Immune regulatory factors in sheep fetuses

After an antigenic stimulus in vitro, a fraction was found in the supernatant fluids of spleen (S-1) and thymus (T-1) cell cultures of 70 to 80-day-old sheep fetuses infected with ovine adenovirus in utero. The fraction agreed with alpha-1-fetoprotein in mobility and its molecular weight was 67 000. Injected into adult sheep, S-1 and T-1 had a suppressive effect on the humoral immune response to both adenovirus and Clostridium perfringens D vaccine. Tests with peripheral lymphocytes suggested that fetal cell supernatants do not affect blastogenesis but markedly inhibit Ig synthesis as it could be demonstrated by immunofluorescence tests.