IRF5 and systemic lupus erythematosus: In addition, to determine whether our findings were restricted to lupus models or whether they might reflect GC responses more broadly, we measured changes in IRF5 expression in GC B cells and plasmablasts in C57BL/6 mice 14 days after immunization with the hapten 4-hydroxy-3-nitrophenylacetyl coupled to chicken γ-globulin.