The percentage of CD56bright natural killer (NK) is increased in patients with systemic lupus erythematosus (SLE). (a) On the left, an example of gating of CD3− CD56+ NK cells on gated blood lymphocytes from a healthy control is shown. On the right, CD56bright NK cells defined as CD16− NK cells are shown in the square. (b) The percentage of CD56bright NK cells of total blood CD3− CD56+ NK cells is plotted for patients with SLE during active disease (n = 15), patients during inactive disease (n = 8), patients with immunoglobulin A nephritis (IgAN) (n = 10), patients with rheumatoid arthritis (RA) (n = 13) and healthy blood donors (n = 20). Analysis of variance test P = 0·0009, followed by Tukey's post hoc test: active SLE compared to healthy control P = 0·01, and inactive SLE compared to healthy control P = 0·004. (c) The percentage of CD56bright NK cells of total blood CD3− CD56+ NK cells is plotted for three patients with SLE sampled during active and again during inactive diseases. Results from the active sample are included in (b).