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      Inflammation and Immunity in Radiation Damage to the Gut Mucosa

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          Abstract

          Erythema was observed on the skin of the first patients treated with radiation therapy. It is in particular to reduce this erythema, one feature of tissue inflammation, that prescribed dose to the tumor site started to be fractionated. It is now well known that radiation exposure of normal tissues generates a sustained and apparently uncontrolled inflammatory process. Radiation-induced inflammation is always observed, often described, sometimes partly explained, but still today far from being completely understood. The thing with the gut and especially the gut mucosa is that it is at the frontier between the external milieu and the organism, is in contact with a plethora of commensal and foreign antigens, possesses a dense-associated lymphoid tissue, and is particularly radiation sensitive because of a high mucosal turnover rate. All these characteristics make the gut mucosa a strong responsive organ in terms of radiation-induced immunoinflammation. This paper will focus on what has been observed in the normal gut and what remains to be done concerning the immunoinflammatory response following localized radiation exposure.

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          Most cited references67

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          Endothelial apoptosis as the primary lesion initiating intestinal radiation damage in mice.

          Gastrointestinal (GI) tract damage by chemotherapy or radiation limits their efficacy in cancer treatment. Radiation has been postulated to target epithelial stem cells within the crypts of Lieberkühn to initiate the lethal GI syndrome. Here, we show in mouse models that microvascular endothelial apoptosis is the primary lesion leading to stem cell dysfunction. Radiation-induced crypt damage, organ failure, and death from the GI syndrome were prevented when endothelial apoptosis was inhibited pharmacologically by intravenous basic fibroblast growth factor (bFGF) or genetically by deletion of the acid sphingomyelinase gene. Endothelial, but not crypt, cells express FGF receptor transcripts, suggesting that the endothelial lesion occurs before crypt stem cell damage in the evolution of the GI syndrome. This study provides a basis for new approaches to prevent radiation damage to the bowel.
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            Interleukin-22 protects intestinal stem cells from immune-mediated tissue damage and regulates sensitivity to graft versus host disease.

            Little is known about the maintenance of intestinal stem cells (ISCs) and progenitors during immune-mediated tissue damage or about the susceptibility of transplant recipients to tissue damage mediated by the donor immune system during graft versus host disease (GVHD). We demonstrate here that deficiency of recipient-derived IL-22 increased acute GVHD tissue damage and mortality, that ISCs were eliminated during GVHD, and that ISCs as well as their downstream progenitors expressed the IL-22 receptor. Intestinal IL-22 was produced after bone marrow transplant by IL-23-responsive innate lymphoid cells (ILCs) from the transplant recipients, and intestinal IL-22 increased in response to pretransplant conditioning. However, ILC frequency and IL-22 amounts were decreased by GVHD. Recipient IL-22 deficiency led to increased crypt apoptosis, depletion of ISCs, and loss of epithelial integrity. Our findings reveal IL-22 as a critical regulator of tissue sensitivity to GVHD and a protective factor for ISCs during inflammatory intestinal damage. Copyright © 2012 Elsevier Inc. All rights reserved.
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              Mast cells.

              Mast cells are found resident in tissues throughout the body, particularly in association with structures such as blood vessels and nerves, and in proximity to surfaces that interface the external environment. Mast cells are bone marrow-derived and particularly depend upon stem cell factor for their survival. Mast cells express a variety of phenotypic features within tissues as determined by the local environment. Withdrawal of required growth factors results in mast cell apoptosis. Mast cells appear to be highly engineered cells with multiple critical biological functions. They may be activated by a number of stimuli that are both Fc epsilon RI dependent and Fc epsilon RI independent. Activation through various receptors leads to distinct signaling pathways. After activation, mast cells may immediately extrude granule-associated mediators and generate lipid-derived substances that induce immediate allergic inflammation. Mast cell activation may also be followed by the synthesis of chemokines and cytokines. Cytokine and chemokine secretion, which occurs hours later, may contribute to chronic inflammation. Biological functions of mast cells appear to include a role in innate immunity, involvement in host defense mechanisms against parasitic infestations, immunomodulation of the immune system, and tissue repair and angiogenesis.
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                Author and article information

                Journal
                Biomed Res Int
                Biomed Res Int
                BMRI
                BioMed Research International
                Hindawi Publishing Corporation
                2314-6133
                2314-6141
                2013
                19 March 2013
                : 2013
                : 123241
                Affiliations
                Laboratory of Radiopathology and Experimental Therapeutics, Institute for Radiological Protection and Nuclear Safety, 31 Avenue de la Division Leclerc, 92262 Fontenay-aux-Roses, France
                Author notes

                Academic Editor: Silvia Gregori

                Article
                10.1155/2013/123241
                3614034
                23586015
                ae3e6983-c4d2-4085-a468-b98943560f0b
                Copyright © 2013 Agnès François et al.

                This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 30 October 2012
                : 18 February 2013
                Categories
                Review Article

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