CD19 and systemic lupus erythematosus: However, the observation that CD19+ B cells were detectable in peripheral circulation at an earlier time point after treatment with rituximab in patients with SLE compared with RA suggests that BCD was less pronounced and/or that repopulation of distinct B cell subpopulations occurred sooner in patients with SLE compared with those with RA and/or that CD19+CD20– plasma blasts and plasma cells, which may, at least in part, explain the disparity in clinical response reported in clinical trials involving patients with RA and SLE.