Complement activation by cigarette smoke

Lung disease secondary to cigarette smoking is associated with an influx of neutrophils and monocytes into the lower respiratory tract. To determine whether cigarette smoke can generate chemotactic activity, human serum was exposed to cigarette smoke and evaluated for neutrophil and monocyte chemotactic activity. Serum exposed to cigarette smoke attracted significantly greater numbers of neutrophils and monocytes compared with normal human serum exposed to air (P < 0.01, both comparisons). The increase in chemotactic activity was partially attenuated by EDTA but not by ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) and MgCl₂ (P > 0.05, both comparisons), suggesting activation of the alternate complement pathway. To evaluate the capacity of cigarette smoke to activate the complement system, smoke-exposed serum was evaluated for cleavage of properdin factor B and C3 using immunoelectrophoresis and for C5a using a radioimmunoassay. Cleavage of properdin factor B and C3 was observed in the smoke-exposed serum and C5a was detected in the smoke-exposed serum (112 ± 31 ng/ml). These data suggest that complement activation may play a role in directing the influx of neutrophils and monocytes into the lungs of cigarette smokers.