Abstract
Human thymus cells synthesize immunoglobulin in short-term culture, the nascent immunoglobulin appearing in both cytoplasmic and membrane fractions. Surface immunoglobulin was demonstrated by lactoperoxidase radioiodination of the cells. The demonstration of intracellular and surface immunoglobulin required procedures that minimize proteolytic degradation. Noncovalently linked, monomeric mu chains and light chains were found in the cytoplasm and on the surface of the cells by means of acrylamide gel electrophoresis and by specific immunoprecipitation of the isolated chains.