Immunomodulation by 17β-Estradiol in bivalve hemocytes

In mammals, estrogens have both doseand cell-type specific effects on immune cells and may act as pro-inflammatory and anti-inflammatory stimuli depending on the setting. Evidence has been provided that in the bivalve mollusc Mytilus the natural estrogen 17β-estradiol (E2) can affect neuro-immune functions. In this work the immunomodulatory role of E2 in Mytilus hemocytes, the cells responsible for the innate immune response, was investigated. E2, in a narrow concentration range (5-25 nM), rapidly stimulated phagocytosis and oxyradical production in vitro; higher concentrations inhibited phagocytosis. E2-induced oxidative burst was prevented by the nitric oxide synthase inhibitor L-NMMA and by SOD, indicating the involvement of both NO and O2; NO production was confirmed by nitrite accumulation. The effects of E2 were prevented by the antiestrogen Tamoxifen and by specific kinase inhibitors, indicating a receptor-mediated mechanism and involvement of p38 MAPK and PKC. E2 induced rapid and transient increases in the phosphorylation state of PKC, as well as of a CREB-like transcription factor, as indicated by WB with specific anti-phospho-antibodies. Localization of ERαand ERβ-like proteins in hemocytes was investigated by immunofluorescence confocal microscopy. The effects of E2 on the immune function were also investigated in vivo, at longer exposure times (6 and 24 hrs) in the hemocytes of E2-injected mussels. E2 significantly affected hemocyte lysosomal membrane stability, phagocytosis and extracellular release of hydrolytic enzymes: lower concentrations resulted in immunostimulation, whereas higher concentrations were inhibitory. Overall, the obtained data indicate that the physiological role of E2 in immunomodulation is conserved from invertebrates to mammals.