"This is the first time someone has shown how the immune system and lipid metabolism merge," says Associate Professor Luc Teyton, M.D., Ph.D., of Scripps Research. Teyton is the lead author of the study.
In the study, Teyton and his colleagues were examining what is known as a natural killer (NK) T cell. NK T cells are key players in the immune system and have been implicated in autoimmune diseases, such as diabetes, and in cancer--although scientists have not yet discerned exactly how.
NK T cells are unusual in that they fall somewhere between innate and adaptive immunity. They arise in the thymus, and, as mature cells, they stimulate an adaptive immune response and regulate a range of disease states, including diabetes, cancer, and pathogenic infections.
Like other T cells, they express T cell receptors (TCR)--although without the normal antigenic variability. Classical immune recognition involves a process in which variable TCRs recognize various proteins--pieces of protein from foreign pathogens, for instance--when these are presented by "antigen presenting cells" via a molecule called the major histocompatability complex (MHC). MHC molecules are like the burglar alarms that warn the immune system that a pathogen is invading.
However, NK T cells also express the "NK" innate immune cell receptors and may have the ability to see some of the lipids that bacteria like Mycobacterium tuberculosis, the bacteria that cause tuberculosis, display on their outer surface. NK T cells become activated when they bind to a cell surface protein called CD1 that bears an unknown lipidic ligand.