Fine Structure of Human Malaria In Vitro*†

Abstract

The erythrocytic cycle of the human malaria parasite, Plasmodium, falciparum, was examined by electron microscopy. Three strains of parasites maintained in continuous culture in human erythrocytes were compared with in vivo infections in Aotus monkeys. The ultrastructure of P. falciparum is not altered by continuous cultivation in vitro. Mitochondria contain DNA-like filaments and some cristae at all stages of the erythrocytic life cycle. The Golgi apparatus is prominent at the schizont stage and may be involved in the formation of rhoptries. In culture, knob-like protrusions first appear on the surface of trophozoite-infected erythrocytes. The time of appearance of knobs on cells in vitro correlates with the life cycle stage of parasites which are sequestered from the peripheral circulation in vivo. Knob material of older parasites coalesces and forms extensions from the erythrocyte surface. Some of this material is sloughed from the host cell surface. The parasitophorous vacuole membrane breaks down in erythrocytes containing mature merozoites both in vitro and in vivo. Merozoite structure is similar to that of P. knowlesi. The immature gametocytes in culture have no knobs.

A new model for hemoglobin ingestion and transport by the human malaria parasite Plasmodium falciparum

“…1E), the FV. Although the relationship between the cytostome and the FV has not been empirically established, the prevailing theory is that the FV is formed from the fusion of several cytostomederived vesicles (Langreth et al, 1978). In this scenario, cytostome formation would precede FV formation.…”

“…Because of the similarities between the current model for hemoglobin transport and the endocytic pathway in higher eukaryotes (Goldberg et al, 1990;Hoppe et al, 2004;Langreth et al, 1978;Saliba et al, 2003), we investigated the role of actin dynamics in hemoglobin transport to the FV. Actin has been shown to play various regulatory roles in endocytosis, including recruiting endocytic components to the plasma membrane, initiating plasma membrane invaginations, vesicle scission and transport to endocytic compartments (Kaksonen et al, 2006;Qualmann et al, 2000;Smythe and Ayscough, 2006).…”

Ultrastructure and function of mitochondria in gametocytic stage ofPlasmodium falciparum

“…(Sinden & Smalley, 1979;Alano & Carter, 1990;Lobo & Kumar, 1998). Several lines of evidence on morphological, ultrastructural and genetic analyses of the mitochondria in P. falciparum suggest that the organelle may be functionally regulated during differentiation in the human host (Aikawa et al, 1966;Aikawa, 1971;Langreth et al, 1978;Fry & Beesley, 1991;Feagin & Drew, 1995;Petmitr & Krungkrai, 1995;Learngaramkul et al, 1999).…”

Identification of Novel Membrane Structures in Plasmodium falciparum Infected Erythrocytes

“…2A). Vesicles or tubules, similar to membrane-bound structures described in schizont-infected erythrocytes (Langreth et al 1978, Atkinson & Aikawa 1990, were found within the space defined by the outermost membrane and the residual body ( Fig. 2A).…”

“…The fact that these structures are not detectable on schizontinfected erythrocytes either by transmission (Langreth et al 1978, Atkinson & Aikawa 1990 or SEM (Gruenberg et al 1983), suggests that the formation of such membrane modifications might be functionally related to the release of merozoites from infected erythrocytes.…”