Abstract： Background:SmD1-amino-acid 83-119 peptide (SmD183-119) is the major epitope of Smith (Sm) antigen,which is specific for adult systemic lupus erythematosus (SLE).The anti-SmD183-119 antibody has exhibited higher sensitivity and specificity than anti-Sm antibody in diagnosing adult SLE.However,the utility of anti-SmD183-119 antibodies remains unclear in children with SLE (cSLE).This study aimed to assess the characteristics of anti-SmD 183-119 antibody in the diagnosis of cSLE.Methods:Samples from 242 children with different rheumatological and immunological disorders,including autoimmune diseases (SLE [n =46] and ankylosing spondylitis [AS,n =11]),nonautoimmune diseases (Henoch-Schonlein purpura [HSP,n =60],idiopathic thrombocytopenia purpura [n =27],hematufia [n =59],and arthralgia [n =39]) were collected from Shanghai Children's Medical Center from March 6,2012 to February 27,2014.Seventy age-and sex-matched patients were enrolled in this study as the negative controls.All the patients' sera were analyzed for the anti-SmD 183-119,anti-Sm,anti-U 1-nRNP,anti-double-stranded DNA (dsDNA),anti-nucleosome,anti-SSA/Ro60,anti-SSA/Ro52,anti-SSB,anti-Scl-70,and anti-histone antibodies using the immunoblotting assay.The differences in sensitivity and specificity between anti-SmD183-119 and anti-Sm antibodies were compared by Chi-square test.The correlations between anti-SmD183-119 and other auto-antibodies were analyzed using the Spearman's correlation analysis.A value of P ＜ 0.05 was considered statistically significant.Results:Thirty-six out of 46 patients with cSLE were found to be positive for anti-SmD183-119,while 12 patients from the cSLE cohort were found to be positive for anti-Sm.Compared to cSLE,it has been shown that anti-SmD183-119 was only detected in 27.3％ of patients with AS and 16.7％ of patients with HSP.In comparison with anti-Sm,it has been demonstrated that anti-SmD 183-119 had a higher sensitivity (78.3％ vs.26.1％,x2 =25.1,P ＜ 0.05) and a lower specificity (90.8％ vs.100％,x2 =13.6,P ＜ 0.05) in the diagnosis of cSLE.Further analysis revealed that anti-SmD183-119 antibodies were positively correlated with anti-dsDNA,anti-nucleosome,and anti-histone antibodies in cSLE.Moreover,it has been clearly shown that anti-SmD183-119 was more sensitive than anti-Sm in discriminating autoimmune diseases from nonautoimmune disorders in patients with arthralgia or hematuria.Conclusions:Measurement of anti-SmD183-119 in patients with cSLE has a higher sensitivity and a marginally lower specificity than anti-Sm.It has been suggested that inclusion of anti-SmD183-119 testing in the integrated laboratory diagnosis of cSLE may significantly improve the overall sensitivity in child populations.