Effects of polyamines on cellular innate immune response and the expression of immune-relevant genes in gilthead seabream leucocytes

It is well known that the polyamines spermidine and spermine, along with the diamine putrescine, are involved in many cellular processes and they are known to play an important role in the control of the innate immune response in higher vertebrates. However, to the best of our knowledge, no studies have focused on their immunological implications in other vertebrates, such as fish. For this reason, the effects of polyamines on the cellular innate immune response and immune-related gene expression were evaluated in vitro, using seabream head-kidney leucocytes (HKL). For this study, head-kidney leucocytes were incubated with the polyamines putrescine, spermine or spermidine (0.005 and 0.0025%) for 0.50, 1, 2 or 4 h. No significant effect was observed on either leucocyte viability or the innate cellular immune responses (peroxidase content and phagocytic and respiratory burst activities). The polyamines produced an increase in respiratory burst and phagocytic ability when leucocytes were incubated principally with putrescine (0.005 and 0.0025%) after 2 and 4 h of the experiment. Finally, the expression levels of immune-associated genes (IgM, MHCIα, MHCIIα, C3, IL-1β, CD8, Hep, NCCRP-1, CSF-1 and TLR) were quantified by real-time PCR and some of them (C3, MHCI, CD8, IgM and Hep) were up-regulated by the higher polyamine concentration. Further studies are needed to ascertain how polyamines control the immune system of seabream as well as which mechanisms are involved.