PECAM-1 and leukosialin (CD43) expression correlate with heightened inflammation in rat adjuvant-induced arthritis

A hallmark of both adjuvant-induced arthritis (AIA) and rheumatoid arthritis is chronic joint inflammation characterized by ingress of leukocytes into the inflamed synovial tissue. The timing of expression of adhesion molecules, which govern the ingress of leukocytes, is important in the orchestration of an inflammatory response. We examined the expression of vascular cell adhesion molecule-1 (VCAM-1), sialo adhesin, platelet and endothelial cell adhesion molecule-1 (PECAM-1), and leukosialin (CD43) in AIA, starting at adjuvant injection (day 0), through the peak of inflammation (day 18 postadjuvant injection), until day 54. VCAM-1 is constitutively expressed on the lining layer and ECs and its expression levels do not change throughout the progression of AIA. Sialoadhesin synovial tissue lining cell expression is decreased after adjuvant injection. In contrast, PECAM-1 expression is increased on synovial tissue lining cells on day 7 and is elevated through day 54 (peaking on day 54 with six-fold more cells expressing PECAM-1). PECAM-1 expression on endothelial cells peaks on day 7 with three-fold more cells expressing it, while on macrophages expression maximizes on day 25 with six-fold more cells expressing PECAM-1. CD43 expression is increased on synovial tissue lining cells, macrophages, neutrophils, and lymphocytes on days 18 and 25, before going back to basal levels. The increased expression of PECAM-1 and CD43 on leukocytes at the height of inflammation in AIA suggests important roles for these adhesion molecules in potentially binding their EC ligands resulting in leukocyte ingress into the synovial tissue.