Ascertainment of IgA1 (kappa)-transferrin complex in a case of multiple myeloma associated with hypersiderinemia.

IgA1(kappa)-transferrin complex was ascertained in a case of multiple myeloma with hypersiderinemia. On gel filtration, this complex disclosed an orange-colored protein with two peaks between the 19S and 7S fractions. On polyacrylamide gel electrophoresis and Western blotting analysis, the complex migrated at molecular weights of 430 and 700 kD in the non-reducing condition. A small amount of free transferrin was detected simultaneously. The complex was further separated into monoclonal IgA1(kappa) and transferrin at pH 4.5; these recombined at pH 7.2 after incubation (37 degrees C, 2 h). We also showed that the pepsin-digested F(ab')2 fragment of IgA1(kappa) combined with the transferrin. From these results it can be suggested that monoclonal IgA1(kappa) has an antibody activity for the transferrin. Clinically, this complex distributed the iron transport to erythroid cells in the bone marrow, resulting in hypersiderinemia, anemia, and iron deposits in the liver.