C3a and C3b activation products of the third component of complement (C3) are critical for normal liver recovery after toxic injury

Although the complement system has been implicated in liver regeneration after toxic injury and partial hepatectomy, themechanism or mechanisms through which it participates in these processes remains ill-defined. In this study, we demonstrate thatcomplement activation products (C3a, C3b/iC3b) are generated in the serum of experimental mice after CCl4 injection and thatcomplement activation is required for normal liver regeneration. Decomplementation by cobra venom factor resulted in impairedentry of hepatocytes into S phase of the cell cycle. In addition, livers from C3-deficient (C3/) mice showed similarly impairedproliferation of hepatocytes, along with delayed kinetics of both hepatocyte hyperplasia and removal of injured liver parenchyma.Restoration of hepatocyte proliferative capabilities of C3/ mice through C3a reconstitution, as well as the impaired regeneration of C3a receptor-deficient mice, demonstrated that C3a promotes liver cell proliferation via the C3a receptor. These findings, together with data showing two waves of complement activation, indicate that C3 activation is a pivotal mechanism for liver regeneration after CCl4 injury, which fulfills multiple roles; C3a generated early after toxin injection is relevant during thepriming of hepatocytes, whereas C3 activation at later times after CCl4 treatment contributes to the clearance of injured tissue.