Inflammatory bowel diseases (IBDs) are recurrent intestinal pathologies characterized by a compromised epithelial barrier and an exaggerated immune activation. Mediators of immune cell infiltration may represent new therapeutic opportunities.
Metallothioneins (MTs) are stress-responsive
proteins with immune-modulating functions.
Metallothioneins have been linked to IBDs, but their role in intestinal
inflammation is inconclusive. We investigated MT expression in colonic biopsies from IBDs and acute infectious
colitis patients and healthy controls and evaluated MT's role in experimental
colitis using MT knockout mice and anti-MT
antibodies. Antibody potential to target extracellular MT and its mechanism was tested in vitro. Biopsies of patients with active
colitis showed infiltration of MT-positive cells in a pattern that correlated with the grade of
inflammation. MT knockout mice displayed less severe acute
dextran sulphate
sodium (DSS)-induced
colitis compared to congenic wild-type mice based on survival,
weight loss, colon length, histological
inflammation and leukocyte infiltration. Chronic DSS-
colitis confirmed that Mt1 and Mt2 gene disruption enhances clinical outcome. Blockade of extracellular MT with
antibodies reduced F4/80-positive macrophage infiltration in DSS- and trinitrobenzene sulphonic
acid-
colitis, with a tendency towards a better outcome. Whole-body single-photon emission computer tomography of mice injected with radioactive anti-MT
antibodies showed antibody accumulation in the colon during
colitis and clearance during recovery. Necrotic and not apoptotic cell death resulted in western blot MT detection in HT29 cell supernatant. In a Boyden chamber migration assay, leukocyte attraction towards the necrotic cell supernatant could be abolished with anti-MT antibody, indicating the chemotactic potential of endogenous released MT. Our results show that human
colitis is associated with infiltration of MT-positive inflammatory cells. Since antibody blockade of extracellular MT can reduce
colitis in mice, MT may act as a danger signal and may represent a novel target for reducing leukocyte infiltration and
inflammation in IBD patients.