Our approach, optimizing the dosage of siRNA, allowed us to successfully silence our target gene-product (SphK1) in vivo, and enabled us to validate SphK1 as a key player in our in vivo model of C5a-induced acute peritonitis and systemic inflammation including multi-organ damage, demonstrating that this improved siRNA-silencing method not only allowed us to identify SphK1 as a key therapeutic target, but brings us a step closer to the usage of siRNA for therapeutic intervention.