During the past several years, substantinl progress in understanding the receptors and signal transduction processes for peptidyl leukotrienes has been reported. Receptors have been identified and characterized, the major steps in the signal transduction pathway have been described, and the genetic and epigenetic regulatory processes have been characterized. Very recent studies have defined the mechanisms by which LTE4 acts as a partial agonist at the LTDl receptor. The cloning of the genes for the proteins involved in the major steps of the signalling process has also been initiated. Stanley Crooke and coauthors summarize this recent progress and present their current notions about the LTD4 receptor signalling process.

A model of the signal transduction processes of leukotriene LTD4 receptors is presented in Fig. 1. LTD, interacts with highly selective and specific LTD4 receptors1 located in the plasma membranti; these receptors differ both from LTBd receptors and from binding sites for LTC4 (Refs 3-6). No evidence of specific LTl $ receptors has been found in any tissue or cell line. However, there are data that suggest that there may be tissuespecific