Activation of the human complement system by phenolic glycolipid 1 of Mycobacterium leprae

B lymphocytes deficiency results in altered immune response and increased susceptibility to Mycobacterium leprae in a murine leprosy model

Leprosy is a chronic and infectious disease that primarily affects the skin and peripheral nervous system, presenting a wide spectrum of clinical forms with different degrees of severity. The distinct host immune response patters developed in the response to the bacillus Mycobacterium leprae, the leprosy etiologic agent, are associated with the spectral clinical forms and outcome of the disease. In this context, B cells are allegedly involved in the disease immunopathogenesis, usually as antibody-producing cells, but also as potential effector or regulatory elements. In order to determine the regulatory B cells role in experimental leprosy, this study evaluated the outcome of M. leprae infection in B cell deficient mice (BKO) and WT C57Bl/6 control, by means of microbiological/bacilloscopic, immunohistochemical and molecular analysis, performed 8 months after M. leprae inoculation. The results demonstrated that infected BKO showed a higher bacilli number when compared with WT animals, demonstrating the importance of these cells in experimental leprosy. The molecular analysis demonstrates that the expression of IL-4, IL-10 and TGF-β was significantly higher in the BKO footpads when compared to WT group. Conversely, there was no difference in IFN-γ, TNF-α and IL-17 expression levels in BKO and WT groups. IL-17 expression was significantly higher in the lymph nodes of WT group. The immunohistochemical analysis revealed that M1 (CD80⁺) cells counts were significantly lower in the BKO group, while no significant difference was observed to M2 (CD206⁺) counts, resulting a skewed M1/M2 balance. These results demonstrated that the absence of B lymphocytes contribute to the persistence and multiplication of M. leprae, probably due to the increased expression of the IL-4, IL-10 and TGF-β cytokines, as well as a decrease in the number of M1 macrophages in the inflammatory site.

The envelope layers of mycobacteria with reference to their pathogenicity

The review discusses current knowledge of the biosynthesis, composition and arrangement of the mycobacterial envelope, describes the biological activities of the constituents and considers how these activities may be relevant to the pathology of mycobacterial disease. The envelope possesses three structural components: plasma membrane, wall and capsule. Although the major biomolecules occurring in each of these parts are known, the distribution of numerous minor substances is poorly understood; an attempt has been made to assign them to particular positions on rational grounds. The plasma membrane appears to be a typical bacterial membrane but, though vital to the mycobacterium, probably plays little part in pathological processes. The wall partly resembles a Gram-positive wall, but is unusual in having a layer of lipid (mycolate esters) which is probably arranged to form a permeability barrier to polar molecules. The capsule, whose chemical composition has only recently been recognized, consists of polysaccharide and protein with traces of lipid; the arrangement of these components is imperfectly understood. Constituents of all parts of the envelope have biological activities which may be relevant. The likely importance of these activities in the overall effect of the envelope is considered.

A role for natural antibody in the pathogenesis of leprosy: antibody in nonimmune serum mediates C3 fixation to the Mycobacterium leprae surface and hence phagocytosis by human mononuclear phagocytes

We have previously determined that complement receptors on human mononuclear phagocytes and complement component C3 in nonimmune serum mediate phagocytosis of the intracellular bacterial pathogen Mycobacterium leprae, the agent of leprosy. We have also determined that C3 fixes selectively to the major surface glycolipid of M. leprae, phenolic glycolipid 1 (PGL-1). In this study, we have explored the role of natural antibody in nonimmune serum in C3 fixation and C1q binding to M. leprae and PGL-1. At serum concentrations within the range at which phagocytosis of M. leprae is maximal, C3 fixation was mediated by both the classical and the alternative complement pathways. At the low end of this serum concentration range (2.5%), C3 fixation was mediated predominantly by the classical pathway. Consistent with a role for both pathways, C3 fixation to M. leprae was enhanced by the addition of either pure C1q to C1q-depleted serum or pure factor B to factor B-depleted serum. C3 fixation to M. leprae was strictly antibody dependent regardless of the serum concentration used. C3 fixation to M. leprae occurred in nonimmune serum but not in agammaglobulinemic serum unless heat-inactivated nonimmune serum or small amounts of pure immunoglobulin G (IgG) or IgM were added. C3 fixation by both the alternative and the classical complement pathways was mediated by antibody, and the antigen-binding portion of the antibody molecule was required. C3, IgG, IgM, and C1q were readily detected on the surface of M. leprae. Consistent with the previously demonstrated exclusive role of the classical complement pathway in C3 fixation to PGL-1, C1q bound to PGL-1 in a dose-dependent fashion; C1q binding was evident in > 1.25% nonimmune serum. C1q binding to PGL-1 was strictly antibody dependent. When PGL-1 was incubated with pure C1q, little or no C1q bound to PGL-1 unless heat-inactivated nonimmune serum or pure IgG or IgM was added. When PGL-1 was incubated in nonimmune serum, C3 bound directly to PGL-1 and not to anti-PGL-1 antibody, since the amount of C3 bound to PGL-1 was not reduced by acid elution of the antibody. However, the amount of C3 bound to PGL-1 was markedly reduced by hydroxylamine treatment, providing evidence for C3 fixation via a covalent ester bond. Nonimmune serum contained antibody to all four major M. leprae surface carbohydrates. Relative to PGL-1, nonimmune serum contained more antibody to the other surface carbohydrates.(ABSTRACT TRUNCATED AT 400 WORDS)