Additionally, component C3, the cornerstone of a complement system and the multifunctional immune mediator placed in the crossroad of several pathways [73], which are involved in the pathogenesis of various inflammatory lung diseases, including asthma [74], COPD [75], infectious disease [76], and bleomycin-induced fibrosis [77] was also chosen for further study. This evidence concerns the gene C3 and chronic obstructive pulmonary disease.