NEUTROPHILS IN BEIGE MICE SECRETE NORMAL AMOUNTS OF CATHEPSIN-G AND A46 KDA LATENT FORM OF ELASTASE THAT CAN BE ACTIVATED EXTRACELLULARLY BY PROTEOLYTIC ACTIVITY

Among other phenotypic defects, the beige mouse is susceptible to infe ction and has large neutrophil granules that apparently secrete a decr eased amount of elastolytic activity. We have shown using in vitro met hods that cytosolic inhibitors in beige neutrophils are normal, Althou gh cathepsin G is tightly bound to lysosomal membranes, normal amounts of activity are released in response to degranulating agents. Decreas ed elastolytic activity is secreted by beige neutrophils because elast ase is present in the granules as a 46 kDa proenzyme, which can be act ivated extracellularly by a protease-dependent mechanism. The current experiments were undertaken to explore the in vivo functions of neutro phils from C57 BI/6J (bg/bg) beige mice using the model of casein-indu ced acute peritonitis; normal C57 BI/6J (+/+) mice served as controls. The kinetics of neutrophil accumulation in the peritoneum were normal , suggesting normal neutrophil migration. Cathepsin G activity in the cell-free supernatant of peritoneal lavage fluid was normal; elastolyt ic activity was initially very low but increased to about twice baseli ne level after 4 h at 25 degrees C and to about 20-fold at 36 h. The a ppearance of this activity was inhibited to varying degree (54 to 83%) by different protease inhibitors (pepstatin, antipain, aprotinin, leu peptin and chymostatin), We conclude that the decreased amount of elas tolytic activity secreted by beige neutrophils into an inflammatory ex udate is due to a genetic defect that results in production of a 46 kD a proelastase rather than the normal 29 kDa active elastase; the proel astase can be spontaneously activated by a protease-dependent mechanis m. In light of these data, the use of the beige mouse as a model for t he Chediak-Higashi syndrome, and as a model in which neutrophils do no t produce elastase, must be reconsidered.