More recently, complement component C3d was proposed, since it correlates with both radiographic emphysema and severity of the emphysema in AATD, but not in usual COPD; also, in PiZZ AATD after intravenous AT, AAT disrupts C3 activation, thereby decreasing C3d plasma levels. This evidence concerns the gene SERPINA1 and alpha 1-antitrypsin deficiency.