RESUMO
The detection of hundreds of thousands of new cases of leprosy every year suggests that transmission of Mycobacterium leprae infection still continues. Unfortunately, tools for identification of asymptomatic disease and/or early-stage M. leprae infection (likely sources of transmission) are lacking. The recent identification of M. leprae-unique genes has allowed the analysis of human T-cell responses to novel M. leprae antigens. Antigens with the most-promising diagnostic potential were tested for their ability to induce cytokine secretion by using peripheral blood mononuclear cells from leprosy patients and controls in five different areas where leprosy is endemic; 246 individuals from Brazil, Nepal, Bangladesh, Pakistan, and Ethiopia were analyzed for gamma interferon responses to five recombinant proteins (ML1989, ML1990, ML2283, ML2346, and ML2567) and 22 synthetic peptides. Of these, the M. leprae-unique protein ML1989 was the most frequently recognized and ML2283 the most specific for M. leprae infection/exposure, as only a limited number of tuberculosis patients responded to this antigen. However, all proteins were recognized by a significant number of controls in areas of endemicity. T-cell responses correlated with in vitro response to M. leprae, suggesting that healthy controls in areas where leprosy is endemic are exposed to M. leprae. Importantly, 50% of the healthy household contacts and 59% of the controls in areas of endemicity had no detectable immunoglobulin M antibodies to M. leprae-specific PGL-I but responded in T-cell assays to >or=1 M. leprae protein. T-cell responses specific for leprosy patients and healthy household contacts were observed for ML2283- and ML0126-derived peptides, indicating that M. leprae peptides hold potential as diagnostic tools. Future work should concentrate on the development of a sensitive and field-friendly assay and identification of additional peptides and proteins that can induce M. leprae-specific T-cell responses.
Assuntos
Interferon gama/biossíntese , Hanseníase/diagnóstico , Mycobacterium leprae/imunologia , Linfócitos T/imunologia , Adulto , Antígenos de Bactérias , Bangladesh , Brasil , Etiópia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Nepal , Paquistão , Proteínas Recombinantes , Sensibilidade e Especificidade , Adulto JovemRESUMO
The identification of human T-cell antigens of Mycobacterium leprae could improve treatment and help to disrupt the transmission of leprosy by directing diagnosis and vaccine programs. This study screened a panel of M. leprae recombinant proteins for T-cell recall responses, measured by gamma interferon (IFN-gamma) production, among leprosy patients. After initial studies using peripheral blood mononuclear cells from leprosy patients, we transitioned our studies to simple whole-blood assays (WBA), which are more applicable in field or clinical settings. T-cell responses generated in WBA using blood from individuals in Goiânia, Brazil, demonstrated that several M. leprae antigens (ML0276, ML0840, ML1623, ML2044, and 46f) elicited >0.5 IU/ml IFN-gamma, and these proteins were classified as immunogenic and leprosy specific. Several of these individual antigens were recognized by cells from >60% of Brazilian paucibacillary (PB) leprosy patients, and ML0276, ML0840, ML1623, and 46f complemented each other such that 82% of PB patients had strong (>1.25 IU/ml IFN-gamma) responses to at least one of these proteins. These proteins were also recognized by cells from a significant proportion of the household contacts of multibacillary leprosy patients, but in contrast, few responses were observed in active tuberculosis patients or healthy control groups from areas of endemicity. Our results indicate several potential candidate antigens which may be useful for either leprosy diagnosis or vaccination and demonstrate the utility of leprosy WBA that can be applied broadly in clinical or field settings.