Intestinal CD14+ Macrophages Protect CD4+ T Cells From Activation-induced Cell Death via Exosomal Membrane TNF in Crohn’s Disease

Abstract

Background and aims: Sustained activation of CD4(+)T cells plays important roles in the pathogenesis of Crohn's disease [CD]. Under physiologic conditions, activated T cells can be timely eliminated by a process termed activation-induced cell death [AICD], restraining T cell over-activation and preventing immunological destruction. We inquired whether defective AICD might explain CD4(+)T cell over-activation in CD and investigated the underlying mechanisms. Methods: CD14(+) macrophages [M-phi] and CD4(+) T cells were isolated from intestinal tissues or peripheral blood of controls and CD patients. An ex vivo evaluation system was employed to simulate AICD and cell apoptosis was measured by flow cytometry. Results: CD4(+) T cells from CD patients fail to undergo AICD in the ex vivo system. Specifically, proinflammatory type 1 helper T [Th1] and type 17 helper T [Th17] cells, rather than immunosuppressive regulatory T [Treg] cells evade AICD in CD. CD14(+) M-phi in the intestinal inflammatory microenvironment of CD promote AICD resistance in CD4(+)T cells via a cell-to-cell contact-independent manner. Mechanistically, CD14(+) My released exosomes express membrane tumour necrosis factor [TNF] which engages TNFR2 on CD4(+) T cells and triggers NF-kappa B signalling, thereby causing AICD resistance. Importantly, clinically applicable anti-TNF antibodies effectively blocked exosomal membrane TNF-induced CD4(+)T cell AICD resistance. Conclusions: CD14(+) M-phi participate in CD pathogenesis by inducing AICD resistance through release of exosomal membrane TNF to activate the TNFR2/NF-kappa B pathway in CD4(+) T cells. These results present new insights into CD pathogenesis and extend mechanistic understanding of anti-TNF agents. Proposed model: CD14(+) M-phi in the intestinal microenvironment of CD patients maintain the sustained activation of CD4'T cells through exosomal membraneTNF to induce apoptosis resistance viaTNFR2/NE-kappa B signalling, which could be effectively blocked by clinically applicable anti-TNF agents.