Ham test of RBC treated RBC. Samples of PNH RBC were incubated for 1 hour with RBC eluate, HDL, or microvesicles at 37°C, washed with PBS, and incubated with acidified serum as a source of complement. Optical density measurements at 540 nm are shown on the right. Histograms of corresponding samples stained with CD59-FITC are seen at the left. CD55 expression was greater on the RBC incubated with HDL than on those incubated with RBC eluate (data not shown). Untreated samples showed 30% hemolysis, HDL treated 7%, RBC eluate treated 15%.