The Presence of the li Blood Group System on Human Platelets

To examine platelets for the Ii antigens, high-titer human IgM anti-I and anti-i antibodies were affinity purified, radiolabeled with 125I, and incubated with adult and cord platelets. Saturation binding curves were performed by incubating adult platelets with serial dilutions of concentrated 125I-anti-I. Inhibition binding curves were performed by incubating adult platelets with doubling dilutions of concentrated unlabeled anti-I mixed with 125I-labeled anti-I. Adult platelets bound significantly more anti-I than anti-i, while cord platelets bound more anti-i than anti-I (P less than 0.025). Both anti-I and anti-i show a temperature-dependent dose-response curve of maximum binding at 4 degrees C. Binding of 125I-labeled anti-I was inhibited by preincubation with 100-fold concentration of unlabeled anti-I. The authors conclude that platelets express I/i antigens in parallel with that of red blood cells.