Annexins are structurally similar proteins that bind to phospholipids and may be involved in regulation of membrane transport, membrane channel activity, and interaction of the cell membrane with the extracellular matrixproteins. Annexin A1 is a Ca2+ dependent phospholipid-binding protein. This antibody recognizes annexin A1 protein in human cell membrane and cytoplasm of cells dereived from patients with hairy cell leukemia.