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Monocyte-macrophage release of IL-1 is inhibited by type-1 plasminogen activator inhibitors
S C Robson1, R Saunders, R E Kirsch
1Department of Medicine, University of Cape Town, Observatory, Republic of South Africa.
Abstract:
Interleukin-1 (IL-1) release from monocyte-macrophages (Mo) appears dependent on pericellular proteolysis mediated by plasmin. Thus plasminogen activator inhibitors (PAI) which bind the serine proteases responsible for the conversion of plasminogen to plasmin, may inhibit IL-1 release from Mo. We have examined the effect of purified PAI from a hepatoma cell line Hep G2, on IL-1 release from Mo with secondary effects on lymphocyte proliferation in vitro. Fast acting inhibitors of both urokinase (u-PA) and tissue plasminogen activator (two chain t-PA) were noted in harvest fluids of Hep G2 cells. These inhibitors were stable at pH 3 but lost activity at 45 degrees C. They were SDS-stable and migrated with Mr53 and 104 kDa. These properties conformed to characteristics of type-1 plasminogen activator inhibitor (PAI-1). Partially purified PAI-1 added to human Mo cultured on 125I fibrin layer both in the presence and absence of plasminogen inhibited secretion of IL-1 by Mo in response to LPS. This effect, however, did not correlate with the inhibition of plasminogen dependent fibrinolysis. This suggested a degree of sequestration and inaccessibility of membrane bound u-PA of LPS activated Mo to PAI-1. PAI-1, in addition, inhibited mitogen stimulated peripheral blood mononuclear cell (PBMC) proliferation at similar concentration ranges. This effect was abrogated by the addition of specific antisera to PAI-1. PAI-1 may be released as part of an acute phase response. In addition to influencing fibrinolysis, PAI-1 may constitute a negative feedback pathway on Mo IL-1 release and subsequent immune activation in vivo.
Insights
Plasminogen activator inhibitor-1 (PAI-1) from Hep G2 cells inhibits interleukin-1 (IL-1) release from monocyte-macrophages (Mo). PAI-1 also suppresses lymphocyte proliferation, suggesting a role in immune regulation.
Area of Science:
- Immunology
- Biochemistry
- Cell Biology
Background:
- Interleukin-1 (IL-1) release from monocyte-macrophages (Mo) is crucial for immune responses.
- IL-1 release is linked to pericellular proteolysis mediated by plasmin.
- Plasminogen activator inhibitors (PAI) target proteases involved in plasmin generation and may modulate IL-1 release.
Purpose of the Study:
- To investigate the effect of purified plasminogen activator inhibitor-1 (PAI-1) from Hep G2 cells on IL-1 release from Mo.
- To assess the impact of PAI-1 on lymphocyte proliferation.
- To characterize the properties of PAI-1 isolated from Hep G2 cells.
Main Methods:
- Isolation and partial purification of PAI from Hep G2 cell harvest fluids.
- Incubation of human Mo with PAI-1 on 125I fibrin layers in the presence or absence of plasminogen.
- Stimulation of Mo with lipopolysaccharide (LPS) to induce IL-1 secretion.
- Measurement of IL-1 release and fibrinolysis.
- Assessment of PAI-1 effects on mitogen-stimulated peripheral blood mononuclear cell (PBMC) proliferation.
Main Results:
- Hep G2 cells released fast-acting PAI with characteristics of PAI-1 (stable at pH 3, thermolabile, SDS-stable, Mr 53 and 104 kDa).
- Partially purified PAI-1 inhibited IL-1 secretion by Mo in response to LPS, independent of fibrinolysis inhibition.
- PAI-1 suppressed mitogen-stimulated PBMC proliferation, an effect reversed by anti-PAI-1 antisera.
Conclusions:
- PAI-1 from Hep G2 cells directly inhibits IL-1 release from Mo.
- PAI-1's inhibition of IL-1 release may not solely depend on fibrinolysis.
- PAI-1 can suppress lymphocyte proliferation, indicating a potential role in negative feedback of immune activation.