- Last Update On : 2013-01-06
The complement sequence consists of classical and alternate (Properdin) pathways which may be activated sequentially by a number of different causes. In general, the classic pathway is activated by antigen-antibody and cell‑antibody complexes and the alternate pathway by bacteria, fungi and some immune complexes. The sequence of activation in the classical pathway is C1, C4, C2, C3 and C5 to C9. In the alternate pathway C1, C4 and C2 are bypassed and C3 is activated by an initiating factor (IF), and two substances called Properdin Factors D and B.
The most frequently occurring alterations of complement are increased levels, since most complement proteins are acute phase reactants.The main clinical application of complement assays is the detection of decreased levels, which may indicate an on‑going immunological disorder.Total hemolytic complement (CH50) is the best functional assay of the complete complement sequence.CH50 is often decreased in SLE, glomerulonephritis and