Histopathological Evaluation of Carrageenan-Induced Rat Arthritis

The rats were killed after 9 days of carrageenan and control treatments. Immunohistochemical staining was performed to determine the degree of immune cells infiltration into the joints. Rat ankles were dissected, fixed in 10% formalin, dehydrated through a graded ethanol series, cleared in xylene, and processed for embedding in paraffin wax with routine protocols. A microtome was used to cut 4 μm-thick sections that were subsequently stained with hematoxylin and eosin (H&E) stain. The degree of inflammation was evaluated on a scale from 0 to 5 by three different pathologists that had been blinded to the treatments. The scale was defined as follows: 0 = no inflammation, 1 = mild inflammation, 2 = mild/moderate inflammation, 3 = moderate inflammation, 4 = moderate/severe inflammation, and 5 = severe inflammation.