Analyzing serologic calling cards of inflammatory bowel disease

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The inflammatory changes in the gut lining of patients suffering from IBD are thought to result from an overexuberant mucosal immune response to dietary antigens, intestinal pathogens and the patient’s own leukocytes.^1-3 In human medicine, serologic markers, including autoantibodies, are used clinically to aid diagnosis of IBD.⁴ A recent study explored the development of comparable assays in dogs,⁵ formatted as enzyme-linked immunosorbent assays to detect immunoglobulins (IgA, specifically) against various proteins associated with the immunologic triggers or with the humoral response to these triggers.

Study design

Study subjects consisted of 151 dogs of varied breed, age and gender that presented for different reasons to three hospitals in Southern California. The dogs were grouped as follows:

• IBD cohort: 70 dogs showing chronic gastrointestinal (GI) signs, including vomiting, diarrhea, anorexia and weight loss, for at least three weeks. Underlying infectious, endocrine and neoplastic diseases were ruled out. Intestinal biopsies, harvested at least 10 days after the last dosing of immunosuppressive or antimicrobial drugs, confirmed histologic changes consistent with IBD.
• Non-IBD sick cohort: 23 dogs presenting with GI signs that were episodic, of short duration and associated with underlying causes not related to IBD, such as dietary indiscretion and parasitism.
• Normal cohort: 58 apparently healthy dogs, free of both current GI disease and a history of recurrent GI illness.

In dogs with IBD, biopsy samples were scored by a pathologist based on their severity. In 20 of these dogs, microorganisms were cultured and genetic regions of interest were amplified by polymerase chain reaction testing. Serum titers against genes of interest, including those coding for flagellin and the immune byproduct calprotectin, were measured, as were antibodies to microbial outer membrane porin C (OmpC), food-derived proteins (gliadins) and autoantibodies to canine polymorphonuclear leukocytes.

Results

More than 85% of the dogs with IBD had visible endoscopic lesions in the duodenum or colon, with the most frequent diagnosis being lymphoplasmacytic enteritis followed by eosinophilic or mixed inflammation. Biopsies of the duodenum and colon, graded according to World Small Animal Veterinary Association guidelines, showed 9% of the dogs being severely affected, 48% moderately affected and 43% mildly affected.

Microbial communities, evaluated in 20 dogs with IBD, included Pseudomonas, Escherichia, Enterococcus, Enterobacter, Acinetobacter and Proteus. Autoantibody detection assays were performed to detect the presence of IgAs against immunologic elements.

Dogs with IBD had high rates of seropositivity against canine polymorphonuclear leukocytes (APMNA, 77%), canine calprotectin (ACNA, 43%), OmpC (ACA, 76%), flagellins (AFA, 39%) and gliadins (AGA, 54%).

For non-IBD sick dogs, 52% displayed positive titers against gliadins, indicating low specificity of this assay for IBD. Just 13% tested positive for APMNA, ACNA and ACA, while none tested positive for AFA. Among the normal cohort, 3% tested positive for ACA, and 8% to 9% were positive for the other four markers.

Differences between dogs with IBD and normal dogs were statistically significant for all of the markers. When comparing the IBD cohort and the non-IBD sick cohort, differences were statistically significant for all markers but gliadin.

The implications

Serologic markers in IBD represent the host’s immune response to translocation of bacteria and dietary proteins across the intestinal mucosal barrier, as well as to leukocytes and other immunologic components that play a role in the inflammatory changes present in chronic enteropathies.

This study focused on IgA because of its key role in mucosal immunity. IgA seropositivity was present at a significant rate for polymorphonuclear leukocytes, calprotectin, bacterial OmpC, flagellins and gliadins. Prevalences ranged from 39% to 79%, depending on the marker.

IgA associated with leukocytes (APMNA) had marked prevalence (77%) in the IBD cohort. Also notable in the IBD cohort was the bacterial OmpC (ACA) response (76%), which aligns with the abundance of Enterobacteriaceae in dogs with IBD.

The discriminating performance for the APMNA and ACA markers was excellent. For APMNA, seropositivity for IBD dogs versus non-IBD sick and normal dogs was 77% versus 13% and 9%, respectively. For ACA, seropositivity was 76% versus 13% and 3% for IBD versus non-IBD sick and normal dogs, respectively. The investigators’ analysis of the ACA performance parameters suggested 95% specificity and 85% sensitivity, coupling it tightly to the diagnosis of IBD.

The findings in this study provide evidence of serologic markers for microbes and immune physiologic processes tied to IBD. These markers might one day serve as data points used in the diagnosis of IBD. The markers described in this report might be incorporated into later studies aimed at differentiating dogs with and without IBD, and defining discrete subsets of affected dogs to better target treatments and nail down prognoses.

Dr. Capuzzi, who earned her BS and VMD degrees from the University of Pennsylvania, works in small animal practice in the Philadelphia area and is a published author. She has written for The Philadelphia Inquirer, Time, Business Philadelphia, Dog Fancy and Dog World, among others. She is especially interested in public health and animal welfare, and is involved with several organizations whose missions are to improve the lives of domesticated and wild animals.

References

1. Xavier RY, Podolsky DK. Unravelling the pathogenensis of inflammatory bowel disease. Nature 2007;448:427-434.

2. Allenspach K, Luckschander N, Styner M, et al. Evaluation of assays for perinuclear antineutrophilic cytoplasmic antibodies and antibodies to Saccharomyces cerevisiae in dogs with inflammatory bowel disease. Am J Vet Res2004;65:1279-1283.

3. Mancho C, Sainz A, Garcia-Sancho M, et al. Detection of perinuclear antineutrophil cytoplasmic antibodies and antinuclear antibodies in the diagnosis of canine inflammatory bowel disease. J Vet Diagn Invest 2010;22:552-558.

4. Nakamura RM, Matsutani M, Barry M. Advances in clinical laboratory tests for inflammatory bowel disease. Clin Chim Acta 2003;335:9-20.

5. Estruch JJ, Barken D, Bennett N, et al. Evaluation of novel serological markers and autoantibodies in dogs with inflammatory bowel disease. J Vet Intern Med 2020;1-10.