Roles of inflammatory cells in the pathogenesis of acute lung injury in guinea pigs exposed to heat-killed bacteria

To study the contribution of polymorphonuclear (PMN) and mononuclear (MN) phagocytes to the development of acute lung injury, we studied lung injury after intratracheal instillation of lipopolysaccharide (0.02 mg/kg) in guinea pigs previously exposed to heat-killed Corynebacterium parvum. In one group, cyclophosphamide was given to deplete peripheral PMNs. In another group, gadolinium chloride (GdCl₃) was injected to suppress the function of MNs. Four hours after instillation of lippoly soccharide, the animals were killed, bronchoalveolar lavage was done, and the lungs were examined histopathologically. ¹²⁵I-labeled albumin was injected to estimate the endothelial damage, and ¹³¹I-labeled albumin was injected to correct for blood contamination in the samples. In the group given cyclophosphamide, lung injury was no less than in the control group. In contrast, lung injury was less severe in the group given GdCl₃ than in the control group. These findigns suggest that MN are important in the pathogenesis of lung injury, especially in individuals who are immunologically primed by infection.