Immunological profiles of leprosy patients and healthy family contacts toward M. leprae antigens.

In this study, we measured simultaneously the in vitro and in vivo T lymphocyte reactivities and the antibody responses of leprosy patients and healthy family contacts (HFC) toward Mycobacterium leprae antigens. The in vitro lymphoproliferative response of the HFC to leprosin A was comparable to that of tuberculoid leprosy patients. However, their skin-test reactivity to Dharmendra lepromin was considerably higher compared to the in vitro response to leprosin A. A significant number of HFC failed to respond to M. leprae antigens, both in vitro and in vivo, and the unresponsiveness to either test was not related to the type of leprosy patients in the household. A marginal correlation was observed between the skin-test reactivity of HFC and the age of the individuals. Even though a significant proportion of HFC showed positive anti-PGL-I IgM levels, none showed a positive titer in the serum antibody competition test toward the M. leprae-specific epitope My2. A positive anti-PGL-I IgM response together with a negative lepromin skin-test reactivity showed a clear downward trend from the lepromatous pole toward the tuberculoid pole. A small number of HFC, all contacts of lepromatous patients, were lepromin skin-test negative with positive anti-PGL-I IgM levels, but the majority among them showed T-cell reactivity to mycobacterial antigens in vitro. These results are discussed in relation to immunological correlates of the susceptibility to M. leprae infection.

IgG subclass antibodies to mycobacterial sonicate and recombinant antigens in leprosy.

In this study the IgG subclass antibodies to sonicated preparations of Mycobacterium leprae (leprosin A) and BCG (BCG-S) as well as to purified recombinant 65 kDa protein of M. leprae (rML65) were analysed in sera from leprosy patients and healthy household contacts (HFC) and noncontacts (HNC) in a leprosy endemic population. In LBI+ (lepromatous bacterial index positive) patients, IgG3 was predominant in the responses to sonicated antigens of M. leprae. Following chemotherapy, IgG3 responses were reduced while IgG2 levels were increased. On the other hand, IgG response to rML65 was dominated by IgG1 in all the patient and control groups. Interestingly, the level of antileprosin A IgG antibody in erythema nodosum leprosum (ENL) was similar to that of lepromatous groups, while the level of anti-rML65 IgG antibody was significantly reduced in ENL. IgG4 antibodies to the antigens studied were only at low levels in all groups, including ENL. Significant differences were observed between HNC and HFC in the pattern of IgG subclass antibodies to sonicated antigens, even though their antigen specific IgG levels were similar. While HNC showed equivalent proportion of IgG1 and IgG2 in their responses to leprosin A and BCG-S, HFC showed a specific increase in IgG1 levels, suggesting that both groups are distinctly different. Further studies are required to elucidate the functional significance of IgG subclass pattern in pathogenesis and the mechanism of immunoregulation resulting in the high levels of IgG1 and IgG3 antibodies to M. leprae protein antigens in lepromatous leprosy.

Antibody response to recombinant 65-kDa, 70-kDa and 18-kDa mycobacterial antigens in leprosy patients and healthy contacts in a leprosy-endemic population.

Antibody responses to recombinant Mycobacterium leprae 65-kDa (rML65) and 18-kDa (rML18), M. bovis BCG 65-kDa (rMB65) and M. tuberculosis 70-kDa (rMT70) antigens were measured by indirect ELISA in sera from leprosy patients and healthy contacts in a leprosy-endemic area in southern India. Antibody responses to M. leprae-specific epitopes on phenolic glycolipid-I (PGL-I) and a 35-kDa protein antigens also were measured simultaneously by PGL-I ELISA and the serum antibody competition test (SACT), respectively. Significantly higher levels of antibodies of the IgG isotype to rML65 and rMB65 were observed in bacterial index (BI)-positive, lepromatous (LBI+) patients but not in other groups of leprosy patients and endemic controls [healthy family contacts (HFC), healthy hospital contacts (HHC), and healthy non-contacts (HNC)]. LBI+ patients could be distinguished from LBI- patients on the basis of their higher levels of IgG antibodies to rML65, rMB65 and rMT70; lower levels of IgM antibodies to these antigens and higher levels of anti-PGL-I IgM levels. In the former group, 84% were SACT positive in contrast to 39% in the latter groups. Among lepromatous patients good positive correlations were observed between IgG antibody responses to rML65 and rMB65 and anti-PGL-I IgM levels, SACT ID50 titers as well as BIs. Among healthy controls, HFC had higher levels of IgG antibodies to rML65, but lower levels to rMB65 than did HNC. Thirty-nine percent of the HFC were seropositive to anti-PGL-I IgM antibodies in contrast to 4% in the HNC. On the basis of these criteria, the immune profile of the HFC appears to be distinctly different from that of the HNC, even though both groups are from the same endemic area. It is therefore possible that antibody response to defined protein antigens of mycobacteria is influenced by the lesional bacterial load in leprosy patients and by exposure to homologous proteins of M. leprae and/or related environmental mycobacteria in the case of healthy contacts and noncontacts. The above results are discussed in relation to T- and B-cell activity toward M. leprae antigens and the immunoregulatory mechanisms of antibody production in leprosy.

T lymphocyte reactivity of leprosy patients and healthy contacts from a leprosy-endemic population to delipidified cell components of Mycobacterium leprae.

In this study, we measured in vitro proliferative responses of peripheral blood mononuclear cells from both leprosy patients across the clinical spectrum and also healthy contacts from a leprosy-endemic population to delipidified cell components of Mycobacterium leprae (DCC) and Dharmendra lepromin. Dharmendra lepromin was poor in inducing in vitro T cell proliferation in all the study groups, even though it elicited marked in vivo skin test reaction in tuberculoid leprosy patients and healthy contacts. In contrast, Dharmendra preparation of BCG induced marked T-cell response in tuberculoid as well as bacterial index negative lepromatous patients. DCC induced a significantly higher lymphoproliferative response than Dharmendra lepromin in all study groups. A significant positive correlation was observed between the lymphoproliferative responses to DCC and BCG. The present study, based on a large number of leprosy patients and healthy contacts, clearly demonstrates that DCC, depleted of glycolipids and lipopolysaccharides, is a good antigenic preparation for evaluating T-cell reactivity to M. leprae.