NR2-reactive antibody decreases cell viability through augmentation of Ca ²⁺ influx in systemic lupus erythematosus

Objective Anti-N-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 Ca ²⁺ level. We also investigated the efficacy of zinc as a modulator of the intracellular Ca ²⁺ 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 Ca ²⁺ level in NR1/NR2a-transfected HEK 293 cells (R ² = 0.69, P < 0.0001). Intracellular Ca ²⁺ levels were significantly higher in cells incubated with IgG derived from NR2-reactive 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 Ca ²⁺ level in a dose-dependent manner. NR2-reactive antibody-positive SLE IgG weakened the efficacy of zinc as a negative modulator of the intracellular Ca ²⁺ level. Conclusion Our findings indicate that NR2-reactive antibody decreases cell viability by Ca ²⁺ influx in SLE through inhibition of the binding capacity of zinc.