Background: This study investigated prognostic factors for early recovery of coronary artery lesion (CAL) in children with Kawasaki disease (KD). Methods: Patients hospitalized for KD were enrolled less than 2 wk from the onset of illness and divided into two groups: KD with CAL and KD without CAL. The CAL group was further divided into two subgroups according to the degree of CAL: mild (n = 31) and moderate/severe (n = 6) and further divided into two subgroups according to the age: younger than 1 y (n = 9) and older than 1 y (n = 28). Lectin pathway-related factors MASP-1, CD59, and C5b-9 were measured, along with C-reactive protein, white blood cell counts, erythrocyte sedimentation rate, and platelet count. Patients were followed up for 3 mo. Correlation between the measured factors and the length of time of recovery from CAL was analyzed. results: Plasma concentrations of MASP-1 in the CAL group were significantly lower than those without CAL. MASP-1 and gender positively correlated with the recovery time of CAL. There was no difference in MASP-1 between mild and moderate/severe CAL. At 3-mo follow-up, there was a positive correlation between plasma MASP-1 concentration and recovery time of the patients with CAL older than 1 y. conclusion: Plasma MASP-1 concentration at the early stage of KD is predictive of length of time of recovery from CAL. k awasaki disease (KD), also known as mucocutaneous lymph node syndrome, is an acute nonspecific systemic vascular inflammatory syndrome occurring mainly in children under 5 y of age. A considerable volume of research has shown that the pathological process of KD is characterized by immune activation and immune vasculitis of the vascular endothelial cells (1). KD mostly affects the small and mediumsized arteries, especially the coronary artery (2), resulting in coronary artery lesion (CAL), such as dilation, aneurysm formation, or advanced stenosis, and it is the leading cause of death in children with KD (3). It has been reported that 15-25% of untreated KD patients may develop CAL (4). Although treatment with intravenous immunoglobulin within 10 d of onset of fever reduces the incidence of CAL, 5-8% of patients still develop it. The degree of CAL varies considerably between individuals, ranging from mild to moderate ectasia of the coronary artery to giant aneurysm formation. The recovery time of CAL also differs between patients. There is a very little information about the length of time for which different degrees of CAL persists. Little is known on the relationship between the complement system and the recovery time of CAL resulting from KD. Our previous study indicated that the lectin pathway of the complement system is activated in KD. CAL is associated with endothelial cell dysfunction induced by T-cell activation (5). Endothelial cells are a source of complement-related factors and complement regulatory factors (6), and MASP-1 activates endothelial cells directly, which then activates the complement lectin pathway (7). Endothelial cell dysfunction (8) and com...