The German shepherd dog (GSD) has clear breed predisposition to inflammatory bowel disease (IBD) and antibiotic responsive diarrhoea (ARD). Both of these enteropathies are likely to involve an abnormal interaction of the intestinal immune system with antigens derived from the luminal microflora, and as such a good candidate mechanism to explain the strong breed association would be defective mucosal IgA production. Insufficiency of luminal IgA would contribute to reduced barrier function in affected small intestine, thus resulting in greater exposure to causative antigen. The nature of the intestinal inflammatory response in these disorders has now been well characterized in terms of the phenotype of lamina propria and intraepithelial lymphocytes and cytokine mRNA expression, although the most recent investigations of the latter area have failed to confirm earlier observations suggesting elevation of transcription of genes encoding pro-inflammatory and Th1-related cytokines.