Janssen WJM, et al. - PSTPIP1 (Proline-Serine-Threonine Phosphatase Interacting Protein 1) is a cytosolic adaptor protein involved with T-cell activation, differentiation, and migration. Researchers performed genetic screening of primary immunodeficiency patients and found 2 mutations in PSTPIP1, R228C and T274M which they further characterized in primary patient T-cells. It was proposed that defective control of f-actin polymerization caused PSTPIP1 T-cell differentiation defects. A pre-activated polymerized f-actin status, as seen in PSTPIP1-T274M T-cells, appeared particularly damaging. Via its function as orchestrator of the f-actin cytoskeleton, PSTPIP1 controls immune synapse (IS) formation and cell adhesion.