An immunosuppressive factor in serum of rabbits lethally infected with the herpesvirus of bovine malignant catarrhal fever.

Virus-neutralizing antibody does not protect animals challenged with the herpesvirus of bovine malignant catarrh; therefore, other parameters of the immune response were investigated. In vitro transformation of peripheral blood lymphocytes with mitogens and specific antigens was monitored throughout the course of disease in lethally infected New Zealand white rabbits. The whole-blood culture method was used. Transformation with mitogens was normal throughout the incubation period but fell precipitously from the day of disease onset until death. Specific stimulation with viral antigens was not detected at any time following challenge. Purified and washed lymphocytes, however, reesponded normally to mitogens and were transformed in the presence of viral antigens. Acute-phase serum from rabbits inhibited transformation of normal rabbit lymphocytes, but this inhibition was reversible by washing. It is proposed that the development of a serum suppressive factor(s) is important in the determination of whether an animal is capable of controlling infection with this virus.