Table 3. The actual weight and numbers of apoptotic cells of subcutaneous tumors at killing (Experiment 2).

Treatment groupa	activity of interferon (IU)	Tumor weight (g)	Apoptosis (Number of cells/0.25mm2)
Control	0 IU	0.726 ± 0.09b, c	7.6 ± 0.9d
IFN-α2a (0.0042 µg)	840 IU	0.588 ± 0.07d	7.9 ± 0.9g
IFN-α2a (0.042 µg)	8,400 IU	0.531 ± 0.04e	7.6 ± 0.7h
PEG-IFN-α2a (0.06 μg)	840 IU	0.493 ± 0.04f	8.9 ± 0.9
PEG-IFN-α2a (0.6 μg)	8,400 IU	0.355 ± 0.03	9.7 ± 1.0*

^a Cultured HAK-1B cells (1.0 X 10⁷) were subcutaneously transplanted into nude mice. Five groups of 8 mice received either PBS (Control), PBS with 0.0042 or 0.042 µg of IFN-α2a (840 or 8,400 IU, respectively), or PBS with 0.06 or 0.6 µg of PEG-IFN-α2a (840 or 8,400 IU, respectively). All mice were killed and the tumor weight was measured on the 15th day. The number of apoptotic cells was counted in at least three 0.25 mm²-areas in each section stained with hematoxylin and eosin, and the average number per area in each group was obtained. ^b Mean ± SE. ^c P < 0.005, versus the PEG-IFN-α2a (0.6 μg) group. ^d P < 0.02, versus the PEG-IFN-α2a (0.6 μg) group. ^e P < 0.03, versus the PEG-IFN-α2a (0.6 μg) group. ^f P < 0.02, versus the PEG-IFN-α2a (0.6 μg) group. ^g P < 0.05, versus the PEG-IFN-α2a (0.6 μg) group. ^h P < 0.001, versus the PEG-IFN-α2a (0.6 μg) group.