Changes

The mucosal immune system of the host and the enteric bacterial flora interact constantly in the gastro-intestinal (GI) tract.  The host must remain tolerant of the enteric flora but must still be able to recognise and respond to potentially pathogenic organisms.  These apparently contradictory tasks are resolved by the ability of the immune system to 'tolerate' certain antigens if these are presented to macrophages and dendritic cells in an appropriate manner.  More recent theories regarding ARD suggest that it results from alterations in the interaction between the mucosal immune system and the enteric flora, particularly a loss of immune tolerance to commensal bacteria.

The mucosal immune system of the host and the enteric bacterial flora interact constantly in the gastro-intestinal (GI) tract.  The host must remain tolerant of the enteric flora but must still be able to recognise and respond to potentially pathogenic organisms.  These apparently contradictory tasks are resolved by the ability of the immune system to 'tolerate' certain antigens if these are presented to macrophages and dendritic cells in an appropriate manner.  More recent theories regarding ARD suggest that it results from alterations in the interaction between the mucosal immune system and the enteric flora, particularly a loss of immune tolerance to commensal bacteria.

*According to two studies, dogs with idiopathic ARD have higher levels of expression of some cytokines and greater numbers of IgA plasma cells and CD4 T-cells in their intestinal mucosa, suggesting that ARD might occur due to a breakdown in the normal host tolerance of the bacterial microflora<ref number="one">German AJ, Hall EJ, Day MJ. '''Immune cell populations within the duodenal mucosa of dogs with enteropathies.''' ''J Vet Intern Med. 2001 Jan-Feb;15(1):14-25.''</ref><ref>German AJ, Helps CR, Hall EJ, Day MJ. '''Cytokine mRNA expression in mucosal biopsies from German shepherd dogs with small intestinal enteropathies.''' ''Dig Dis Sci. 2000 Jan;45(1):7-17.''</ref>.  However, a later study using similar methods of reverse transcriptase polymerase chain reaction (PCR) suggested that there was no significant difference in cytokine levels between mucosal biopsy samples from normal dogs and those with SIBO<ref>Peters IR, Helps CR, Calvert EL, Hall EJ, Day MJ. '''Cytokine mRNA quantification in duodenal mucosa from dogs with chronic enteropathies by real-time reverse transcriptase polymerase chain reaction.''' ''J Vet Intern Med. 2005 Sep-Oct;19(5):644-53.''</ref>.  This discrepancy may relate to the nature of the method used to detect cytokine expression, as PCR gives an indication of expression levels at a single point in time and may not reflect the level at which these proteins are actually transcribed by intestinal cells.    The loss of immune tolerance theory is supported by the finding that dogs with ARD had reduced levels of two cytokines (tumour necrosis factor alpha and transforming growth factor beta) after receiving antibacterial treatment<ref number="one"></ref>, even though this therapy did not significantly reduce the number of intestinal bacteria that were present.  This finding could be explained by the fact that many of the antibiotics used in the treatment of ARD (particularly metronidazole and oxytetracycline) have immunomodulatory activity.     

*According to two studies, dogs with idiopathic ARD have higher levels of expression of some cytokines and greater numbers of IgA plasma cells and CD4 T-cells in their intestinal mucosa, suggesting that ARD might occur due to a breakdown in the normal host tolerance of the bacterial microflora<ref name="one">German AJ, Hall EJ, Day MJ. '''Immune cell populations within the duodenal mucosa of dogs with enteropathies.''' ''J Vet Intern Med. 2001 Jan-Feb;15(1):14-25.''</ref><ref>German AJ, Helps CR, Hall EJ, Day MJ. '''Cytokine mRNA expression in mucosal biopsies from German shepherd dogs with small intestinal enteropathies.''' ''Dig Dis Sci. 2000 Jan;45(1):7-17.''</ref>.  However, a later study using similar methods of reverse transcriptase polymerase chain reaction (PCR) suggested that there was no significant difference in cytokine levels between mucosal biopsy samples from normal dogs and those with SIBO<ref>Peters IR, Helps CR, Calvert EL, Hall EJ, Day MJ. '''Cytokine mRNA quantification in duodenal mucosa from dogs with chronic enteropathies by real-time reverse transcriptase polymerase chain reaction.''' ''J Vet Intern Med. 2005 Sep-Oct;19(5):644-53.''</ref>.  This discrepancy may relate to the nature of the method used to detect cytokine expression, as PCR gives an indication of expression levels at a single point in time and may not reflect the level at which these proteins are actually transcribed by intestinal cells.    The loss of immune tolerance theory is supported by the finding that dogs with ARD had reduced levels of two cytokines (tumour necrosis factor alpha and transforming growth factor beta) after receiving antibacterial treatment<ref name="one"></ref>, even though this therapy did not significantly reduce the number of intestinal bacteria that were present.  This finding could be explained by the fact that many of the antibiotics used in the treatment of ARD (particularly metronidazole and oxytetracycline) have immunomodulatory activity.     

===Secondary Antibiotic Responsive Diarrhoea===

===Secondary Antibiotic Responsive Diarrhoea===