Increased expression of microRNA-21 in peripheral blood mediates the down-regulation of IFN-γ and increases the prevalence of stroke-associated infection.

Background: Increasing levels of microRNA (miRNA)-21 can lead to IFN-γ deficiency, thereby suppressing immune function. Whether changes in the peripheral blood expression of miRNA-21 in patients with acute stroke are related to stroke-associated infection (SAI) remains unsettled.

Methods: MiRNA-21 and IFN-γ expression levels in peripheral blood plasma were measured in stroke patients presenting within 24h of symptom onset to assess whether these expression levels are associated with the prevalence of SAI.

Results: The stroke with SAI group had significantly higher miRNA-21 expression and lower IFN-γ levels than the stroke without SAI group (p<0.05). A significant negative correlation was observed between miRNA-21 expression and IFN-γ levels (r=-0.303, p=0.026). ROC curves were constructed to measure the performance of the miRNA-21 and IFN-γ to judge SAI. The areas under the ROC curve (AUC) for miRNA-21 and IFN-γ were 0.667 (95% CI, 0.525 to 0.798, p=0.028) and 0.698 (95% CI, 0.558 to 0.816, p=0.005), respectively. The optimal cutoff value was miRNA-21>0.53 and IFN-γ≤72.57pg/ml. There was a significantly different prevalence of SAI between the high miRNA-21 group and the low miRNA-21 group (p=0.008, log rank test). There was also a significant difference between the high IFN-γ group and the low IFN-γ group (p=0.003, log rank test).

Conclusions: Plasma up-regulated miRNA-21 and decreased IFN-γ in acute stroke can be considered new biological predictors for SAI and thus, new therapeutic targets.