AQP4 and rheumatoid arthritis: CNS, central nervous system; CSF, cerebrospinal fluid; SLE, systemic lupus erythematosus; NPSLE, neuropsychiatric systemic lupus erythematosus; pSS, primary Sjögren’s syndrome; NMOSD, neuromyelitis optica spectrum disorder; RA, rheumatoid arthritis; NP, neuropsychiatric; AQP4-IgG, Aquaporin-4 immunoglobulin G; anti-NR2, antibodies against N-methyl-D-aspartate receptor subunit 2; anti-SSA (Ro), anti-Sjögren’s syndrome A (Ro) antibodies; anti-CCP, anti-cyclic citrullinated peptide antibodies; IgG, immunoglobulin G; CCL2, chemokine (C-C motif) ligand 2; P0/P1/P2, ribosomal P protein subunits