Asthma is the commonest long-term disease affecting children. It develops because of allergies to substances like dust and animal dander, associated with repeated colds, caused by viruses and bacteria during early life. These result in lifelong effects including a permanent reduction in lung function. Although the cells lining the airways (airway epithelial cells) have a central role in determining the response of a baby's immune system to inhaled allergens and infections, how the airway epithelium develops in health and disease is unknown. We know that the bacteria that normally keep our lungs healthy (called microbiota) are changed in asthma. We will study how airway cells from the nose and lungs work from birth and during early life, and how these cells interact with the immune system, the microbiota and genes. We will compare actions of cells from children who do and do not develop wheezing and look at these following exposure to infection with viruses and bad bacteria and allergens. We want to understand what triggers asthma and find out ways of predicting which babies will develop the disease; so we know which ones to treat and ultimately improve lifelong lung health.