PTPRC and systemic lupus erythematosus: In B220+ cells derived from atacicept (TACI-IgG)-treated lupus-prone MRL/lpr mice, expression of plasma cell-associated transcription factors including Prdm1 and Xbp1 was increased, whereas expression of GC B cell-associated transcription factor Bcl6 and the mature B cell-associated transcription factor Pax5 was decreased (Table 1).