The mouse study, published in Immunity, suggests that altering the length of fatty acids (FAs) consumed has an effect on the function of immune cells in involved in autoimmunity (known as T helper cells) in the gut, resulting in either intensifying or alleviating symptoms of autoimmune disease.
Led by senior author Ralf Linker from Friedrich-Alexander-University and first author Aiden Haghikia from the Ruhr-University Bochum, the team used mice to compare the effects of short-chain fatty acids, which are solely metabolised by gut bacteria and are typically found in fibre-rich diets, with the effects of long-chain fatty acids, the most abundant component of western diets.
The German team reported that long-chain fatty acids, including lauric acid and palmitic acid, promoted the development and release of pro-inflammatory T cells (Th1 and Th17) from the intestinal wall to other areas in the body, including the brain – leading to increased disease severity.
On the other hand, short-chain fatty acids like propionate were found to promote the development and circulation of regulatory T cells (Treg), which kept the immune response in check and improved the symptoms of disease in the mice.
“This study identifies dietary saturated fatty acids as crucial modulators in the gut, shifting Th1 and Th17 versus Treg cell balance in autoimmune neuro-inflammation,” wrote the team.
Dietary triggers and treatments?
Recent epidemiological studies have shown that lifestyle factors such as smoking, obesity, and salt intake might constitute a risk for autoimmune diseases like MS, said the team, noting that such lifestyles generally include a diet that is also typically rich in long chain fatty acids.
“Our present data offer important immunological and functional groundwork for epidemiological observations and identify saturated FAs as a new dietary, non-infectious trigger involved in intestinal T cell differentiation due to the interaction of gut-hosted microbiota and nutritional metabolites,” they said.
Linker noted that the majority of current treatments for autoimmune disease (immunotherapies) work by weakening or blocking the pro-inflammatory components of the immune system. But by strengthening the regulatory pathways – for example by using propionate as a supplement to established drugs – these treatments could be further optimised, he said.
"It is now our plan to employ our gained insights to develop innovative dietary add-on therapies to established immunotherapies in multiple sclerosis," added Haghikia – who noted that none of the effects of dietary fatty acids were seen in animals whose intestines were made germ-free, suggesting that gut bacteria are directly involved.
“Further studies in humans to explore the supplementary therapeutic potential of enriched diets are highly warranted,” the team concluded.
Volume 43, Issue 4, 20 October 2015, Pages 817–829, doi: 10.1016/j.immuni.2015.09.007
“Dietary Fatty Acids Directly Impact Central Nervous System Autoimmunity via the Small Intestine”
Authors: Aiden Haghikia, et al