Augmented plasma microparticles during acute Plasmodium vivax infection.

Background: In the last few years, the study of microparticles (MPs)--submicron vesicles released from cells upon activation or apoptosis--has gained growing interest in the field of inflammation and in infectious diseases. Their role in the human malaria parasite Plasmodium vivax remains unexplored. Because acute vivax malaria has been related to pro-inflammatory responses, the main hypothesis investigated in this study was that Plasmodium vivax infection is associated with elevated levels of circulating MPs, which may play a role during acute disease in non-immune patients.

Methods: Plasma MPs were analysed among thirty-seven uncomplicated P. vivax infections from an area of unstable malaria transmission in the Brazilian Amazon. The MP phenotype was analysed by flow cytometry using the classical MP marker, annexin, and fluorochrome-labeled monoclonal antibodies against specific cell surface markers. The frequencies of plasma MPs in P. vivax patients (n=37) were further compared to malaria-unexposed controls (n=15) and ovarian carcinoma patients (n=12), a known MPs-inducing disease non-related to malaria.

Results: The frequencies of plasma circulating MPs were markedly increased in P. vivax patients, as compared to healthy age-matched malaria-unexposed controls. Although platelets, erythrocytes and leukocytes were the main cellular sources of MPs during vivax malaria, platelet derived-MPs (PMPs) increased in a linear fashion with the presence of fever at the time of blood collection (β=0.06, p<0.0001) and length of acute symptoms (β=0.36, p<0.0001). Finally, the results suggest that plasma levels of PMPs diminish as patient experience more episodes of clinical malaria (β=0.07, p<0.003).

Conclusions: Abundant circulating MPs are present during acute P. vivax infection, and platelet derived-MPs may play a role on the acute inflammatory symptoms of malaria vivax.