Loss of the Knops blood group system antigens from stored blood

Complement receptor type one (CR1) is a polymorphic glycoprotein, present on red blood cells (RBCs), that carries the Knops blood group system antigens. Since Knops system antigens can vary in strength, we investigated whether CR1 deteriorated upon storage, thus affecting Knops blood group system antigen reactivity. Units of whole blood were collected in CPDA-1 and evaluated at day 0 and day 35 for antigen strength, using routine serologic techniques. CR1 was quantitated by an enzyme-linked immunoassay and by flow cytometry measurements. The CR1 expression polymorphism was ascertained by a Hind III restriction fragment length polymorphism analysis. RBC membrane proteins were separated by SDS-PAGE and analyzed for CR1 size by immunoblotting. During the 35-day study interval, no notable decrease was found in RBC-CR1 by flow cytometry. However, CR1 protein was shown to be lost by proteolytic cleavage, as well as by vesiculation. This CR1 protein loss may contribute to the variability of serologic reactions characteristic of the Knops blood group system antigens. Titration results showed a significant decrease in score between day 0 and day 35 using anti-McC^a and anti-Yk^a. Anti-Kn^a and anti-Sl^a did not demonstrate statistically significant differences in titration scores. Immunohematology 1995;11:46–50.