GENERATION OF SENESCENT CELL ANTIGEN ON OLD CELLS INITIATES IGG BINDING TO A NEOANTIGEN

An aging antigen, senescent cell antigen, resides on the 911 aminoacid membrane protein band 3. It marks cells for removal by initiating spe cific IgG autoantibody binding. Band 3 is a ubiquitous membrane transp ort protein found in the plasma membrane of diverse cell types and tis sues, and in nuclear, mitochondrial and Golgi membranes. Band 3 in tis sues such as brain performs the same functions as it does in red cells . Senescent cell antigen is generated on brain membranes. Oxidation is a mechanism for generating senescent cell antigen. Neither cross-link ing nor hemoglobin appear to play a role in generating senescent cell antigen. Although storage is the only in vitro model that mimics cellu lar aging in situ, we have discovered three alterations /mutations of band 3 that permit insight into aging in situ. One mutation with an ad dition to band 3 has normal or decelerated red cell aging. In contrast , another band 3 alteration with a suspected deletion or substitution that renders band 3 more susceptible to proteolysis, shows accelerated aging. The third alteration which is also more susceptible to proteol ysis is associated with neurologic defects. Peptide technology was use d to map the aging antigenic sites and anion transport sites on band 3 using a competitive inhibition assay and immunoblotting with IgG dire cted against the aging antigen on old cells. Results indicate that: a) aging antigenic sites reside on human band 3 residues 538-554, and 81 2-830; b) a putative ankyrin binding region peptide is not involved in senescent cell antigen activity and c) carbohydrate moieties are not required for the antigenicity or recognition of senescent cell antigen since synthetic peptides alone abolish binding of senescent cell IgG to erythrocytes. Peptide residues 588-594 (a 7 amino acid peptide), 82 2-839 and 869-883 were the most active inhibitors of anion transport ( P less-than-or-equal-to 0.001 compared to control without peptide). Lo calization of the active antigenic and transport sites on band 3 molec ule facilitates the definition of molecular changes occuring during ag ing that initiate molecular as well as cellular degeneration. The role of senescent cell antigen and band 3 in brain aging and Alzheimer's d isease is discussed.