Attenuation of collagen-induced arthritis by pro/thrombin^WE. (A) Representative experiment of wild-type (n = 9) and fII^WE (n = 8) mice in which animals were immunized with CII and the development of arthritis within distal joints was scored by investigators blinded to genotype and expressed as a median arthritic index. Note that within a week of secondary CII immunization and to the end of the evaluation period, fII^WE mice exhibited significantly less macroscopic arthritis relative to wild-type animals. Daily scores were analyzed by Mann-Whitney U test and found to be consistently significant beyond day 28. *P < .05; **P < .02. Three independent experiments yielded similar results. (B) Knee joint sections prepared from cohorts of wild-type (n = 16) and fII^WE (n = 12) animals processed for histologic evaluation on day 42 of the CIA protocol. The data for each parameter and the total histopathology score are expressed as the means ± SEM and were analyzed by Mann-Whitney U test. *P < .05; **P < .03. (C) Representative examples of knee histopathology from wild-type and fII^WT/WE CIA-challenged animals. Hematoxylin/eosin–stained sections revealed a profound loss of joint architecture in CIA-challenged wild-type animals, with significant inflammatory cell infiltrates and synovial hyperplasia (arrows). In contrast, knee joints from CIA-challenged fII^WT/WE mice displayed only mild inflammatory cell infiltrates and little synovial hyperplasia. Mason trichrome staining of CIA-challenged knee joint sections revealed a loss of articular cartilage in wild-type mice (arrowheads), whereas cartilage surfaces were smooth and well preserved in fII^WT/WE mice. Fibrin appeared qualitatively more widespread and pronounced in the knee joints of CIA-challenged wild-type mice relative to the knee joints of CIA-challenged fII^WT/WE analyzed in parallel. (D) The adaptive immune response at the level of T cells was similar in CII-immunized control and mutant mice. Popliteal lymph node cells were harvested from wild-type (n = 4) and fII^WT/WE (n = 4) mice 10 days after footpad injection with CII/CFA, and cultured T cells were stimulated with either 100 or 30 μg/mL CII. Anti-CD3–activating T cell–receptor antibody was used as a positive control. Results are expressed as the mean value of ³H-dT incorporated in counts per minute (cpm) ± SEM (E) Determination of anti–CII-specific IgG antibody titers by ELISA using plasma harvested at day 42 of the CIA protocol from wild-type (n = 9) and fII^WT/WE (n = 9) mice. Titers are expressed as arbitrary units relative to titers found in wild-type DBA/1 mice at day 28 of CIA. Results are expressed as the means ± SEM (F) Summary of experimental manipulations in cohorts of CIA-challenged mice treated with recombinant murine thrombin^WE. Beginning at day 21 of the CIA protocol, mice were given daily administrations of either 0.1 mg/kg murine thrombin^WE or normal saline as a vehicle control. (G) Analysis of macroscopic CIA in the paws of wild-type mice treated with either thrombin^WE or saline (n = 6 per group). Note that thrombin^WE treatment significantly limited the development of inflammatory joint disease relative to saline-treated control mice over a wide observation period. * P < .05 by Mann-Whitney U test.