Complement is an important evolutionary conserved element of the innate immune system. Human complement system comprises more than 20 proteins which are present as inactive precursors. Complement is the final effector mediating tissue damage and injury in a host of autoimmune disease. Inherited deficiencies of early complement components lead to a lupus-like manifestations Deficiencies of component of alternative pathway leads to monogenic forms of atypical haemolytic uremic syndrome