C3 in High Molecular Weight Complexes: Separation from Plasma of Nephritic Patients and Normal Subjects by a Method that Avoids in Vitro Artifacts

Abstract

The demonstration of host γ globulin and complement components in glomeruli of patients with post-streptococcal glomerulonephritis (1–3) or the nephritis associated with systemic lupus erythematosus (2, 4, 5) supports the view that the inflammatory lesions are caused by deposition of circulating complement-fixing soluble antigen-antibody complexes (6). Immune complexes, therefore, might be present in the circulation during active disease and, given sufficient assay sensitivity, should be detectable. When immune complexes activate complement, the third component (C3) becomes bound to the complex and can, therefore, be used as a marker of immune complexes. Since C3 has a molecular weight of about 185,000 (7) and in an immune complex behaves like a much larger molecule, separation of unreacted from complexed C3 on the basis of size is possible by gel filtration on Sephadex G-200.

The proteins of normal whole serum are eluted from Sephadex G-200 in three main peaks.