Activation of neutrophils in vitro and in vivo. To examine anti-mBP180 IgG-induced neutrophil activation in vitro, mouse neutrophils from WT and Mac-1 KO mice were stimulated with pathogenic anti-mBP180 IgG (R530) plus mBP180 antigen, and the supernatant was then assayed for MMP-9 (A) and NE (B) by MMP-9 colorimetric and NE enzymatic activity assay, respectively. Mac-1 KO and WT neutrophils showed no difference in neutrophil release of these proteinases. To examine anti-mBP180 IgG-induced neutrophil activation in vivo, WT and Mac-1 KO mice were injected intradermally with pathogenic anti-mBP180 IgG R530, and extracellular levels of released MMP-9 (C) and NE (D) in the IgG injection sites at 4- and 24-hour time points were quantified by MMP-9 colorimetric and NE enzymatic activity assays. Data shown are the mean ± SEM.