Nucleophosmin-binding activity of sera from patients with SLE. (a) Sera from patients with systemic lupus erythematosus (SLE) (◆) or from healthy controls (-) were analysed by ELISA using recombinant human nucleophosmin. The dotted line represents the cutoff value (mean A405 of controls + 3 SD). Sera giving an A405 < 0.286 were considered negative. (b) Different dilutions of serum from an SLE patient (◆) and a control (■) were tested in ELISA.