Presence of human T-cell responses to the Mycobacterium leprae 45-kilodalton antigen reflects infection with or exposure to M. leprae

Molecular epidemiology of leprosy: An update

Molecular epidemiology investigations are notoriously challenging in the leprosy field mainly because the inherent characteristics of the disease as well as its yet uncultivated causative agents, Mycobacterium leprae and M. lepromatosis. Despite significant developments in understanding the biology of leprosy bacilli through genomic approaches, the exact mechanisms of transmission is still unclear and the factors underlying pathological variation of the disease in different patients remain as major gaps in our knowledge about leprosy. Despite these difficulties, the last two decades have seen the development of genotyping procedures based on PCR-sequencing of target loci as well as by the genome-wide analysis of an increasing number of geographically diverse isolates of leprosy bacilli. This has provided a foundation for molecular epidemiology studies that are bringing a better understanding of strain evolution associated with ancient human migrations, and phylogeographical insights about the spread of disease globally. This review discusses the advantages and drawbacks of the main tools available for molecular epidemiological investigations of leprosy and summarizes various methods ranging from PCR-based genotyping to genome-typing techniques. We also describe their main applications in analyzing the short-range and long-range transmission of the disease. Finally, we summarise the current gaps and challenges that remain in the field of molecular epidemiology of leprosy.

Analysis of antigens of Mycobacterium leprae by interaction to sera IgG, IgM, and IgA response to improve diagnosis of leprosy

Till 2010, several countries have declared less than one leprosy patient among population of 10,000 and themselves feeling as eliminated from leprosy cases. However, new leprosy cases are still appearing from all these countries. In this situation one has to be confident to diagnose leprosy. This review paper highlighted already explored antigens for diagnosis purposes and finally suggested better combinations of protein antigens of M. leprae versus immunoglobulin as detector antibody to be useful for leprosy diagnosis.

Evaluation of Recombinant Serine-rich 45-kDa Antigen (ML0411) for Detection of Antibodies in Leprosy Patients

The potential of the recombinant serine-rich 45-kDa antigen (ML0411) of Mycobacterium leprae to aid in detecting M. leprae-specific serum antibodies was assessed by an enzyme-linked immunosorbent assay (ELISA) in leprosy patients and controls comprising of tuberculosis patients, other unrelated skin-diseased patients and healthy individuals from India. All 18 multibacillary (MB) and 18/38 (47.4%) of the paucibacillary (PB) leprosy patients were found positive. None of the controls was positive, yielding complete (0/49) specificity in the series tested here. On the other hand, an anti-phenolic glycolipid-1 (PGL-I) antibody-detecting assay yielded detectable responses in 94.4% (17/18) of MB and 36.8% (14/38) of PB leprosy patients. Only two of 49 (4.1%) controls were positive, giving a specificity of 95.9%. Further, there was a good concordance (agreement of 83.8%; chi(2) = 40.3, P < 0.001; kappa = 0.63) between the two assays. Thus, the 45-kDa-based assay was slightly better than anti-PGL-I antibody-detecting assay. Interestingly, when combining the results of both the assays together for all leprosy patients (MB + PB), the combined sensitivity was significantly higher than that of the anti-PGL-I antibody-detecting ELISA alone (73.2% versus 55.4%; P < 0.05), but not (P > 0.05) compared with the 45-kDa antigen-based assay alone. Similarly, in case of PB patients, using both assays in combination, the sensitivity was significantly higher compared with anti-PGL-I antibody-detecting assay alone (60.5% versus 36.8%; P < 0.05). While adopting the combinatorial approach, the specificity remained invariably high (>95%). In conclusion, the results of the present study indicate that the M. leprae 45-kDa protein is a potent B-cell antigen and may be a useful serodiagnostic reagent.

Gamma interferon responses induced by a panel of recombinant and purified mycobacterial antigens in healthy, non-mycobacterium bovis BCG-vaccinated Malawian young adults

We have previously shown that young adults living in a rural area of northern Malawi showed greater gamma interferon (IFN-gamma) responses to purified protein derivatives (PPD) prepared from environmental mycobacteria than to PPD from Mycobacterium tuberculosis. In order to define the mycobacterial species to which individuals living in a rural African population have been exposed and sensitized, we tested T-cell recognition of recombinant and purified antigens from M. tuberculosis (38 kDa, MPT64, and ESAT-6), M. bovis (MPB70), M. bovis BCG (Ag85), and M. leprae (65 kDa, 35 kDa, and 18 kDa) in >600 non-M. bovis BCG-vaccinated young adults in the Karonga District of northern Malawi. IFN-gamma was measured by enzyme-linked immunosorbent assay (ELISA) in day 6 supernatants of diluted whole-blood cultures. The recombinant M. leprae 35-kDa and 18-kDa and purified native M. bovis BCG Ag85 antigens induced the highest percentages of responders, though both leprosy and bovine tuberculosis are now rare in this population. The M. tuberculosis antigens ESAT-6 and MPT64 and the M. bovis antigen MPB70 induced the lowest percentages of responders. One of the subjects subsequently developed extrapulmonary tuberculosis; this individual had a 15-mm-diameter reaction to the Mantoux test and responded to M. tuberculosis PPD, Ag85, MPT64, and ESAT-6 but not to any of the leprosy antigens. We conclude that in this rural African population, exposure to M. tuberculosis or M. bovis is much less frequent than exposure to environmental mycobacteria such as M. avium, which have antigens homologous to the M. leprae 35-kDa and 18-kDa antigens. M. tuberculosis ESAT-6 showed the strongest association with the size of the Mantoux skin test induration, suggesting that among the three M. tuberculosis antigens tested it provided the best indication of exposure to, or infection with, M. tuberculosis.

Human T cell responses to peptides of the Mycobacterium leprae 45-kD serine-rich antigen

In order to identify T cell epitopes within the Mycobacterium leprae 45-kD serine-rich antigen, we analysed responses to overlapping 17-mer peptides encompassing the whole antigen in non-exposed UK controls, Pakistani leprosy patients and tuberculosis patients in both the United Kingdom and Pakistan. This antigen has been described as M. leprae-specific, although it has a hypothetical homologue in M. tuberculosis. Human peripheral blood mononuclear cells were stimulated with peptide for 5 days and IFN-gamma measured in supernatants by ELISA. Some peptides were recognized more frequently by T cells from tuberculoid leprosy patients than those from UK controls, suggesting that such T cell epitopes might have diagnostic potential, while other peptides induced greater responses among UK control subjects. Short-term cell lines confirmed that these assays detected specific T cell recognition of these peptides. However, many tuberculosis patients also recognized these potentially specific peptides suggesting that there could be a true homologue present in M. tuberculosis.