Reduced T Regulatory cells (TREGS) may predispose to Autoimmune diseases, Primary immunodeficiencies, Allergies, Asthma etc. Absence of TREGS helps in evaluating patients with clinical features of IPEX (Immune dysregulation, Polyendocrinopathy, Enteropathy, X linked inheritance). Increased TREGS in donor stem cell allografts are associated with reduced occurrence of graft vs host disease after stem cell transplantation. Increased TREGS are also associated with some malignancies.