Cellular adhesion molecules in rat adjuvant arthritis

Objective. To examine adhesion molecule expression during the progression of inflammation in a rheumatoid arthritis model of adjuvant‐induced arthritis (AIA) in rats. Methods. Immunohistochemical analysis was used to determine the distribution of the following adhesion molecules: lymphocyte function–associated antigen 1 (LFA‐1; CD11a/CD18), Mac‐1 and p150/95 (CD11bc/CD18), intercellular adhesion molecule 1 (ICAM‐1), and CD44 in tissue sections from the ankle joints of rats with AIA. Control animals and those with AIA were killed at intervals over a 54‐day period after injection with mineral oil and Mycobacterium butyricum, respectively. Results. CD44 and LFA‐1 were expressed on lymphocytes, macrophages, and synovial (ST) lining cells. CD44 expression on macrophages was found to be increased compared with control animals by day 18, and was significantly increased by day 41. CD44 expression on lymphocytes significantly increased earlier, on days 11–18. Increased LFA‐1 expression on macrophages occurred late, on day 41. LFA‐1 expression on lymphocytes was significantly increased on days 25, 47, and 54. ST lining cells exhibited two distinct periods of increased expression, one early, on days 11–25 and one later, on days 41–54. CD11b/c was expressed on macrophages and ST lining cells, showing a significant increase on AIA rat ST lining cells compared with control animals on day 4. No differences in ICAM‐1 expression on endothelial cells between rats with AIA and controls were found on any of the days examined. Conclusion. CD44 expression is up‐regulated on macrophages and lymphocytes during the early development of AIA, while LFA‐1 expression is up‐regulated later in the development of AIA. The up‐regulation of CD44 and LFA‐1 at different times in the development of AIA suggests an important role for these adhesion molecules in establishing and sustaining an inflammatory response in the AIA joint.