Respiratory Syncytial Virus (RSV) is the most common cause of lower respiratory tract infections in children. No fully effective active vaccine or treatments exist. Complete understanding of how RSV works still remains unclear. Studies have suggested that uncontrolled inflammatory responses of the immune system plays a major role in disease development in the lower airways. We will study factors that can regulate these inappropriate immune-system responses without affecting the body's ability to fight the virus. We will investigate the role of proteins called PD-1 and HMGB1 in the development of severe bronchiolitis and pneumonia during RSV infection. Our research could be valuable in developing new treatments and preventive strategies for RSV.