Exposition of phosphatidylserine in amastigotes intracellular of Leishmania (L) amazonensis and its paper in the modulation of the macrophage reply.
Macrophages are host cells for Leishmania infection. Their intracellular survival depends on mechanisms of parasite evasion from the host microbicidal mechanisms. Previous work from our group showed that amastigotes of Leishmania (L) amazonensis, purified from lesions in mice, expose phosphatidylserine (PS)on their surface, a mechanism described as Apoptotic Mimicry. Macrophage recognition of PS on amastigote surface induces parasite internalization by macropinocytosis, increase in the synthesis of anti-inflammatory cytokines, TGF-b and IL-10, and inhibition of Nitric Oxide (NO) production, contributing to the enhancement of amastigote infectivity and proliferation inside host cell. The amount of exposed PS on amastigote surface ismodulated by the host: parasites purified from BALB/c mice expose higher amounts of PS than those purified from C57BL/6 mice. Now we show that no differences in PS exposure can be detected in amastigotes purified from in vitro cultivated macrophages derived from the two different mouse strains. In addition, amastigotes derived from T-cell deficient mice BALB/cnu/nu display significant less PS exposure than the wild-type strain. These results strongly indicate that PS exposure on parasite purified from in vivo lesions is induced by T-cell activation of the host macrophage. The in vitro kinetics of PS exposure during promastigote to amastigote differentiation inside parasitophorous vacuole (PV) is independent of the genetic origin of the macrophage. Anincrease in PS exposure by the parasite that correlates with an enlargement of the PV and an increase in macrophage macropinocytic activity is observed. Macropinocytic vesicles fuse with the PV membrane suggesting that the increased macropinocytic activity by macrophages can provide nutrients for the intracellular parasites. PV alkalinization inhibits macrophage macropinocytic activity. As the PS exposure increases inside PV a concomitant increase of TGF-b synthesis and inhibition of NO production by infected macrophages areobserved. This comprises a mechanism of interaction between Leishmania and host cell in which the capacity of the amastigotes to signal, from within the PV, through exposed PS mediates the establishment of the infection bythis parasite. Amastigotes with high amounts of exposed PS display these molecules in patches, preferentiallylocalized on the posterior end of cell. Parasites interact with PV membrane by this region, and the PS exposurein patches may contribute to recognition and signaling by this molecule on PV membrane. This mechanism ofinteraction between parasite and host cell mediates down-regulation of macrophage anti-parasitic activity andthus contributes to the establishment of the infection .
Advisor:Marcello André Barcinski
School:Faculdades Oswaldo Cruz
Source Type:Master's Thesis
Keywords:r imunologia celular
Date of Publication:06/12/2008