Unraveling the Mysteries of Self-Preservation
Red Blood Cell Aging
By: Dr. Gregory Denomme PhD, FCSMLS (D)
The Cellular Workhorses: Structure and Function of Red Blood Cells
Red blood cells (RBCs) are specialized cells responsible for gas transport. They have a unique biconcave shape, which increases their surface area and optimizes the diffusion of gases. RBCs are enucleated, meaning they lose their nucleus and other organelles during maturation, which further enhances their efficiency in gas exchange.
Structure of Red Blood Cells
The RBC membrane is a phospholipid bilayer with embedded proteins. Key proteins include:
- Ankyrin: Links the membrane to the cytoskeleton by binding to Band 3 and Spectrin.
- Spectrin: Provides structural support and flexibility.
- Actin: Works with Spectrin to maintain the cell’s shape and flexibility.
This intricate structure allows RBCs to withstand the mechanical stresses they encounter while traveling through the circulatory system.
Senescence and Eryptosis
RBCs have a lifespan of approximately 120 days. As they age, they undergo a process known as senescence, which is akin to programmed cell death but specific to RBCs and termed eryptosis. This process involves several changes:
- Loss of water and membrane shedding: RBCs become spherocytic, losing their biconcave shape.
- Exposure of phosphatidylserine: This phospholipid flips from the inner to the outer leaflet of the membrane.
- Increase in surface immunoglobulin G (IgG): Aged RBCs exhibit higher levels of IgG, marking them for removal by the immune system.
In healthy individuals, only a small fraction of RBCs at any time show significant signs of aging. However, in autoimmune diseases, the level of IgG on RBC surfaces can increase markedly, detectable by routine diagnostic tests.