Plasma cell leukemia with excretion of half-molecules of immunoglobulin A (alpha1 lambda1).

A patient with plasma cell leukemia and myelofibrosis excreted free immunoglobulin light chains and an abnormal monoclonal immunoglobulin (Ig) A in her urine. The IgA that was present in serum and urine had a sedimentation coefficient of 4.0 S. The molecule was comprised of both heavy and light chains but was antigenically deficient compared to normal IgA. As excreted in the urine, the protein appeared to be a half-molecule of IgA, with a partial deletion in the heavy chain, probably involving part or all of the C-terminal domain.