Neutrophil emigration in response to acid aspiration does not require the adhesion complex, CD11/CD18. This study examined the role of CD11b/CD18 using the anti-CD1 lb F(ab')2 1B6, in focal HCl-induced intracapillary neutrophil sequestration and edema formation within rat lungs, as well as the effect of pretreatment with endotoxin on this injury. The results show that at the site of aspiration pneumonia, anti-CD11b F(ab')2 did not inhibit neutrophil sequestration or edema formation, either with

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... or without endotoxin pretreatment. In the contralateral lung, focal HCl aspiration induced neutrophil sequestration that was inhibited by the anti-CD11b F(ab')2 but no edema formation. The combined effect of endotoxin pretreatment and HCl aspiration induced CD11b/CD18-independent edema formation in the contralateral lung. These data indicate that CD11b/CD18-independent pathways mediate neutrophil sequestration and edema formation at that pneumonic site with or without pretreatment with endotoxin. CD11b/CD18 mediates neutrophil sequestration at distant sites when no endotoxin is present, although this CD11b/CD18-dependent sequestration is not association with edema formation. The combined effects of endotoxin and HCl aspiration induce edema formation at distant sites that could not be prevented by inhibiting the function of the CD11b/CD18 prior to aspiration.