Determination of CD59 protein in normal human serum by enzyme immunoassay, using octyl-glucoside detergent to release glycosyl-phosphatidylinositol-CD59 from lipid complex.

In this study we have optimised the enzyme immunoassay (ELISA) to quantify CD59 antigen in human serum or plasma. The glycosyl-phosphatidylinositol (GPI)-linked form of CD59 is known to complex with serum high-density lipoprotein. For ELISA optimisation, therefore, we investigated the effect of detergents, added to the sample diluent, on the determined values of CD59. Values obtained in the presence of octyl-glucoside (OG) for 20 adults aged 18-35 years and 17 children 1-5 years old were, respectively, 33-119 ng/ml (mean +/- S.D.: 66+/-22 ng/ml) and 37-143 ng/ml (76+/-33 ng/ml). These results were higher than those measured without OG and were in contrast with published results showing absence, or eight to nine times lower levels, of the protein in serum. A known range for serum concentrations of CD59 in healthy individuals will establish an important reference point for clinical work and for the investigation of diseases involving the complement membrane attack complex (MAC) and its regulation.

Deficiency of red cell bound CD55 and CD59 in patients with systemic lupus erythematosus.

CD55 and CD59 are glycosylphosphatidylinositol-anchored proteins with complement inhibitory properties. Autoimmune hemolytic anemia (AIHA) has been associated with antiphospholipid antibodies (APLA). The aim of this study was to evaluate the presence of APLA and its possible correlation with diminished CD55 and CD59 in red blood cells from patients with primary AIHA or secondary to systemic lupus erythematosus (SLE). Flow cytometric analyses were performed on CD55 and CD59 stained erythrocytes from 24 patients (primary AIHA, n=8; AIHA plus SLE, n=11; and SLE without AIHA, n=5) and 20 healthy controls. Antibodies to several phospholipids were detected in the sera by ELISA. Most patients with AIHA plus SLE and few with primary AIHA showed deficiency of either or both CD55 and CD59 expression and was not associated to the presence of APLA, while SLE patients exhibited a normal expression of these molecules. Although our findings showed CD55 and CD59 deficiency in primary or secondary AIHA, it appears that this defect plays a facilitator rather than a triggering role for the hemolytic process. Additionally, a role of anti-phospholipid antibodies as causative of this acquired defect is questionable.