The appearance of increased numbers of PC in the circulation of subjects with active SLE appears to reflect increased production in germinal centers, since circulating SLE PC contain highly mutated immunoglobulin (Ig) genes and their presence rapidly decreases following administration of a blocking monoclonal antibody to CD154 that limits T cell-B cell collaboration and germinal center formation [6]. This evidence concerns the gene CD40LG and systemic lupus erythematosus.