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CD40 ligand-activated human monocytes amplify glomerular inflammatory responses through soluble and cell-to-cell
T Kuroiwa1, E G Lee, C L Danning
1Arthritis and Rheumatism Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, Bethesda, MD 20892, USA. kuroiwat@arb.niams.nih.gov
Abstract:
Monocytes/macrophages play a critical role in the initiation and progression of a variety of glomerulonephritides. We sought to define the interactions between physiologically activated human monocytes and glomerular mesangial cells (MC) by employing a cell culture system that permits the accurate assessment of the contribution of soluble factors and cell-to-cell contact. Human peripheral blood monocytes, primed with IFN-gamma and GM-CSF, were activated with CD40 ligand (CD40L) or TNF-alpha and cocultured with MC. CD40L-activated monocytes induced higher levels of IL-6, monocyte chemoattractant protein-1 (MCP-1) and ICAM-1 synthesis by MC. Separation of CD40L-activated monocytes from MC by a porous membrane decreased the mesangial synthesis of IL-6 by 80% and ICAM-1 by 45%, but had no effect on MCP-1. Neutralizing Abs against the beta 2 integrins, LFA-1 and Mac-1, decreased IL-6 production by 40 and 50%, respectively. Ligation of mesangial surface ICAM-1 directly enhanced IL-6, but not MCP-1, production. Simultaneous neutralization of soluble TNF-alpha and IL-1 beta decreased MCP-1 production by 55% in membrane-separated cocultures of MC/CD40L-activated monocytes. Paraformaldehyde-fixed CD40L-activated monocytes (to preserve membrane integrity but prevent secretory activity), cocultured with MC at various ratios, induced IL-6, MCP-1, and ICAM-1 synthesis by MC. Plasma membrane preparations from activated monocytes also induced mesangial IL-6 and MCP-1 synthesis. The addition of plasma membrane enhanced TNF-alpha-induced mesangial IL-6 production by approximately 4-fold. Together, these data suggest that the CD40/CD40L is essential for optimal effector function of monocytes, that CD40L-activated monocytes stimulate MC through both soluble factors and cell-to-cell contact mediated pathways, and that both pathways are essential for maximum stimulation of MC.
Insights
Activated monocytes stimulate kidney mesangial cells (MC) via soluble factors and direct cell contact. CD40 ligand (CD40L) is crucial for this monocyte activation, influencing glomerulonephritis progression.
Area of Science:
- Immunology
- Nephrology
- Cell Biology
Background:
- Monocytes/macrophages are key players in glomerulonephritis.
- Understanding monocyte-mesangial cell (MC) interactions is vital for kidney disease research.
Purpose of the Study:
- To investigate the mechanisms of human monocyte and MC interaction.
- To determine the roles of soluble factors and cell-to-cell contact in MC activation.
Main Methods:
- Co-culture of activated human monocytes with MC.
- Use of porous membranes to separate cell types.
- Employing neutralizing antibodies against integrins and cytokines.
- Utilizing fixed monocytes and plasma membrane preparations.
Main Results:
- CD40L-activated monocytes significantly increased IL-6, MCP-1, and ICAM-1 in MC.
- Cell contact was essential for IL-6 and ICAM-1 induction, while MCP-1 relied on soluble factors.
- Integrins LFA-1 and Mac-1 mediated IL-6 production.
- Monocyte plasma membranes induced MC synthesis of IL-6 and MCP-1.
Conclusions:
- CD40/CD40L interaction is critical for monocyte effector function.
- Activated monocytes stimulate MC via both soluble mediators and direct cell contact.
- Both pathways are necessary for maximal MC stimulation, impacting glomerulonephritis pathogenesis.