Surface expression of CD52 negatively correlated with complement 4 (C4) in SLE patients, (r = -0.8061, p = 0.0072), a laboratory measure of disease activity, suggesting that patients with more significant complement consumption, and therefore likely higher disease activity levels, expressed higher levels of CD52 on the surface of their B cells (Figure 1F). Here, C4A is linked to systemic lupus erythematosus.