DOWNSTREAM SIGNALS INITIATED IN MAST-CELLS BY FC-EPSILON-RI AND OTHERRECEPTORS

The significant contributions this past year to our understanding of I gE receptor (Fc epsilon RI) signaling in mast cells include studies wi th truncated Syk in a vaccinia expression system and Syk-negative vari ants of rat basophilic (RBL-2H3) cells. These studies demonstrate an e ssential role for Syk in initiating signals for secretion and release of arachidonic acid via phospholipase A(2) and mitogen-activated prote in kinase. A newly recognized addition to the repertoire of Fc epsilon RI-mediated signaling systems is the activation of sphingosine kinase , which contributes to calcium mobilization in mast cells. Advances ha ve been made in our understanding of other receptors that regulate pro liferation and differentiation of mast cells, and in our understanding of the ability of mast cells to mount acquired and acute responses to antigenic and bacterial challenge.