Antibody-secreting cells as a source of NR1-IgGs in N-methyl-D-aspartate receptor-antibody encephalitis

The pathogenicity of NR1-IgGs in N-methyl-D-aspartate receptor (NMDAR)-antibody encephalitis is known, but the immunobiological mechanisms underlying their production remain unclear. For the first time, we explore the origin of NR1-IgGs and evaluate the contribution of B-cells to serum NR1-IgGs levels. Peripheral blood mononuclear cells (PBMCs) were obtained from patients and healthy controls (HCs). Naïve, unswitched memory (USM), switched memory B cells (SM), antibody-secreting cells (ASCs), and PBMC depleted of ASCs were obtained by fluorescence-activated cell sorting and cultured in vitro. For some patients, PBMCs spontaneously produced NR1-IgGs. Compared to the patients in PBMC negative group, the positive group had higher NR1-IgG titers in cerebrospinal fluid and Modified Rankin scale scores. The proportions of NR1-IgG positive wells in PBMCs cultures were correlated with NR1-IgGs titers in serum and CSF. The purified ASCs, SM, USM B cells produced NR1-IgGs in vitro. Compared to the patients in ASCs negative group, the positive group exhibited a worse response to second-line IT at 3-month follow-up. Naïve B cells also produce NR1-IgGs, implicating that NR1-IgGs originate from naïve B cells and a pre-germinal centres defect in B cell tolerance checkpoint in some patients. For HCs, no NR1-IgG from cultures was observed. PBMC depleted of ASCs almost eliminated the production of NR1-IgGs. These collective findings suggested that ASCs might mainly contribute to the production of peripheral NR1-IgG in patients with NMDAR-antibody encephalitis in the acute phase. Our study reveals the pathogenesis and helps develop tailored treatments (eg, anti-CD38) for NMDAR-antibody encephalitis.