IRF4 and plasma cell myeloma: For this analysis we used A20, a mature B cell line known to secrete basal IL-10 [16], BCL-1-3B3 cell line, a leukemic cell line that can be differentiated in vitro to plasma cells [63], and P3X63Ag8, a mouse plasmacytoma/myeloma cell line that expresses high levels of endogenous IRF4.