Charles J. Sherr ¹, Sonia Baur ¹, Inge Grundke ¹, Joseph Zeligs ¹, Barbara Zeligs ¹, and Jonathan W. Uhr ¹

¹ From the Irvington House Institute and the Department of Medicine, New York University School of Medicine, New York 10016

Cells from an established line of Burkitt lymphoma (Daudi) were enzymatically radioiodinated, and labeled Ig from the cell surface was isolated and studied. Subcellular fractionation of labeled cells confirmed that intracellular proteins from the cytoplasm are not iodinated by this method. Radioactive Ig was identified as monomeric (8S) IgM, and an average of 10⁵ Ig molecules was found per cell. Ig molecules could be released from the plasma membrane by detergent lysis under nonreducing conditions indicating that attachment of Ig to the plasma membrane occurs via noncovalent interactions. The ratio of µ/L radioactivity in surface Ig was the same as that of total cellular Ig radioiodinated in solution suggesting that a large portion of the Fc fragment is not buried within the membrane. In contrast to the results obtained with cell surface Ig, most intracellular Ig was found as "free" µ- and L chains regardless of whether lysates were labeled with ¹²⁵I or cells were labeled with leucine-³H. The results indicate that only a small percentage of the total Ig of Daudi cells is associated with the cell surface and suggest that covalent assembly of Ig occurs at or near the time that the molecule becomes part of the plasma membrane. Similarities between cell surface Ig on normal splenic lymphocytes and Daudi cells suggest that the latter is a neoplasm of bone marrow-derived lymphocytes.

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This article has been cited by other articles:

• Rowley, D. A., Fitch, F. W., Stuart, F. P., Kohler, H., Cosenza, H. (1973). Specific Suppression of Immune Responses. Science 181: 1133-1141 [Abstract]  

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