Acrp30 (adipocyte complement-related protein of 30kD), also known as AdipoQ, APM1, Adiponectin, Gelatin binding protein 28kD/GBP28 or adipocyte most abundant gene transcript) was identified as a novel adipocyte-specific synthesized and secreted protein with structural resemblance to complement factor C1q. Like adipsin, Acrp30 secretion is induced ~10-fold during adipocyte differentiation. Plasma levels are reduced in obese humans, and low levels are associated with insulin-resistance. C1q is serum glycoprotein of 18-polypeptides chains consisting of three nonidentical subunits, A (29kD), B (26kD), and C (246 aa, 19kD) in molar ratio of 1:2:2. C1Q in the plasma is complexed with two proenzymes C1r and two C1s molecule to form the first component of complement (C1). Activation of complement via classical pathway is triggered by binding of globular head of C1q to immune complexes containing IgG (Fc-region) or IgM or to a variety of other activating substances, including C-reactive protein, retrovirus, and mitochondria. Subsequent to C1q binding, c1r and C1s are converted to proteolytic enzymes that are responsible to continuation of activation via the classical pathway.