Low molecular weight IgM in the sera of patients with chronic lymphocytic leukemia

With the use of 2 independent techniques, circulating monomeric and oligomeric IgM were detected in the majority of 29 patients with chronic lymphocytic leukemia (CLL). In contrast it was detected only in trace quantities in a minority of healthy subjects. In the CLL group no significant correlation was observed between monomeric IgM and the total serum IgM level or the absolute lymphocyte count. Mitogen stimulated peripheral blood mononuclear cells from CLL patients were observed to secrete monomeric and oligomeric IgM in-vitro. Experiments manipulating the microenvironment of an IgM secreting cell line revealed that the addition of low concentrations of the reducing reagent 2-mercaptoethanol to the culture medium would enhance the proportions of monomeric IgM in the culture supernatant and the cellular cytoplasmic lysate. However the same concentrations would not directly reduce the secreted IgM. We conclude that the secretion of incompletely assembled IgM is commonly found in CLL and suggests an intrinsic defect(s) in the mechanisms involved in the polymerization of the monomeric units into the pentameric molecule.