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From the * Intramural Research Support Program, Science Applications International Corporation
Frederick, National Cancer Institute-Frederick Cancer Research and Development Center, and Macrophage infiltration into inflammatory sites is generally preceded by neutrophils. This suggests neutrophils may be the source of chemotactic factors for monocytes. To identify these putative monocyte attractants, we have systematically prepared neutrophil granules, lysed them,
and sequentially purified the released proteins by several reverse phase chromatography procedures. Assays for monocyte chemotactic activity of the chromatography fractions yielded a major peak of activity associated with a protein of 30 kD, according to SDS-PAGE analysis. NH2-terminal sequence of the protein revealed this to be identical to cathepsin G. The monocyte
chemotactic activity of human cathepsin G was dose dependent with optimal concentration at
0.5-1 µg/ml. Cathepsin G is chemotactic rather than chemokinetic for monocytes, as demonstrated by checkerboard analysis. Cathepsin G-induced monocyte chemotaxis is partially pertussis toxin sensitive implying the involvement of a G protein-coupled receptor. Enzymatic
activity of cathepsin G is associated with its monocyte chemotactic activity, since DFP- or PMSF-inactivated cathepsin G no longer induced monocyte migration. The chemotactic activity of
cathepsin G can also be completely blocked by
Laboratory of Molecular Immunoregulation, National Cancer Institute, National Institutes of Health,
Frederick Cancer Research and Development Center, Frederick, Maryland 21702
1 antichymotrypsin, a specific inhibitor of chymotrypsin-like proteinases present in human plasma. In addition, cathepsin G is also a potent
chemoattractant for neutrophils and a chemokinetic stimulant for T cells. In the course of pursuing these in vitro studies, we established that the T cell chemoattractant, azurocidin/CAP37
from human neutrophil granules, at doses of 0.05 to 5 µg/ml, was chemotactic for monocytes and neutrophils. As predicted from the in vitro chemotactic activity, subcutaneous injection of
cathepsin G into BALB/c mice led to infiltration of both mononuclear cells and neutrophils.
Thus, the transition of inflammatory exudate from neutrophil to mononuclear cells can be mediated, at least in part, by extracellular release of neutrophil granule proteins such as cathepsin
G and azurocidin/CAP37.
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