Reversal of T cell anergy in leprosy patients: in vitro presentation with Mycobacterium leprae antigens using murabutide and Trat peptide in liposomal delivery.

Mycobacterium leprae, the causative agent of leprosy resides and multiplies within the host monocytes and macrophages, thereby evading host immune system. Cell-mediated immune response (CMI) plays a vital role as evidenced from the high CMI in BT/TT (borderline and tuberculoid) patients and conversely low in BL/LL (borderline and lepromatous) patients. In the present study, an attempt was made to immunomodulate the anergized T cells of lepromatous leprosy patients by presenting the mycobacterial antigen in combination with T cell adjuvant, murabutide (active analog of muramyl' dipeptide, MDP-BE) and a Trat peptide (T cell epitope of Integral membrane protein (Trat) from Escherichia coli) in particulate form (liposomes) or soluble form (media). PBMNC of normal, BT/TT and BL/LL were stimulated in vitro with five mycobacterial antigens (Ag) in the following formulations, Ag, Ag+murabutide, Ag+murabutide+Trat peptide either in liposomes or in medium. All the five antigen(s) when delivered in liposomes containing murabutide and Trat peptide showed a very high lymphoproliferative response (p<0.001) in all the three groups. IFN-gamma and IL-2 were significantly (p<0.001) high in these culture supernatants compared to IL-10 and IL-4 confirming a shift from CD4+Th2 to Th1 response in leprosy patients with particulate mode of antigen presentation. Interestingly, PBMNC derived from lepromatous patients also showed consistent T cell proliferation with all the formulations. Further, the mechanism of liposomal processing of antigens was studied using different inhibitors that interfere at different stages of antigen presentation. Results indicate that this study may pave way for an immunotherapeutic approach for reverting the anergic T cells of lepromatous patients to proliferating T cells with the release of Th1 cytokines thereby restoring the CMI response in these patients.

Absence of antibodies to muramyl dipeptide in patients with tuberculosis or leprosy.

The enzyme-linked immunosorbent assay (ELisa) was used to detect the presence of antibodies to muramyl dipeptide (MDP) in serum of patients with leprosy or tuberculosis. Using a conjugate of MDP-lysine to horse radish peroxidase, no such antibodies could be detected in sera of either patients or controls. Antibodies to a sonicate antigen of Mycobacterium tuberculosis were found in sera of all individuals tested and the binding of these antibodies to the M. tuberculosis antigen could not be inhibited by MDP. On the other hand, binding of MDP to anti-MDP antibodies, raised in rabbits, was largely inhibited by free MDP, slightly inhibited by M. tuberculosis antigen and was not inhibited by the patients' sera.

Activation of the alternative pathway of complement by mycobacteria and cord factor.

The ability of a number of mycobacteria and some of their components to activate complement was examined. Mycobacterium bovis BCG (Glaxo strain), Mycobacterium leprae, Mycobacterium lepraemurium, and cord factor activated the alternative pathway of complement in normal human serum and normal and C4-deficient guinea pig sera and generated biologically active products. BCG (Pasteur strain) and muramyl dipeptide did not activate complement. The relevance of activation of complement by mycobacteria to their induction of granulomas is discussed.