Mechanism of aging of human red cells
Abstract
An essential biological process is the removal of old or faltering erythrocytes from circulation after a finite lifespan. The process involves at least in part, immunoglobulin G binding and consequent recognition of opsonized red cells by macrophages in the reticuloendothelial system. Our laboratory has previously demonstrated that hemoglobin denaturation in the red cell triggers antibody binding in vitro by clustering the major transmembrane protein band 3. Since these studies were conducted in vitro using artificial hemoglobin denaturants, we decided to examine the process in vivo to investigate their physiological relevance. We first examined erythrocytes containing unstable hemoglobins as they denature prematurely. We demonstrated by immunofluorescence microscopy that band 3 was indeed clustered in vivo in sickle erythrocytes at sites of hemichrome binding. Peripheral proteins such as ankyrin and band 4.1 were also included in the band 3-hemichrome cluster. We isolated these protein complexes or aggregates from sickle erythrocytes and found that the major proteins at these sites were globin and band 3. Although these aggregates constituted only 1% of the total membrane protein, almost 75% of the total cell surface antibody were localized at these sites. Similar results were obtained from thalassemic erythrocytes which also contain denatured hemoglobin. Finally, we examined senescent erythrocytes from normal human blood and demonstrated the presence of protein aggregates similar in composition to those obtained from cells with unstable hemoglobins. These aggregates were shown to contain 50% of the total cell surface antibody. Therefore, we suggest that these antibody coated sites in abnormal and normal senescent erythrocytes are responsible for immune recognition and ultimately phagocytosis of the erythrocyte.
Degree
Ph.D.
Advisors
Low, Purdue University.
Subject Area
Biochemistry|Anatomy & physiology|Animals|Cellular biology
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