Increased inflammation and destruction of the joint is associated with more macrophages in Bid-/- compared to wild-type (Wt) mice following transfer of serum. Mice (Wt, n = 9; Bid-/-, n = 7) underwent K/BxN serum transfer as described in Figure 1 and were euthanized at seven days post-serum transfer. Both ankles from each mouse were harvested, fixed, embedded in paraffin, sectioned, and stained with either (a) hematoxylin (blue) and eosin (pink) (H&E) or (b) F4/80 antigen (macrophage specific marker). Shown are representative photomicrographs of the synovium and pannus formation from Wt and Bid-/- mice. B, bone; SL, synovial lining; P, pannus.