ABSTRACT
Mast cells (MCs) are present in the upper and lower airways. These immune cells express high affinity IgE and complement (C3a and C5a) receptors on their surfaces, and it is widely appreciated that MCs release a diverse array of biologically active molecules (including cytokines, chemokines, leukotrienes, prostaglandins, amines, proteoglycans, and proteases) when activated via either family of receptors. Less widely appreciated is the fact that all MCs that have been examined to date also express functional protease-activated receptor (PAR)1 and PAR2 on their surfaces. The four known members of this family of G proteincoupled receptors possess an exposed amino terminal peptide that when cleaved by thrombin, cathepsin G, or a tryptic-like serine protease at a specific site results in cellular activation. The first aspect of this review focuses on recent advances in the PAR field in the context of the proposed roles of these receptors in the lung and in MC-mediated immune responses.
