Pulmonary Manifestations of Complement Deficiencies

The complement system has an important role in host defense against infections, removal of apoptotic cells and immune complexes, and modulating the adaptive immune response. Deficiencies of the proteins or regulators of the complement system contribute to infections affecting the respiratory tract. The main etiological agents associated with complement deficiencies are encapsulated bacteria as Streptococcus, Haemophilus, and Neisseria, related to the role of this system to bacteria opsonization and clearance. MBL deficiency contributes to infectious risk in some diseases like cystic fibrosis and common variable immunodeficiency (CVID), whose pulmonary impairment is relevant. Many complement deficiencies do not have a severe phenotype; thus, there is restricted information about long-term effects and specific infections such as pulmonary infections. Immunization against encapsulated bacteria is recommended for all these defects.