NR2-reactive antibody decreases cell viability through augmentation of Ca2+ influx in systemic lupus erythematosus

Objective AntiN-methyl-D-aspartate (anti-NMDA) receptor subunit NR2-reactive antibody may play a crucial role in neuronal manifestations of systemic lupus erythematosus (SLE). However, how NR2-reactive antibody acts as a critical modulator of the NMDA receptor is unknown. This study was undertaken to investigate the biologic function of NR2-reactive antibody in patients with SLE. Methods. The study included 14 patients with SLE, 9 of whom had NR2-reactive antibody. We analyzed the effects of NR2-reactive antibody on cell viability and intracellular Ca2+ level. We also investigated the efficacy of zinc as a modulator of the intracellular Ca2+ level in the presence of NR2-reactive antibody. Results. There was a significant inverse correlation between the NR2-reactive antibody titer and cell viability (R-2 = 0.67, P < 0.0001; n = 23), and there was a significant association between the NR2-reactive antibody titer and the intracellular Ca2+ level in NR1/NR2a-transfected HEK 293 cells (R-2 = 0.69, P < 0.0001). Intracellular Ca2+ levels were significantly higher in cells incubated with IgG derived from NR2reactive antibody-positive SLE patients than in those incubated with IgG derived from NR2-reactive antibody-negative SLE patients (P = 0.0002). The addition of zinc decreased the intracellular Ca2+ level in a dose-dependent manner. NR2-reactive antibodypositive SLE IgG weakened the efficacy of zinc as a negative modulator of the intracellular Ca2+ level. Conclusion. Our findings indicate that NR2-reactive antibody decreases cell viability by Ca2+ influx in SLE through inhibition of the binding capacity of zinc.