Autoimmunity in ulcerative colitis (UC): a predominant colonic mucosal B cell response against human tropomyosin isoform 5

We set out to examine if the IgG-producing cells in the colonic mucosa in U C are committed to tropomyosin isoform 5 (hTM5), a putative autoantigen in UC. Lamina propria mononuclear cells (LPMC) were isolated from colonoscopic biopsy specimens from recto-sigmoid and proximal colon. Twenty-three patie nts with UC, eight with Crohn's colitis (CC), and 10 non-inflammatory bowel disease (non-IBD) controls were included. The ELISPOT assays were used to quantify lamina propria B cells producing total immunoglobulin (IgA, IgG, I gM), IgG, IgA, as well as IgG against hTM5 isoform. The median value of per centage of total IgG-producing lymphocytes was similar in UC (12%) and CC ( 11%), but was significantly (P < 0.0002) higher than non-IBD controls (6%). However, in UC, but not in CC and non-IBD, a large number of lamina propri a B cells produced IgG against hTM5 (median values: UC 42%, CC 2.5%, non-IB D 0%). This difference in UC when compared with CC and non-IBD was highly s ignificant (P < 0.00001). Twenty-one of 23 (91%) patients with UC had perce ntage of anti-hTM5 IgG-producing immunocytes more than 2 s.d. above the mea n for non-UC patients. In UC but not in CC and non-IBD controls, the increa sed number of IgG-producing cells are largely committed to produce IgG agai nst hTM5-related epitope(s).