Specific antibodies against recombinant protein of insertion element 900 of Mycobacterium ovium subspecies paratuberculosis in Japanese patients with Crohn's disease

Background: Mycobacterial avium subspecies paratuberculosis (MAP) infection has been hypothesized as an etiological factor of Crohn's disease (CD). However, the involvement of MAP in the pathophysiology of CD is controversial. The aim of this study is to investigate whether MAP is involved in the pathogenesis of CD with the glutathione S-transferase fusion recombinant protein encoding a portion of insertion element (IS) 900 (IS900-GST), which is specific for MAP. Methods: Serum samples from the patients with CD (n = 50), ulcerative colitis (n = 40), colonic tuberculosis (n = 20), and non-IBD) controls (n = 44), were applied for solid-phase enzyme-linked immunosorbent assay (ELISA) to detect antibodies against MAP and Saceharomyces cerevisiae. IS900-GST, which was made by the pGST-4T-2 vector inserted with polymerase chain reaction-amplified IS900DNA, was used as an antigen of MAP. Moreover, we studied the relationship between antibodies against IS900-GST and clinical characteristics. Results: ELISA showed that the serum level of immunoglobulin G and immunoglobulin A antibodies against IS900-GST (anti-IS900) in patients with CD were significantly higher than those with ulcerative colitis, colonic tuberculosis, and control subjects. The levels of anti-IS900 tended to be higher in CD patients with small intestinal involvement than with colonic involvement alone. Anti-IS900 in patients with penetrating- and stricture-type CD was significantly higher than with inflammatory-type CD. Furthermore, a negative correlation was found between the titer of anfi-IS900 and disease duration. Anti-IS900 was not associated with surgical treatment nor was it associated with the use of immunosuppressants. No significant correlation was observed between the serum levels of anti-IS900 and anti-Scerevisiae antibody. Conclusions: This is the first demonstration of the ELISA system of detecting antibodies against IS900 in IBD patients. MAP could be involved in the pathophysiology of Japanese patients with CD.