AQP4 and sinus histiocytosis with massive lymphadenopathy: To address this, we performed spectral flow cytometry on blood samples from healthy individuals (young/old) and people with MS (relapsing/progressive), AE (anti‐LGI1/‐IgLON5/‐GAD65), or RDD (anti‐AQP4 NMOSD/MOGAD) who did not receive any immunomodulatory treatment at the time of sampling (Figure 1A).