COMPARISON OF THE SEVERITY OF INFLAMMATION IN RATS WITH A PRIMARY REACTION AND SECONDARY IMMUNOLOGICAL REACTION TO AN INJECTION OF FREUND’S COMPLETE ADJUVANT

Abstract

The model of chronic immune inflammation caused by the administration of Freund’s complete adjuvant (CFA) into a hind paw of rats is used as a model of rheumatoid arthritis. Under this condition, the joints of other limbs, along with those subject to the action of CFA, are damaged. The aim of this study was to compare the severity of the inflammatory process in rats with a primary reaction (edema of the left hind paw) and a secondary immunological inflammatory response (edema of the right hind paw) towards a sub-plantar injection of CFA in the left hind paw of the experimental animals.Inflammation was induced by the sub-plantar administration of 0.1 ml of CFA into the left hind paw of outbred rats. Such indicators as the edema of the metatarsus and the ankle joints of the hind paws, the weight of the animals and the skin temperature of the paws were recorded on the 7th, 14th, 21st and 28th day of the experiment. The pain threshold was recorded using a plantar test on the 15th day. Hematological parameters were assessed on the 14th and 28th day.Both a primary reaction and a secondary immunological reaction was developed on the 7th day of the experiment in 11 out of 20 animals having received CFA, while the rest of the rats demonstrated inflammation exclusively in the left hind paw. On the 7th day of the experiment, the animals with inflammation showed a higher skin temperature in the hind paws compared to the control group. The maximum edema in the rats with a primary reaction and secondary immunological inflammatory response was recorded on the 14th day of the experiment. On the 14th day, the rats with induced inflammation showed an increase in a number of hematological parameters, with the elevation being more pronounced in the animals with generalized inflammation. As a result of inflammation, pain sensitivity increased in both groups of animals with induced inflammation. In these groups, both a decrease in the edema of the paws and the normalization of hematological parameters were observed on the 28th day of the experiment. It is concluded that the most pronounced inflammatory reaction has developed by the 14th day following CFA administration, with its intensity having reduced by the 28th day. These results might be useful when assessing the pharmacological activity of various compounds using this model.