`Lipid asymmetry` plays key role in activating immune cells
(PHYSorg.com Chemistry)

A cell`s membrane is its natural barrier between the inside of a cell and the outside world-composed of a double layer (bilayer) of lipids (such as fats, waxes, sterols, or fat-soluble vitamins). Intriguingly, it`s been known for decades that the layer facing the inside of cells is made of different lipids than the outside-facing layer.