Immunohistochemical and cytokine analysis of eyes from rats with adjuvant arthritis

Adjuvant induced arthritis in the rat is an animal model of juvenile chronic arthritis (JCA). An anterior uveitis may also develop in this model which closely resembles that seen in association with JCA in the human. Female Lewis rats (150-225 g) were injected intradermally with either Freund's complete adjuvant (FCA, n=5) or Freund's incomplete adjuvant (FIA, n=5). Eyes were examined by slit-lamp biomicroscopy every two days, and the animals sacrificed 21 days post-immunisation. Aqueous humour and serum interleukin-6 (IL-6) levels were determined using the B(9) bioassay, and serial tissue sections of the globes were stained with a variety of monoclonal antibodies. In the FCA group, arthritis was detected in two rats, but no rats from either group developed clinical uveitis. Immunohistochemical analysis revealed greater numbers of macrophages and MHC class II+ve cells in the irises and ciliary bodies of FCA treated rats than were seen in the FIA group. No other cellular infiltrate was detected. Serum IL-6 levels were greater in the FCA group (range 6-122 U/ml, median 42) than the FIA group (range 2-27, median 3) (p=0.018), the highest values seen in the two rats which developed arthritis (100, 122 U/ml). In the aqueous of both groups, IL-6 levels were <5 U/ml, and albumin levels were not significantly different (FCA median=2.0 mg/ml, FIA median=1.8). The authors″ results suggest that in the adjuvant induced arthritis model, infiltration with macrophages and MHC class II+ve cells occurs in the absence of clinical uveitis.