Evidence for an active hydrophobic form of factor H that is able to induce secretion of interleukin 1-beta or by human monocytes
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Activation and Measurement of NLRP3 Inflammasome Activity Using IL-1β in Human Monocyte-derived Dendritic Cells
Published on: May 22, 2014
D Iferroudjene1, M T Schouft, C Lemercier
1INSERM Unité 78, Bois-Guillaume, France.
Insights
Human factor H stimulates monocytes to secrete lymphocyte-activating factor (LAF), a form of interleukin 1-beta (IL 1 beta). This interaction involves factor H binding to its specific receptor on monocytes.
Area of Science:
- Immunology
- Cell Biology
Background:
- Human factor H is a key regulator of the complement system.
- Monocytes are crucial immune cells involved in inflammation and host defense.
Purpose of the Study:
- To investigate the role of human factor H in stimulating human monocytes to secrete lymphocyte-activating factor (LAF).
- To elucidate the mechanism of factor H-induced LAF secretion and identify the specific form of factor H involved.
Main Methods:
- Human monocytes were cultured under serum-free conditions with purified human factor H.
- Lymphocyte-activating factor (LAF) secretion was assessed using the mouse thymocyte proliferation assay.
- Interleukin 1-beta (IL 1 beta) levels were quantified using radioimmunoassay.
- Factor H subpopulations were characterized by their binding to phenyl-Sepharose and specific cell receptors.
Main Results:
- Human factor H significantly induced dose-dependent secretion of LAF by monocytes.
- Polymyxin B did not inhibit factor H-induced LAF secretion, indicating it's not due to endotoxin contamination.
- Specific binding of factor H to anti-factor H-Sepharose confirmed the activity's specificity.
- A subpopulation of factor H (phi 2), which binds to phenyl-Sepharose and Raji cells, was a stronger inducer of LAF secretion.
- LAF activity correlated directly with secreted IL 1 beta levels.
- Factor H (phi 2) was identified as a ligand for the human factor H receptor.
Conclusions:
- Human factor H stimulates monocytes to secrete IL 1 beta, a key inflammatory cytokine.
- The interaction between factor H and its specific monocyte receptor mediates this effect.
- The phi 2 subpopulation of factor H is crucial for inducing IL 1 beta secretion via receptor binding.
Abstract:
We studied the capacity of human factor H to promote the secretion of a lymphocyte-activating factor (LAF) by human monocytes cultured under serum-free conditions. Presence of LAF in the culture supernatants was assessed with the mouse thymocyte assay. Highly purified factor H alone had no effect on thymocyte proliferation. When monocytes were cultured with factor H for 24 h, a significant secretion of LAF was observed. The effect was dose dependent over a range of factor H concentrations from 1 to 15 micrograms/ml. Polymyxin B did not abrogate the capacity of factor H to induce LAF secretion. Adsorption of factor H preparations onto anti-factor H-Sepharose completely suppressed the phenomenon. Conversely, the activity was recovered in the acidic eluate. Furthermore, factor H subpopulation phi 2, that was able to bind to phenyl-Sepharose, was a stronger inducer of LAF secretion by monocytes than the subpopulation phi 1 (which did not bind to phenyl-Sepharose). Using a specific radioimmunoassay for interleukin 1-beta (IL 1 beta), we observed a good correlation between the LAF activity and the amount of IL 1 beta secreted by human monocytes stimulated with factor H. We have shown previously that factor H (phi 2) bound specifically on Raji cells whereas factor H (phi 1) did not. These results argue for the participation of the interaction of factor H with its receptor to stimulate the secretion of IL 1 by monocytes and that the phi 2 form of factor H is a ligand for the human factor H receptor.
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