Bid-/- mice have fewer TUNEL positive cells following serum transfer. (a) Decreased numbers of apoptotic cells in Bid-/- ankle joints following transfer of K/BxN serum. Ankle sections from Bid-/- mice and wild-type (Wt) mice as described in Figure 2 were stained with Hoechst (blue) and TUNEL (green) as detailed in the Materials and methods section. Shown are representative photomicrographs (200 × magnification) of ankle joints (n = 14 for Bid-/- and n = 18 for Wt) isolated seven days post-serum transfer. (b) Percentage of TUNEL-positive cells in the joint. Ankle joints as described above were stained with TUNEL and Hoechst. Three areas of TUNEL positive cells were examined (400 × magnification) and percentages of TUNEL-positive cells were determined as described in Materials and methods. The values represent the mean ± standard error, which were compared by Student's t-test. The asterisk denotes p < 0.001 compared to Wt under parallel conditions.