FIG 3 .

The opal stop codon is required by CHIKV to induce severe disease. (A) Twenty-four-day-old C57BL/6J mice were either mock infected (n = 6) or infected with 100 PFU of wild-type CHIKV or the Opal524R mutant (9 to 10 mice per group) in the left rear footpad. Mice were monitored for 7 days, and footpad swelling was measured in millimeters using calipers. (B, D) Mice from panel A were sacrificed at day 7 postinfection and perfused intracardially with paraformaldehyde. Tissue sections were prepared from the ipsilateral foot and embedded in paraffin, and 5-μm sections were prepared. Tissues were deparaffinized and stained with either hematoxylin and eosin (B) or nitrotyrosine (D). Representative images of the ankles at a 10× magnification are shown. (C) Hematoxylin-eosin sections from panel B were scored blind for damage to the tendon and ankle joint. Horizontal lines indicate the arithmetic mean. B, bone; BM, bone marrow; J, joint space; M, muscle; T, tendon; arrowhead, synovial lining. Data shown are from at least two independent experiments. Data were analyzed by ANOVA for significance, with corrections for multiple comparisons. Statistical significance is indicated as follows: *, P < 0.05, and **, P < 0.01.