Immunomodulation by 17β-estradiol in bivalve hemocytes

In mammals, estrogens have dose- and cell-type-specific effects on immune cells and may act as pro- and anti-inflammatory stimuli, depending on the setting. In the bivalve mollusc Mytilus, the natural estrogen 17 beta-estradiol (E-2) has been shown to affect neuroimmune functions. We have investigated the immunomodulatory role of E2 in Mytilus hemocytes, the cells responsible for the innate immune response. E2 at 5-25 nM rapidly stimulated phagocytosis and oxyradical production in vitro; higher concentrations of E-2 inhibited phagocytosis. E-2-induced oxidative burst was prevented by the nitric oxide ( NO) synthase inhibitor N-G-monomethyl-L-arginine and superoxide dismutase, indicating involvement of NO and O-2(-); NO production was confirmed by nitrite accumulation. The effects of E-2 were prevented by the antiestrogen tamoxifen and by specific kinase inhibitors, indicating a receptor-mediated mechanism and involvement of p38 MAPK and PKC. E-2 induced rapid and transient increases in the phosphorylation state of PKC, as well as of a aCREB-like ( cAMP responsive element binding protein) transcription factor, as indicated by Western blot analysis with specific anti-phospho-antibodies. Localization of estrogen receptor-alpha- and -beta-like proteins in hemocytes was investigated by immunofluorescence confocal microscopy. The effects of E2 on immune function were also investigated in vivo at 6 and 24 h in hemocytes of E-2-injected mussels. E-2 significantly affected hemocyte lysosomal membrane stability, phagocytosis, and extracellular release of hydrolytic enzymes: lower concentrations of E-2 resulted in immunostimulation, and higher concentrations were inhibitory. Our data indicate that the physiological role of E-2 in immunomodulation is conserved from invertebrates to mammals.