Pathogenic role of a monoclonal IgA (kappa ) anti-IgG paraprotein associated with hemorrhagic diathesis, rheumatoid arthritis, vascular purpura, and acute membranoproliferative glomerulonephritis.

Sixteen years earlier a 42-year-old woman with an IgA kappa plasma cell neoplasm presented with bleeding disorder. Her prolonged course was complicated by subsequent development of rheumatoid arthritis, vascular purpura, and an acute membranoproliferative glomerulonephritis (MPGN). The paraprotein and its (Fab')2 fragment showed affinity for a test myeloma IgG2 (lambda ) paraprotein. The patient's serum and the IgA-IgG complex separated by gel filtration did not exhibit cryoprecipitation. The complex also did not dissociate by ultracentrifugation. Electron microscopic and immunofluorescent studies of a renal biopsy sample taken during the episode of nephritis showed subendothelial deposits and a lacy fluorescent pattern strongly positive for IgA and IgG. The same immunoglobulins were eluted from the kidney at postmortem. A low concentration of monoclonal IgA kappa (antibody) and excess unbound polyclonal IgG (antigen) were demonstrated in the patient's serum at the time of MPGN, apparently analogous to the conditions necessary for the induction of experimental immune complex nephritis.