Suppression of lymphocyte proliferation by ovarian cavity fluid from the viviparous fish Neoditrema ransonnetii (Perciformes; Embiotocidae)

As the fetus expresses paternal major histocompatibility complex molecules, viviparous vertebrates require sophisticated mechanisms to modulate maternal immunology to ensure successful pregnancy. We anticipated that ovarian cavity fluid (OCF) is likely to feature significantly in the modulation of ovarian cavity immunology. Consequently, we examined the effects of OCF upon leukocyte function in Neoditrema ransonnetii. OCF did not affect phagocytosis or superoxide production by phagocytes. However, OCF suppressed lymphocyte proliferation induced by ConA almost completely. As OCF contained PGE2 at high levels during late pregnancy, we also investigated the effect of PGE2 upon lymphocyte expansion. PGE2 exhibited negative effects upon lymphocyte mitogenesis in a dose-dependent manner (10–1000 ng/ml). PGE2 significantly suppressed lymphocyte proliferation when present at levels equivalent to that seen in OCF (30.2 ± 16.1 ∼ 185.4 ± 107.4 ng/ml). Data indicate that PGE2 is one of the key modulatory molecules of the maternal immune system ensuring successful pregnancy in this viviparous species.