LUTTON, B.L.*; CALLARD, I.P.; Boston University: Endocrine-Immune Interactions In The Little Skate, Leucoraja erinacea

The cartilaginous fish offer a novel approach to the study of endocrine-immune interactions. In these species the gonads are directly associated with a unique lymphomyeloid tissue, the epigonal organ. It is known that steroid hormones affect both the innate and acquired immune systems by up- or down-regulation of the cells and factors they produce. Also, the cells and factors of the immune system modulate various gonadal functions. In this study we have utilized various methods to elucidate the possibility of interactions between the epigonal organ and the ovaries of Leucoraja erinacea. To investigate effects of the epigonal organ on the ovary, co-cultures of increasing concentrations of epigonal leukocytes with consistent numbers of follicle wall cells were performed. Then, epigonal leukocytes were either left unstimulated or were treated with 10ug/ml lipopolysaccharide, and increasing concentrations of conditioned media and cell lysates were incubated with follicle wall cells. The results of radioimmunoassay from co-culture media showed concentration-dependent inhibition of estradiol (E₂) and testosterone (T) production from follicle wall cells. Treatment of follicle wall cells with conditioned media and cell lysates caused significant modulation of E₂ and T production. To investigate effects of the ovary on the epigonal organ, DNA fragmentation analysis was performed on epigonal leukocytes treated with 10^-5M steroids after 24 hours in culture. The results indicated an induction of apoptosis, with increasing magnitude by E₂< progesterone< T< dexamethasone. Because steroids induce apoptosis of epigonal leukocytes, and cells/factors from the epigonal organ appear to regulate steroidogenesis of the ovary, this study may be the first evidence for a bi-directional feedback system between the reproductive and immune systems of Leucoraja erinacea.