This schematic drawing highlights potential and probable roles for the actions of protease-activated receptors in the cell biology of allergic respiratory diseases. Many allergens derived from fungi/molds, dust mites and plant pollens (illustrated at the top, left to right) contain protease activities. These serine and cysteine proteases likely play several roles in airway inflammation. For example, the processes in asthma would include damage to epithelial cells lining the lungs and bronchial tubes (the blue cells with the cilia) induced by chemicals released (red dots) from degranulating eosinophils. In addition, airway tissue cells (smooth muscle and fibroblasts) increase in numbers and show reduced flexibility; blood vessel cells (endothelial cells) secrete cytokines and bring in more immune cells; mast cells and lymphocytes (immune cells) increase production of several immune response signals and factors; and nerve cells (neurons) likely release chemical signals. Figure is copyright © 2004 the American Academy of Allergy, Asthma and Immunology. For more details, see Reed CE, Kita H: The role of protease activation of inflammation in allergic respiratory diseases. Journal of Allergy and Clinical Immunology, 114:997-1008, 2004.