A case of mu heavy-chain disease associated with hyperglobulinemia, anemia, and a positive Coombs test.

We report here for the first time a patient with mu heavy-chain disease (HCD), hyperimmunoglobulinemia, and a positive direct antiglobulin test (DAT, Coombs test). The heavy-chain diseases involve the proliferation of lymphoplasma cells of B cell origin and are characterized by the production of incomplete heavy chains devoid of light chains. The association of mu heavy-chain disease with either hyperglobulinemia or a positive DAT has not been reported in the literature to date. In this patient, immunofixation of serum proteins with monospecific antisera to alpha-, gamma-, mu,- or delta-chains and to kappa- and lambda-chains revealed a precipitation band with antibody to IgM, but not with kappa and lambda light-chain antibodies, indicating mu heavy-chain disease. Hyperglobulinemia was present, which is very uncommon for HCD. A DAT of the patient's red blood cells (RBC) was found to be strongly positive for anti-IgG but negative for anti-IgM, -IgA, -C3c, and -C3d. However, when the eluate from the patient's red blood cells was investigated with nephelometry, it was found to contain antigens reactive with anti-y as well with anti-mu-antiserum. When a DAT was performed with a randomly chosen test cell incubated with the eluate, the antibody-containing eluate was shown to react with anti-IgG as well as with anti-IgM-antiserum. In summary, the eluate from the patient's RBCs contained IgG and an immunoglobulin structure reactive with anti-IgM in an RBC agglutination assay as well as with anti-mu antiserum in a nephelometric investigation. Whether this IgM on the patient's erythrocytes is penta- or oligomeric, complete IgM, or the heavy chain cannot be concluded from these observations.