The control of leprosy will be facilitated by the identification of major Mycobacterium leprae-specific antigens which mirror the immune response to the organism across the leprosy spectrum. We have investigated the host response to a 35-kDa protein of M. leprae. Recombinant 35-kDa protein purified from Mycobacterium smegmatis resembled the native antigen in the formation of multimeric complexes and binding by monoclonal antibodies and sera from leprosy patients. These properties were not shared by two forms of 35-kDa protein purified from Escherichia coli. The M. smegmatis-derived 35-kDa protein stimulated a gamma interferon-secreting T-cell proliferative response in the majority of paucibacillary leprosy patients and healthy contacts of leprosy patients tested. Cellular responses to the protein in patients with multibacillary leprosy were weak or absent, consistent with hyporesponsiveness to M. leprae characteristic of this form of the disease. Almost all leprosy patients and contacts recognized the 35-kDa protein by either a T-cell proliferative or an immunoglobulin G antibody response, whereas few tuberculosis patients recognized the antigen. This specificity was confirmed in guinea pigs, with the 35-kDa protein eliciting strong delayed-type hypersensitivity in M. leprae-sensitized animals but not in those sensitized with Mycobacterium tuberculosis or Mycobacterium bovis BCG. Therefore, the M. leprae 35-kDa protein appears to be a major and relatively specific target of the human immune response to M. leprae and is a potential component of a diagnostic test to detect exposure to leprosy or a vaccine to combat the disease.

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The immunomodulatory drug thalidomide is the treatment of choice for erythema nodosum leprosum (ENL), an inflammatory cutaneous and systemic complication of multibacillary leprosy. To elucidate the mechanism of action of thalidomide in this syndrome, we prospectively investigated 20 patients with ENL who were treated with thalidomide for 21 days. All patients responded to treatment, with the majority of them having complete resolution of cutaneous lesions within 7 days. This response was associated with a marked but transient increase in ex vivo mitogen-induced expression of interleukin (IL)-2 and interferon- gamma by CD4(+) and CD8(+) T cells that was observed on treatment day 7, but these returned to pretreatment levels by day 21. Plasma tumor necrosis factor- alpha levels were not high at baseline, and they increased modestly during treatment. Plasma levels of IL-12 increased steadily during thalidomide treatment. Hence, the therapeutic effect of thalidomide in ENL appears to be associated with transient immune stimulation, which suggests that the drug may promote an active immunoregulatory response.

Development of an immunological tool to detect infection with Mycobacterium leprae would greatly benefit leprosy control programmes, as demonstrated by the contribution of the tuberculin test to tuberculosis control. In a new approach to develop a 'tuberculin-like' reagent for use in leprosy, two new fractions of M. leprae depleted of cross-reactive and immunomodulatory lipids- MLSA-LAM (cytosol-derived) and MLCwA (cell wall-derived)-have been produced in a form suitable for use as skin test reagents. T cell responses (interferon-gamma (IFN-gamma) and lymphoproliferation) to these two new fractions were evaluated in a leprosy-endemic area of Nepal using a simple in vitro whole blood test. The two fractions were shown to be highly potent T cell antigens in subjects exposed to M. leprae-paucibacillary leprosy patients and household contacts. Responses to the fractions decreased towards the lepromatous pole of leprosy. Endemic control subjects also showed high responses to the fractions, indicating high exposure to M. leprae, or cross-reactive mycobacterial antigens, in this Nepali population. The new fractions, depleted of lipids and lipoarabinomannan (LAM) gave enhanced responses compared with a standard M. leprae sonicate. The cell wall fraction appeared a more potent antigen than the cytosol fraction, which may be due to the predominance of the 65-kD GroEL antigen in the cell wall. The whole blood assay proved a robust field tool and a useful way of evaluating such reagents prior to clinical trials.

An unexpectedly high proportion of healthy contacts of leprosy patients presented with PB leprosy within 12 weeks after receiving BCG vaccination, possibly as a result of boosted cell-mediated immunity by homologues of Mycobacterium leprae antigens in BCG. Various immunological mechanisms could underlie this phenomenon, including an immune reconstitution inflammatory syndrome (IRIS). Further studies are required to determine whether BCG vaccination merely altered the incubation period or actually changed the course of the infection from self-limiting, subclinical infection to manifest disease.

