P036 Human peripheral blood monocytes and intestinal macrophage populations activate transforming growth factor beta via expression of the integrin alpha v beta 8
Shuttleworth E.*1,2,3, Kelly A.1,2,3, Fenton T.1,2,3, Smedley C.1,2,3, Levison S.4, Travis M.1,2,3
1University of Manchester, MCCIR, Manchester, United Kingdom 2University of Manchester, Wellcome Trust Centre for Cell-Matrix Research, Manchester, United Kingdom 3University of Manchester, Manchester Immunology Group, Manchester, United Kingdom 4Central Manchester NHS Hospitals Foundation Trust, Department of Gastroenterology, Manchester, United Kingdom
Intestinal immune cells must be poised to clear invading pathogens while remaining tolerant to the trillions of commensal bacteria present in the gut, with perturbations in this process implicated in development of inflammatory bowel disease (IBD). The cytokine transforming growth factor beta (TGFβ) is a key factor in regulating intestinal immunity, but is secreted as an inactive complex that requires activation to function. Although recent data have established important ways that TGFβ activity is controlled in the mouse, the pathways present in humans remain unclear. Here we aimed to identify mechanisms regulating TGFβ activity in the human immune system, and establish the functional importance of TGFβ activation in intestinal homeostasis.
Healthy human peripheral blood mononuclear cells, monocyte-derived macrophages (MDMs), and colonic lamina propria cells from control and IBD patients were analysed by flow cytometry. Cells of interest were co-cultured with an active TGFβ reporter cell line to determine TGFβ activation.
Here, we show that human CD14+ blood monocytes activate high levels of TGFβ, which is not apparent with the equivalent murine monocytes. Mechanistically, we show that activation of TGFβ by CD14+ monocytes requires expression of the integrin, alpha v beta 8 (αvβ8). When monocytes are differentiated to MDMs, expression of αvβ8 and TGFβ activation was observed on MDMs cultured with M-CSF, which are proposed to represent a more anti-inflammatory macrophage population. In addition, integrin αvβ8 expression was increased on these cells by exposure to IL-10, TLR-4 and -7/8 ligands. In contrast, MDMs cultured with GM-CSF expressed lower levels of the integrin and activated minimal amounts of TGFβ. In the intestine, integrin αvβ8 is highly expressed on CD64+ macrophage population expressing CD163 and CD206, which are proposed to represent a more regulatory phenotype, and are decreased in patients with active Crohn's disease.
Our results suggest that expression of integrin αvβ8 by CD14+ monocytes may play an important role in the induction and function of anti-inflammatory macrophages in the intestine via TGFβ activation. Further work will provide important new insights into how myeloid cells regulate immune responses in the human intestine to maintain homeostasis and prevent IBD.