The aim of our study was to evaluate the role of the IgG, IgM and IgA isotypes in the diagnosis of SLE, and their association with clinical features and disease activity, in a large cohort of SLE patients, using isotype-specific ELISA assays based on human recombinant dsDNA as antigen source. The gene discussed is CD40LG; the disease is systemic lupus erythematosus.