Adjuvant Induced Arthritis - Adjuvants
Adjuvant-Induced Arthritis (AIA) was used as a model for rheumatoid arthritis (RA) and is currently considered as a model for reactive arthritis. Chondrex provides various types of Complete Freund’s Adjuvant (CFA) for inducing AIA. AIA can be easily induced in susceptible strains of rats by a single subcutaneous injection of adjuvant (0.05-0.1 ml) into a footpad or at the base of the tail.
Complete Freund's Adjuvants for AIA
|Product||Content of M. Tuberculosis H-37 RA||Quantity||Catalog #||Price (USD)|
|Complete Freund's Adjuvant, 5 mg/ml||5 mg/ml||5 ml||7023||68.00|
|Complete Freund's Adjuvant, 10 mg/ml||10 mg/ml||5 ml||7027||101.00|
|Complete Freund's Adjuvant, 20 mg/ml||20 mg/ml||5 ml||7024||184.00|
In 1956, Pearson found that rats immunized with Complete Freund’s Adjuvant containing Mycobacterium tuberculosis developed arthritis. This arthritis model, called Adjuvant-Induced Arthritis (AIA), has been widely used as a model for rheumatoid arthritis (RA). Although AIA was used as a model for RA in the past, it is a more appropriate model for reactive arthritis rather than RA, due to the apparent differences in histological and immunological features between the two.
Please note that CFA containing 1 mg/ml of heat-killed Mycobacterium is seldom effective in inducing AIA. For the effective induction of AIA, CFA containing 10 mg/ml of Mycobacterium has been most widely used, although CFA containing 5 mg/ml of heat-killed Mycobacterium is capable of inducing AIA.
NOTE: It is very important to re-suspend CFA with a vortex before each injection, since the mycobacteria particles will settle. It is not necessary to use an emulsified adjuvant for inducing AIA. However, in order to avoid an injection of inconsistent amounts of heat-killed mycobacteria, CFA containing 20 mg/ml of mycobacterium can be emulsified by mixing an equal volume of saline or a buffer solution, and used for inoculation. This method has been reported for immunizing F344 rats with mycobacterial peptidoglycans and muramyl dipeptide (MDP) for inducing AIA.
AIA-Susceptible Strains of Rats and Environmental Factors
Wistar-Lewis, Sprague-Dawley (SD), Wistar, and Buffalo (BUF) rat strains are known as high responders to AIA, whereas Fisher 334 (F344), the diabetic resistant sub-line of diabetic BB (DRBB), and Brown Norway (BN) rats are medium to low responders to AIA. Several factors affect the susceptibility of a given strain. They include animal vendors, the dose and species of Mycobacterium, and the type of oil used to make the suspension. Environmental factors are also important for the successful induction of AIA. For example, germ free F344 rats are highly susceptible to AIA and develop severe arthritis followed by 4 specific pathogen free (SPF) rats. Although conventional F344 rats also develop AIA, the arthritis is less severe and incidence is as low as 20%.
NOTE: DA rats are extremely susceptible to AIA, collagen-induced arthritis (CIA) as well as oil induced-arthritis OIA), which is triggered by the injection of incomplete Freund’s adjuvant or pristine alone. The pathological mechanisms active in this strain may differ from those of ‘authentic’ AIA reported in other strains. Thus, the use of DA rats to study AIA is complex and requires extra consideration.
Figure 1 - A typical example of evaluating anti-inflammatory agents using rat AIA model
Foot pads inoculated with CFA developed severe inflammatory reaction (primary inflammation) immediately after
inoculation with CFA, whereas un-inoculated foot pads also developed severe inflammatory reactions (secondary
inflammation) 12-14 days later. The anti-inflammatory effect of a test compound can be determined by simply
comparing foot pad volumes in treated and un-treated rats.