Lymphocytes from ponies experimentally infected with equine herpesvirus 1: subpopulation dynamics and their response to mitogens.

Six pony foals, free of detectable serum neutralization (SN) antibody against equine herpesvirus type 1 by the standard virus-neutralization (VN) test, were inoculated with equine herpesvirus type 1. The ponies showed typical clinical signs of respiratory tract disease and developed a transient leukopenia, involving lymphocytes as well as neutrophils. The leukopenia reached its lowest point on postinoculation days (PID) 3 to 5 and then returned to base-line values by PID 8 to 10. On quantitation of lymphocyte subpopulations, T and B lymphocytes were decreased during the onset of leukopenia and then recouped during the recovery from leukopenia. However, the proportions of the T and B lymphocytes remained constant during the lymphopenia, ranging from 70% to 80% and 20% to 30%, respectively. The lymphocyte blastogenic response to mitogens increased to peak by PID 2 to 5 and then decreased to base line values or below by PID 7. Mitogen responses of T lymphocyte and mixed lymphocyte preparations were nearly similar. However, the responses of 2 ponies wee somewhat different from the responses of others in that there was an increase in the B lymphocytes in the range of 40% to 50% during the recovery phase of lymphopenia. Also, the 2 ponies' mixed lymphocyte response to mitogens was considerably higher and the T lymphocyte response to mitogen was lower as compared with that of mixed lymphocyte preparation. The importance of these 2 types of responses is discussed.