Role of Complement Components in Asthma: A Systematic Review.

Asthma is a chronic inflammatory airway disease characterized by recurrent symptoms in response to a wide range of external stimuli, including allergens, viral infections, and air pollution together with internal host-derived danger signals. The disease is traditionally associated with adaptive immune responses; recent research emphasizes the critical role of innate immunity in its pathogenesis. The complement system, activated as part of the defense mechanisms, plays a crucial role in bridging innate to adaptive immunity. While experimental models demonstrate complement cascade activation in asthma, human studies remain limited. This systematic review summarizes existing literature on the complement system in asthma patients, gathering data from PubMed, Web of Science, Scopus, and Google Scholar. The protocol was registered in the OSF. Out of 482 initially identified articles, only 24 met the eligibility criteria, revealing disparities in sample origin, methodologies, and populations. Despite observed heterogeneity, a consistent result was found in the elevation of complement regulatory proteins, such as complement Factor H, in samples from patients with asthma compared to those from healthy subjects. The increased level of regulatory proteins, such as Factor H and I highlight that these may influence asthma pathophysiology. The role of complement factors as potential biomarkers of asthma activity and severity needs further evaluation.