Fibronectin shedding by Leishmania may influence the parasite-macrophage interaction

Fibronectin (FN) is a large extracellular matrix protein involved in the endocytosis of several types of particles by different phagocytes. Here we investigated the role of FN in the entry and destruction of Leishmania amazonensis promastigotes (flagellated form) by murine resident peritoneal macrophages. We also studied the lateral mobility of this protein on the surface of the parasite cells using a immunogold technique. We compared the effects of addition and depletion of FN on infective and non-infective populations of Leishmania promastigotes. The invasion by the latter but not by the former, was increased by FN, and the uptake of these cells was more sensitive to FN depletion from the culture medium. We also observed enhanced killing of intracellular infective promastigotes upon FN addition to the macrophage cultures. Immunocytochemical localization of FN on the surface of the flagellates revealed that the parasite cells released bound FN by membrane shedding in a constitutive fashion. Therefore we conclude that FN removal by shedding may be part of a physiological mechanism by which the parasites evade intracellular destruction by host cells.