Cyclophosphamide and cortisone acetate inhibit complement biosynthesis by guinea pig bronchoalveolar macrophages

To explore mechanisms of drug-induced alterations in local host defenses in the lung, the capacity of guinea pig alveolar macrophages to synthesize the second (C2) and fourth (C4) components of complement was studied following treatment with cyclophosphamide and cortisone acetate. Administration of either drug significantly inhibited biosynthesis of C2 and C4 within 1 day. After 1 week of treatment, local complement synthesis was inhibited approximately 80%, although serum levels of the corresponding proteins were normal.