A similar positive correlation was shown between the CSF sTREM2 expression level and the CSF CD44 (r = 0.702, p < 0.0001, Fig. 2B) and between the CSF sTREM2 expression level and the serum MMP9 expression levels (r = 0.428, p = 0.021, Fig. 2C) in the anti-NMDAR encephalitis patients. This evidence concerns the gene MMP9 and viral encephalitis.