Hindawi Publishing Corporation Bone Marrow Research Volume 2011, Article ID 579268, 3 pages doi:10.1155/2011/579268 Research Article Hyperbaric Oxygen Therapy as a Sole Agent Is Not Immunosuppressant in a Highly Immunogenic Mouse Model Adam Gassas,1 Weixian Min,2 A. Wayne Evans,3 Susan Carter,4 George K. S a´ndor,5, 6 and Eyal Grunebaum2 1 Division of Haematology/Oncology/BMT, The Hospital for Sick Children, University of Toronto, 555 University Avenue, Toronto, ON, Canada M5G 1X8 2 Division of Immunology and Allergy, The Hospital for Sick Children, University of Toronto, ON, Canada M5G 1X8 3 Hyperbaric Medicine Unit, University Health Network, Toronto General Hospital, Faculty of Medicine, University of Toronto, ON, Canada M5G 2C4 4 Animal Facilities, Faculty of Dentistry, University of Toronto, Toronto, ON, Canada M5G 1G6 5 Oral and Maxillofacial Surgery, University of Toronto, Toronto, ON, Canada M5G 1G6 6 Tissue Engineering, Regea Institute for Regenerative Medicine, University of Tampere, 33520 Tampere, Finland Correspondence should be addressed to Adam Gassas, adam.gassas@sickkids.ca Received 7 May 2010; Accepted 18 June 2010 Academic Editor: Axel R. Zander Copyright © 2011 Adam Gassas 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. Background. Hyperbaric oxygen (HBO) therapy, which is used for many conditions, may also have immunosuppressive eﬀects and could be used for prevention or treatment of graft-versus-host disease (GvHD). If HBO is immunosuppressant, then we hypothesize that HBO therapy will delay the T-cell mediated skin graft rejection. Methods. C57/BL6 black-coated (H2B) mice received skin graft from CBA (H2D) white-coated mice. Mice were treated with either 19 session of 240 kpa oxygen or 29 session of 300 kpa oxygen, for 90 minutes. Mice were housed either 4 per cage or separately, to prevent friction and mechanical factors that may aﬀect graft survival. Skin grafts were assessed daily. Results. There was no diﬀerence in length of graft survival between mice that received either regimens of HBO therapy and mice that did not receive HBO therapy. Conclusions. HBO therapy, as a sole agent, did not delay skin graft rejection in a highly immunogenic mouse model. 1. Introduction Exposure to HBO therapy, at least in rodents, appears to be immunosuppressant and leads to an anti-inﬂammatory eﬀect. Several mechanisms have been proposed; inhibition of interferon-γ [1], interleukin-1 β, and tumor necrosis factor α release [2], a temporary drop in the CD4 : CD8 lymphocyte ratio [3], and a decrease of lymphocyte prolifer- ation [4]. As a result, HBO exposure attenuates the immune system, increases the susceptibility to respiratory infections [5, 6], and delays allograft rejection in mice [7–9]. On the contrary, other reports suggest no immunosuppressant eﬀect of HBO or even immunostimulant eﬀect in particular neutrophiles activation [10, 11]. At present, there is a wide spectrum of indications for HBO therapy. According to the Undersea and Hyperbaric Medical Society, HBO therapy is indicated for carbon monoxide poisoning and gas embolism [12], clostridial myonecrosis [13], compartment syndrome and other traumatic ischemia with nonhealing wounds [14], necrotizing soft tissue infections, sepsis, and others [15–18]. Given the increasing availability of HBO therapy in recent years and the rarity of serious side eﬀects, HBO therapy as an immunosuppressant is an attractive option. Perhaps, HBO therapy could be added to prevent or to treat GvHD in allogeneic hematopoietic stem cell transplantation (HSCT). Therefore, our aim was to test the eﬀect of HBO therapy on the immune system by measuring the integrity and the duration of skin allo- geneic graft in mice. Graft rejection is a T-cell mediated phenomenon, and if HBO therapy is immunosuppressant,