Lack of Correlation between Mucosal Immunoglobulin A-positive Plasma Cell Numbers and TLR5 Genotypes in German Shepherd Dogs with Idiopathic Chronic Enteropathy

Genomic association and further characterisation of faecal immunoglobulin A deficiency in German Shepherd dogs

BACKGROUND

Immunoglobulin A (IgA) deficiency, chronic enteropathies and exocrine pancreatic insufficiency (EPI) have a high prevalence in German Shepherd dogs (GSD). This prospective study determined the prevalence of faecal IgA deficiency (IgAD) in GSD and investigated several candidate genes and the canine genome for a region or locus co-segregating with IgAD in GSD. Faecal IgA concentrations were quantified and genomic DNA was extracted from 8 GSD with an undetectable faecal IgA (classified as IgAD) and 80 non-IgAD GSD. The canine minimal screening set II microsatellite markers were genotyped, with evidence of an association at p < 1.0 × 10-3 . Faecal IgA concentrations were also tested for an association with patient clinical and biochemical variables.

RESULTS

Allele frequencies observed using the candidate gene approach were not associated with faecal IgAD in GSD. In the genome-wide association study (GWAS), the microsatellite marker FH2361 on canine chromosome 33 approached statistical significance for a link with IgAD in GSD (p = 1.2 × 10-3 ). A subsequent GWAS in 11 GSD with EPI and 80 control GSD revealed a significant association between EPI and FH2361 (p = 8.2 × 10-4 ).

CONCLUSIONS

The lack of an association with the phenotype of faecal IgAD in GSD using the candidate gene approach and GWAS might suggests that faecal IgAD in GSD is a relative or transient state of deficiency. However, the prevalence of faecal IgAD in GSD appears to be low (<3%). The relationship between faecal IgAD, EPI and loci close to FH2361 on canine chromosome 33 in GSD warrants further investigation.

What are the potential biomarkers that should be considered in diagnosing and managing canine chronic inflammatory enteropathies?

Chronic inflammatory enteropathies in dogs are characterized by persistent or recurrent gastrointestinal signs that last for more than 3 weeks. Despite unclear etiopathogenesis, it is considered that a genetic predisposition associated with environmental factors, such as dietary antigens and intestinal microbiota, might induce an abnormal immune response in the host. The diagnosis of this condition requires full investigation in order to exclude all other possible causes. Currently, the observation of clinical signs associated with histopathologic evaluation and systematic therapeutic trials is the gold standard for the diagnosis of chronic enteropathies. Furthermore, diagnosis, monitoring the disease progression, and treatment response evaluation can be exhausting, since this whole process is time-consuming, costly, and partially invasive. Therefore, biomarkers appear as non-invasive tools, which can be useful in evaluating gastrointestinal function, identifying the presence of the disease and assessing its natural progression, monitoring gastrointestinal inflammation, predicting response to treatment, and clinical outcomes. Over the past decade, several studies were conducted in order to explore the clinical utility of biomarkers. Thus, the aim of this dissertation is to provide an overview of the biomarkers considered relevant in the diagnosis and management of dogs with chronic inflammatory enteropathies. The biomarkers addressed in this study may be serological, present in urine and feces, or even tissue-derived. This study argues that biomarkers, in particular calprotectin and calgranulin C, have great potential to be used in clinical practice in the diagnosis and management of affected dogs. However, a single biomarker cannot assuredly predict disease severity, progression, response to treatment, and clinical outcomes. Therefore, in order to achieve greater accuracy, it would be beneficial if these tools are used in conjunction with contemporary ones. Future research is needed with the aim to better determine the usefulness of these tools in chronic inflammatory enteropathies in dogs.

Clinical utility of currently available biomarkers in inflammatory enteropathies of dogs

Chronic inflammatory enteropathies (CIE) in dogs are a group of disorders that are characterized by chronic persistent or recurrent signs of gastrointestinal disease and histologic evidence of mucosal inflammation. These CIEs are classified as either food-responsive, antibiotic-responsive, or immunosuppressant-responsive enteropathy. Patients not clinically responding to immunomodulatory treatment are grouped as nonresponsive enteropathy and dogs with intestinal protein loss as protein-losing enteropathy. Disease-independent clinical scoring systems were established in dogs for assessment of clinical disease severity and patient monitoring during treatment. Histopathologic and routine clinicopathologic findings are usually not able to distinguish the subgroups of CIE. Treatment trials are often lengthy and further diagnostic tests are usually at least minimally invasive. Biomarkers that can aid in defining the presence of disease, site of origin, severity of the disease process, response to treatment, or a combination of these would be clinically useful in dogs with CIE. This article summarizes the following biomarkers that have been evaluated in dogs with CIE during the last decade, and critically evaluates their potential clinical utility in dogs with CIE: functional biomarkers (cobalamin, methylmalonic acid, folate, α1 -proteinase inhibitor, immunoglobulin A), biochemical biomarkers (C-reactive protein, perinuclear anti-neutrophilic cytoplasmic antibodies, 3-bromotyrosine, N-methylhistamine, calprotectin, S100A12, soluble receptor of advanced glycation end products, cytokines and chemokines, alkaline phosphatase), microbiomic biomarkers (microbiome changes, dysbiosis index), metabolomic biomarkers (serum metabolome), genetic biomarkers (genomic markers, gene expression changes), and cellular biomarkers (regulatory T cells). In addition, important performance criteria of diagnostic tests are briefly reviewed.

Pattern-recognition receptors: signaling pathways and dysregulation in canine chronic enteropathies—brief review

Pattern-recognition receptors (PRRs) are expressed by innate immune cells and recognize pathogen-associated molecular patterns (PAMPs) as well as endogenous damage-associated molecular pattern (DAMP) molecules. With a large potential for synergism or convergence between their signaling pathways, PRRs orchestrate a complex interplay of cellular mediators and transcription factors, and thus play a central role in homeostasis and host defense. Aberrant activation of PRR signaling, mutations of the receptors and/or their downstream signaling molecules, and/or DAMP/PAMP complex–mediated receptor signaling can potentially lead to chronic auto-inflammatory diseases or development of cancer. PRR signaling pathways appear to also present an interesting new avenue for the modulation of inflammatory responses and to serve as potential novel therapeutic targets. Evidence for a dysregulation of the PRR toll-like receptor (TLR)2, TLR4, TLR5, and TLR9, nucleotide-binding oligomerization domain–containing protein (NOD)2, and the receptor of advanced glycation end products (RAGE) exists in dogs with chronic enteropathies. We describe the TLR, NOD2, and RAGE signaling pathways and evaluate the current veterinary literature—in comparison to human medicine—to determine the role of TLRs, NOD2, and RAGE in canine chronic enteropathies.