Circulating forms of ICAM-3 (cICAM-3). Elevated levels in autoimmune diseases and lack of association with cICAM-1.

The intercellular adhesion molecule-3 (ICAM-3) has been identified as the third LFA-1 ligand in addition to ICAM-1 and ICAM-2. In this report we have identified circulating forms of ICAM-3 (cICAM-3) in human serum. Using a sandwich ELISA with two monoclonal anti-ICAM-3 Abs, we detected cICAM-3 in concentrations between 40 and 360 ng/ml in all of 112 healthy controls. An analysis of patient sera from 10 different immune-mediated diseases revealed a distinct pattern of expression. Significantly elevated cICAM-3 levels were found in rheumatoid arthritis, systemic lupus erythematosus, Guillain-Barré syndrome, and multiple sclerosis, but not in type I diabetes, Grave's disease, chronic autoimmune thyroiditis, ulcerative colitis, or Crohn's disease. cICAM-3 levels were significantly higher in systemic lupus erythematosus patients with active compared with nonactive disease. Despite their binding to the same integrin receptor, serum levels of cICAM-3 did not correlate with cICAM-1 concentrations in either normal persons or in patients. The majority of patients had either elevated cICAM-3 or cICAM-1 levels but not both. In conclusion, a circulating form of ICAM-3 is present in human sera. cICAM-3 expression is elevated in certain immune-mediated diseases but occurs independently of cICAM-1.