In healthy people, T cells play a crucial role in helping fight infection, but in people with autoimmune diseases, they can start to attack the body’s own tissues.
By studying cells from mice and people, the researchers found vitamin D caused dendritic cells to produce more of a molecule called CD31 on their surface and that this hindered the activation of T cells.
The team observed how CD31 prevented the two cell types from making a stable contact – an essential part of the activation process – and the resulting immune reaction was far reduced.
Professor Richard Mellanby, of the University of Edinburgh’s Centre for Inflammation Research, said: “Low vitamin D status has long been implicated as a significant risk factor for the development of several autoimmune diseases.
“Our study reveals one way in which vitamin D metabolites can dramatically influence the immune system.”