Cell Membrane IgD: Demonstration of IgD on Human Lymphocytes by Enzyme-Catalyzed Iodination and Comparison with Cell Surface Ig of Mouse, Guinea Pig, and Rabbit
A substantial fraction of human cord blood and peripheral blood lymphocytes have recently been shown to bear IgD. Although IgD has not been identified in mice, it has been suggested that it is also a major surface immunoglobulin of murine lymphocytes. Thus, lactoperoxidase-catalyzed iodination of surface immunoglobulin of mouse spleen and lymph node cells reveals the existence of an Ig H chain differing from µ, γ, and α-chain both antigenically and by mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This new H chain class has been previously proposed to be the mouse homologue of δ-chain. In this paper, we analyzed human, mouse, guinea pig, and rabbit lymphoid cell membrane Ig by lactoperoxidase-catalyzed iodination, extraction with non-ionic detergent, precipitation with a variety of specific anti-Ig sera, and electrophoresis of dissolved reduced precipitates on sodium dodecyl sulfate-polyacrylamide gels. Our studies confirm the previous reports of a new mouse cell membrane H chain with a mobility more rapid than that of µ-chain. However, we fail to detect a molecule with this electrophoretic mobility on the surface of guinea pig or rabbit lymph node and spleen cells. Moreover, neither anti-κ nor anti-δ antibody precipitates a molecule with an H chain of this mobility from labeled extracts of human cord blood or peripheral blood lymphocytes. Cell surface δ was identified on both human cord blood and peripheral blood lymphocytes, but it proved to have mobility similar to human and mouse µ-chain. This result indicates either that mouse δ-chain has an electrophoretic mobility on sodium dodecyl sulfate-polyacrylamide gels which differs appreciably from that of human membrane δ-chain or that the newly described mouse H chain is not the homologue of human δ-chain.