OBJECTIVETo explore the expression levels of terminal complement complex (C5b-9) and CD62p on platelets and the soluble C5b-9 (sC5b-9) level in serum in patients with PNH or PNH-aplastic anemia (AA).

METHODSSerum levels of sC5b-9, complement C3 and C4 were detected by using ELISA in 25 patients with PNH/PNH-AA. The quantities of C5b-9 and CD62p on the membrane of platelets were detected by flow cytometry.

RESULTS①In PNH/PNH-AA group, the serum sC5b-9 level [390.27(265.73-676.87) μg/L] was lower than that in control group [540.39(344.20-1 576.78) μg/L] (P<0.01). ②The platelet PNH clone (CD59⁻CD61⁺/CD61⁺) size [50.58(23.29-81.60)%] was bigger in the PNH/PNH-AA group than that [23.57(15.58-29.02)%] in control group (P<0.01). The percentages of C5b-9 deposition (C5b-9⁺CD61⁺/CD61⁺) were higher on the PNH clone platelets (CD59⁻CD61⁺) in the PNH/PNH-AA group [(17.53 ± 6.27)%] than those on the normal platelets (CD59⁺CD61⁺) in PNH patients 11.33±5.03）%］ and control [(10.88±3.58)%] group (P<0.01). ③ The expression of CD62p (CD62p⁺CD61⁺/CD61⁺) on PNH clone platelets in PNH patients [(61.98 ± 11.71)%] was higher than that on the normal platelets in PNH patients [(43.76±11.30)%] and control group [(38.23±18.07)%] (P<0.01). In addition, the expression of CD62p on normal platelets was higher in PNH patients than control (P<0.05). ④The deposition of C5b-9 positively correlated with the expression of CD62p on the platelets (r=0.559, P=0.002).

CONCLUSIONDeficiency of CD59 antigen on platelets in PNH patients may lead to the deposition of C5b-9 on its membrane and its dysfunction, which may contribute to thrombosis events in PNH.