Developmentally regulated changes in the cell surface architecture of Leishmania parasites

The cell surface of Leishmania parasites is coated by a highly unusual glycocalyx which varies markedly during the parasite life cycle. The predominant molecule on the extracellular promastigote (sandfly) stage is a complex lipophosphoglycan (LPG), which together with a number of GPI-anchored proteins and a family of low molecular weight glycoinositolphospholipids (GIPLs), forms a morphologically distinct protective coat over the plasma membrane. The structure of the LPG has been shown to vary in different species and during promastigote development in the sandfly. This polymorphism is thought to be important in allowing Leishmania parasites to colonize a range of insect hosts, and in facilitating the regulated migration of promastigotes along the sandfly alimentary canal. Stage-specific changes in LPG are also involved in preadapting promastigotes to life in the mammalian host. This complex glycocalyx coat is absent from the amastigote stage that proliferates in the phagolysosomes of mammalian macrophages, as the expression of both the LPG and GPI-anchored proteins is massively down-regulated. Instead, the plasma membrane of amastigotes is coated by a densely packed layer of parasite-derived GIPLs and host-derived glycosphingolipids. We propose that the down-regulation of the promastigote macromolecules and the acquisition of host glycolipids by amastigotes represents an important strategy to avoid detection by specific and non-specific components of the immune system.