Among the genes with variations linked to autoimmune diseases, including type 1 diabetes, rheumatoid arthritis, and Crohn's disease, is PTPN2, which templates a protein known as TCPTP. A team of researchers led by Tony Tiganis, at Monash University, Australia, has now identified a new immune function for TCPTP that might explain the link between PTPN2 genetic variations and autoimmune diseases.