Toll-like receptor 2-mediated downstream cytokine levels as determinant of malaria pathogenesis

Toll-like receptors (TLRs) are transmembrane proteins that recognize specific molecular patterns and activate downstream cytokine production usually for the eradication of invading pathogens. The objective of this study was to evaluate the genetic polymorphism of TLR2 Arg753Gln (rs 5743708) and soluble cytokines and TLR2 expression levels in malaria disease cases.

The study included prospectively collected 2 ml blood samples from 153 individuals clinically suspected for malaria and confirmed by microscopy and RDT from Assam. Stratification of the study groups was done as healthy control (HC, n=150), uncomplicated malaria (UC-M, n=128) and severe malaria (SM, n=25). The PCR-restriction fragment length polymorphism (RFLP) method was applied for the analysis of TLR2 Arg753Gln polymorphism and following the ELISA for soluble serum TLR2 (sTLR2) and its associated downstream cytokines, viz. tumour necrosis factor (TNF)-α and interferon (IFN)-γ levels.

Variation in TLR2 Arg753Gln gene showed no association with the susceptibility and the severity of malarial infection. Soluble TLR2 expression was significantly higher in uncomplicated malaria (UC-M) cases compared to healthy controls (P=0.045) and in terms of SM cases, the expression was also found to be higher in UC-M cases (P=0.078). The TNF-α expression was significantly higher in SM cases compared to both UC-M and control (P=0.003 and P=0.004). Similarly, significantly elevated expression of IFN-γ was noted in SM cases compared to both UC-M (P=0.001) and healthy controls (P<0.001).

The present study suggests the association of deregulated TLR2 pathway that leads to the deleterious downstream immune response in the development of malarial pathogenicity.