Lipid phosphatases in the immune system

In the last 10 years we have come to appreciate the central role that phosp hatidylinositol (PI)-4,5-P-3 plays in regulating a vast array of biological responses to extracellular signals. The level of this phospholipid is low in resting cells but increases rapidly in response to growth factor/cytokin e-stimulated plasma membrane recruitment and activation of PI-3-kinase. Wit hin the last 3 years three enzymes, SHIP: SHIP2 and PTEN, that play hey rol es in regulating the level of PI-3,4,5-P3 have been cloned. In this review I have attempted to summarize our current knowledge regarding these three i ntriguing phosphatases.