Immunomodulatory effects of alpha melanocyte stimulating hormone on common carp (Cyprinus carpio L.) Hironobu Watanuki a , Masahiro Sakai b,* , Akiyoshi Takahashi c a United Graduate School of Agricultural Sciences, Kagoshima University, Korimoto 1-21-24, Kagoshima 890-0065, Japan b Faculty of Agriculture, Miyazaki University, 1-1 Gakuenkibanadai-nichi, Miyazaki City, Miyazaki 889-2192, Japan c School of Fisheries Sciences, Kitasato University, Iwate 022-01, Japan Received 31 December 2001; received in revised form 8 October 2002; accepted 1 November 2002 Abstract The immunomodulatory effects of phagocytic cells in common carp Cyprinus carpio L., by alpha melanocyte stimulating hormone (a-MSH) was analyzed in vitro. Carp head kidney leucocytes were cultured in RPMI 1640 medium containing 0.05, 0.1, 1 and 10 nM a-MSH and the production of superoxide anion was measured via the reduction of nitroblue tetrazolium (NBT) in vitro. Macrophages incubated with a-MSH showed an increase in the production of superoxide anion in comparison to control macrophages cultured without hormone. Phagocytic cells treated with a-MSH also displayed increased phagocytosis. Furthermore, carp lymphocytes treated with a-MSH increased the mitogenic responses to phytohaemoagglutinin (PHA-P). These results show that a-MSH directly influences fish immune responses. # 2002 Elsevier Science B.V. All rights reserved. Keywords: a-MSH; Carp; Phagocytosis; Lymphocyte proliferation 1. Introduction Pro-opiomelanocortin (POMC) products have long been established to be key players in neuro-endocrine immune networks. In mammals, these melanocortins are generated not only in the pituitary, but also in B and T lymphocytes and epidermal cells like keratino- cytes, melanocytes and Langerhans cells (Bhardwaj et al., 1996). These are known to have various functions includ- ing thermoregulatory, neuro-endocrine, pigmentary, cardiovascular, cognitive, behavioral, lipolytic and immunomodulatory activities (Luger et al., 1998). Alpha melanocyte stimulating hormone (a-MSH) has been recognized as a potent immunomodulatory agent. It inhibits the production and activity of immu- noregulatory and pro-inflammatory cytokines such as interleukin (IL)-1, IL-2, interferon (IFN)-g and down- regulates the expression of co-stimulatory molecules (B7) on antigen-presenting cells. It also has been reported to be a potent inducer of inhibitory mediators such as the cytokine synthesis inhibitory factor IL-10 (Luger et al., 1998; Bhardwaj et al., 1996). Further, Luger et al. (1998) has reported that a-MSH has an immunostimulatory effect by increasing the produc- tion of immunoglobulin E (IgE), mast cell degranula- tion, natural killer (NK) cell activity and cytokines. Veterinary Immunology and Immunopathology 91 (2003) 135–140 * Corresponding author. Tel: þ81-985-58-7219; fax: þ81-985-58-7219. E-mail address: m.sakai@cc.miyazaki-u.ac.jp (M. Sakai). 0165-2427/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0165-2427(02)00309-4