Albumin-immunoglobulin complexes in human serum: classification and immunochemical analysis.

A complex between serum albumin and immunoglobulins was observed on immunoelectrophoresis in six patients. Two patients with multiple myeloma had monoclonal IgA-albumin complexes; one of these complexes was formed by covalent bonds and the other by non-covalent bonds. Four patients displayed non-covalent IgG-albumin complexes: of these, one had multiple myeloma, two had been treated with nitrofurantoin for prolonged periods, and one had diabetes mellitus. The IgG-albumin complex of the last patient was subjected to a detailed immunochemical analysis. The albumin-specific antibodies were isolated by affinity chromatography and analysed, using a sensitive tritium labelling technique. The antibodies were polyclonal, complexed with serum albumin through their Fab portion, and showed a high specificity for the human albumin as compared with bovine and rabbit albumins. The serum albumin of two patients displayed an abnormal behaviour in reduced SDS-polyacrylamide gel electrophoresis (PAGE). The abnormal albumins had an apparent molecular weight of 52,000 and could react with rabbit anti-human serum albumin like the normal protein. No abnormal albumin could be detected in 20 other patients' sera, including nitrofurantoin-treated patients and normal controls. These findings suggest a possible role for an altered self-component in the triggering of a specific autoimmune reaction.