Partial passive protection with two monoclonal antibodies and frequency offeeding of hyperimmune anti-transmissible gastroenteritis virus (TGEV) serum for protection of three-day-old piglets from a TGEV challenge infection

Passive protection experiments were conducted to determine the frequency an d amounts of hyperimmune antiserum needed to block a transmissible gastroen teritis virus (TGEV) challenge infection and to identify monoclonal antibod ies that are partially protective against TGEV. Hyperimmune antiserum or mo noclonal antibodies were added to milk at each feeding or at selected feedi ngs when the amount of antiserum was reduced. Three-day-old piglets were ch allenged with virulent virus that had been preincubated with antiserum or m onoclonal antibodies. The results indicated that supplementing antiserum ev ery other day was not efficacious for protection. Supplementing even small quantities of hyperimmune antiserum (0.5 ml) at least once a day in most ca ses was sufficient for piglet survival but did not prevent morbidity, Incre asing the amount (>2 ml) and providing, antiserum 3 times/day completely bl ocked the TGEV challenge infection. Two monoclonal, antibodies were discove red that also provided passive protection for baby pigs. One monoclonal ant ibody, 5G1, had a high neutralizing titer, and the other, 6C4, was more eff ective in neutralizing and binding to virulent TGEV than to attenuated TGEV s. Both of these monoclonal antibodies were partially effective as suppleme nts in milk for passive protection. Furthermore, these monoclonal antibodie s were useful for boosting the efficacy of TGEV-neutralizing, colostrum, wh ich by itself was ineffective. These results show that other antigenic site s, different from the 4-well characterized epitopes on the S glycoprotein o f TGEV, also are important for passive protection.