Blocking PS (right) reduces Leishmania infection (arrows).

Barcinski/Elsevier

By faking its own death, Leishmania can gain access to macrophages. Once in the macrophage, say Marcello André Barcinski (Universidade de São Paulo and Instituto Nacional de Câncer, Rio de Janeiro, Brazil) and colleagues, the fake death signal then suppresses the host's ability to kill the invading parasite.Leishmania makes the fake death signal by exposing phosphatidylserine (PS) on its surface. Exposed PS is also seen on apoptotic cells, where it induces engulfment by macrophages, and reduces inflammation by prompting production of TGF-β. The same two activities are seen with Leishmania, although the parasite also induces both an increase in IL-10 production (which distracts the immune system by shifting it away from cell-mediated immunity) and a reduction in NO production. The latter change favors parasite survival, as NO is one of the main mechanisms by which macrophages kill Leishmania. ▪

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