Platelet disturbances correlate with endothelial cell activation in uncomplicated Plasmodium vivax malaria
Authors: Dos-Santos João Conrado Khouri , Silva-Filho João Luiz , Judice Carla C , Kayano Ana Carolina Andrade Vitor , Aliberti Júlio , Khouri Ricardo , de Lima Diógenes S. , Nakaya Helder , Lacerda Marcus Vinicius Guimarães , De Paula Erich Vinicius , Lopes Stefanie Costa Pinto , Costa Fabio Trindade Maranhão 
Published: July 2019

ABSTRACTIntroductionPlatelets drive endothelial cell activation in many diseases. However, if this occurs in Plasmodium vivax malaria is unclear. As platelets have been reported to be activated and to play a role in inflammatory response during malaria, we hypothesized that this would correlate with endothelial alterations during acute illness.MethodsWe performed platelet flow cytometry of PAC-1 and P-selectin. We measured Platelet markers (CXCL4, CD40L, P-selectin, Thrombopoietin, IL-11) and endothelial markers (ICAM-1, von Willebrand Factor and E-selectin) in plasma with a multiplex-based assay. The values of each mediator were used to generate heatmaps, K-means clustering and Principal Component analysis. In addition, we determined pair-wise Pearson’s correlation coefficients to generate correlation networks.ResultsPlatelet counts were reduced, and mean platelet volume increased in malaria patients. The activation of circulating platelets in flow cytometry did not differ between patients and controls. CD40L levels (Median [IQ]: 517 [406-651] vs. 1029 [732- 1267] pg/mL, P=0.0001) were significantly higher in patients, while P-selectin (Median [IQ]: 17.0 [15.4-20.6] vs. 22.2 [17.6-25.7] ng/mL, P=0.0621) and CXCL4 showed a nonsignificant trend towards higher levels in patients. The network correlation approach demonstrated the correlation between markers of platelet and endothelial activation, and the heatmaps revealed a distinct pattern of activation in two subsets of P. vivax patients when compared to controls.Conclusionplatelet activation occurs in uncomplicated vivax malaria and this correlates with higher endothelial cell activation, especially in a subset of patients.AUTHOR SUMMARYEndothelial cell activation is a key process in the pathogenesis of Plasmodium vivax malaria. Platelets are classically involved endothelial cell activation in several diseases, but their role in context of vivax malaria remains unclear. Thrombocytopenia is the most common hematological disturbance in P. vivax-infected patients, and platelets have been implicated in parasitemia control. In this study, we studied the activation of platelets in association with endothelial cell activation in vivax malaria. Platelets retrieved from infected peripheral blood were non-activated when analyzed by flow cytometry; however, they displayed higher mean volume and significantly reduced counts. We also found higher levels of circulating factors associated with platelet activation (especially CD40L), thrombopoiesis and endothelial cell activation in infected patients. Further, through pair-wise correlation and clustering analysis, we found a subgroup of patients showing significant associations between markers of platelet and endothelial activation in a pattern different from that of endemic controls. Collectively, our findings point to a peculiar role of platelets in endothelial cell activation in vivax malaria and indicate a heterogeneous host response in the setting of uncomplicated disease, a finding to be further explored in future studies.