Immune system homeostasis is determined by the balance between responses that control infection and tumour growth and reciprocal responses that prevent inflammation and autoimmune diseases. Dysregulated immune responses, such as those that occur with autoimmune disorders and organ rejection, result when and an individual’s immune system mistakenly attacks normal cells. Current treatment approaches involve following a strict regimen of immunosuppressive drugs for the duration of a patient’s life. These treatments, however, seriously compromise an individual’s ability to fight infection and are associated with an increased risk of developing cancer. Sarah Crome’s research has two main focuses. The first is on the regulation and function of a newly discovered class of inflammatory white blood cells (WBC), termed T helper 17 (Th17) cells, which serve an essential function in host defense against extracellular pathogens. While being key players that protect the body from harmful pathogens, Th17 cells are also linked to inflammatory diseases including rejection of transplanted organs and cells, rheumatoid arthritis, psoriasis and inflammatory bowel disease. Therefore, it is essential to understand the mechanisms that regulate this cell population in order to be able to treat patients with dysregulated immune responses. Secondly, Ms. Crome and colleagues are examining interactions between Th17 cells and another WBC population, termed T regulatory (Treg) cells, which serve a protective function by suppressing harmful immune responses. Currently, Treg cells are being clinically tested as a cell-based therapeutic alternative to immunosuppressive drugs. However, the diseases where Treg cell-based therapies are being investigated are the same diseases that are associated with Th17 cell activity. Therefore, understanding the interactions between these two cell populations will be essential for clinical based studies of Treg cells, and the development of improved therapies.