Serum-borne H-Y antigen in the fetal bovine freemartin

In mammals, ovarian cells that have been exposed to soluble H-Y antigen acquire the H-Y+ cellular phenotype. They absorb H-Y antibody in serological tests. To determine whether masculinization of the bovine freemartin, the synchorial female twin of a bull, could be due to attachment of circulating bull-twin-derived H-Y in the freemartin gonad, we exposed normal fetal ovarian cells to serum from fetal bulls, fetal cows and fetal freemartins. Ovarian target cells became H-Y+ after exposure to serum from fetal bulls or fetal freemartins, but not after exposure to serum from fetal cows. In a new competitive binding radioassay, uptake of Daudi-secreted tritiated H-Y was inhibited in fetal ovarian target cells first exposed to mouse testis supernatant, a demonstrated source of soluble H-Y. It was also inhibited in ovarian target cells exposed to serum from fetal bulls or fetal freemartins; uptake was unaffected by exposure to serum from fetal cows. Since Daudi-secreted H-Y is known to induce precocious testicular organogenesis in XX indifferent gonads in culture, we infer that initial transformation of the freemartin gonad is due to H-Y antigen that is secreted in the fetal bull, transmitted in the common chorionic vasculature and bound by gonadal receptors of the fetal cow.