C3 and systemic lupus erythematosus: MPs from SLE patients induced more ROS production than did MPs from healthy controls, and this was statistically significant for the total group of SLE patients (p = 0.006) and for those with high disease activity, as measured by the level of circulating C3 (p = 0.0008), but not for those with a correspondingly low disease activity (Fig. 5a).