T cell responses to fractionated Mycobacterium leprae antigens in leprosy. The lepromatous nonresponder defect can be overcome in vitro by stimulation with fractionated M. leprae components

Abstract

Protective immunity against Mycobacterium leprae is dependent on M. leprae-reactive T lymphocytes. M. lepare-directed T cell reactivity is high in the localized tuberculoid form of leprosy but specifically absent in the disseminated lepromatous type of the disease. Two important questions that are relevant for the understanding of the immune response in leprosy as well as for the design of rational immunoprophylaxis and -therapy strategies are: (a) what are the antigens that trigger T cell responses in tuberculoid patients and thus protect these individuals from developing lepromatous leprosy and (b) is it possible to restore T cell responsiveness to M. leprae in lepromatous patients by rechallenging the immune system with selected antigens that will trigger help but not suppression? We have addressed these question by directly probing the peripheral T cell repertoire of 10 tuberculoid and 18 lepromatous patients with large numbers of different M. leprae and BCG antigenic components that had been separated on the basis of their relative molecular mass (Mr) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electroblotted onto nitrocellulose. This technique allows the identification of T cell-stimulating antigens independent of the expression of B cell epitopes by these antigens. So far T cell epitopes have only been mapped on M. leprae proteins that had previously been defined by antibodies. Our results show that: (a) tuberculoid patients' T cells responded preferentially to M. leprae and BCG antigens in the lower (i.e. less than 70 kDa) Mr range with a peak in the 10-25 kDa range; (b) 6 out of 18 lepromatous patients that did not respond to whole M. leprae responded strongly to isolated M. leprae components; antigens in the lower Mr. range were recognized by five out of these six patients and thus commonly seen by both tuberculoid and lepromatous patients' T cells; however, antigens in the higher Mr range, in particular greater than 150 kDa, were only recognized by lepromatous patients' T lymphocytes; (c) furthermore, the T and B cell repertoires in leprosy patients are skewed towards different antigenic fractions.

Immunological suppression by human CD8+ T cells is receptor dependent and HLA-DQ restricted.

“…As noted above, a majority of such patients can be immunized therapeutically to clinically upgrade their immune responses to M. Ieprae and, in some cases, cure their infection (11). Lymphocytes from a third of lepromatous patients studied, although unresponsive to intact M. leprae, have been reported to be able to respond to electrophoretic fractions of M. leprae extracts (26). These findings are most consistent with the interpretation that suppression is one mechanism of peripheral tolerance in leprosy.…”

Definition of a human suppressor T-cell epitope.

“…Several lines of evidence suggest that the M. leprae-specific T-cell nonresponsiveness observed in LL patients is not due to an absence ofM. leprae-reactive T cells or to defective antigen presentation as claimed in earlier reports (10,11) but may be due to active down-regulation of M. leprae-specific T-cell responses, presumably by suppressor T (Ts) cells induced by M. leprae (12)(13)(14). Supporting this latter premise, we and others have previously isolated CD4+ and CD8+ T-cell clones from the peripheral blood and skin lesions of LL patients and shown that these T cells specifically suppress mycobacterium-specific T-cell responses in vitro (15)(16)(17).…”

Lack of cytotoxic activity against Mycobacterium leprae 65-kD heat shock protein (hsp) in multibacillary leprosy patients

“…bovis bacille Calmette-Guerin (BCG)-vaccinated individuals against Myco. leprae recombinant proteins [11][12][13] and induction of cytotoxic T lymphocytes by the recombinant 65-kD heat shock protein (hsp65) of Myco. bovis BCG have been demonstrated [14][15][16].…”