Leukocyte recruitment in inflammation is critical for host defense, but excessive accumulation of inflammatory cells can lead to tissue damage. Neutrophil-derived serine proteases (cathepsin G [CG], neutrophil elastase [NE], and proteinase 3 [PR3]) are expressed specifically in mature neutrophils and are thought to play an important role in inflammation. To investigate the role of these proteases in inflammation, we generated a mouse deficient in dipeptidyl peptidase I (DPPI) and established that DPPI is required for the full activation of CG, NE, and PR3. Although DPPI(-/-) mice have normal in vitro neutrophil chemotaxis and in vivo neutrophil accumulation during sterile peritonitis, they are protected against acute arthritis induced by passive transfer of monoclonal antibodies against type II collagen. Specifically, there is no accumulation of neutrophils in the joints of DPPI(-/-) mice. This protective effect correlates with the inactivation of neutrophil-derived serine proteases, since NE(-/-) x CG(-/-) mice are equally resistant to arthritis induction by anti-collagen antibodies. In addition, protease-deficient mice have decreased response to zymosan- and immune complex-mediated inflammation in the subcutaneous air pouch. This defect is accompanied by a decrease in local production of TNF-alpha and IL-1 beta. These results implicate DPPI and polymorphonuclear neutrophil-derived serine proteases in the regulation of cytokine production at sites of inflammation.

A variety of neutral serine proteases are important for the effector functions of immune cells. The neutrophil-derived serine proteases cathepsin G and neutrophil elastase are implicated in the host defense against invading bacterial and fungal pathogens. Likewise, the cytotoxic lymphocyte and NK cell granule-associated granzymes A and B are important for the elimination of virus-infected cells. The activation of many of these serine proteases depends on the N-terminal processing activity of the lysosomal cysteine protease cathepsin C/dipeptidyl peptidase I (DPPI). Although mice deficient in DPPI have defects in serine protease activation in multiple cellular compartments, the role of DPPI for human serine protease activation is largely undefined. Papillon-Lefèvre syndrome (PLS) is a rare autosomal recessive disease associated with loss-of-function mutations in the DPPI gene locus. In this study, we established that the loss of DPPI activity is associated with severe reduction in the activity and stability of neutrophil-derived serine proteases. Surprisingly, patients with PLS retain significant granzyme activities in a cytotoxic lymphocyte compartment (lymphokine-activated killer) and have normal lymphokine-activated killer-mediated cytotoxicity against K562 cells. Neutrophils from patients with PLS do not uniformly have a defect in their ability to kill Staphylococcus aureus and Escherichia coli, suggesting that serine proteases do not represent the major mechanism used by human neutrophils for killing common bacteria. Therefore, this study defines the consequences of DPPI deficiency for the activation of several immune cell serine proteases in humans, and provides a molecular explanation for the lack of a generalized T cell immunodeficiency phenotype in patients with PLS.

Leukocyte recruitment in inflammation is critical for host defense, but excessive accumulation of inflammatory cells can lead to tissue damage. Neutrophil-derived serine proteases (cathepsin G [CG], neutrophil elastase [NE], and proteinase 3 [PR3]) are expressed specifically in mature neutrophils and are thought to play an important role in inflammation. To investigate the role of these proteases in inflammation, we generated a mouse deficient in dipeptidyl peptidase I (DPPI) and established that DPPI is required for the full activation of CG, NE, and PR3. Although DPPI–/– mice have normal in vitro neutrophil chemotaxis and in vivo neutrophil accumulation during sterile peritonitis, they are protected against acute arthritis induced by passive transfer of monoclonal antibodies against type II collagen. Specifically, there is no accumulation of neutrophils in the joints of DPPI–/– mice. This protective effect correlates with the inactivation of neutrophil-derived serine proteases, since NE–/– × CG–/– mice are equally resistant to arthritis induction by anti-collagen antibodies. In addition, protease-deficient mice have decreased response to zymosan- and immune complex–mediated inflammation in the subcutaneous air pouch. This defect is accompanied by a decrease in local production of TNF-α and IL-1β. These results implicate DPPI and polymorphonuclear neutrophil–derived serine proteases in the regulation of cytokine production at sites of inflammation

Granzyme (gzm) B-deficient cytotoxic lymphocytes (CTL) have a severe defect in the rapid induction of target cell apoptosis that is almost completely corrected by prolonged incubation of the CTL effectors and their targets. We show in this report that perforin-dependent, gzmB-independent cytotoxicity is caused by gzmA (or tightly linked genes). CTL deficient for gzmA and gzmB retain normal perforin function, but these CTL have a cytotoxic defect in vivo that is as severe as perforin-deficient CTL. Collectively, these results suggest that perforin provides target cell access and/or trafficking signals for the gzms, and that the gzms themselves deliver the lethal hits. The gzmA pathway appears to function independently from gzmB and may therefore provide a critical "back-up" system when gzmB is inhibited in the target cell.