A dual role for complement in allergic asthma.

Complement is an ancient danger-sensor system of innate immunity, providing first-line defence against pathogens. Concordant with its pro-inflammatory properties, complement contributes to airway inflammation, hyperresponsiveness and mucus production during the effector phase of allergic asthma. In contrast to these pro-allergic properties, complement can also protect from the development of the maladaptive Th2-biased immune response that drives airway inflammation and hyperreactivity in allergic asthma. As such, selective targeting of pro-allergic complement pathways appears an attractive therapeutic option in allergic asthma.