Isolation and characterization of a colonic autoantigen specifically recognized by colon tissue-bound immunoglobulin G from idiopathic ulcerative colitis.

Patients with idiopathic ulcerative colitis (UC) have a colon- bound antibody (CCA-IgG) that reacts with colon tissue extracts. We have partially characterized a colonic protein that is specifically recognized by CCA-IgG. CCA-IgG was eluted from operative colon specimens from 10 patients with UC. A colon tissue-bound IgG was similarly eluted from six patients with Crohn's colitis, two with ischemic colitis, and one with diver- ticulitis. Purified serum IgG from patients with Crohn's disease, from normal subjects and a patient with myeloma were also used as additional controls. For detection of antigen(s), tissue extracts were prepared from 26 specimens of colon (UC, 12; Crohn's disease, 6; normal, 4; other controls, 4), 8 specimens of human normal stomach, duodenum, ileum, and liver (2 each). Tissue extracts were also prepared from rats and mice, including germ-free rat colons and rat's fetal colons. Immunorecognition of CCA-IgG to the tissue extracts was examined by affinity-column chromatography and by transblot analysis. Tissue-extracted proteins were electrophoresed in SDS-polyacrylamide gel, transferred to nitrocellulose sheet, and probed with iodinated CCA-IgG, colonic IgG from other inflammatory bowel disease patients, UC serum IgG, and control serum IgG. Although many proteins were present in colon tissue extracts, 9 of 10 CCA-IgG consistently recognized a protein of 40 kD. None of the nine IgG preparations from colon specimens of patients with Crohn's colitis and other colonic inflammatory diseases reacted with the 40-kD protein. Five of six symptomatic UC serum IgG and none of eight control serum IgG reacted with the 40-kD protein. The 40-kD protein was present in all colon specimens and it appeared to be organ specific. It was absent in mouse and rat tissues, including colon. The 40-kD protein is not actin and nor a part of the Ig molecule. These results suggest that the 40-kD protein is a colonic "autoantigen" that may initiate a specific IgG antibody response in UC.