To be in a position to better understand the roles played by different immune cells in healthy and disease settings we must first be able to purify these cells. Only once we can obtain these cells as a pure fraction can we truly assess their individual contributions in any given setting. In recent years, our ability to discriminate between different cells types that often look similar has improved dramatically. By marking the cells with many different fluorescently-labelled antibodies recognising proteins on the surface of specific cell types, we can now accurately identify the cells.