Journal of Toxicology and Environmental Health, Part A, 67:555–582, 2004 Copyright© Taylor & Francis Inc. ISSN: 1528–7394 print / 1087–2620 online DOI: 10.1080/15287390490425597 555 DOES HIGH ORGANOCHLORINE (OC) EXPOSURE IMPAIR THE RESISTANCE TO INFECTION IN POLAR BEARS (Ursus maritimus)? Part I: EFFECT OF OCs ON THE HUMORAL IMMUNITY Elisabeth Lie, 1 Hans Jørgen S. Larsen, 2 Stig Larsen, 3 Grethe Marie Johansen, 2 Andrew E. Derocher, 4 Nicholas J. Lunn, 5 Ross J. Norstrom, 6 Øystein Wiig, 7 Janneche Utne Skaare 8 1 National Veterinary Institute, Oslo, Norway 2 The Norwegian School of Veterinary Science, Department of Food Safety and Infection Biology, Oslo, Norway 3 Norwegian School of Veterinary Science, Department of Large Animal Clinical Science, Epidemiological Section, Oslo, Norway 4 Norwegian Polar Institute, Tromsø, Norway 5 Canadian Wildlife Service, Edmonton, Alberta, Canada 6 Canadian Wildlife Service, National Wildlife Research Centre, Carleton University, Ottawa, Ontario, Canada 7 Zoological Museum, University of Oslo, Blindern Oslo, Norway 8 National Veterinary Institute, Norwegian School of Veterinary Science, Oslo, Norway This study was undertaken to assess if high levels of organochlorines (OCs) are associated with decreased ability to produce antibodies in free-ranging polar bears (Ursus maritimus) and thus affect the humoral immunity. In 1998 and 1999, 26 and 30 polar bears from Svalbard, Norway, and Churchill, Canada, respectively, were recaptured 32–40 d following immunization with inacti- vated influenza virus, reovirus, and herpes virus and tetanus toxoid. Blood was sampled at immun- ization and at recapture for determination of plasma levels of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs), serum immunoglobulin G (IgG) concentrations, and specific antibodies against influenza virus, reovirus, and herpes virus, tetanus toxoid, and Mannheimia haemolytica. The OCs alone contributed with up to 7% to the variations in the immunological parameters. The combination of ∑PCBs (sum of 12 individual PCB congeners), ∑OCPs (sum of 6 OCPs), and biological factors accounted for 40–60% of the variation in the immunological parameters. Negative associations were found between ∑PCBs and serum immunoglobulin G (IgG) levels and between ∑PCBs and increased antibody titers against influenza virus and reovirus following immunization. In contrast, a positive association was registered between ∑PCBs and increased antibodies against tetanus toxoid. ∑OCPs also contributed significantly to the variations Accepted 31 October 2003. The authors thank the Norwegian Research Council (NFR 125693/720 and 140730/720), the Norwegian Ministry of Environment Transport and Effect Programme, and the Toxic Substances Research Initiative in Canada for funding this study. The authors thank Tine Borgen for performing the serological analysis. Current address for Andrew E. Derocher is University of Alberta, Department of Biological Sciences, T6G 2E9 Edmonton, Alberta, Canada. Address correspondence to Janneche Utne Skaare, National Veterinary Institute, The Norwegian School of Veterinary Science, PO Box 8156, Dep. N-0033 Oslo, Norway. E-mail: janneche.skaare@vetinst.no