Cross-reactivity of Mycobacterium leprae and M. tuberculosis and the implications for assessment of in vitro T cell function in leprosy patients.

The cross-reactivity in vitro between Mycobacterium leprae and M. tuberculosis was studied in 41 Aboriginal Australians with leprosy, 78 uninfected contacts of leprosy patients and 38 control individuals. A vigorous T cell response to epitopes cross-reactive between these two mycobacteria was found for healthy uninfected contacts or non-contacts (controls) of leprosy patients, but not for the patients themselves. The data suggest that a vaccine based on antigen shared between M. leprae and other mycobacteria is unlikely to be useful in preventing leprosy. Further studies of responses in vitro to purified T cell-reactive antigens would be useful in designing newer vaccines for more widespread field studies of leprosy prevention.

Leprosy and immunity: genetics and immune function in multiple case families.

Genetic susceptibility to infection with M. leprae was studied in 10 multiple case families of Australian Aborigines. Of the 87 members available for study, 24 had proven stable clinical leprosy which had been or was still being treated with diamino diphenyl sulphone. Evidence of contact with M. leprae in the remaining 63 members as assessed by ELISA to M. leprae sonicate and phenolic glycolipid (PGL) or by indirect immunofluorescence antibody assay was found in 78%, 64% and 71%, respectively. By contrast, in vitro assays of T cell function (LMAT and LTT) were less reliable indicators of exposure. Evidence was sought for possible linkages between human leucocyte antigen (HLA) or non-HLA genes and four marker phenotypes including clinical leprosy, clinical subtype of leprosy and lymphocyte transformation or leucocyte migration inhibition factor (LIF) production in response to M. leprae antigen. No associations were found with any particular HLA or non-HLA gene. On the other hand, sequential analysis of the data from the 10 families was strongly suggestive of a linkage between HLA haplotype and non-responsiveness to M. leprae as manifest by lack of LIF production but not lymphocyte transformation. The model which best fits the data is for a gene on chromosome 6 in close linkage with the HLA haplotype, with two alleles, autosomal recessive inheritance and penetrance of 90%. On this basis, it can be suggested that disease type (lepromatous leprosy) rather than disease susceptibility may be controlled by genes within or closely linked to the major histocompatibility gene complex.

Clinical significance of changes in serum proteins, immunoglobulins, and autoantibodies in leprosy.

Changes in the level of acute phase reactants such as C-reactive protein (CRP), serum globulins, and autoantibodies have been reported previously in patients with leprosy, particularly at the lepromatous end of the spectrum. The clinical significance of these findings was investigated by comparing the same parameters of humoral immune function in populations of Australian Aboriginals with stable treated leprosy and relevant contact groups including a) noninfected European sporadic contacts and b) healthy Aboriginal relatives of patients with confirmed leprosy. Raised levels of CRP and immunoglobulins and the higher frequency of autoantibodies seen in leprosy patients compared with sporadic contacts are probably related to differences in the incidence of nonleprous infection rather than to leprosy per se. Comparable results were obtained in the leprosy patients and their family contacts. The data highlight the need to use antigen-specific assays for determining the significance of changes in acute phase reactants and for distinguishing between the primary and secondary effects of Mycobacterium leprae infection.