Immunochemical and physical studies of the Sia test

The Sia test was performed in strictly standardized conditions in boiled, bidistilled, deionized water (BBD) and in 0.01 M phosphate buffers pH 5.0 and 7.0. Normal human sera and sera from patients with diffuse hypergammaglobulinemia ( greater than 2.0 g/100 ml), immunoglobulin G (IgG) myeloma (M component greater than 5.0 g/100 ml), and Waldenstrom's macroglobulinemia were studied. In BBD all normal sera were Sia-negative, whereas 16 per cent of sera with diffuse hypergammaglobulinemia, 60 per cent of sera with IgG M component, and 44 per cent of macroglobulinemic sera with Sia-positive. Almost all sera from the above mentioned four groups gave positive results in phosphate buffer pH 5.0 and the majority of them, with the exception of normal human sera, gave positive results at pH 7.0. All precipitates isolated from the sera tested showed beta-alpha 2 bands in cellulose acetate electropherograms. Precipitates from the sera with diffuse hypergammaglobulinemia also showed gamma bands, and those from the myelomatous or macroglobulinemic sera showed strong bands corresponding to the M components. Whereas immunoelectrophoresis of the four-fold-concentrated precipitates showed up to 11 precipitation lines, radial immunodiffusion detected up to 18 proteins. The characteristic pattern of IgM/IgG immune complexes was observed in immunoelectrophoresis of Sia precipitates from hypergammaglobulinemic sera with rheumatoid factor. The recovery of immunoglobulins in the Sia precipitates varied greatly but that of IgM was usually greater than that of IgG or IgA. It may be concluded that the Sia test is entirely nonspecific regardless of the buffer or pH at which it is performed. The only advantages of this test seem to be the quick partial purification of IgM components and identification of their light chains, and the possible detection of immune complexes.