The seasonal changes in innate immunity of the common carp (Cyprinus carpio)

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.