Neutral protease secretion by human monocytes. Effect of surface-bound immune complexes

Area of Science:

• Immunology
• Biochemistry
• Cell Biology

Background:

• Human peripheral monocytes play a role in immune responses.
• Neutral proteases secreted by monocytes can degrade extracellular matrix.
• Immune complexes are implicated in various inflammatory diseases.

Purpose of the Study:

• To investigate the effect of surface-bound immune complexes on neutral protease secretion by human monocytes.
• To characterize the types of proteases secreted and their activity.
• To understand the role of these proteases in potential tissue injury.

Main Methods:

• Monocytes were cultured on 125I-fibrin with and without surface-bound immune complexes.
• Fibrinolytic activity was measured, distinguishing between plasminogen-dependent and independent pathways.
• Protease inhibitors were used to characterize the secreted enzymes.
• Deiodination activity was assessed.

Main Results:

• Monocytes cultured on immune complexes showed a burst of plasminogen-independent fibrinolytic activity.
• This activity was primarily due to leukocyte elastase secreted by monocytes.
• Plasminogen activator secretion was inhibited under these conditions.
• Deiodinating enzymes were also secreted.

Conclusions:

• Surface-bound immune complexes induce monocytes to secrete plasminogen-independent proteases, predominantly elastase, and deiodinating enzymes.
• This secretion occurs with concurrent inhibition of plasminogen activator release.
• These monocyte-derived proteases may contribute to tissue damage in diseases with immune complexes.