Type I interleukin-1 receptor is required for pulmonary responses to subacute ozone exposure in mice

Abstract

Interleukin (IL)-1, a proinflammatory cytokine, is expressed in the lung after ozone (O(3)) exposure. IL-1 mediates its effects through the type I IL-1 receptor (IL-1RI), the only signaling receptor for both IL-1alpha and IL-1beta. The purpose of this study was to determine the role of IL-1RI in pulmonary responses to O(3.) To that end, wild-type, C57BL/6 (IL-1RI(+/+)) mice and IL-1RI-deficient (IL-1RI(-/-)) mice were exposed to O(3) either subacutely (0.3 ppm for 72 h) or acutely (2 ppm for 3 h). Subacute O(3) exposure increased bronchoalveolar lavage fluid (BALF) protein, interferon-gamma-inducible protein (IP)-10, soluble tumor necrosis factor receptor 1 (sTNFR1), and neutrophils in IL-1RI(+/+) and IL-1RI(-/-) mice. With the exception of IP-10, all outcome indicators were reduced in IL-1RI(-/-) mice. Furthermore, subacute O(3) exposure increased IL-6 mRNA expression in IL-1RI(+/+), but not IL-1RI(-/-) mice. Acute (2 ppm) O(3) exposure increased BALF protein, IL-6, eotaxin, KC, macrophage inflammatory protein (MIP)-2, IP-10, monocyte chemotactic protein-1, sTNFR1, neutrophils, and epithelial cells in IL-1RI(+/+) and IL-1RI(-/-) mice. For IL-6, eotaxin, MIP-2, and sTNFR1, there were small but significant reductions of these outcome indicators in IL-1RI(-/-) versus IL-1RI(+/+) mice at 6 hours after exposure, but not at other time points, whereas other outcome indicators were unaffected by IL-1RI deficiency. These results suggest that IL-1RI is required for O(3)-induced pulmonary inflammation during subacute O(3) exposure, but plays a more minor role during acute O(3) exposure. In addition, these results suggest that the induction of IL-6 via IL-1RI may be important in mediating the effects of O(3) during subacute exposure.

Figure 1.

(A) IL-1α and (B) IL-1β mRNA expression in lung tissue from room air– or O₃-exposed wild-type (C57BL/6) mice. Lungs were harvested 30 minutes after cessation of exposure to 0.3 ppm O₃ for 72 hours, or 3, 6, or 24 hours after cessation of exposure to 2 ppm O₃ for 3 hours. Lungs from air-exposed controls were obtained at the same time. mRNA transcript copy number was normalized to β-actin transcript copy number. n = 7–13 mice for each group. *P < 0.05 compared with air-exposed controls.

Figure 2.

The concentrations of protein, interferon-γ–inducible protein (IP)-10, soluble tumor necrosis factor receptor 1 (sTNFR1), as well as the total number of macrophages, neutrophils, and epithelial cells in the bronchoalveolar lavage fluid (BALF) of wild-type, C57BL/6 (IL-1RI^+/+; solid bars) and IL-1RI–deficient (IL-1RI^−/−; open bars) mice 30 minutes after the cessation of a 72-hour exposure to either room air or 0.3 ppm ozone (O₃). n = 8–26 for each treatment group. *P < 0.05 compared with genotype-matched, air-exposed controls. ^#P < 0.05 compared with IL-1RI^−/− mice within the same exposure group.

Figure 3.

(A) IL-6 and (B) intercellular adhesion molecule (ICAM)-1 mRNA expression in lung tissue from room air– or O₃-exposed, wild-type C57BL/6 (IL-1RI^+/+; solid bars) and IL-1RI–deficient (IL-1RI^−/−; open bars) mice. Lungs were harvested 30 minutes after cessation of exposure to 0.3 ppm O₃ for 72 hours. Lungs from air-exposed controls were obtained at the same time. mRNA levels for each treatment group were normalized for 18S rRNA and expressed as the fold-induction of the values determined for air-exposed, wild-type C57BL/6 (IL-1RI^+/+) mice. n = 8–10 mice for each group. *P < 0.05 compared with air-exposed controls.

Figure 4.

The concentrations of protein, IL-6, eotaxin, KC, macrophage inflammatory protein (MIP)-2, IP-10, MCP-1, and sTNFR1 in the BALF of wild-type, C57BL/6 (IL-1RI^+/+; solid bars) and IL-1RI–deficient (IL-1RI^−/−; open bars) mice 3, 6, or 24 hours after the cessation of a 3-hour exposure to either room air or 2 ppm ozone (O₃). The concentrations of BALF protein, IP-10, and sTNFR1 from air-exposed mice are identical to those found in Figure 2 and are included here to demonstrate the effect of O₃ on our outcome indicators. n = 5–26 for each treatment group. *P < 0.05 compared with genotype-matched, air-exposed controls. ^#P < 0.05 compared with IL-1RI^−/− mice within the same exposure group.

Figure 5.

The total number of macrophages, neutrophils, and epithelial cells in the BALF of wild-type, C57BL/6 (IL-1RI^+/+; solid bars) and IL-1RI–deficient (IL-1RI^−/−; open bars) mice 3, 6, or 24 hours after the cessation of a 3-hour exposure to either room air or 2 ppm ozone (O₃). The data shown here from air-exposed mice are identical to those found in Figure 2 and are included here to demonstrate the effect of O₃ on our outcome indicators. n = 8–26 for each treatment group. *P < 0.05 compared with genotype-matched, air-exposed controls. ^#P < 0.05 compared with IL-1RI^−/− mice within the same exposure group.