Therefore, B-1a cells in lupus-prone mice consist of two principal subsets with CD3 surface expression, CD3+CD4-CD8-B220+CD23-CD5+ cells (CD3+ B-1a cells) and CD3-CD4-CD8-B220+CD23-CD5+ cells (classical B-1a cells). The gene discussed is FCER2; the disease is systemic lupus erythematosus.