CD40 ligand-activated human monocytes amplify glomerular inflammatory responses through soluble and cell-to-cell contact-dependent mechanisms

Monocytes/macrophages play a critical role in the initiation and progressio n of a variety of glomerulonephritides. We sought to define the interaction s between physiologically activated human monocytes and glomerular mesangia l cells (MC) by employing a cell culture system that permits the accurate a ssessment of the contribution of soluble factors and cell-to-cell contact. Human peripheral blood monocytes, primed with IFN-gamma and GM-CSF, were ac tivated with CD40 ligand (CD40L) or TNF-alpha and cocultured with MC. CD40L -activated monocytes induced higher levels of IL-6, monocyte chemoattractan t protein-1 (MCP-1) and ICAM-1 synthesis by MC. Separation of CD40L-activat ed 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 product ion by 40 and 50%, respectively. Ligation of mesangial surface ICAM-1 direc tly enhanced IL-6, but not MCP-1, production. Simultaneous neutralization o f soluble TNF-alpha and IL-1 beta decreased MCP-1 production by 55% in memb rane-separated cocultures of MC/CD40L-activated monocytes, Paraformaldehyde -fixed CD40L-activated monocytes (to preserve membrane integrity but preven t secretory activity), cocultured with MC at various ratios, induced IL-6, MCP-1, and ICAM-1 synthesis by MC, Plasma membrane preparations from activa ted monocytes also induced mesangial IL-6 and MCP-1 synthesis. The addition of plasma membrane enhanced TNF-alpha-induced mesangial IL-6 production by similar to 4-fold. Together, these data suggest that the CD40/CD40L is ess ential for optimal effector function of monocytes, that CD40L-activated mon ocytes stimulate MC through both soluble factors and cell-to-cell contact m ediated pathways, and that both pathways are essential for maximum stimulat ion of MC.