Autoantibodies against human tropomyosin isoform 5 in ulcerative colitis destroys colonic epithelial cells through antibody and complement-mediated lysis.
BACKGROUND
Patients with ulcerative colitis (UC) have IgG1 antibodies in serum and colon against human tropomyosin isoform 5 (hTM5), a cytoskeletal microfilament protein found intracellularly and on the surface of colonic epithelial cells (EC). These antibodies may be pathogenic in UC.


METHODS
Sera from patients with UC (n=110) or Crohn's disease (CD) (n=50) and from healthy individuals (Hl) (n=30) were preincubated with recombinant hTM5 or bovine serum albumin (BSA), then cultured for 4h with (51)Cr-labelled colonic adenocarcinoma cells (LS180). Cytotoxicity was determined by (51)Cr release assay.


RESULTS
All serum samples lysed up to 36% of LS180 cells regardless of the source of the serum. However, adding hTM5 to UC, but not to CD or HI, sera reduced cytotoxicity by up to 75%. This hTM5-induced inhibition of cytotoxicity was found especially with sera from UC patients with active disease, and was found even after total colectomy. The hTM5-induced inhibition was mediated by purified IgG from UC sera. Complement was involved since hTM5-induced inhibition of cytotoxicity declined with either heat inactivation of the sera or premixing sera with Fc fragments.


CONCLUSIONS
This study shows that hTM5-specific IgG autoantibodies present in UC sera destroy LS180 cells by antibody and complement-mediated lysis. Such a phenomenon was not seen in CD or HI. This suggests an autoantigenic role of hTM5 and anti-hTM5 antibodies in the pathogenesis of UC. This observation may lead to novel diagnostic and therapeutic possibilities.
Ebert
Ellen C
EC
Crohn's and Colitis Center of NJ, Department of Medicine, UMDNJ-Robert Wood Johnson Medical School, 1 Robert Wood Johnson Place, MEB 478, New Brunswick, NJ 08903, USA. jeydels@comcast.net
Geng
Xin
X
Lin
Jim
J
Das
Kiron M
KM
D001323:Autoantibodies / Q000097:blood / Q000276:immunology*; D003093:Colitis, Ulcerative / Q000097:blood / Q000276:immunology* / Q000473:pathology; D003106:Colon / Q000276:immunology / Q000473:pathology; D003171:Complement Pathway, Classical; D003424:Crohn Disease / Q000276:immunology; D004847:Epithelial Cells / Q000276:immunology* / Q000473:pathology; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007413:Intestinal Mucosa / Q000276:immunology / Q000473:pathology; D014335:Tropomyosin / Q000276:immunology*
D001323:Autoantibodies; D007074:Immunoglobulin G; C498783:TPM3 protein, human; D014335:Tropomyosin