Assay, isolation and characterization of circulating immune complexes from serum of gastrointestinal cancer, stage III and IV melanoma and chronic inflammatory bowel disease patients.

Circulating immune complexes (CIC) have been detected in several autoimmune diseases, and studies have also suggested that CIC provide a useful tool as tumor markers. In order to identify differences or similarities in antigenic composition, CIC from 23 patients with gastrointestinal (GI) tumors, from 20 patients with stage III and IV melanoma and from 6 patients with inflammatory bowel disease (IBD) were studied. Serum from all GI, melanoma and IBD patients showed higher levels of CIC than controls. SDS/PAGE electrophoresis under reducing conditions revealed some differences between cancer and IBD patients as far as the CIC protein composition was concerned. In melanoma patients, two fast-migrating bands, in the regions of 71-74 and 30-49 kD, were found, consistent with previously isolated and characterized antigens described in the literature.