CD4 and systemic lupus erythematosus: In the case of rheumatoid arthritis and systemic lupus erythematosus, CD19+CD21hiCD23hiCD24hi transitional 2 marginal-zone precursor (T2-MZP) B cells significantly ameliorate collagen-induced arthritis (20), while the transfer of T2-like B cells suppresses lupus in MRL/lpr mice by restraining Th1 responses and inducing the differentiation of IL-10+CD4+ T cells (21).