JAK2 blockade ameliorates collagen antibody-induced arthritis (CAIA) paw inflammation. Female DBA/1 mice were injected intravenously (i.v.) with purified anti-collagen type II (anti-CII) antibodies, and then 25 μg of lipopolysaccharide (LPS) was administered intraperitoneally (i.p.) 3 days later to induce arthritis by day 5. Mice that met the arthritis criteria score of 1 per paw were entered into the study. CEP-33779 was administered p.o. twice daily (b.i.d.) throughout the experiment, 1.5 mg/kg dexamethasone (Dex) was administered i.p. three times weekly and vehicle (PEG400 + 1% dimethyl sulfoxide (DMSO)) was administered p.o. (A) Mean paw size (individual paws measured for thickness) measured over time (top) and total clinical score from each paw were recorded (bottom). *P < 0.05; black star, P < 0.01; #P < 0.001. Statistical significance was measured by using two-way analysis of variance (ANOVA), n ≥ 10 mice per group. (B) Pharmacokinetics (PK) of CEP-33779 at 55 mg/kg, 30 mg/kg and 10 mg/kg, p.o., once daily (s.i.d.), in the plasma, paw and spleen of treated mice, with statistical significance not determined; n = 4 mice per group tested. All graphs show means ± SEM. Study size shows n ≥ 10 mice per group and n ≥ 5 mice for individual assays. Black arrows in parts A and B indicate treatment start.