Effects of epithelial and neutrophil CXCR2 on innate immunity and resistance to kidney infection

The murine chemokine receptor 2 (mCXCR2) controls resistance to urinary tract infection. We have previously shown that mCXCR2 knockout mice develop severe acute pyelonephritis and renal tissue damage with sub-epithelial neutrophil entrapment. In this study we examined the relative importance of neutrophil- and epithelial-specific mCXCR2 expression for bacterial clearance in bone marrow chimeric mice infected with uropathogenic Escherichia coli. Mice expressing mCXCR2 on their neutrophils responded rapidly to experimental urinary tract infection, clearing the infection from the kidneys. Mice lacking epithelial mCXCR2, however, showed delayed exit of neutrophils from the tissues. Mice lacking neutrophil mCXCR2 and mice with no mCXCR2 had no neutrophil recruitment and bacterial clearance. Mice expressing mCXCR2 only in their epithelial cells had a transient epithelial chemokine response; however, neutrophil recruitment was inhibited and bacteria grew without constraint. Our study shows that the expression of mCXCR2 on hematopoietic cells was crucial for bacterial clearance, while its expression on non-bone marrow-derived cells influenced the neutrophil response. These results emphasize the importance of mCXCR2 for the innate defense against urinary tract infection.