Immuno- and physicochemical studies of an IgA-IgG mixed cryoglobulin

An IgA-IgG mixed cryoglobulin was investigated. The IgA, which had ‘cryoprecipitating’ activity, was a monoclonal protein possessing light chains <i>λ </i>and heavy chains <i>α</i>₂<i>, </i>and existed either in monomeric (6.6S) or polymeric (9.4S) form. Treatment of the cryoglobulin with 0.1 m 2-mercaptoethanol at pH 7.4 resulted in about 50% decrease in amount. Rheumatoid factor activity was not detected in serum or in cryoglobulin. But, after the separation of each constituent, latex fixation tests were positive with both components. Tanned cell haemagglutination tests revealed that the IgG component was reactive to urea-denatured IgGs of polymer type and polymerized <i>γ</i>-chain. The IgA component showed a positive haemagglutination only with polymerized <i>γ</i>-chain. Cryoglobulin-depleted serum yielded further cryoprecipitate when the pH value was reduced to 6.2.