in studies to characterize DETs’ contribution to host defense against these parasites.