Internalization and processing of antibodies to surface antigens on human B cells. Monoclonal anti‐IgM antibodies are processed differently than monoclonal antibodies towards non‐Ig surface receptors

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Abstract
The internalization and intracellular processing of monoclonal antibody to immunoglobulin μ heavy chain (Maμ) have been investigated in two human Burkitt lymphoma cell lines (Ramos and Raji), in a human B cell lymphoma and in normal human peripheral blood B cells. In addition to the degradation of 125I-labeled Maμ to trichloroacetic acid (TCA) soluble material, a distinct pattern of larger 125I-Map fragments was detected in all sources of B cells tested. The particular fragmentation pattern, as revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis, involved the cleavage of both peptide bonds and disulfide bridges. This type of antibody fragmentation appeared to be a selective mechanism associated with sIgM, as no other degradation than that leading to TCA-soluble material could be detected after the internalization and degradation of radiolabeled monoclonal antibodies towards a variety of non-Ig B cell surface receptors. Three fragments of 125I-Maμ degradation were also detected in the supernatant of Ramos cells, implying that the recycling and exocytosis of certain 125I-Maμ fragments also took place.