The expression and activation of Toll-like receptors (TLRs) was investigated in leprosy, a spectral disease in which clinical manifestations correlate with the type of immune response mounted toward Mycobacterium leprae. TLR2-TLR1 heterodimers mediated cell activation by killed M. leprae, indicating the presence of triacylated lipoproteins. A genome-wide scan of M. leprae detected 31 putative lipoproteins. Synthetic lipopeptides representing the 19-kD and 33-kD lipoproteins activated both monocytes and dendritic cells. Activation was enhanced by type-1 cytokines and inhibited by type-2 cytokines. In addition, interferon (IFN)-gamma and granulocyte-macrophage colony-stimulating factor (GM-CSF) enhanced TLR1 expression in monocytes and dendritic cells, respectively, whereas IL-4 downregulated TLR2 expression. TLR2 and TLR1 were more strongly expressed in lesions from the localized tuberculoid form (T-lep) as compared with the disseminated lepromatous form (L-lep) of the disease. These data provide evidence that regulated expression and activation of TLRs at the site of disease contribute to the host defense against microbial pathogens.

Leprosy is a chronic and debilitating human disease caused by infection with the Mycobacterium leprae bacillus. Despite the marked reduction in the number of registered worldwide leprosy cases as a result of the widespread use of multidrug therapy, the number of new cases detected each year remains relatively stable. This indicates that M. leprae is still being transmitted and that, without earlier diagnosis, M. leprae infection will continue to pose a health problem. Current diagnostic techniques, based on the appearance of clinical symptoms or of immunoglobulin M (IgM) antibodies that recognize the bacterial phenolic glycolipid I, are unable to reliably identify early-stage leprosy. In this study we examine the ability of IgG within leprosy patient sera to bind several M. leprae protein antigens. As expected, multibacillary leprosy patients provided stronger responses than paucibacillary leprosy patients. We demonstrate that the geographic locations of the patients can influence the antigens they recognize but that ML0405 and ML2331 are recognized by sera from diverse regions (the Philippines, coastal and central Brazil, and Japan). A fusion construct of these two proteins (designated leprosy IDRI diagnostic 1 [LID-1]) retained the diagnostic activity of the component antigens. Upon testing against a panel of prospective sera from individuals who developed leprosy, we determined that LID-1 was capable of diagnosing leprosy 6 to 8 months before the onset of clinical symptoms. A serological diagnostic test capable of identifying and allowing treatment of early-stage leprosy could reduce transmission, prevent functional disabilities and stigmatizing deformities, and facilitate leprosy eradication.Cases in which Mycobacterium leprae infection manifests to cause leprosy present as a bacteriologic, clinical, immunologic, and pathological spectrum ranging from the extremes observed in paucibacillary (PB) and multibacillary (MB) patients (21,24). PB patients have one or a few skin lesions and a low or absent bacterial index (BI; a measure of the number of acidfast bacilli in the dermis, expressed on a logarithmic scale) and demonstrate specific cell-mediated immunity against M. leprae, but they have low or absent titers of M. leprae-specific antibodies and a granulomatous dermatopathology. In marked contrast, MB patients have multiple symmetric skin lesions and a high BI and demonstrate high titers of anti-M. leprae antibodies but an absence of specific cell-mediated immunity and a dermatopathology largely devoid of functional lymphocytes (21). Despite the implementation of a WHO-directed eradication program over the last 20 years, the worldwide annual rate of new case detection for leprosy remains stable at approxi-