Time course of arthritis in EP4 receptor–deficient animals. (a) Disease progression. EP4 wild-type littermate controls and EP4^–/– animals were monitored for the duration of the disease and scores were determined as previously described. An unpaired Student t test was performed on the final day of the experiment (*P < 0.05). (b) Distribution of affected joints. The total number of affected joints (0–4) in each animal is determined in the two genotypes. Data shown is from a representative experiment performed in triplicate.