Plasmodium vivax in vitro continuous culture: the spoke in the wheel

Abstract

Understanding the life cycle of Plasmodium vivax is fundamental for developing strategies aimed at controlling and eliminating this parasitic species. Although advances in omic sciences and high-throughput techniques in recent years have enabled the identification and characterization of proteins which might be participating in P. vivax invasion of target cells, exclusive parasite tropism for invading reticulocytes has become the main obstacle in maintaining a continuous culture for this species. Such advance that would help in defining each parasite protein's function in the complex process of P. vivax invasion, in addition to evaluating new therapeutic agents, is still a dream. Advances related to maintenance, culture medium supplements and the use of different sources of reticulocytes and parasites (strains and isolates) have been made regarding the development of an in vitro culture for P. vivax; however, only some cultures having few replication cycles have been obtained to date, meaning that this parasite's maintenance goes beyond the technical components involved. Although it is still not yet clear which molecular mechanisms P. vivax prefers for invading young CD71⁺ reticulocytes [early maturation stages (I-II-III)], changes related to membrane proteins remodelling of such cells could form part of the explanation. The most relevant aspects regarding P. vivax in vitro culture and host cell characteristics have been analysed in this review to explain possible reasons why the species' continuous in vitro culture is so difficult to standardize. Some alternatives for P. vivax in vitro culture have also been described.

Keywords: In vitro culture; Ligand; Plasmodium vivax; Receptor; Reticulocyte.

Fig. 1

Plasmodium vivax and P. falciparum merozoite host cell adhesion proteins. The figure shows the P. vivax (left-hand side) and P. falciparum (right-hand side) proteins described to date having a binding-related function regarding receptors identified on target cells: reticulocyte and mature erythrocytes, respectively. Mrz proteins’ subcellular localization is indicated. An asterisk indicates those molecules with unknown subcellular localization

Fig. 2

Conditions evaluated for culturing Plasmodium vivax in vitro. The figure shows modifications made to culture medium, parasite sources and the target cells which have been used in culturing the P. vivax parasite. Each combination evaluated is described in the culture medium section. For example, 14 indicates RPMI 1640 medium, which contains HEPES, NaHCO₃, neomycin, vitamin B12, hypoxanthine, ascorbic acid, MgCl₂, biotin, choline and 15% AB⁺ human serum (box showing typology). The reticulocyte source section lists these cells’ enrichment methodology using the letters a–e. Sections of the graphic enclosed by a red discontinuous line indicate the best target cell sources and/or enrichment methods available so far