Difference in geometry of young and old human erythrocytes explained by a filtering mechanism.

A mechanism for the geometric difference between young and old human red blood cells is proposed. It is assumed that the bone marrow produces a population of cells with a range of sizes and shapes, but only those cells which can pass through a theoretical 3.65//, cylindrical channel survive in the circulation. The important geometric parameters of an erythrocyte are the area and the volume. We suggest that as cells age they have a constant area but swell in proportion to their original volume. This hypothesis of aging was tested on 1,016 normal cells using the IBM 7040 computer. When the cells were theoretically swelled by approximately 15%, the population of cells which could still pass through the filter had a smaller mean area and volume and were more osmotically fragile than the same cells before swelling. Young and old cells were separated by centrifugation. The heaviest 10% of the cells (old cells) had a lower diameter, area, and volume and higher sphericity index than the lightest 20% (young cells). The calculated minimum filter diameter was not significantly different. The good agreement between the predicted and observed changes in cellular geometry between young and old cells provides supporting evidence that a cylindrical filter exists in the circulation and may play a role in determining the life span of the erythrocyte. ADDITIONAL KEY WORDS minimum cylindrical diameter area and volume theoretical aging centrifugation • For years many investigators have been inquiring about the destruction of red blood cells. Theories to describe the early stages of red cell breakdown range from cellular fragmentation to physical trapping. Canham and Burton (1) recently demonstrated that the linear relation between the area and volume of single erythrocytes in a population of cells was evidence for a filtering network in the circulation. Their results indicated that somewhere in the circulation the red cell is required to squeeze through very narrow cylindrical channels. If the cell increased in volume so much that it could no longer get through these hypothetical channels, it would get trapped and eventually hemolyze. The hot-dog shape is the most suitable shape for the flexible red cell to adopt when it is required to navigate narrow channels (less than 4(JL). Canham and Burton suggested that the filter was located in the spleen. The importance of the spleen in removing defective cells is well established (2, 3), but the function of the spleen in …