Special delivery brings fats to immune system

It was both unexpected and unsurprising when, in the mid -1990s, Michael Brenner, the Theodore Bevier Bayles professor of medicine, and his colleagues showed that some antigen- presenting cells display fats rather than proteins. Arrayed on CD1, a new type of serving tray distinct from MHC molecules, fat-containing antigens derived from the tuberculosis bacterium ably turned on a specialized subset of lipid-reactive T cells.

The route that peptide antigens take to MHC is well understood, but far less was known about where and how lipid antigens come to bind to CD1. Now, Brenner and his colleagues report that fat antigens find their target via an unexpected messenger. In a paper published in the Oct. 6, 2005 Nature, the researchers show that the immune system uses apolipoproteins, best known for their role as cholesterol carriers, to deliver lipid antigens to CD1.

"This work brings together two previously unrelated systems - the apolipoprotein-mediated delivery of dietary fats and the delivery of lipid antigens to the immune system," Brenner said. This convergence has profound implications for understanding how the immune system patrols the body for lipid antigens, he added.