Receptors for IgM on human B lymphocytes.

Using a rosette technique with IgM coated bovine red blood cells (EA-IgM) receptors for IgM can be demonstrated on human B-lymphocytes. While in the peripheral blood B cells with IgM receptors are found only occasionally, between 7 and 33%, mean 16%, of tonsil B-lymphocytes exhibit receptors for IgM. This was shown in double marker studies using EA-IgM for the demonstration of IgM receptors and fluorochrome labelled conjugates for the demonstration of S-IgD, S-IgM and B cell antigens. These receptors are specific for IgM, they can be completely blocked by IgM-anti OVA complexes and partially by free IgM, but not at all by aggregated human IgG. They are sensitive to trypsin and pronase but reconstitute after further incubation at 37 degrees C. These data show that not only T and CLL cells but also some normal B-lymphocytes have receptors for IgM. We favour the view that CLL lymphocytes may derive from these B-lymphocytes, which may represent a certain maturation step in B cell development.