RESUMO
BACKGROUND Leprosy remains a health problem in many countries, with difficulties in diagnosis resulting in delayed treatment and more severe disabilities. Antibodies against several Mycobacterium leprae antigens have, however, shown value as diagnostic and/or prognostic markers. OBJECTIVES The objective of this study was to evaluate serum immunoglobulin (Ig) IgM and IgG subclass reactivity against three M. leprae specific antigens: NDO-HSA, a conjugate formed by natural octyl disaccharide bound to human serum albumin; LID-1, the fusion protein product of the ml0405 and ml2331 genes; and NDO-LID, a combination of LID-1 and NDO. METHODS Sera from healthy controls, paucibacillary (PB) and multibacillary (MB) leprosy patients, and their respective household contacts, were evaluated for the presence of antigen-specific IgM, IgG, and IgG subclass antibodies by enzyme-linked immunosorbent assay (ELISA). The sensitivity and specificity of each ELISA were evaluated by receiver operating characteristic (ROC) curve analysis. FINDINGS Our data confirm that serum IgM antibodies against NDO-HSA and IgG antibodies against LID-1, as well as IgG/M antibodies against NDO-LID, are markedly increased in MB patients. For the first time, our data reveal a selective increase in IgG1 and IgG3 antibodies against LID-1 and NDO-LID in MB patients, demonstrating that these antibody isotypes are suitable for differentiation between MB and PB patients. ROC curve analysis indicates an improved capacity for diagnosing MB leprosy patients using the detection of IgG antibodies, particularly the IgG1 isotype, specific to LID-1 and NDO-LID over the performance levels attained with NDO-HSA. CONCLUSIONS Our findings indicate that serological tests based on the detection of antigen-specific IgG1 antibodies are a useful tool to differentiate MB from PB patients, and indicate the enhanced performance of the LID-1 and NDO-LID antigens in the serodiagnosis of leprosy.