Salivary Bacteria and Inflammation

A really interesting new study looked at the bacterial contents of saliva and its relationship to the development of inflammatory bowel diseases.[i]  Salivary samples from healthy and IBD-afflicted individuals were given to germ-free mice.  After several weeks, the microbial content of the mice’ feces was examined, and amazingly, 20 different kinds of oral bacteria were found.  This is a clear demonstration that the 1.5 liters of saliva we swallow every day do affect our intestinal microbiome.

Apparently, those with IBD, HIV and colon cancer are already known to have higher bacterial contents in their saliva.  To figure out which of these 20 potential culprits was the instigator of the inflammation they found in the mice, the researchers isolated and cultured each species from the feces, and then separately inoculated these to germ-free mice.  It turned out that Klebsiella pneumoniae  in particular evoked a strong Th1 response, leading to inflammation.

Klebsiella pneumoniae is a normal resident of the mouths of healthy people.  However, in an experiment on mice treated and untreated with antibiotics, it was shown that in disturbing the gut flora with antibiotics, Klebsiella can colonize the intestine.

And yet one more incredibly significant finding.  In a subsequent experiment, the researchers found that the strong Th1 inflammatory response only happened in IL-10 deficient mice who were given antibiotics.   That is:  low levels of IL-10 (which is one of the most significant regulatory cytokines) put the animals at much greater risk of adverse reactions when given antibiotics.

“Interleukin 10 (IL-10) is a cytokine with potent anti-inflammatory properties that plays a central role in limiting host immune response to pathogens, thereby preventing damage to the host and maintaining normal tissue homeostasis. Dysregulation of IL-10 is associated with enhanced immunopathology in response to infection as well as increased risk for development of many autoimmune diseases.”[ii]

 Low levels of IL-10 are implicated in diseases ranging from autism[iii] to multiple sclerosis and Parkinson’s.[iv]   Remember that helminths  are an incredibly powerful inducer of regulatory cytokines, including IL-10.   We humans living in the industrialized world have lost our macrobiotic helminths.  Wouldn’t it be interesting to see if inoculating animals with helminths prevented salivary bacteria from inducing inflammation and autoimmunity?

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[i] https://www.sciencedaily.com/releases/2017/11/171114104216.htm

[ii] Iyer SS, Cheng G. Role of Interleukin 10 Transcriptional Regulation in Inflammation and Autoimmune Disease. Critical reviews in immunology. 2012;32(1):23-63.

[iii] Molloy, Cynthia A. et al. Elevated cytokine levels in children with autism spectrum disorder.  Journal of Neuroimmunology . 2006.  172(1): 198 – 205

[iv] Kwilasz AJ, Grace PM, Serbedzija P, Maier SF, Watkins LR. The therapeutic potential of interleukin-10 in neuroimmune diseases. Neuropharmacology. 2015;96(Pt A):55-69. doi:10.1016/j.neuropharm.2014.10.020.