Titration of DRS-1 Abs in sera of patients using ELISA. Antibody titers against purified His-tag DRS-1 in the sera of 71 PNH⁺ AA patients, 32 PNH^– AA patients, 13 PNH⁺ MDS patients, 42 PNH^– MDS patients, and 52 healthy individuals were determined using sera diluted at a 1:1000 dilution. The dotted line denotes a cutoff value defined as mean + 2 SD for absorbance in 52 healthy individuals. Asterisks indicate a prevalence of DRS-1 Ab titers significantly higher than that of PNH^– AA patients, PNH^– MDS patients, and healthy individuals (*P < .001, **P < .05).