During programmed cell death («apoptosis»), a lipid usually found on the inner side of the cell membranes,
specifically phosphatidylserine (PS), shifts to the surface, making itself readily available to any passing cellular stranger.
Using standard enzyme - linked immunosorbent assays (ELISA) and peripheral blood mononuclear cell (PBMC) assays, researchers discovered that unlike previously described human antibodies to lipids, WR321 did not react with any of 17 other lipids it was tested against, including cholesterol, glycolipids, and other phospholipids such as cardiolipin and
phosphatidylserine, but it bound
specifically only to two phosphoinositides.