Background Pro- and anti-inflammatory cytokines are important mediators of immunity and are associated with malaria disease outcomes. However, their role in the establishment of asymptomatic infections, which may precede the development of clinical symptoms, is not as well-understood. Methods We determined the association of pro and anti-inflammatory cytokines and other immune effector molecules with the development of asymptomatic malaria. We measured and compared the plasma levels of pro-inflammatory mediators including tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), interleukin (IL)-6, IL-12p70, IL-17A, and granzyme B, the anti-inflammatory cytokine IL-4 and the regulatory cytokine IL-10 from children with asymptomatic malaria infections (either microscopic or submicroscopic) and uninfected controls using Luminex. Results We show that individuals with microscopic asymptomatic malaria had significantly increased levels of TNF-α and IL-6 compared to uninfected controls. Children with either microscopic or submicroscopic asymptomatic malaria exhibited higher levels of IFN-γ, IL-17A, and IL-4 compared to uninfected controls. The levels of most of the pro and anti-inflammatory cytokines were comparable between children with microscopic and submicroscopic infections. The ratio of IFN-γ/IL-10, TNF-α/IL-10, IL-6/IL-10 as well as IFN-γ/IL-4 and IL-6/IL-4 did not differ significantly between the groups. Additionally, using a principal component analysis, the cytokines measured could not distinguish amongst the three study populations. This may imply that neither microscopic nor submicroscopic asymptomatic infections were polarized toward a pro-inflammatory or anti-inflammatory response. Conclusion The data show that asymptomatic malaria infections result in increased plasma levels of both pro and anti-inflammatory cytokines relative to uninfected persons. The balance between pro- and anti-inflammatory cytokines are, however, largely maintained and this may in part, explain the lack of clinical symptoms. This is consistent with the generally accepted observation that clinical symptoms develop as a result of immunopathology involving dysregulation of inflammatory mediator balance in favor of pro-inflammatory mediators.

Background In malaria, clinical disease has been associated with increased levels of endothelial activation due to the sequestration of infected erythrocytes. However, levels and impact of endothelial activation and pro-angiogenic molecules such as vascular endothelial growth factor (VEGF)-A and its receptor VEGFR2 in asymptomatic malaria have not been well characterized. Methods Blood samples were obtained from community children for malaria diagnosis using microscopy and PCR. A multiplex immunoassay was used to determine the levels of Intracellular adhesion molecule (ICAM)-1, VEGF-A, and VEGFR2 in the plasma of children with microscopic or submicroscopic asymptomatic parasitaemia and compared with levels in uninfected controls. Results Levels of ICAM-1, VEGF-A and VEGFR2 were significantly increased in children with microscopic asymptomatic parasitaemia compared with uninfected controls. Also, levels of VEGF-A were found to be inversely associated with age. Additionally, a receiver operating characteristic analysis revealed that plasma levels of ICAM-1 (AUC =0.72), showed a moderate potential in discriminating between children with microscopic malaria from uninfected controls when compared to VEGF-A (AUC =0.67) and VEGFR2 (AUC =0.69). Conclusion These data imply that endothelial activation and pro-angiogenic growth factors could be one of the early host responders during microscopic asymptomatic malaria, and may play a significant role in disease pathogenesis.

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