Some characteristics of the human erythrocyte as a function of donor and cell age.

Erythrocytes from healthy human donors of various ages (18-93 years) were separated on Percoll into four density fractions. Increased cell density has been reported to correlate with the age of the erythrocyte. Aged individuals, while having normal hematocrits, show an increased percentage of low-density young erythrocytes and almost twice as many reticulocytes in their circulation as do young adults. This evidence for increased, well-compensated, red cell turnover in elderly humans is supported by the finding in older individuals of increased levels of erythrocytes bearing autologous IgG on their membranes. Using fluorescent anti-IgG, erythrocytes with bound autologous IgG could be found in all density fractions from donors of all age groups. The old donors had an increased number of fluorescent cells that appeared in all density fractions albeit with a definite skewing toward the more dense cell fractions. Erythrocytes from young donors had higher levels of intact hemoglobin per cell than those from old donors. The relevance of these results to the aging process and the ability of senescing individuals to withstand hematologic stress are discussed.