In CD patients with active illness, the frequency of SLAMF1+ ILC2s correlates inversely with disease severity, and SLAMF1+ ILC2s appear to represent a mature population that produces IL-13 and high amounts of prostaglandin D2 receptor 2 (PTGDR2/CRTH2), CD161, and GATA3. Here, SLAMF1 is linked to Cowden disease.