Dynamics of IgA and IgG Coated Bacteria in Dogs with Chronic Enteropathy

Canine chronic enteropathies (CE) constitute a group of disorders that cause chronic gastrointestinal tract inflammation, and persistent or recurrent gastrointestinal signs in dogs and are also termed inflammatory bowel disease (IBD) when immunosuppressive treatment is required. Although they occur frequently in dogs, many aspects of their pathogenesis remain unravelled and the therapeutic approach in some cases remains challenging. In general, it is considered that the triad host genetics-immune system-microenvironment; particularly dietary antigens and the gastrointestinal flora; are closely related to the development of gastrointestinal disease Previous studies have found dysbiosis and reduced bacterial diversity in CE dogs. However, the precise nature of the intestinal microbiota dysfunction and whether the microbiota has a causative role or is secondarily affected remain to be clarified. Studies in people with IBD have found higher proportions of immunoglobulin coated bacteria compared to healthy people and it has also been found that those highly coated bacteria possess strong immunogenic properties. The present case-controlled study aimed to characterise highly immunoglobulin A (IgA) and G (IgG) coated bacteria in faecal samples from dogs with chronic enteropathy using flow cytometry and 16S rRNA sequencing and to assess their correlation with the disease stage and resolution of the clinical signs. The study showed that IgA and IgG-coated faecal bacterial levels were significantly higher during active disease compared to remission periods. In addition, the amount of immunoglobulin coating throughout active disease was also higher than those found in healthy dogs. Characterization of taxa-specific coating of the intestinal microbiota with immunoglobulin A and G showed that members of the Bacteroidaceae, Erysipelotrichaceae and Enterobacteriaceae families, were the target of the IgA and G response in dogs with active disease. This coating was highly individualised and unstable, despite similar clinical presentations. Although, members of these bacterial groups have been associated with strong immunogenic properties and could potentially constitute important biomarkers of disease, their significance and role still need to be further investigated.