Grant: Operating Grant

White blood cells known as neutrophils form the body's first line of defense against infection. They release a potent array of substances that kill invading bacteria, and so are essential to surviving a life-threatening infection. But these same substances can cause unwanted damage to healthy host tissues. Tissue injury by neutrophils, for example, contributes to a condition known as sepsis in critically ill patients in an ICU, and to joint injury in patients with arthritis. In health, the potential for injury is minimized because of the neutrophil lives for only a very brief period, before dying a death by cellular suicide through a process known as apoptosis. During inflammation, the neutrophil's ability to undergo apoptosis is inhibited, with the result that its capacity for both host defense and tissue injury is enhanced. We have found that neutrophil survival is dependent on changes to the structure of an enzyme called caspase-8 that initiates the process of apoptosis. The addition of a phosphate molecule to an amino acid in capase-8 (a process called phosphorylation) blocks its activity. In the studies proposed here, we will first determine whether phosphorylated caspase-8 is needed to activate a protein known as PI3 kinase, which regulates the survival program in the neutrophil. We will define the role in neutrophil survival of a new survival gene that we have recently identified and called ILIP-1 (Interleukin-1-Induced Protein-1). These processes - caspase-8 phosphorylation, PI3 kinase activation, and expression of ILIP-1 - comprise an integrated complex that we have termed the 'casapase-8 survivalsome'. Finally, we will determine whether modulation of the survivalsome in neutrophils from critically ill patients with sepsis can restore the normal expression of apoptosis. Together the studies will provide the insights necessary to develop new treatments for life-threatening inflammation that are based on preventing the persistence of inflammation.