Morte celular de macrófagos infectados in vitro com Leishmania: indução de apoptose por Leishmania (Leishmania) amazonensis e de necrose por Leishmania (Viannia) guyanensis

Abstract

Leishmania are protozoan parasites transmitted by the insect vector during blood meal to the vertebrate host as promastigotes. In the mammal host, amastigotes replicate inside macrophages and are transmitted to healthy cells, amplifying the infection. Although transfer of amastigotes from infected to healthy cells is a crucial step that may shape the outcome of the infection, it is not fully understood. In the present work, L. amazonensis and L. guyanensis infection in C57BL/6 and BALB/c macrophages were compared and macrophages death was investigated. As previously shown, infection of mice results in distinct outcomes: L. amazonensis causes a chronic infection in both strains of mice (although milder in C57BL/6), whereas L. guyanensis infection is controlled by the strains. In vitro, infection is persistent in L. amazonensis-infected macrophages whereas L. guyanensis growth is controlled by host cells from both strains of mice. L. amazonensis induces apoptosis of both C57BL/6 and BALB/c macrophages in vitro, characterized by phosphatidylserine (PS) exposure, DNA cleavage into nucleosomal size fragments, and consequent hypodiploidy. None of these signs were seen in macrophages infected with L. guyanensis, which seem to die through necrosis, as indicated by increased propidium iodide (PI)-, but not Annexin V-, positive cells. L. amazonensis-induced macrophage apoptosis was through activation of caspases-3, -8 and -9, in both strains of mice. Considering these two species of Leishmania and strains of mice, macrophage apoptosis, induced at the initial moments of infection, is associated with chronic infection, regardless of its severity. Healthy macrophages were observed phagocytizing L. amazonensis-infected cells, which had not been verified so far, and could be a way of amastigote spreading, leading to the amplification of infection.