The seasonal changes in innate immunity of the common carp (Cyprinus carpio) Soňa Buchtíková a, 1 , Andrea Šimková b , Karolína Rohlenová b , Martin Flajšhans c , Antonín Lojek a, d , Esa-Matti Lilius e , Pavel Hyršl a, ⁎ , 1 a Institute of Experimental Biology, Faculty of Science, Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic b Department of Botany and Zoology, Faculty of Science, Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic c University of South Bohemia in České Budějovice, Faculty of Fisheries and Protection of Waters, South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses, Zátiší 728/II, Vodňany, Czech Republic d Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Královopolská 135, 61265 Brno, Czech Republic e Department of Biochemistry and Food Chemistry, University of Turku, 20014 Turku, Finland abstract article info Article history: Received 7 April 2010 Received in revised form 22 April 2011 Accepted 5 May 2011 Available online 13 May 2011 Keywords: Cyprinus carpio Respiratory burst Phagocytes Complement Innate immunity 11-Ketotestosterone The innate immune response in fishes includes both cellular (phagocytes) and humoral (complement system mainly) components. In fish, as in mammals, reactive oxygen metabolites (ROM) are involved in the respiratory burst of phagocytes and three pathways of complement activation can be discerned. The aim of this study was to analyze the innate immune response of fish using parameters such as respiratory burst of phagocytes and the complement activity of plasma of the common carp (Cyprinus carpio, Cyprinidae). Samples from a total of 160 individuals were collected in five periods of the year (early summer, late summer, autumn, winter and spring). Respiratory burst activity of a constant blood volume was measured luminometrically and also calculated per phagocyte number. A trend of negative relation between respiratory burst activity and water temperature was observed, thus the respiratory activity reached the lowest values in summer. Total complement activity of plasma was determined as bacteriolytic activity against bioluminescent bacteria. The highest total complement activity was observed in autumn, it decreased in summer and winter and the lowest activity was detected in spring. The highest activity of alternative pathway of complement activation was detected in spring, which decreased in autumn and the lowest values were found in winter and in summer. To evaluate the effect of steroid hormones, the level of 11-ketotestosterone was analyzed in males and the maximum was found in spring. A negative correlation was found between 11-ketotestosterone and both respiratory burst and total complement activity. Our results indicate that the measured parameters of innate immunity in the common carp are strongly affected by seasonal changes. Moreover, we confirmed that the innate immune response is immuno-suppressed by 11-ketotestosterone in spring. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The immune system of the teleost fish contains various mecha- nisms of non-specific (innate or natural) immunity and specific (acquired or adaptive) immunity that determine resistance against pathogenic or parasitic organisms (Du Pasquier, 1993). The non- specific immune response of fish includes cellular (phagocytes) and humoral components (complement system mainly) or the systemic inflammation; specific defence includes cellular (stimulated lympho- cytes) and humoral (immunoglobulins) factors (Bols et al., 2001). The immunoglobulins known in fish include mainly IgM, although IgD (Harding et al., 1990; Hirono and Aoki, 2003; Hordvik et al., 1999; Stenvik and Jørgensen, 2000; Wilson et al., 1997) and even IgZ and IgT (Danilova et al., 2005; Hansen et al., 2005; Savan et al., 2005) have also been recently described. The phagocytes (granulocytes, monocytes or macrophages) are considered to be the non-specific cellular factors of the immune system elaborated against pathogens which overcome the natural barriers. In fish, as in mammals, the stimulation of the phagocyte cell membrane with accompanying activation of the membrane associat- ed NADPH-oxidase initiates increased oxygen consumption and production of reactive oxygen species (ROS) with microbicidal activity in a process termed as the respiratory burst (RB). Production of several ROS, such as the superoxide anion radical (O 2 - ), hydrogen peroxide (H 2 O 2 ), singlet oxygen (1O 2 ) and the hydroxy radical (OH - ), has been reported in fish (Halliwell and Whiteman, 2004; Tarpey and Fridovich, 2001; Tarpey et al., 2004). Complement and lytic enzymes (including lysozyme) play an important role of natural defence against pathogens. The complement system is composed of more than 30 individual proteins. In general, Aquaculture 318 (2011) 169–175 ⁎ Corresponding author at: Department of Animal Physiology and Immunology, Institute of Experimental Biology, Faculty of Science, Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic. Tel.: +420 532 146 211; fax: +420 541 211 214. E-mail address: hyrsl@mail.muni.cz (P. Hyršl). 1 Contributed equally. 0044-8486/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2011.05.013 Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online