Progression and severity of arthritis in 11 BALB/c colonies sorted into three different groups (listed in Table 1), correlation between the onset of arthritis and spine involvement, and comparison of the three arthritic groups with different spine inflammation scores. (a) Each animal was scored for arthritis three times a week, and scores are shown as mean ± standard error of the mean. Arrow indicates the third injection, administrated on day 42. Significant differences (P < 0.01), calculated by one-way analysis of variance, were found from day 32 between groups I, II, and III. (b) The ratio of the number of inflamed intervertebral discs (IVDs) per the total number of IVDs showed positive significant correlation (Pearson correlation coefficient ρ = 0.485; P < 0.0005) with the onset of arthritis. (c-e) Significant differences were found among the three arthritic groups when compared with three spine representative scores: cumulative spondylitis score (c), the mean spondylitis score (d), and the ratio of the number of inflamed IVDs per total number of IVDs (e). Asterisks indicate the level of significance between groups (*P < 0.05 and **P < 0.01) using Tamhane (c, e) (n = 127) and least significant difference (d) (n = 79) post hoc tests.