Abstract: Disclosed are novel inhibitors of the alternative complement pathway and particularly, novel anti-factor B antibodies. Also disclosed is the use of such inhibitors to reduce or prevent airway hyperresponsiveness and/or airway inflammation by selectively inhibiting the alternative complement pathway, thereby treating diseases in which such conditions play a role. Also disclosed is the use of such inhibitors to reduce or prevent other diseases and conditions, including ischemia-reperfusion injury, by inhibition of the alternative complement pathway.