Short communication Glucan receptor but not mannose receptor is involved in the phagocytosis of Saccharomyces cerevisiae by seabream (Sparus aurata L.) blood leucocytes M.A. Esteban*, A. Rodrı ´guez, J. Meseguer Department of Cell Biology, Faculty of Biology, University of Murcia, 30100 Murcia, Spain Received 14 April 2003; accepted 14 July 2003 Keywords: Mannose-receptor; Glucan-receptor; Phagocytosis; Saccharomyces cerevisiae; Blood leucocytes; Gilthead seabream (Sparus aurata L.); Teleosts; Flow cytometry Glycoproteins and glycoconjugates of higher organisms have N-linked oligosaccharide chains, in which either mannose or glucose is practically never found in the terminal position, except for lysosomal hydrolases [1]. In contrast, lower organisms possess abundant mannose, glucose and other sugars on their surface. During their evolution, higher organisms have acquired the ability to recognise these sugars through specific receptors, called lectin-like receptors. These receptors constitute an essential part of the host defense system because they are involved in phagocytosis of infectious agents and in the internalisation of parasites that manage to survive and replicate inside the immune cells, mainly macrophages [2]. Among lectin-like receptors the most studied is the mannose-receptor, whose expression is highly regulated and correlates with the functional state of the monocyte/macrophage. In other words, resting macrophages express higher levels than activated macrophages [3] while blood monocytes show no mannose-receptors [4,5]. Another studied lectin-like receptor is the glucan-receptor, which is expressed in both blood monocytes and macrophages, as well as in blood granulocytes [6,7]. In spite of the importance of the phagocytic process as the main immune defensive mechanism in fish, very few papers have focused on the lectin-like receptors which mediate phagocytosis by fish leucocytes [8–10], and, to our knowledge, there are no works on these receptors in fish blood leucocytes. In a previous work carried out in the same fish species, we demonstrated that a mannose-receptor is involved in the phagocytosis of Saccharomyces cerevisiae by head-kidney leucocytes [10]. The aim of the present study was to elucidate the possible presence of a lectin-like receptor in gilthead seabream (Sparus aurata L.) blood phagocytes by studying any role it might have in the binding and internalisation of heat killed Saccharomyces cerevisiae cells, in order to ascertain whether the expression of this receptor in fish is as tightly modulated during monocyte/macrophage differentiation as in higher vertebrates. For that, gilthead seabream (Sparus aurata L.) (weight 17520 g) obtained from Culmarex S.A. (Murcia, Spain) were kept in running seawater aquaria, at 202 (C, with a natural photoperiod and fed * Corresponding author E-mail address: aesteban@um.es (M.A. Esteban). Fish & Shellfish Immunology 16 (2004) 447–451 Fish & Shellfish Immunology www.elsevier.com/locate/fsi 1050-4648/04/$ - see front matter  2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.fsi.2003.07.004