Here we observed that SLE peripheral B cell subsets, activated B cells and differentiated plasma cells (PCs) had abnormally elevated levels of YTHDF1, the deficit of which attenuated PC differentiation both in vitro and in mouse models that have been immunized with keyhole limpet hemocyanin (KLH) or N-propionyl polysialic acid (NP–KLH). The gene discussed is YTHDF1; the disease is systemic lupus erythematosus.