FIG. 4.

Analysis of IBDV-induced apoptosis by TUNEL assay. CEF cells were either mock infected (a, d, and g) or infected with rD78NSΔ (b, e, and h) or rD78 (c, f, and i) IBDV at an MOI of 1. Cells were fixed at 24 h (a to c), 48 h (d to f), and 72 h (g to i) postinfection and assayed by immunofluorescence for DNA breakage (TdT assay; green signal). The TUNEL staining of CEF cells, infected with NS protein-deficient mutant IBDV, show a substantial reduction in IBDV-induced apoptosis. Magnifications, ×100.