CXCR2 is essential for maximal neutrophil recruitment and methacholine responsiveness after ozone exposure

Physiology Program, Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts Submitted 22 March 2004 ; accepted in final form 7 September 2004 Ozone (O 3 ), a common air pollutant, induces airway inflammation and airway hyperresponsiveness. In mice, the neutrophil chemokines KC and macrophage inflammatory protein-2 (MIP-2) are expressed in the lungs following O 3 exposure. The purpose of this study was to determine whether CXCR2, the receptor for these chemokines, is essential to O 3 -induced neutrophil recruitment, injury to lungs, and increases in respiratory system responsiveness to methacholine (MCh). O 3 exposure (1 ppm for 3 h) increased the number of neutrophils in the bronchoalveolar lavage fluid (BALF) of wild-type (BALB/c) and CXCR2-deficient mice. However, CXCR2-deficient mice had significantly fewer emigrated neutrophils than did wild-type mice. The numbers of neutrophils in the blood and concentrations of BALF KC and MIP-2 did not differ between genotypes. Together, these data suggest CXCR2 is essential for maximal chemokine-directed migration of neutrophils to the air spaces. In wild-type mice, O 3 exposure increased BALF epithelial cell numbers and total protein levels, two indirect measures of lung injury. In contrast, in CXCR2-deficient mice, the number of BALF epithelial cells was not increased by O 3 exposure. Responses to inhaled MCh were measured by whole body plethysmography using enhanced pause as the outcome indicator. O 3 exposure increased responses to inhaled MCh in both wild-type and CXCR2-deficient mice 3 h after O 3 exposure. However, at 24 h after exposure, responses to inhaled MCh were elevated in wild-type but not CXCR2-deficient mice. These results indicate CXCR2 is essential for maximal neutrophil recruitment, epithelial cell sloughing, and persistent increases in MCh responsiveness after an acute O 3 exposure. inflammation; KC; lung; macrophage inflammatory protein-2; mouse Address for reprint requests and other correspondence: R. A. Johnston, Bldg. 1, Rm. 1304A, Physiology Program, Dept. of Environmental Health, Harvard School of Public Health, 665 Huntington Ave., Boston, MA 02115-6021 (E-mail: rajohnst{at}hsph.harvard.edu )