In vivo effects of 17-β-estradiol on plasma immunoglobulin levels and leukocyte density in zebrafish Danio rerio

Estradiol, or 17-beta-estradiol (E-2), the most potent naturally occurring estrogen, is involved in the hormone-immune system interaction in both mammals and fish. However, in vivo studies are largely limited, and little is known about whether E-2 exerts similar effects on both female and male zebrafish (Danio rerio). Here, we show exposure of both sexes of D. rerio to 20 nmol/L E-2 resulted in a significant increase in Vg1 expression, but caused little damage to the hepatocytes, suggesting that this is the optimum E-2 concentration. Also, exposure to 20 nmol/L E-2 for 20 days caused a marked increase in plasma IgM levels, but had little influence on the peripheral leukocyte density, providing the first evidence of a hormone-immune system interaction in this species.