The overall objective of this project is to delineate the role of properdin and the Properdin Activator System in the activation of complement. The proposed work aims at further defining the interaction of C1 with properdin convertase and properdin as well as the role of CeNeF in that interaction. The involvement of antibody and C1 in the activation of properdin has recently been uncovered. In addition, this proposal aims at delineating the interaction of properdin convertase and properdin with both factors B and D. Those experiments will involve both activation and inhibitory processes. Further efforts will be made to demonstrate the role of properdin convertase activated properdin in the modulation of both the classical and alternative pathways. These experiments involve elucidation of those mechanisms of properdin interaction with factor B, C1, and C4. Finally, this project will more completely evaluate the meaning of properdin activation in patients with various types of vasculitis including those patients with allergies.