Distribution of Border disease virus antigen in lymphocyte subpopulations in the peripheral blood of experimentally infected lambs.

Ten lambs were experimentally infected with Border disease virus and the distribution of viral antigen in lymphocyte subpopulations studied by flow cytometry. The virus was isolated in culture from the peripheral blood mononuclear cells (MNC) of all experimentally infected lambs for a mean period of 9.8 +/- 1.03 days. The peak virus titre of 3.26 log10 TCID50 per 10(6) MNC was attained Day 9 post-inoculation (pi). Viral antigen was present in peripheral blood lymphocytes of experimentally infected lambs as early as 24 h pi and continued to be detected up to Day 10 pi. The number of lymphocytes expressing viral antigen rose from 12.38 +/- 1.22% in samples taken Day 3 pi to 23.21 +/- 2.82% on those collected Day 7 pi, dropping gradually thereafter. During the peak period of infection, 12.46 +/- 2.09% of B cells, 37.71 +/- 10.96% of T cells and 52.33 +/- 8.27% of lymphocytes which were neither B nor T lymphocytes expressed viral antigen. Most of the infected lymphocytes expressed the OvCD5 (T cell) molecule. The virus affected all T cell subsets but the suppressor/cytotoxic (OvCD8+) cells appeared to be the main targets. During the peak period of infection, 54.20 +/- 6.16% of the infected T cells expressed the OvCD8 molecule, 31.58 +/- 7.12% were OvCD4+, and 12.67 +/- 6.50% were OvWC1+ (T-19+, gamma/delta).