FIGURE 6.

Ptpn22^−/− mice are protected from K/B×N arthritis. K/B×N serum transfer arthritis was induced in Ptpn22^−/− [knockout (ko)] and matched control (wt) mice. (A) Clinical scores (means ± SEM) of the experimental groups were plotted over 20 d. Four experiments were carried out with five to eight animals in each experimental group; a representative experiment is shown; experimental groups behaved significantly differently; p = 0.02. (B) Wax sections of decalcified joints were H&E stained to visualize joint erosion and leukocyte infiltration on day 5 after serum transfer. Representative examples from sections obtained with right rear joints of arthritogenic serum–injected control (wt) and Ptpn22^−/− (ko) mice are shown (scale bar, 500 μm); panels wt′ and ko′ are higher power images of the boxed areas in panels wt and ko (scale bar, 50 μm). (C) Wax sections of decalcified joints were stained with an Ab specific for Ly6G and counterstained with hematoxylin to visualize neutrophil infiltration at day 2 following administration of arthritogenic serum. An arrow in Ptpn22^−/− points out a rare neutrophil (scale bar, 25 μm).