Short communication Effect of sex-steroid hormones, testosterone and estradiol, on humoral immune parameters of gilthead seabream A. Cuesta a , L. Vargas-Chacoff b , A. Garcı ´a-Lo ´pez c , F.J. Arjona b , G. Martı ´nez-Rodrı ´guez c , J. Meseguer a , J.M. Mancera b , M.A. Esteban a, * a Department of Cell Biology, Faculty of Biology, University of Murcia, 30100 Murcia, Spain b Department of Biology, Faculty of Marine Sciences, University of Cadiz, 11510 Puerto Real, Ca ´diz, Spain c Andalusian Institute for Marine Sciences, CSIC, 11510 Puerto Real, Ca ´diz, Spain Received 13 November 2006; revised 9 January 2007; accepted 11 January 2007 Available online 23 January 2007 Abstract The role of sex-steroid hormones, testosterone (T) and 17b-estradiol (E2), on the humoral immune parameters of the teleost gilthead seabream Sparus aurata was studied attempting to deepen on the knowledge of the immuneereproductive system inter- actions. Fish were injected intraperitoneally with coconut oil containing different dosages of T (0, 2, or 5 mgg 1 body weight [bw]) or E2 (0, 1, or 2 mgg 1 bw) and sampled 1, 3, and 7 days later. Hormonal levels and immune parameters (complement, peroxidase and antiprotease activities and IgM levels) were determined in plasma. Plasma hormone levels peaked at 1 day post-injection de- creasing thereafter. Treatment with T significantly increased both complement and peroxidase activities after 3 days of injection but antiprotease activity and IgM levels remained unchanged. Treatment with E2 enhanced complement activity 1 day post-injection while decreased it after 3 and 7 days. However, peroxidase activity increased at 3 and 7 days post-injection while total IgM levels decreased. Implications of T and E2 in the immune-reproductive system interactions were discussed. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Testosterone; Estradiol; Immune-reproductive system; Complement; IgM; Teleosts; Gilthead seabream In addition to their role in fish reproduction, sex-steroids are known to be involved in fish growth [1], digestion and food utilization [2], gut transport [3], shifts in body composition [4], intermediary metabolism [5], osmoregulation [6,7] and immunity [8e15]. Focusing on the last one, sex-steroid hormones, such as 17b-estradiol (E 2 ) or testosterone (T), affect mammalian specific and non-specific defence responses [16] while several cytokines have been related to the growth and development of follicles, ovulation, luteal development, spermatogenesis and steroidogenesis [17]. Although some information exists confirming similar patterns in teleost fish less attention has been paid to this group of vertebrates. In rainbow trout, Oncorhynchus mykiss, the elevation of sex-steroids (E 2 and T in females, and T and 11-ketotestosterone [11-KT] in males during sexual maturation) was correlated with immunosuppression and in- creased disease susceptibility, likely due to the decreased antibody secreting cells and circulating levels [8e10], * Corresponding author. Tel.: þ34 968367665; fax: þ34 968363963. E-mail address: aesteban@um.es (M.A. Esteban). 1050-4648/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.fsi.2007.01.015 www.elsevier.com/locate/fsi Fish & Shellfish Immunology 23 (2007) 693e700