T-Cell antigens and skin test reagents
New developments in T-cell studies are allowing T-cell responses to M. leprae to be measured in large-scale field studies. These include the development of simple, whole blood culture assays to measure T-cell proliferation or cytokine production in response to antigen. These assays are currently being used in Nepal to test the antigenicity of new skin test reagents, and in Malawi to monitor changes in T-cell immunity induced by BCG vaccination in 700 volunteers. Such assays could be used to measure T-cell responses and their relationship to antibody responses in household contacts.
A new tuberculin-like skin test reagent for leprosy could be used to monitor the prevalence of preclinical infection in the community, to monitor interventions and to focus leprosy control efforts. Two initiatives to develop M. leprae-specific skin test reagents are underway. Cell wall and cytosolic antigen fractions have been produced in the first initiative. The fractions are depleted of carbohydrates and lipids and go into phase I testing in late 1998. Phase II and III trials are planned for Nepal. Another WHO initiative is screening synthetic peptides for M. leprae in a multi-enter study to identify M. leprae-specific peptide epitopes and preliminary results have identified some promising candidates. Specificity testing must be met prior to advancing these reagents in the study protocol. It is anticipated that completion of the genome project may give rise to other M. leprae-specific proteins useful for testing as potential skin test reagents.
Nasal carriage of M. leprae
An important area gaining much interest involves defining rates of nasal carriage of M. leprae in leprosy endemic communities. PCR for M. leprae DNA and monoclonal anti-body-directed staining of M. leprae-specific antigen have been used successfully for this purpose. Initial results range between 3-9 % Positivity in household contacts of MB and PB index cases. New large-scale studies need to be performed to determine the relationship between transient contamination of the nose, continuous carriage of the bacilli (colonization?) and development of lesions on the nasal mucosa. Results from these types of studies may be pivotal in determining maintenance of an M. leprae reservoir in the community and eventually how M. leprae is transmitted. Studies to improve the reliability of these types of assays need to be performed. For example, large-scale screening of uninfected individuals needs to be performed to establish realistic levels of false-positive rates using these very sensitive assays.
Participants：
T Gillis, Chairman, P Brennan, Rapporteur, Sang-Nae Cho, Maria DaGraca S. Cunha, Jim Douglas, Stella Van Beers, Francoise Portaels, Hazel Dockrell, Tranquilino Fajardo, Utpal Sengu pta.
T Gillis GW Long Hansen's Disease Center, LA, U.S.A
