Neutrophil emigration in the skin, lungs, and peritoneum: Different requirements for CD11/CD18 revealed by CD18-deficient mice

To determine the role of CD11/CD18 complexes in neutrophil emigration, inflammation was induced in the skin, lungs, or-peritoneum of mutant mice deficient in CD18 (CD18(-/-) mutants). Peripheral blood of CD18(-/-) contained 11-fold more neutrophils than did mutants blood of wild-type (WIT) mice. During irritant dermatitis induced by topical application of croton oil, the number of emigrated neutrophils in histological sections of dermis was 98% less in CD18(-/-) mutants than in WT mice. During Streptococcus pneumonia pneumonia, neutrophil emigration in CD18(-/-) mutants was not reduced. These data are consistent with expectations based on studies using blocking antibodies to inhibit CD11/CD18 complexes, and on observations of humans lacking CD11/CD18 complexes. The number of emigrated neutrophils in lung sections during Escherichia coli pneumonia, or in peritoneal lavage fluid after 4 h of S. pneumoniae peritonitis, was not reduced in CD18(-/-) mutants, but rather was greater than the WT values (240 +/- 30 and 220 +/- 30% WT, respectively). Also, there was no inhibition of neutrophil emigration during sterile peritonitis induced by intraperitoneal injection of thioglycollate (90 +/- 20% WT). These data contrast with expectations. Whereas CD11/CD18 complexes are essential to the dermal emigration of neutrophils during acute dermatitis, CD18(-/-) mutant mice demonstrate surprising alternative pathways for neutrophil emigration during pneumonia or peritonitis.