Monocyte/macrophage mediates the impact of depression on Crohn's disease

Background: Depression increases the risk of Crohn's disease (CD) and worsens its prognosis. Monocytes/macrophages, immune modulate cells, play vital roles in both depression and CD. Objectives: We investigated whether monocyte/macrophage could mediate the impact of depression on CD through induction of CD4+ T lymphocyte differentiation and epithelial barrier dysfunction, in addition to the alteration of their own phagocytic ability and cytokines production. Methods: Circulating monocytes and intestinal macrophages were isolated from eligible CD patients, divided into depressed and non-depressed groups. Phagocytosis was determined using flow cytometry while in vitro cytokine production was quantified using Luminex assay and qPCR. CD4 +T cells were cocultured with monocytes, then Type 1 Helper T Lymphocytes Th1/Type 2 Helper T Lymphocytes (Th2) /Type 17 Helper T Lymphocytes (Th17)/Treg subsets were analyzed using flow cytometry and qPCR. Caco-2 monolayers simulating epithelial barrier were cocultured with macrophages, and integrity and proliferation were evaluated. Tight junction protein expression was detected using immunofluorescence and western blot. Results: Decreased monocyte/macrophage phagocytosis and enhanced production of pro-inflammatory cytokines including Tumor necrosis factor-alpha (TNF-alpha), Interleukin-6 (IL-6) and Interleukin-1 beta (IL-1 beta) were revealed in the depressed versus non-depressed CD groups. Higher proportions of Th1 and Th17 cells with a lower proportion of Treg cell were observed after cocultured with monocytes from the depressed versus non- depressed CD patients. So were the expressions of their corresponding transcription factors T-bet, Retinoic Acid Related Orphan Nuclear Receptor gamma T (ROR gamma t) and Forkhead box protein P3 (FoxP3). Caco-2 cells cocultured with macrophages from depressed CD displayed lower Transepithelial electric resistance (TEER), reduced proliferation activity, and decreased tight junction protein expressions compared with their counterpart cocultured with macrophages from non- depressed CD. Conclusions: Monocyte/macrophage may underlie the impact of depression upon CD via decreased phagocytosis, increased pro-inflammatory cytokine production, inducing CD4 + T cell differentiation toward Th1/Th17 cells rather than Treg cell, and impairing macrophage-enhanced epithelial barrier.

Automated summary

This study investigated the mechanism of the impact of depression on Crohn's disease (CD) and found that monocytes/macrophages in blood and intestine play significant roles in both depression and CD. These cells mediate the effects of depression on CD through modulation of CD4+ T lymphocyte differentiation, epithelial barrier dysfunction, phagocytic ability, and cytokine production.