The team from the University of Wisconsin-Madison say that one of the CLA isomers is a natural regulator of the COX-2 protein, which plays a significant role in diseases like arthritis and cancer.
"It's clear from previous research that conjugated linoleic acid, or CLA, prevents inflammatory damage resulting from immune response," said Mark Cook, a professor of animal science.
"We've identified the biochemical mechanism by which this occurs."
The new work will be welcomed by firms marketing the fatty acid for health foods and supplements. While a number of studies have pointed to CLA's benefits in the area of cancer prevention, experts have warned that there is not enough evidence yet to support increasing intake of the fat.
CLA exists naturally in a number of structural forms. Cook's team tested both the 10trans,12cis-CLA and 9cis,11trans-CLA on COX-2 protein expression and prostaglandin production. They found the first of these to have a significant inhibitory effect on COX-2 expression in both the lab and an animal test.
The researchers report in this month's issue of the Journal of Lipid Research (vol 46, issue 10, pp2134-42) that COX-2 protein expression was inhibited 80 per cent by 10t, 12c-CLA and only 26 per cent by 9c,11t-CLA in an in vitro test.
The 10t,12c-CLA also decreased prostaglandin production more than the other CLA form.
The mice tests confirmed the results. Animals fed this form of CLA but not 9c,11t-CLA were found to have a 34 per cent decrease in COX-2 protein and a 43 per cent reduction of PGE(2) release in the lung.
The COX-2 protein is known to play a significant role in many inflammatory diseases and is an important drug target for treating arthritis and cancer.
After further analysis, the researchers found that the reduced COX-2 protein and prostaglandin release was probably caused by 10t,12c-CLA blocking a key cellular pathway, the nuclear factor kappaB (NF-kappaB).
While the amount of the anti-inflammatory isomer of CLA in milk is small relative to other fatty acids in milk, there may still be enough to elicit an effect if someone consumes dairy products every day, said Cook.
He believest that CLA could be used as a natural way to prevent 'collateral damage' from the immune system's response to invading pathogens.
"The ideal solution is to let the immune system fight bacteria, but at the same time to maintain the overall health of the system," he said.
The researcher is planning a study to determine whether the amount of anti-inflammatory CLA in milk can be increased by changing dairy cow diets.
The current study was partially funded by BASF and Natural Lipids.