Non-HLDA8 animal homologue section anti-leukocyte mAbs tested for reactivity with equine leukocytes Sherif Ibrahim a , Falko Steinbach a,b, * a Institute for Zoo and Wildlife Research, Alfred Kowalke Str. 17, 10315 Berlin, Germany b Virology Department, Veterinary Laboratories Agency (VLA), Woodham Lane, New Haw, Addlestone, Surrey KT15 3NB, UK Abstract In addition to the 379 monoclonal antibodies (mAbs) tested in the animal homologues section of HLDA8, another 155 mAbs were screened at the Institute for Zoo and Wildlife Research, Berlin for cross-reactivity with equine leukocytes. For this purpose, one colour flow-cytometric analysis was performed as screening test. This additional screening indicated further 16 mAbs as positive with staining homologous to human pattern, 1 mAb with weak (positive) reactivity, 11 mAbs with positive, but likely not valuable staining, 12 mAbs with alternate expression pattern from that expected from human immunology, 2 mAbs with questionable variable staining, 13 mAbs with weak-positive expression and alternate pattern, and 78 negative mAbs. In 23 cases, more appropriate target cells, such as thymocytes or stem cells, were not available for screening. The results support and add to the value of the ‘‘cross-reactivity’’ approach for equine immunology. Crown Copyright # 2007 Published by Elsevier B.V. All rights reserved. Keywords: Horse; Immunology; Leukocyte differentiation 1. Introduction Well characterized, commercially available, mono- clonal antibodies directed against surface antigens of human cells are an important tool for veterinary immunology (e.g. Steinbach et al., 2002; Saalmu ¨ller et al., 2005). Based on this knowledge, anti-human monoclonal antibodies were tested for their reactivity against equine immune cells to broaden the toolbox for equine immunology. In the present study, we used flow-cytometry to screen mAbs obtained in addition to the mAb derived from the animal homologues section of the 8th international workshop on Human Leukocyte Differ- entiation Antigens (HLDA8). These mAbs again were tested for reactivity on equine leukocytes and platelets. Taking into account that some of the previous descriptions of cross-reactive mAbs were not confirmed later, we put strong emphasis on the comparability of equine and human staining patterns and on data and experiences using human cells. Some of the mAbs analysed have been described before and were used as controls – but also for re-analysis. Only mAbs that stained comparable to human leukocytes in several consecutive tests with independent animals were finally assigned ‘‘positive’’ in this study. The study comple- ments the HLDA8 equine part (Ibrahim et al., 2007) and the positive mAbs were later added to further analysis such as double labelling or immunohistochemistry (Flaminio et al., 2007). www.elsevier.com/locate/vetimm Veterinary Immunology and Immunopathology 119 (2007) 81–91 * Corresponding author at: Virology Department, Veterinary Laboratories Agency (VLA), Woodham Lane, New Haw, Addlestone, Surrey KT15 3NB, UK. Tel.: +44 1932 357 566; fax: +44 1932 357 239. E-mail address: f.steinbach@vla.defra.gsi.gov.uk (F. Steinbach). 0165-2427/$ – see front matter. Crown Copyright # 2007 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.vetimm.2007.06.033