Australasian Science: Australia's authority on science since 1938

Immune Alarm Call Identified

An international team of scientists has identified the biochemical key that wakes up the body’s immune cells and sends them into action against invading bacteria and fungi.

The patented work, published in Nature, provides the starting point in understanding our first line of defence and what happens when it goes wrong. It will lead to new ways of diagnosing and treating inflammatory bowel disease, peptic ulcers and even tuberculosis, and could also lead to new protective vaccines.

The research, the result of an international collaboration between Monash University and the universities of Melbourne, Queensland and Cork, builds on the discovery last year that a group of immune cells called MAITs, which line the gut, lungs and mouth, act as defenders against bacteria. Making up to 10% of T cells, MAITs initiate the immune system’s action against foreign invaders when they are exposed to vitamin B2 (riboflavin), which is made by bacteria and fungi.

The significance of this finding is that humans and other mammals use, but do not make, riboflavin; only bacteria and fungi do. This means that only bacteria and fungi are associated with the riboflavin precursors that send MAITs into action. This makes MAITs a useful guard against infection in our gut, mouth and lungs.

The researchers have now narrowed down the biochemical trigger for MAIT cells to a small group of compounds that form when the riboflavin precursor molecules interact with specific bacterial metabolites. This reaction is only possible in certain, but by no means all, bacteria and fungi. As a result, the diseases and microbes targeted by MAITs can now be traced.

“The finding that these human immune cells have evolved to detect bacterial synthesis of riboflavin, but not the actual vitamin in our diet, may be a valuable clue to disease pathology and new drug development strategies,” said Prof David Fairlie of the University of Queensland’s Institute for Molecular Bioscience.

Prof James McCluskey of The University of Melbourne said that little is known about the role of MAITs, beyond the fact that they have an association with bacteria. “MAIT cells are a discovery so recent that they have not even made it into the textbooks,” he said, “yet they constitute about one cell in ten of the body’s T cells and half of all the T cells in the liver.”