Partial hepatectomy (removal of the two largest lobes of the liver) induces a regenerative response in the remaining liver tissue. A regulatory feedback loop exists in which complement activation, involving the cleavage of C3 and C5 to produce the C3a and C5a anaphylatoxins, leads to the recruitment of NKT cells to the liver (independently of anaphylatoxin activity), and the subsequent production of IL-4 by these cells. IL-4 maintains IgM levels, and increased IgM deposition in the liver induces further complement activation. C3a and C5a are thought to act on macrophages, leading to production of IL-6, a cytokine important for the hepatocyte proliferation and protection that is necessary for proper liver regeneration.