Comparison of cellular and humoral immunoassays for the assessment of summer eczema in horses Kathrin F.A. Langner a, * , Karin E. Darpel b , Barbara S. Drolet c , Angelika Fischer a , Stefan Hampel a , Julia E. Heselhaus a , Philip S. Mellor b , Peter P.C. Mertens b , Wolfgang Leibold a a Immunology Unit, University of Veterinary Medicine, Bischofsholer Damm 15, 30173 Hannover, Germany b Pirbright Laboratory, Institute for Animal Health, Ash Road, Pirbright, Surrey GU24 0NF, UK c United States Department of Agriculture, Agricultural Research Service, Arthropod-Borne Animal Diseases Research Laboratory, 1000 E. University Avenue, Laramie, WY 82071, USA Received 28 August 2007; received in revised form 30 October 2007; accepted 1 November 2007 Abstract The objective of this study was to compare and analyze three common diagnostic methods for summer eczema (SE) in horses, an allergic dermatitis caused by bites of Culicoides spp. Nine horses with a medical history of SE and nine control animals were intradermally challenged with whole body extracts (WBE) and the saliva of a native (C. nubeculosus) and exotic (C. sonorensis) Culicoides species. Blood and serum samples of the horses were examined for basophil reactivity by a histamine release test (HRT) and for Culicoides-specific serum immunoglobulin E (IgE) and G (IgG) by enzyme-linked immunosorbent assay (ELISA). The results of intradermal testing (IDT) at 30 min (immediate reactivity) and 4 h (late-phase reactivity) post challenge with most insect preparations revealed significant differences between horses with and without SE. Overall, the HRT showed the most accurate results with a sensitivity of 1.00 for all Culicoides preparations and specificities of 0.78 (WBE) and 1.00 (saliva). By contrast, delayed reactions of the IDT (24 h), and levels of Culicoides-specific IgE and IgG in the native serum showed little or no distinction between allergic and non-allergic horses. However, the use of purified serum IgE and IgG indicated the possibility for elevated titers of insect-specific serum immunoglobulins in horses with SE. The IDT and HRT did not reveal obvious differences in onset and intensity of positive reactions for the native verses exotic Culicoides species, whereas the ELISA showed slightly higher numbers of positive reactions for serum IgG with the indigenous species. Saliva, as compared to WBE, was found to have improved sensitivity and/or specificity for the HRT and for the late-phase immune reactions as measured by the IDT. Overall, the results indicate that allergy tests utilizing effector cells (mast cells, basophils) are more accurate in diagnosing SE in horses than serological analysis by ELISA. # 2007 Elsevier B.V. All rights reserved. Keywords: Culicoides spp; Equine; Summer eczema; Skin testing; Histamine release test; Serological testing 1. Introduction Summer eczema (SE), also known as sweet itch or insect bite hypersensitivity, is a seasonal recurrent allergic dermatitis that affects a substantial number of horses worldwide (Anderson et al., 1988; Braverman, www.elsevier.com/locate/vetimm Available online at www.sciencedirect.com Veterinary Immunology and Immunopathology 122 (2008) 126–137 Abbreviations: IDT, intradermal test; HRT, histamine release test; ELISA, enzyme-linked immunosorbent assay; SE, summer eczema; SE+ horses, horses with summer eczema; WBE, whole body extract; Ig, immunoglobulin. * Corresponding author. Tel.: +49 511 856 7241; fax: +49 511 856 7682. E-mail address: kathrin.langner@tiho-hannover.de (K.F.A. Langner). 0165-2427/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.vetimm.2007.11.001