OP10 IgA coating of intestinal microbiota is associated with inflammatory bowel disease in twin pairs discordant for inflammatory bowel disease

Abstract

Abstract Background The pathogenesis of inflammatory bowel disease (IBD) is thought to result from an interplay between microbiota, the immune system and the environment in genetically susceptible hosts. Immunoglobulin A (IgA) produced by the immune system can be specifically directed against bacteria. The IgA-coating pattern of intestinal bacteria thus reflects interactions between the immune system and specific bacteria. Studying IBD in twins, concordant and discordant for IBD, reduces the impact of genetic predisposition and childhood exposures and therefore offers the unique opportunity to focus on other factors such as intestinal microbiota composition and immune-interactions in IBD. Methods Faecal samples from twin pairs discordant for Crohn’s disease (CD) or ulcerative colitis (UC) were collected. Employing fluorescence-activated cell sorting, IgA+ and IgA− bacteria from the intestinal microbiota were sorted. Subsequently, (1) the total, (2) IgA+ and (3) IgA− microbial composition was determined by 16S rRNA sequencing (IgA-SEQ). We estimated the relative IgA coating per bacterial species by dividing the abundance of that species in the IgA+ fraction over the abundance in the IgA- fraction, representing the IgA coating index. Linear discriminant analyses were performed with LefSE. Results We included 31 twin pairs (62 individuals) discordant for IBD (CD: 15, UC: 16). 15/32 twin pairs were monozygotic, 43/62 of participants were female, the median age was 47 years (interquartile range: 34–58.5). Of 31 participants with IBD, 7 had signs of active inflammation based on endoscopy, Harvey–Bradshaw index or short clinical colitis activity index. Differences (log-linear discriminant analysis score >3) in the microbial composition of IgA-coated bacteria were observed between CD patients and their twin-siblings not affected by IBD: Dorea formicigenerans (increased in IgA coating), Parabacteroides sp., Christensenellaceae sp., Clostridium sp. and Mollicutes RF39 sp. (decreased in IgA coating). In ulcerative colitis patients, an increase in IgA-coating was observed for Ruminococcus gnavus and Dorea formicigenerans, while Turicibacter sp., Barnesiellaceae sp. and an unclassified Clostridiales sp. were decreased in IgA-coating compared with their twin-siblings not affected by IBD. Conclusion In twins affected by IBD, the pattern of IgA-coated bacteria differs between IBD and non-IBD affected individuals. These data on immune-bacteria interactions could serve as a starting point for the elucidation of the immune-responses triggered by specific bacteria in IBD.