Impairment of endotoxin-induced macrophage inflammatory protein 2 gene expression in alveolar macrophages in Streptozotocin-induced diabetes in mice

To elucidate the mechanism of the high incidence of lower respiratory tract infections in patients with diabetes mellitus, we investigated the kinetics of production of macrophage inflammatory protein 2 (MIP-2), an important mediator of lung neutrophil recruitment, using mice with streptozotocin-induced diabetes. Intratracheal challenge with 1 mg of lipopolysaccharide (LPS), an endotoxin, per kg of body weight resulted in a time-dependent increase in the levels of MIP-2 protein in bronchoalveolar lavage (BAL) fluid, with the peak concentration (49.4 +/- 13 ng/ml) occurring at 3 h and significant neutrophil accumulation becoming apparent by 3 h in normal mice. In diabetic mice, the peak level of MIP-2 protein in BAL fluid did not occur until 6 h and was reduced to 21.9 +/- 10 ng/ml. Immunohistochemical studies using anti-MIP-2 antibody confirmed that the main cellular source of MIP-2, in the lung after LPS challenge was alveolar macrophages (AMs) in normal mice. The lungs in diabetic mice, however, showed no AR ls staining for MIP-2 within 3 h after LPS challenge. PCR analysis using whole-lung RNA showed a time-dependent increase in MIP-2 mRNA levels after LPS instillation. The level of MIP-2 mRNA in diabetic mice was markedly decreased compared to that in normal mice. Our results indicate that impairment of MIP-2 mRNA expression in the AMs in diabetic mice resulted in delayed neutrophil recruitment in the lungs, and this may explain the development and progression of pulmonary infection in diabetes mellitus.