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.

Antibodies to Mycobacterium tuberculosis-specific epitopes in lepromatous leprosy.

Sera from patients with leprosy or tuberculosis and healthy subjects have been analysed for the presence of antibodies to four species-specific mycobacterial epitopes, four different viruses and five autoantigens. Antibodies to the Mycobacterium leprae-specific 35-kD protein and phenolic glycolipid I epitopes were not present in patients with active pulmonary tuberculosis. In contrast, antibody levels to species-specific epitopes of the 38-kD and 14-kD antigens M. tuberculosis were significantly elevated in patients with lepromatous leprosy. Neither of the two antigens is cross-reactive with M. leprae at the B cell level. However, it was considered that cross-reactive helper T cells could recall the response of M. tuberculosis-specific memory B cells, which had been primed through prior self-healing tuberculous infection. As an alternative explanation, the possible role of polyclonal B cell stimulation was considered. This seemed unlikely, however, since: (i) antibody levels to autoantigens, except anti-smooth muscle, were not elevated, and (ii) antibody levels to four distinct viruses, unlike those to all mycobacterial epitopes, showed no correlation with titres, to M. tuberculosis-specific epitopes.

Total and anti-mycobacterial IgE levels in serum from patients with tuberculosis and leprosy.

A radioallergosorbent assay (RAST) was developed and used to determine the levels of IgE antibodies to soluble antigens of Mycobacterium tuberculosis (BCG vaccine strain) in sera from patients with tuberculosis and leprosy and in healthy control subjects. Total IgE levels in the same sera were quantitated with a commercial radioimmunoassay kit. Patients with tuberculosis and leprosy had higher total and specific IgE levels than the control groups but the overlap of levels in patients and controls was too great to render the difference diagnostically useful. Specific IgE levels were elevated in both tuberculosis and leprosy patients, suggesting that this antibody response is towards the shared mycobacterial antigens. No differences in total or specific IgE levels were found between healthy hospital workers occupationally exposed to patients with tuberculosis and factory workers who are not exposed.

Molecular study of the T cell repertoire in family contacts and patients with leprosy.

The specificity of lymphocyte proliferative responses of 22 family contacts and 7 patients with leprosy were analyzed using Ag fractions from soluble extracts of Mycobacterium leprae and Mycobacterium tuberculosis. Fractions 10-100 kDa m.w. from each extract were separated by SDS-polyacrylamide gel electrophoresis, electroblotted to nitrocellulose membrane and solubilized for use in lymphocyte culture. The main immunogenic fractions for both contacts and patients had m.w. of 12,000 to 22,000, 35,000 to 40,000, and 65,000. Determinants which were either distinct or shared by the two extracts were active in each of the immunogenic fractions. Lymphocyte proliferation following stimulation with separated Ag was found also in five subjects who failed to respond to the whole soluble extracts. Stimulatory synthetic peptides were identified for the 65 kDa protein Ag. This technique has permitted the screening of the T cell immune repertoire for the identification of the immunodominant Ag which merit further purification and molecular characterization.