Background/Purpose:

IgA production is the main barrier mechanism of mucosal surfaces. High affinity IgA is generated through T cell-dependent mechanisms and preferentially binds to invasive or pathogenic bacteria, whereas low affinity IgA is T cell-independent and binds commensal bacteria. Next-generation sequencing of IgA-coated bacteria (IgA-SEQ) identified consortia of bacteria from mouse or human gut microbiota that exacerbate murine colitis, including unclassified Prevotella and Bacteroides species. The colitogenic species, Prevotella copri, was associated with new-onset rheumatoid arthritis, and Prevotella spp. were increased in the cecum of HLA-B27 transgenic rats. BALB/c ZAP-70^W163C (SKG) mutant mice treated with beta-glucan (curdlan) develop an IL-23-dependent disease recapitulating human spondyloarthritis, in which ileitis is microbiota-dependent. SKG mice housed in specific pathogen-free (SPF) conditions have a dysbiosis in which Gram negative bacteria are over-represented. Furthermore, ileitis severity is decreased in TLR4-deficient SKG mice. Our aim was to study SKG mice colonized with a limited bacterial consortium or an unrestricted microbiota to define bacteria driving dysbiosis and the development of ileitis in a genetically susceptible host.

Methods:

Fecal and tissue samples were collected from germ-free (GF) SKG and GF-BALB/c mice recolonized with a limited bacterial consortium known as altered Shaedler microbiota (ASM) (Eubacterium plexicaudatum, Lactobacillus murinus, Mucispirillum schaedleri, 2 Clostridium sp., Lactobacillus sp., Parabacteroides sp., Firmicutes bacterium). Fecal samples were collected from naive SKG mice housed under SPF conditions and IgA-coated bacteria were enriched by magnetic-activated cell sorting, then the IgA^bright and IgA^dim bacteria were enriched by fluorescence-activated cell sorting. Real-time PCR identified the fecal microbiota composition in ASM mice. IgA-, IgA^dim and IgA^bright bacteria were identified by deep sequencing.

Results:

After colonization of GF mice with ASM, four bacterial strains were detected in ASM-SKG and ASM-BALB/c mice: Clostridium sp., Lactobacillus murinus, Mucispirillum schaedleri, Parabacteroides sp. ASM-SKG microbiota exhibited dysbiosis relative to ASM-BALB/c in that the Gram positive Clostridium sp. and Gram negative Parabacteroides sp. were decreased in SKG faces. However, the dominant bacterial species in both strains of mice was the Parabacteroides sp. In naive SKG mice housed under SPF conditions, Gram negative Prevotellaceae were enriched among IgA^bright bacteria, while Gram negative Lactobacillaceae were diminished. Conversely Lactobacillaceae were enriched among IgA^dim bacteria and Prevotellaceae were diminished.

Conclusion:

Interaction of the microbiota with the immune system of SKG mice alters the composition of both a limited consortium and an unrestricted bacterial community. The most immunogenic IgA^bright bacteria within the microbiota of naïve SKG mice are enriched in Prevotellaceae, which have been associated with rheumatoid arthritis and inflammatory bowel disease. IgA-SEQ is a powerful tool to identify potentially immunogenic bacteria from a highly diverse microbiota.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/profiling-immunogenic-bacteria-within-the-microbiota-of-zap-70-mutant-skg-mice-associated-with-spondyloarthritis-and-ileitis-using-iga-seq/