Redistribution of plasma-membrane surface molecules during formation of the Leishmania amazonensis-containing parasitophorous vacuole

Leishmania amazonensis presents two developmental stages that gain access to the host macrophage through phagocytosis. The protozoan resides in a membrane-bound compartment, the parasitophorous vacuole (PV), which can fuse with the endocytic system. For evaluation of the parasite/host-cell interaction process and of PV biogenesis, the two parasite forms or host-cell membrane whose surface had previously been labeled with specific probes for lipids, proteins, and sialoglycoconjugates were allowed to interact for periods varying from 5 to 15 min for adhesion and from 30 to 60 min for PV formation. The fate of fluorescent probes was followed by confocal laser scanning microscopy. In host cells previously labeled with PKH26, DTAF and FITC-thiosemicarbazide, which label membrane lipids, proteins, and sialoglycoconjugates, respectively, interaction with both protozoan forms revealed that adhesion to the macrophage was sufficient for labeling of the parasite surface. In addition, recently formed PVs displayed strongly labeled intravacuolar parasites, except for amastigote-macrophage interaction in a DTAF-labeled macrophage that displayed slight labeling of intravacuolar parasites, with the membrane lining the PV evidently being stained. Therefore, the vacuole modulation presents some particularities such that different host-cell membrane components may be selected, depending on the protozoan form involved. Thereafter, amastigotes labeled with the probes mentioned above displayed a diffuse labeling pattern after interaction with unlabeled macrophages, suggesting the spreading of Leishmania surface molecules during the initial parasite-invasion stages. In particular, intravacuolar DTAF-labeled amastigotes showed a delineating halo around the PV, with the intravacuolar parasite being partially labeled. Promastigotes could not be labeled with 5-(4,6-dichlorotriazinyl)aminofluorescein (DTAF) or with fluorescein-5-thiosemicarbazide, but promastigotes labeled with PKH26 lost the fluorescent probe during the invasion process such that slightly labeled promastigotes were seen inside the PV. These observations indicate the existence of a dynamic process of exchange of membrane-associated glycoproteins and lipids between the parasite and the host cell. Received: 15 May 1999 / Accepted: 10 September 1999