To date, studies that found NR1‐IgM have not related their presence to ongoing de novo production from recent germinal center reactions.20, 21 However, in our study, NR1‐IgM rates were surprisingly high in NMDAR‐antibody encephalitis patients and low in disease controls.22 The higher detection rate in the target population may be explained by use of live cell‐based assays, which are known to enhance sensitivity of NR1‐IgG detection.23 Furthermore, perhaps exclusion of intracellular epitope binding explains the low rate observed in disease controls. This evidence concerns the gene CD40LG and encephalitis.