Figure 1: Role of complement system in SSc with lung involvement. Complement bioactive molecules, such as C3a and C5a anaphylatoxins, trigger a series of events that culminate in the recruitment of phagocytic cells, release of inflammatory molecules, activation of T-cell and augmentation of antibody response at the site of inflammation. The membrane-attack complex (MAC), resulting from distal complement component activation, can directly contribute to tissue damage through the lysis of cells, that are not properly protected by complement regulators.