Background and Objectives:Anti-endothelial cell antibodies (AECA) are found in the sera of many patientswith Kawasaki disease (KD). In this study, the pathogenic role of AECA in the development of coronary arteriallesions of KD was investigated. Subjects and Methods:Serum IgM-AECA concentrations were measured in 22KD patients. Cultured human coronary artery endothelial cells (HCAEC) were incubated with either acute orconvalescent phase sera, and their expressions of intercellular adhesion molecule-1 (ICAM-1) assessed. IgMfractions of the sera were purified, and their ability to induce ICAM-1 mRNA and protein expressions evaluated.To address the signal transduction pathways involved in IgM-AECA-induced ICAM-1 expression, the blockingeffect of four protein kinase inhibitors, PD98059, SB203580, dimethylaminopurine (DMAP) and parthenolidewere measured. Results:IgM-AECA was present in 14 out of 22 (64%) acute KD sera. ICAM-1 expression ofHCAEC incubated with acute KD sera (117.1±46.7) and AECA-positive acute KD sera (143.3±37.5) weresignificantly higher than those of the convalescent KD sera (88.9±14.4, p<0.05) or AECA-negative acute KDsera (71.2±11.8, p<0.05), respectively. IgM-AECA from KD patients significantly induced ICAM-1 protein andmRNA expression. The upregulation of ICAM-1 expression was significantly inhibited by SB203580, DMAPand parthenolide, but not by PD98059. Conclusion:IgM-AECA was detected in the sera of about 2/3 of acuteKD patients, which activated endothelial cells by upregulation of ICAM-1 expression, possibly via p38, JNKMAPK and NF-κB signal transduction pathways. Thus, IgM-AECA may play a pathogenic role in the developmentof coronary arterial lesions in KD patients. (Korean Circulation J 2006;36:723-731)