Discovering α-GalCer: A Hidden Mammalian Antigen

Invariant natural killer T cells, or iNKT cells, are special T cells that recognize lipid antigens with the help of a protein called CD1d. One of the most powerful lipid antigens for these cells is α-galactosylceramide, or α-GalCer, which was first found in marine sponges. Surprisingly, until now, scientists hadn't found α-GalCer in mammals. A new study used a clever method, called supercritical fluid chromatography tandem mass spectrometry (SFC/MS/MS), to separate and detect different types of hexosylceramide, including α-GalCer.

Researchers tested this method on a tumor cell line called B16 melanoma. Normally, these cells don't activate iNKT cells. But when the cells were made to produce CD1d, they did trigger these special T cells, even without adding extra antigens. This suggested that the tumor cells themselves might not make the iNKT cell antigens. Instead, the scientists found antigen activity in the culture fluid of these cells. Using activity-based purification and their new detection method, the team identified a specific type of α-GalCer in the culture fluid, as well as in bile and lymphoid tissues. This is a big deal because it's the first time potent antigenic α-GalCer has been found in mammals.

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