In vivo effects of propolis, a honeybee product, on gilthead seabream innate immune responses Alberto Cuesta, Alejandro Rodrı´guez, M. A ´ ngeles Esteban*, Jose´ Meseguer Department of Cell Biology, Faculty of Biology, University of Murcia, 30100 Murcia, Spain Received 5 April 2004; accepted 4 June 2004 Abstract The potential effect of the intraperitoneal or dietary administration of propolis, a honeybee product, on gilthead seabream (Sparus aurata L.) innate immune responses was evaluated. Fish were intraperitoneally injected with 5 mg of water (WEP), ethanol (EEP) or both (WEP C EEP) extracts of propolis and sampled after 1, 3, 5 and 10 days. When administered in the diet, propolis was dissolved in ethanol and added to a pellet diet at a concentration of 0, 0.1 or 10 g kg ÿ1 diet, the fish being sampled after 1, 2, 4 and 6 weeks of feeding. Humoral (alternative complement activity and peroxidase content) and cellular (leucocyte peroxidase, phagocytosis, cytotoxicity and respiratory burst activity) immune responses were evaluated in both cases. The results suggest that propolis has limited immunostimulatory effects although intraperitoneal administration was more effective than dietary intake. The effects that were noted were at cellular level, namely, phagocytosis and cytotoxicity. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Propolis; Immunostimulants; Innate immunity; Leucocytes; Gilthead seabream (Sparus aurata L.); Teleosts 1. Introduction Propolis (bee glue) is a natural dark-coloured, resinous sticky substance produced by honeybees by mixing their own waxes with resins collected from plants, and is used as a sealant and sterilant in their nests. Propolis has been used since ancient times as a medicine because of its biological properties as an antimicrobial, antifungal, antiprotozoan and antiviral agent [1]. Its chemical composition includes more than 180 compounds (Table 1), so its biological properties are diverse [1]. As regards its role on the immune * Corresponding author. Tel.: C34 968 367 655; fax: C34 968 363 963. E-mail address: aesteban@um.es (M.A ´ . Esteban). 1050-4648/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.fsi.2004.06.002 Fish & Shellfish Immunology 18 (2005) 71e80 www.elsevier.com/locate/fsi