Cryoimmunoglobulinaemia in patients with primary renal disease and systemic lupus erythematosus. I. IgG- and DNA-binding assessed by co-precipitation.
Sera were tested for cryoglobulin precipitates from 206 consecutive patients with renal disease, ninety-eight normals and sixteen patients with systemic lupus erythematosus (SLE) without evident renal disease. Cryoprecipitates were detected in 17% of test subjects overall and 2% of normals; the incidence was highest in patients with SLE, regardless of detectable renal disease. Cryoprecipitates usually were comprised of IgG and IgM or IgG, IgM, and IgA in thirty-six out of forty-two instances, although a single immunoglobulin class was detected in five patients. Co-precipitation experiments showed IgG-binding by virtually all sera forming cryoprecipitates; isolated cryoprecipitates bound radiolabelled homologous IgG, and Fc fragment and sometimes IgG subclass proteins preferentially. Freshly forming cryoprecipitates sometimes co-precipitated DNA, whereas all isolated cryoprecipitates co-precipitated DNA from dilute solutions. The data are compatible with the current hypothesis that cryoimmunoprecipitates are immune complexes that are insoluble in vitro in the cold, that they usually comprise mixed immunoglobulins with anti-IgG activity, and may contain a mixture of antigens and antibodies.