Lipopolysaccharide stimulates alveolar macrophage adherence in vivo and in vitro.

The number of alveolar macrophages (AM) obtained from rats by bronchoalveolar lavage (BAL) decreases significantly within two hours after infusion of E. coli lipopolysaccharide (LPS). To investigate the mechanism of this phenomenon, we evaluated adherence properties of AM obtained from rats 4 hours after intravenous injection of E. coli LPS (3 mg/kg) or normal saline (NS). Significantly fewer AM were present in BAL samples from LPS-treated rats (4.09 x 10(6] compared to NS-treated rats (7.55 x 10(6]. When a 17 mM lidocaine solution (LDC) was used for lavage, the number of AM in BAL samples from LPS-treated rats increased significantly (7.38 x 10(6]. Adherence of AM from LPS-treated rats to rotating plastic tubes was significantly greater than that of AM from NS-treated rats. Incubation of normal AM with LPS (5 or 15 micrograms/ml) in serum-free media increased AM adherence to plastic. LPS-induced adherence was significantly greater at the higher LPS dose. Thus, the decreased number of AM obtained by BAL of LPS-treated rats appears to be due to increased adherence of AM to alveolar structures. This phenomenon may be mediated by direct effects of LPS on AM.