ObjectiveTo detect the alteration of regulatory B cells (Bregs), follicular helper T cells (Tfh), and regulatory T cells (Tregs) frequencies in patients with anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis. Analyze their association with clinical severity and activity, and explore the effects of different immunotherapies on those immune cell subsets.MethodsWe enrolled 21 patients with anti-NMDAR encephalitis, 22 patients with neuromyelitis optica spectrum disorder (NMOSD), 14 patients with idiopathic intracranial hypertension (IIH), and 20 healthy controls (HC) in our study. The frequencies of various immune cell subsets were determined using flow cytometry.ResultsCompared to patients with IIH and HC, the frequencies of CD24hiCD38hitransitional B cells as well as Tregs were significantly lower while the frequency of Tfh was significantly higher in patients with anti-NMDAR encephalitis. The frequency of CD24hiCD38hitransitional B cells was significantly lower in the acute stage than in the recovery stage, and was negatively correlated with the modified Rankin scale (mRS) and the clinical assessment scale for autoimmune encephalitis (CASE). The frequency of CD24hiCD38hitransitional B cells at the last follow-up after rituximab (RTX) treatment was significantly higher than those treated with oral immunosuppressants or untreated. There was no clear difference between anti-NMDAR encephalitis and NMOSD in the above immune cell subsets.ConclusionWe suggested that the frequencies of CD24hiCD38hitransitional B cells and Tregs were decreased while the frequency of Tfh was increased in patients with anti-NMDAR encephalitis. CD24hiCD38hitransitional B cells frequency may be a potential indicator to estimate the disease activity and severity.