Characteristics of immune complexes detectable by two independent assays in gynaecological malignancies

Abstract

Immune complexes from patients with ovarian and endometrial cancer have been examined using the C1q solid phase (C1qSP) and polyethylene glycol (PEG) precipitation assays. The amount of IgG in the PEG precipitates was inversely correlated with the amount of IgM whilst the IgM values correlated positively with the C1qSP assay values. Separation studies revealed that most of the C1qSP activity was not precipitated from cancer sera by 2% PEG. The immune complexes were fractionated on Sephacryl S-300. Both the PEG precipitation and C1qSP assays detected high molecular weight immune complex like activity (greater than 19S). The C1qSP assay also detected a second peak of activity at approximately 7-8S. Most of the PEG detectable immune complexes from sera dissociated during column chromatography, whereas the C1qSP detectable complexes were relatively stable. Furthermore the IgG from fractionated PEG precipitates emerged as a monomer (7S) component. The PEG assay appeared to be detecting a high molecular weight complex containing mostly IgG rather than IgM with a low affinity for C1q, which was easily dissociated. The C1qSP assay detected a more stable high molecular weight complex containing a relatively high proportion of IgM and a low molecular weight complex, both with a high affinity for C1q.