Mu-chain disease in a case of chronic lymphocytic leukaemia and malignant histiocytoma. II. Immunochemical studies.

Agarose gel electrophoresis of serum from the eleventh case of mu-chain disease (mu-CD) showed two distinct abnormal bands due to free light chains and kappa-complexes with other serum proteins. This caused diagnostic difficulties on conventional immunoelectrophoresis, and crossed immunoelectrophoresis with intermediate gel is demonstrated as a superior tool for investigation of mu-CD. A simple rocket immunoelectrophoresis method foe mu-CD screening is also shown. The mu-CD protein had alpha-2-mobility and a part of the protein carried kappa-determinants probably due to secondary binding. Preparative ultracentrifugation and size chromatography on serum demonstrated that the mu-CD protein was present in serum in several sizes, the smallest being a dimer of mu-chains. Due to scarcity of material the abnormal protein could not be characterized further.