Attenuation of live E. coli-induced acute lung injury by x-ray irradiation in guinea pigs

Irradiation is suspected to injure inflammatory cells, such as neutrophils and mononuclear phagocytes, cells known to contribute to the development of acute lung injury (ALI). This study examined whether preexposure to x-ray irradiation modifies ALI induced by E. coli injected intravenously in guinea pig. Thirty animals were divided into two control and two irradiated subgroups: the first control group received saline only (n = 8), and the second control group received E. coli, 2 × 10⁹/kg body weight, suspended in saline (n = 6), IV. The first irradiated group received a single 12-Gy dose + saline (n = 6), and the second irradiated group received a single 12-Gy dose + E. coli (n = 10). The lung wet-to-dry-weight ratio (W/D) and ¹²⁵I-albumin lung tissue/plasma ratio (T/P) were measured as markers of lung injury. W/D was significantly higher in the control E. coli group than in the other groups. T/P in the control E. coli group was also increased compared with T/P measured in the other groups. In the control E. coli group, a marked increase in bronchoalveolar lavage (BAL) neutrophils was observed compared with the control saline group. However, no significant difference in BAL neutrophil counts was observed between the control and irradiated E. coli groups. In contrast, BAL macrophages were significantly reduced in the irradiated E. coli groups compared with the control E. coli group. These findings suggest that x-ray irradiation attenuates E. coli-induced ALI in guinea pigs, an effect explained, at least in part, by a reduction in the number of alveolar macrophages.