1. Vincent Center for Reproductive Biology, Department of Obstetrics and Gynecology (S.F.C., T.M., M.P.L., J.L.T., B.R.R.), Massachusetts General Hospital/Harvard Medical School, Boston, Massachusetts 02114
2. Departamento De Clínica De Grandes Animais (S.F.C., P.B.D.G.), Universidade Federal De Santa Maria, Faculdade de Medicina Veterinária, Rio Grande do Sul, Brazil
3. Section of Immunobiology and Howard Hughes Medical Institute (R.A.F.), Yale University School of Medicine, New Haven Connecticut 06510