Background Recently,studies have disclosed soluble CD40 ligand (sCD40L) during atherosclerosis development and plaque destabilization.The objective of the present study was to test the hypothesis that sCD40L levels are higher in acute coronary syndrome (ACS) patients with a greater extent of angiographic coronary involvement.Methods This cross-sectional study examined ACS patients who underwent coronary angiography by measuring their sCD40L levels.In order to estimate the serum levels of sCD40L,10 ml of peripheral venous blood was drawn within 24 hours of admission.sCD40L levels were measured using an enzyme-linked immunosorbent assay (ELISA,RapidBio,West Hills,CA,USA).Demographic data,presence of concomitant diseases,ACS characteristics,and angiographic findings were evaluated.A review of medical records and patient interviews were conducted to assess coronary risk factors.And the severity of coronary artery disease was evaluated using the Gensini score index.Results Two hundred and eighty-nine patients were included in the study,of whom 186 were male,with an average age of 64.1±10.0 years.Median sCD40L levels were 1.7 ng/ml (0.3-7.3 ng/ml) and Gensini scores were 50 (0-228).After adjusting for demographic variables and cardiovascular risk factors,the Gensini score was associated with the natural logarithm of the sCD40L level (Coefficient b=0.002,95％ CI 0.000-0.003,P=0.029).Conclusion sCD40L levels were independently associated with angiographic severity of coronary artery disease in patients with ACS.