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.

Cellular and humoral immune responses to recombinant 65-kD antigen of Mycobacterium leprae in leprosy patients and healthy controls.

Cellular and humoral immune responses to recombinant 65-kD antigen of Mycobacterium leprae (rML65) were studied in leprosy patients and healthy contacts from a leprosy-endemic population. Peripheral blood mononuclear cells from a considerable proportion of tuberculoid leprosy patients, healthy contacts and non-contacts showed proliferative response to rML65 in vitro. A strong positive correlation was observed between the responses to rML65 and bacille Calmette-Guérin (BCG) or leprosin A. Addition of recombinant IL-2 (rIL-2) enhanced the proportion of responders to rML65 considerably in all groups of leprosy patients, healthy contacts and non-contacts. Among lepromatous patients this enhancement was more pronounced in the bacterial index (BI)-negative group. These results indicate that the 65-kD antigen of Myco. leprae is a dominant T cell immunogen in our study population. Though lepromatous patients showed poor lymphoproliferative response to rML65, their IgG antibody levels to the same antigen were markedly high. Most of the BI-positive lepromatous patients with elevated anti-rML65 IgG levels did not show T cell reactivity even with the addition of rIL-2. On the other hand, tuberculoid leprosy patients, healthy contacts and non-contacts showed good T cell reactivity but low levels of IgG antibodies to rML65, thus indicating the presence of an inverse relationship between cell-mediated and humoral immune responses to a defined protein antigen of Myco. leprae in humans. A significant proportion of individuals among tuberculoid leprosy patients, healthy contacts and non-contacts showed neither T cell reactivity nor elevated levels of IgG antibody to rML65. However, in most of these subjects, a T cell response to rML65 was demonstrable with the addition of rIL-2. These results are discussed with reference to the immunoregulatory mechanisms occurring during Myco. leprae infection on the basis of differential activation of Th1 and Th2 subsets.

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.

Flow cytometric analysis of CD2 modulation on human peripheral blood T lymphocytes by Dharmendra preparation of Mycobacterium leprae.

It has been reported previously that Mycobacterium leprae modulated CD2 on human peripheral blood T lymphocytes and that this modulation was accompanied by a marked reduction in the proliferative response of these cells to mitogens and antigens. In this study, we report that treatment of peripheral blood mononuclear cells from healthy individuals with Dharmendra preparation of M. leprae inhibited their ability to form rosettes with sheep red blood cells. Flow cytometric analysis of Dharmendra lepromin-treated cells showed that, in addition to CD2, CD4 and CD8 were modulated while the surface expression of CD3 was not affected. The specificity of CD2 modulation was confirmed by similar effects of Dharmendra lepromin on thymocytes and lymph node cells from human CD2 transgenic mice. The modulatory effect of Dharmendra lepromin was not observed at lower temperatures. Dharmendra lepromin treatment of activated T cells resulted in reduced binding of monoclonal antibodies to IL-2R and D66 epitope of CD2. The modulatory effects were not observed with Dharmendra preparation of BCG or other preparations of M. leprae. Our results indicate that certain M. leprae factor(s) specifically modulate(s) CD2, CD4, CD8 and IL-2R but not CD3 on T lymphocytes. The suppressive effect of Dharmendra lepromin on the T-cell proliferative response reported earlier may be explained by its modulatory effect on a number of T-cell surface molecules.