This article describes the generation of an adjuvant-induced arthritis mouse model using complete Freund's adjuvant (CFA). The process involves injecting CFA into the ankle joint to induce chronic inflammation, allowing for the study of arthritis mechanisms.
To generate an adjuvant-induced arthritis mouse model, begin with an anesthetized mouse in the prone position.
Take a syringe containing complete Freund's adjuvant or CFA, a suspension of heat-killed Mycobacterium tuberculosis in oil. Inject the CFA into the ankle joint space — a synovial fluid-filled region between the lower leg bone and foot bone — followed by injection into the tissue surrounding the joint, inducing chronic inflammation.
The fluid-filled cavity is bordered by a synovial membrane, consisting of a lining layer enriched with macrophages and fibroblasts — functioning as an immunological barrier — and a sub-lining interstitial tissue.
The macrophages recognize the bacterial antigen and transform to a phagocytic phenotype, disrupting the barrier integrity. The macrophages also release chemoattractants and cytokines. The released chemoattractants mediate the recruitment of circulatory neutrophils to the infection site.
Recognition of the bacterial antigen activates neutrophils, resulting in degranulation. Released matrix metalloproteinases and proteases cause cartilage damage and sustained inflammation.
Macrophage-secreted cytokines also bind to receptors on the synovial fibroblasts. The cytokine binding and antigen recognition induce fibroblast activation.
Activated fibroblasts undergo abnormal proliferation, resulting in synovial hyperplasia — leading to excess synovial fluid production and joint swelling, characteristic of arthritis.
Suspend complete Freund's adjuvant by vortexing at least five seconds. Then, draw 100 microliters of suspension into an insulin injector.
After anesthetizing, mark the chosen paw and inject 20 microliters of complete Freund's adjuvant from the injector into four periarticular spots on the ankle joint space. Put the processed mice in a new chamber. Monitor the mice to ensure that they are breathing until they regain the ability to move. Every three days, use a pocket thickness gauge to measure the ankle joint diameter.
Also, assess arthritis severity by arthritis scoring criterion. Zero is normal. No evidence of erythema and swelling.
One is the mildest arthritis. Erythema and mild swelling confined to the tarsals or ankle joint. Two is the moderate arthritis. Erythema and mild swelling extending from the ankle to the tarsals. Three is the severe arthritis. Erythema and moderate swelling extending from the ankle to metatarsal joints. Four is the most severe arthritis. Erythema and severe swelling encompass the ankle, foot, and digits, or ankylosis of the limb.
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