Red blood cell layers after Percoll density gradient centrifugation.

Seven RBC fractions were generated by Percoll density gradient centrifugation. Least dense fraction on the top consisted of youngest RBC; increasing density indicated increasing RBC age. Arrows indicate the respective density of Percoll solution. Subpopulations were clearly separated and collected. Oldest fraction at the bottom was described as 1.076+ g/ml, with “+” indicating possible even denser RBC than the densest Percoll layer of 1.076 g/ml.