Proline-Serine-Threonine Phosphatase Interacting Protein 1 (PSTPIP1) which is a scaffold protein and a regulator of the actin cytoskeleton binds ABL1, PTPN18, WAS, CD2AP, and PTPN12. PSTPIP1 also binds to the cytoplasmic tail of CD2, an effector of T cell activation and adhesion, negatively affecting CD2-triggered T cell activation. Mutations in PSTPIP1 are a cause of PAPA syndrome.