LUTTON, B.V.*; CALLARD, I.P.; Boston University: Endocrine-Immune Interactions and Reproduction in Elasmobranchs: Investigations of the Little Skate, Leucoraja erinacea

Bi-directional interactions between gonadal hormones and the cells and factors of the immune system are critical for reproduction and immune function. The elasmobranchs (sharks, skates, and stingrays) offer a unique approach to the study of such physiological interactions. These are the only species in which the gonads are directly associated with an autonomous immune tissue, the epigonal organ, and they are the first taxon in which all the components of the adaptive immune system are present. In this study we have begun to characterize the relationship between the epigonal organ and the ovaries of the little skate, Leucoraja erinacea. Timed arterial perfusions demonstrated a vascular pathway from the epigonal organ to the ovarian follicles, and corrosion casting further supported the direct vascular connection between the two tissues. Whole ovary sections were stained with hematoxylin and eosin, and microscopic analysis illustrated direct cellular contact between leukocytes of the epigonal organ and follicle wall cells of the ovary. Immunohistochemistry and in vitro experiments demonstrated that the hypothalamic-pituitary-gonadal axis appears to play a direct role in immune regulation via modulation of leukocyte turnover (proliferation and apoptosis), while the leukocytes and/or secreted factor(s) of the epigonal organ seem to regulate, at least in part, steroidogenesis from follicle wall cells. Interactions between sex hormones and the immune system have been implicated in autoimmune diseases and ovarian cancer, yet current studies continue to search for the mechanisms of action. The sharks, skates and stingrays serve as excellent models because they offer novel perspectives with regard to the evolution of physiological mechanisms.