Arsenic-induced alterations in the contact hypersensitivity response in Balb/c mice Rachel Patterson, a Libia Vega, b Kevin Trouba, a Carl Bortner, a and Dori Germolec a, * a Laboratory of Molecular Toxicology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA b Cinvestav, National Polytechnical Institute, Mexico, D.F., 07360 Received 1 July 2003; accepted 8 October 2003 Available online 9 April 2004 Abstract Previous studies in our laboratory indicate that arsenic alters secretion of growth promoting and inflammatory cytokines in the skin that can regulate the migration and maturation of Langerhans cells (LC) during allergic contact dermatitis. Therefore, we hypothesized that arsenic may modulate hypersensitivity responses to cutaneous sensitizing agents by altering cytokine production, LC migration, and T-cell proliferation. To investigate this hypothesis, we examined the induction and elicitation phases of dermal sensitization. Mice exposed to 50 mg/l arsenic in the drinking water for 4 weeks demonstrated a reduction in lymph node cell (LNC) proliferation and ear swelling following sensitization with 2,4-dinitrofluorobenzene (DNFB), compared to control mice. LC and T-cell populations in the draining lymph nodes of DNFB-sensitized mice were evaluated by fluorescence-activated cell sorting; activated LC were reduced in cervical lymph nodes, suggesting that LC migration may be altered following arsenic exposure. Lymphocytes from arsenic-treated animals sensitized with fluorescein isothiocyanate (FITC) exhibited reduced proliferative responses following T-cell mitogen stimulation in vitro; however, lymphocyte proliferation from nonsensitized, arsenic-treated mice was comparable to controls. Arsenic exposure also reduced the number of thioglycollate-induced peritoneal macrophages and circulating neutrophils. These studies demonstrate that repeated, prolonged exposure to nontoxic concentrations of sodium arsenite alters immune cell populations and results in functional changes in immune responses, specifically attenuation of contact hypersensitivity. D 2004 Published by Elsevier Inc. Keywords: Arsenic; Contact hypersensitivity; Local lymph node assay; Flow cytometry Introduction Chronic exposure to inorganic arsenicals through con- taminated drinking water and inhalation has been associ- ated with disorders and neoplasias in multiple organ systems. The most severely impacted countries are Ban- gladesh and the West Bengal districts of India. The World Health Organization (WHO) estimates that 46–57 million people in Bangladesh consume water with arsenic con- centrations in excess of 10 Ag/l, the WHO standard (Gomez-Caminero et al., 2001; WHO, 1993). In the United States, 350, 000 people consume 50 Ag/l arsenic, the previous EPA standard (USEPA, 1987), and 13 million may be exposed to 10 Ag/l arsenic, the new standard (Gomez-Caminero et al., 2001; WHO, 1993; USEPA, 2001). Although exposure can occur through inhalation of arsenic-containing pesticides, wood preservatives, metal smelting chemicals, semiconductor compounds, and coal residue (Hall, 2002), and ingestion of arsenic containing pharmaceuticals and herbal remedies (Ernst, 2000; Wong et al., 1998), groundwater contamination is the primary means of human exposure. Chronic exposure to inorganic arsenic has been estab- lished as a key etiological component in the development of peripheral vascular disease and skin, lung, liver, bladder, kidney, and prostate cancer (Abernathy et al., 1999; Christensen and Poulsen, 1994; Cuzick et al., 1992; Rahman et al., 1996; Ryan et al., 2000; Wingren and Axleson, 1993). At least nine different possible modes of action of carcinogenesis have been proposed, 0041-008X/$ - see front matter D 2004 Published by Elsevier Inc. doi:10.1016/j.taap.2003.10.012 * Corresponding author. National Institute of Environmental Health Sciences, Environmental Immunology Lab, 111 TW Alexander Drive, PO Box 12233, Research Triangle Park, NC 27709. Fax: +1-919-541-0870. E-mail address: germolec@niehs.nih.gov (D. Germolec). www.elsevier.com/locate/ytaap Toxicology and Applied Pharmacology 198 (2004) 434– 443