Lymphocyte responses to virus and mitogen in ponies during experimental infection with equine herpesvirus 1

Six pony foals, experimentally infected with equine herpesvirus 1 (EHV-1), were studied for their lymphocyte responses to EHV-1 and phytohemagglutinin (PHA) stimulations. Lymphocyte blastic transformation in the presence of EHV-1 appeared as early as 2 days after the foals were inoculated, reached a peak in 7 to 10 days, and subsequently decreased. In contrast, the lymphocyte blastic transformation in the presence of PHA increased sharply, reaching a peak in 2 to 3 days, and then decreased to its lowest level in 10 days after which it returned to its near preinoculation level. As for the mechanism of the transient hyporesponsiveness to mitogen, sera from the ponies after inoculation did not cause lessened stimulatory response of normal lymphocytes to PHA. The possible mechanism of this transient hyporesponsiveness to mitogen is discussed.