The skin is the body's first line of defense against infection, with an extensive network of skin-based immune cells responsible for detecting the presence of foreign invaders. However, in addition to pathogens, an immune response can be triggered by allergens or even our own cells, resulting in unwanted inflammation and allergies. Researchers have now shed new light on the way the immune system in our skin works, paving the way for future improvements in tackling infections, allergies and autoimmune diseases.

An international team, comprising scientists from Monash University and the University of Melbourne in Australia and Harvard University in the US, looked at how our skin’s immune cells make sense of foreign lipids (fat-like molecules derived from bacteria), as well as lipids from human cells.

Scientists have known for years that a molecule found in skin-based immune cells called CD1a played a role in immunity to mycobacteria (a genus of Actinobacteria that includes pathogens that cause serious diseases in mammals, such as tuberculosis) and bee stings, but were unsure exactly what that role was. It is this mystery the research team has solved.

Using x-ray crystallography, which can identify structures at the atomic and molecular level, they found how CD1a binds to lipids – be they from pathogens, allergens or our own cells – highlighting them for recognition by T lymphocytes (or T cells), a type of white blood cell that is an integral part of the immune system.

The scientists not only uncovered this hitherto unknown operation of how the immune system interacts with CD1a molecules, but have also begun to understand how this might be used to improve immunity from infection as well as suppress the kind of immunity that misfires and leads to allergic reaction.

"By understanding how the human immune system can sense and respond to lipids, we can make them more or less potent by subtly altering their structure," says Professor Jamie Rossjohn from Monash University.

However, the scientists stress that the research is still in its nascent stage at this point and direct applications will be some time coming.

The team's findings have been published in the journal Nature Immunology.