To assess the effectiveness of single-dose rifampicin (SDR) after bacillus Calmette-Guérin (BCG) vaccination in preventing leprosy in contacts. Methods: This was a single-centre, cluster-randomized controlled trial at a leprosy control programme in northwest Bangladesh. Participants were the 14 988 contacts of 1552 new leprosy patients who were randomized into the SDR À arm (n = 7379) and the SDR + arm (n = 7609). In the intervention group, BCG vaccination was followed by SDR 8-12 weeks later. In the control group, BCG vaccination only was given. Follow-up was performed at 1 year and 2 years after intake. The main outcome measure was the occurrence of leprosy. Results: The incidence rate per 10 000 person-years at risk was 44 in the SDR À arm and 31 in the SDR + arm at 1 year; the incidence rate was 34 in the SDR À arm and 41 in the SDR + arm at 2 years. There was a statistically non-significant (p = 0.148; 42%) reduction for paucibacillary (PB) leprosy in the SDR+ arm at 1 year. Of all new cases, 33.6% appeared within 8-12 weeks after BCG vaccination. Conclusions: In the first year, SDR after BCG vaccination reduced the incidence of PB leprosy among contacts by 42%. This was a statistically non-significant reduction due to the limited number of cases after SDR was administered. To what extent SDR suppresses excess leprosy cases after BCG vaccination is difficult to establish because many cases appeared before the SDR intervention. Trial registration: Netherlands Trial Register: NTR3087.

SUMMARYLevels of leprosy antigen-induced interferon-gamma (IFN-g), tumour necrosis factor alpha (TNF-a) and interleukin-10 (IL-10) were measured in 96 leprosy patients with type 1 reactions (T1R) before, during and after a standard 12-week course of steroids. Peripheral blood mononuclear cells (PBMC) from leprosy patients with untreated T1R produced significantly more TNF-a than leprosy patients without T1R. Median levels of IFN-g and TNF-a in T1R patients fell during treatment with steroids; however, TNF-a levels increased as the steroid dose was reduced. Median IL-10 levels increased throughout the steroid treatment period and were associated strongly with TNF-a levels. Patients with high cytokine levels had a poorer recovery of sensory or voluntary muscle nerve function, a higher risk of reactivation of symptoms during steroid treatment, and a higher risk of another episode of T1R within 2 months of completing the steroid regimen. Rapid and effective reversal of the inflammatory process in T1R is critical to prevent permanent nerve damage from T1R and monitoring cytokine levels during treatment may be useful.

ObjectivesWe wished to validate our recently devised 16-item ENLIST ENL Severity Scale, a clinical tool for measuring the severity of the serious leprosy associated complication of erythema nodosum leprosum (ENL). We also wished to assess the responsiveness of the ENLIST ENL Severity Scale in detecting clinical change in patients with ENL.MethodsParticipants, recruited from seven centres in six leprosy endemic countries, were assessed using the ENLIST ENL Severity Scale by two researchers, one of whom categorised the severity of ENL. At a subsequent visit a further assessment using the scale was made and both participant and physician rated the change in ENL using the subjective categories of “Much better”, “somewhat better”, “somewhat worse” and “much worse” compared with “No change” or “about the same”.Results447 participants were assessed with the ENLIST ENL Severity Scale. The Cronbach alpha of the scale and each item was calculated to determine the internal consistency of the scale. The ENLIST ENL Severity Scale had good internal consistency and this improved following removal of six items to give a Cronbach’s alpha of 0.77. The cut off between mild ENL and more severe disease was 9 determined using ROC curves. The minimal important difference of the scale was determined to be 5 using both participant and physician ratings of change.ConclusionsThe 10-item ENLIST ENL Severity Scale is the first valid, reliable and responsive measure of ENL severity and improves our ability to assess and compare patients and their treatments in this severe and difficult to manage complication of leprosy.The ENLIST ENL Severity Scale will assist physicians in the monitoring and treatment of patients with ENL. The ENLIST ENL Severity Scale is easy to apply and will be useful as an outcome measure in treatment studies and enable the standardisation of other clinical and laboratory ENL research.