Binding of immune complexes to IgA-sepharose 4B.

A method for the determination and removal of circulating immune complexes in pathological sera was developed using human secretory or dimeric myeloma IgA covalently bound to Sepharose 4B. IgA-Sepharose 4B was able to selectively bind heat or antigen-aggregated human IgG (circulating immune complexes) but not monomeric IgG. The absorbent was also able to remove a very high proportion (95%) of circulating immune complexes from pathological sera as determined by a turbidimetric technique. An immunoradiometric assay for the direct measurement of circulating immune complexes is described. The assay uses IgA-Sepharose 4B as an absorbent (for the binding of IgG immune complexes from sera) and 125I-rabbit anti-IgG antibody (for the quantitation of IgG immune complexes bound to IgA-Sepharose 4B). The mean value obtained for pathological sera (27.1 +/- 0.9) was significantly higher than that of normal sera (4.8 +/- 0.5).