IgA subclass distribution in paraproteinemias: suggestion of an IgG-IgA subclass switch pattern.

IgA subclass distribution in the serum of 40 patients with IgA multiple myeloma and 10 patients with benign monoclonal gammopathy of the IgA class was determined. All were found to be of the IgA 1 subclass. A review of the literature shows a marked predominance (93%) of IgA 1 paraproteins, suggesting an under-representation of IgA2 myelomas. The subclass pattern in 11 double paraproteinemias studied and those previously reported in the literature suggest a pattern of IgG1 - IgA1, IgA1 - IgG4 and possibly also IgG2 - IgA2 switches in malignant cells.