Leishmania infection leads to a broad spectrum of manifestations due to the differences in Leishmania species and host immunity.  They range from self-healing cutaneous, disfiguring mucocutaneous to life-threatening visceral leishmaniasis.  A Brazilian strain of L. chagasi/infantum, the causative agent of visceral leishmaniasis in South America is used in our lab.  Eleven major surface protease (MSP) proteins were detected in the virulent stationary-phase promastigotes using two dimensional electrophoresis and peptide mass fingerprinting, in contrast to only four in the avirulent logarithmic-phase cells.  By a combination of immunoelectron microscopy and surface biotinylation, one third of the total MSP was consistently localized intracellularly.  This pool of internal MSP can be stimulated to be released by conditions mimicking the basement membrane of mammalian skin, where sand-fly vectors inoculate infectious metacyclic promastigotes.  In contrast, release of the surface-localized MSP is enhanced by a sterol-disturbing reagent methyl-β-cyclodextrin in a dose-dependant manner.  Collectively, these data demonstrate various MSP proteins play distinct roles in Leishmania pathogenesis.