IL21 and systemic lupus erythematosus: Mice that have a single-amino-acid mutation in Roquin1 (a negative regulator of ICOS mRNA stability) demonstrate a spontaneous lupus-like phenotype that is accompanied by elevated numbers of Tfh cells expressing higher level of ICOS, IFN-γ OX40, and IL-21 and activated phenotypes of GCs (28, 222).