Interleukin (IL)-33 treatment has been reported to reduce mortality in a rat model of sepsis, and the present study aimed to determine whether this effect of IL-33 is achieved through a reduction in the systemic inflammatory response in Acinetobacter baumannii pneumonia. After induction of pneumonia, rats were treated with normal saline or IL-33, and mortality over 5 days was recorded. Inflammation within lung tissues was evaluated by hematoxylin and eosin staining as well as measurement of the concentrations of IL-8 and tumor necrosis factor alpha (TNF-α) in the bronchoalveolar lavage fluid (BALF) and plasma by enzyme-linked immunosorbent assay. In addition, the expression of Toll-like receptor 4 (TLR4), ST2, and nuclear factor kappa B (NF-κB) in rat lung tissues was assessed by western blotting. The result showed that the mortality rate and systemic inflammation were significantly increased in rats upon infection with A. baumannii, as evidenced by significant increases in the IL-8 and TNF-α levels in BALF and plasma as well as increased NF-κB activity and TLR4 expression in rat lung tissues. Importantly, IL-33 (1 μg/kg) treatment significantly decreased mortality and pulmonary inflammation in A. baumannii-infected rats. Moreover, IL-33 treatment suppressed the elevation of IL-8 and TNF-α levels and inhibited TLR4 expression and NF-κB activation. Overall, these results suggest that IL-33 may decrease the mortality and inhibit the systematic inflammatory response associated with A. baumannii pneumonia by suppressing TLR4/NF-κB signaling.
Keywords: Acinetobacter baumannii; IL-33; Toll-like receptor 4; inflammation; nuclear factor kappa B.