Elevated blood and cerebrospinal fluid biomarkers of microglial activation and blood‒brain barrier disruption in anti-NMDA receptor encephalitis

Abstract

Background: Anti-NMDA receptor (NMDAR) encephalitis is an autoimmune disease characterized by complex neuropsychiatric syndrome and cerebrospinal fluid (CSF) NMDAR antibodies. Triggering receptor expressed on myeloid cells 2 (TREM2) has been reported to be associated with inflammation of the central nervous system (CNS). Matrix metalloproteinase-9 (MMP9) and cluster of differentiation (CD44) were measured to evaluate blood‒brain barrier (BBB) permeability in anti-NMDAR encephalitis. The roles of microglial activation and BBB disruption in anti-NMDAR encephalitis are not well known.

Findings: In this work, we detected increased expression levels of CSF sTREM2, CSF and serum CD44, and serum MMP9 in anti-NMDAR encephalitis patients compared with controls. CSF sTREM2 levels were positively related to both CSF CD44 levels (r = 0.702, p < 0.0001) and serum MMP9 levels (r = 0.428, p = 0.021). In addition, CSF sTREM2 levels were related to clinical parameters (modified Rankin Scale scores, r = 0.422, p = 0.023, and Glasgow Coma Scale scores, r = - 0.401, p = 0.031).

Conclusion: Increased sTREM2 levels in CSF as well as increased CD44 and MMP9 in serum and CSF reflected activation of microglia and disruption of the BBB in anti-NMDAR encephalitis, expanding the understanding of neuroinflammation in this disease. The factors mentioned above may have potential as novel targets for intervention or novel diagnostic biomarkers.

Keywords: Anti-NMDA receptor encephalitis; Blood‒brain barrier disruption; CD44; MMP9; Microglial activation; sTREM2.

Fig. 1

Comparison of sTREM2, MMP9, and CD44 levels in serum and CSF between anti-NMDAR encephalitis patients and controls. A, B The CSF sTREM2 levels were significantly increased (p < 0.001) in the anti-NMDAR encephalitis group, and the serum sTREM2 levels also showed an increasing trend (p = 0.003) compared with the controls. C The serum MMP9 levels were higher (p = 0.016) in the anti-NMDAR encephalitis group than in the controls. D, E CD44 levels in both the serum (D, p = 0.003) and the CSF (E, p = 0.18) were significantly higher in the anti-NMDAR encephalitis group than in the control group. Differences in CSF sTREM2 levels, serum sTREM2 levels, serum MMP9 levels, and CSF CD44 levels were assessed by the Mann‒Whitney test between the anti-NMDAR encephalitis group and the control group. Differences in serum CD44 levels were assessed by the independent two-sample t test. The above statistical results have been adjusted for age and sex

Fig. 2

Correlation analysis of sTRME2 levels in CSF or serum with other parameters. A–C The CSF sTREM2 level was positively related to the serum sTREM2 level (r = 0.426, p = 0.021), the CSF CD44 level (r = 0.702, p < 0.0001), and the serum MMP9 level (r = 0.428, p = 0.021). D–F The CSF sTRME2 level was positively related to the mRS scale (r = 0.422, p = 0.023) and age (r = 0.407, p = 0.028) but negatively related to the GCS score (r = − 0.401, p = 0.031). Spearman correlation coefficients were used for the analysis

Fig. 3

Correlation analysis of CSF CD44 levels with clinical parameters and serum MMP9 levels. A, B The CSF CD44 level was positively related to the mRS scale (r = 0.509, p = 0.005) and negatively related to the GCS score (r = − 0.382, p = 0.041). C The CSF CD44 level was positively related to the serum MMP9 level (r = 0.467, p = 0.011). D The serum MMP9 level is positively related to the Qalb value (r = 0.493, p = 0.007). Spearman correlation coefficients were used for the analysis

Fig. 4

The predictive value of CSF sTREM2 and CSF CD44 for anti-NMDAR encephalitis. A, B Each patient’s clinical outcome was classified as good or poor according to the mRS score (mRS > 3 poor outcome, mRS ≤ 3 good outcome). In anti-NMDAR encephalitis, both CSF sTREM2 (p = 0.010) and CSF CD44 (p = 0.011) showed higher concentrations in patients with poor outcomes than in patients with good outcomes. C Receiver operating characteristic curve (ROC) analysis for CSF sTREM2 (AUC = 0.800, p = 0.009) and CSF CD44 (AUC = 0.794, p = 0.0125) in distinguishing good and poor clinical outcomes in anti-NMDAR encephalitis. D Receiver operating characteristic curve (ROC) analysis was applied to determine the diagnostic value of sTREM2 (CSF sTREM2 AUC = 0.864, p < 0.0001; serum sTREM2 AUC = 0.568, p = 0.4651), CD44 (CSF CD44 AUC = 0.729, p < 0.018; serum CD44 AUC = 0.837, p = 0.0003), and MMP9 (serum MM9 AUC = 0.687, p = 0.0436) in anti-NMDAR encephalitis. The Mann‒Whitney U test was applied when comparing the differences in CSF sTREM2 and CSF CD44 between the good outcome group and poor outcome group in anti-NMDAR encephalitis