Serum IFN-γ in nearly all sheep declined to pre-infection levels except for two CD4+ (#19/23) and one CD8+ (#25) T cell-depleted sheep, which had detectable IFN-γ levels of 5.122 ng/ml, 2.366 ng/ml, and 1.253 ng/ml, respectively, at 20 dpi. The gene discussed is CD4; the disease is infection.