Cilia are microscopic hair-like cellular projections that line some of the airways in the lung.
In order to work properly the cilia must have both a normal microstructure and move in a coordinated fashion. In the lungs the cilia function to move mucus up from the smaller to the large airways where the mucus can be expelled by such mechanisms as cough. In certain diseases, the cilia do not work properly. In these conditions the cilia either have an abnormal structure or fail to move in a coordinated fashion. In either case the result is recurrent lung infections.