ORIGINAL ARTICLE IL-5-overexpressing mice exhibit eosinophilia and altered wound healing through mechanisms involving prolonged inflammation Victoria D Leitch 1,3 , Xanthe L Strudwick 1 , Klaus I Matthaei 2 , Lindsay A Dent 3 and Allison J Cowin 1,4 Leucocytes are essential in healing wounds and are predominantly involved in the inflammatory and granulation stages of wound repair. Eosinophils are granulocytic leucocytes and are specifically regulated by interleukin-5 (IL-5), a cytokine produced by T helper 2 (Th2) cells. To characterize more clearly the role of the IL-5 and eosinophils in the wound healing process, IL-5-overexpressing and IL-5-deficient mice were used as models of eosinophilia and eosinophil depletion, respectively. Our results reveal a significantly altered inflammatory response between IL-5-overexpressing and IL-5 knockout mice post-wounding. Healing was significantly delayed in IL-5-overexpressing mice with wounds gaping wider and exhibiting impaired re-epithelialization. A delay in collagen deposition was observed suggesting a direct effect on matrix synthesis. A significant increase in inflammatory cell infiltration, particularly eosinophils and CD4 + cells, one of the main cell types which secrete IL-5, was observed in IL-5-overexpressing mice wounds suggesting that one of the main roles of IL-5 in wound repair may be to promote the infiltration of eosinophils into healing wounds. Healing is delayed in IL-5-overexpressing mice and this corresponds to significantly increased levels of eosinophils and CD4 + cells within the wound site that may contribute to and exacerbate the inflammatory response, resulting in detrimental wound repair. Immunology and Cell Biology (2009) 87, 131–140; doi:10.1038/icb.2008.72; published online 7 October 2008 Keywords: wound; eosinophil; IL-5 Wound healing is a complex process, vital for the maintenance and integrity of the skin. 1 Leucocytes are imperative in healing wounds and are predominantly involved in the inflammatory and granulation stages. Infiltration of macrophages, 1 neutrophils 2 and monocytes 3 into wounds occurs in a distinctive order 4 and while present in the wound they are responsible for phagocytosis of damaged tissue and invading pathogens, as well as secretion of chemo-attractants. In addition to these leucocytes, mast cells 5 and eosinophils 6 have also been implicated in the healing process. Eosi- nophils are granulocytic leucocytes normally present at low levels in the blood. Under normal conditions, eosinophils typically constitute 1–5% of white blood cells; 7,8 however, the exact function of the eosinophil remains elusive. Eosinophils have phagocytic ability and are present in high numbers in asthma, allergic responses and parasitic infections, 9 suggesting an involvement in the pathology or quite possibly in tissue homoeostasis and repair. The growth, differentiation, activation and survival of eosinophils are regulated by interleukin-5 (IL-5), a cytokine produced by T helper 2 (Th2) cells as well as by eosinophils and mast cells. Although earlier studies suggested additional activities of IL-5 in regulating mouse B cells and antibody production, recent studies using an IL-5-deficient mouse strain indicate that the regulation of eosinophilia may be the only obligatory role for IL-5 in the adult mouse. 10 Eosinophils have been recorded in the cutaneous wounds of mice, rabbits and hamsters, often in close proximity with fibroblasts. 6 Interaction of eosinophils with fibroblasts, causing proliferation 11 and matrix production, 12 along with the accumulation of eosinophils in fibrotic disorders, 13 suggests that eosinophils may influence the remodelling stages of wound healing. Interleukin-5-deficient mice produced by gene targeting of embry- onal stem cells appear normal and do not develop any obvious disease 10 but are resistant to induction of experimental asthma 14 and have impaired resistance to secondary infections with the hel- minth Nippostrongylus brasiliensis. 15 IL-5-deficient mice have near normal levels of baseline eosinophils; however, these eosinophils are less likely to infiltrate into the areas of disease or infection. 10 In contrast, IL-5-overexpressing mice have a more severe asthma phenotype and are highly resistant to primary infections with N. brasiliensis and Strongyloides ratti. 16,17 Received 26 May 2008; revised 28 August 2008; accepted 1 September 2008; published online 7 October 2008 1 Women’s and Children’s Health Research Institute, North Adelaide, South Australia; 2 Division of Molecular Bioscience, The John Curtin School of Medical Research, Canberra, ACT, Australia; 3 School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia and 4 Discipline of Surgery, University of Adelaide, Adelaide, South Australia Correspondence: Dr AJ Cowin, Women’s and Children’s Health Research Institute, 72 King William Road, North Adelaide 5066, South Australia. E-mail: allison.cowin@adelaide.edu.au Immunology and Cell Biology (2009) 87, 131–140 & 2009 Australasian Society for Immunology Inc. All rights reserved 0818-9641/09 $32.00 www.nature.com/icb