Polypeptides immunologically related to band 3 are present in nucleated somatic cells

Band 3, the major transmembrane polypeptide of erythrocytes, mediates the exchange of anions (chloride and bicarbonate) across the membrane. We suspected that band 3 was present on nucleated somatic cells as well as erythrocytes because the senescent cell antigen that is immunologically related to band 3 is present on lymphocytes, platelets, adult liver cells, and embryonic kidney cells; and antibodies prepared against the senescent cell antigen isolated from leukocytes react with erythrocyte band 3. For this reason, we examined human fibroblasts, lung cells, neutrophils, mononuclear leukocytes, squamous epithelial (mouth) cells, lung squamous epithelial carcinoma, mouse neuroblastoma cells, and rat hepatocytes for immunoreactive forms of band 3 by using monospecific antibodies to erythrocyte band 3. The results demonstrated that polypeptides sharing common antigenic determinants with erythrocyte band 3 are present in nucleated somatic cells as determined by immunofluorescence, immunoelectron microscopy, and immunoautoradiography. Peptide mapping revealed substantial sequence homology between erythrocyte band 3 and the band 3-like protein of leukocytes. Immunofluorescence studies indicate that the band 3-like proteins in nucleated cells participate in antibody-induced cell surface capping.