The influence of uremic high cystatin C concentration on neutrophil apoptosis and selected neutrophil functions isolated from healthy subjects

Serum cystatin C and anti-N-methyl-D-aspartate receptor encephalitis

BACKGROUND

Cystatin C (CysC) is associated with many neurodegenerative disorders and autoimmune diseases, but its relationship with anti-N-Methyl-D-aspartate receptor (anti-NMDAR) encephalitis is unknown.

METHODS

Serum levels of CysC were determined in 66 patients with anti-NMDAR encephalitis and 115 healthy controls. Of the 66 patients, 30 had a follow-up evaluation at 3 months after admission. Association of CysC with anti-NMDAR encephalitis and its clinical parameters were evaluated in the patients.

RESULTS

The serum levels of CysC were significantly lower in patients with anti-NMDAR encephalitis than in controls (0.70 ± 0.13 vs 0.83 ± 0.17 mg/mL, P < .001). Disease severity and disease duration were significantly associated with CysC levels. Furthermore, a follow-up evaluation revealed that after treatment anti-NMDAR encephalitis patients had significantly increased serum CysC levels (P < .001) and significantly decreased modified Rankin Scale (mRS) scores (P < .001) compared with before treatment. In addition, a significant negative correlation was observed between the change in CysC levels and the change in mRS scores (r = -.700, P < .001).

CONCLUSION

Our results show that the serum levels of CysC are associated with anti-NMDAR encephalitis and its clinical parameters and that the changes in CysC levels correlate with therapeutic effect. Therefore, our findings provide new insights into the association between serum CysC and anti-NMDAR encephalitis.

Involvement of cystatin C in immunity and apoptosis

As an abundantly expressed cysteine protease inhibitor widely distributed in the organisms, cystatin C is involved in various physiological processes. Due to its relatively small molecular weight and easy detection, cystatin C is commonly used as a measure for glomerular filtration rate. In pathological conditions, however, growing evidences suggest that cystatin C is associated with various immune responses against either exogenous or endogenous antigens, which ultimately result in inflammatory autoimmune diseases or tumor development if not properly controlled. Thus the fluctuation of cystatin C levels might have more clinical implications than a reflection of kidney functions. Here, we summarize the latest development of studies on the pathophysiological functions of cystatin C, with focus on its immune regulatory roles at both cellular and molecular levels including antigen presentation, secretion of cytokines, synthesis of nitric oxide, as well as apoptosis. Finally, we discuss the clinical implications and therapeutic potentials of what this predominantly expressed protease inhibitor can bring to us.