Background/Purpose: Age and sex differences are found in certain subsets of juvenile idiopathic arthritis (JIA). Collagen Induced Arthritis (CIA) in rodents has utility in assessing pathogenic processes in arthritis. This study compared clinical, biomarker and imaging characteristics of CIA in male and female, adult and juvenile animals. The goal was to evaluate CIA as a model for studying age- and sex-related differences in inflammatory joint diseases.

Methods: Juvenile (5 wks old) and adult (13 wks old) male and female Lewis rats were immunized with bovine type II collagen/incomplete Freund’s adjuvant. Naïve juvenile and adult, male and female rats served as controls. For each animal, the Maximum Daily Arthritis Score (MDAS) was recorded. 14 days after arthritis onset, paw swelling was measured, blood collected and paws imaged by micro-CT. Serum was assayed by enzyme immunoassay using a rat 27-plex cytokine/chemokine array. Micro-CT scans were scored on a 6 point scale to evaluate bone erosion and pathological ectopic bone/reactive bone formation. Statistical significance was determined by ANOVA and Holm-Sidak tests.

Results: Juvenile male CIA rats (JMC) had significantly higher MDAS (p<0.0001), Eotaxin (p=0.0116), Interleukin (IL)-4 (p=0.0045) and IL-12(p70) (p=0.0236) than juvenile female CIA rats (JFC). JMC also had higher MDAS than adult male CIA rats (AMC; p<0.0001) and corresponding higher levels of Granulocyte-colony stimulating factor (G-CSF) (p=0.0160), Eotaxin (p=0.0058), IL-4 (p=0.0007) and IL-12(p70) (p=0.0500) compared to AMC. JFC had higher MDAS (p=0.0053) and macrophage inflammatory protein 2 (MIP-2; p=0.0434) than adult female CIA rats (AFC).There was no significant difference between MDAS of AFC and AMC. Two weeks after arthritis onset significant changes in serum C-X-C motif chemokine (CXCL) 10 (p<0.0001) and CXCL5 (p=0.0285) levels were specific to JFC; significant changes in serum IL-1β (p=0.0489) and IL-10 (p=0.0113) levels were specific to AFC; significant changes in serum IL-1a (p=0.0438), IL-13 (0.0286) and IL-17a (0.0356) were specific to JMC; and significant change in serum level of Leptin was specific to AMC (p<0.0001). No significant differences were observed in degree of bone erosion between groups. However, the majority of bone erosion was observed at the tarso-metarsal /metatarsal-phalangeal joints and, consistent with this finding, there were increases in paw thickness at the metatarsus in JFC (p=0.0021), JMC (p=0.0116) and AMC (p=0.0020). AMC had higher levels of reactive bone formation compared to JFC (p=0.0003), AFC (p=0.0003) and JMC (p=0.0006).

Conclusion: Results indicate age- and sex-related differences in arthritis incidence, severity and associated inflammatory biomarker profiling in the CIA model. Maturity of the immune system, rates of bone growth and changing hormonal levels are likely to contribute to these observed differences. These results indicate the importance of age and sex in CIA and the potential value of this model for studying the biologic basis for age- and sex-related differences in humans with arthritis.