The functional state of the complement system in leprosy.

Ninety-one patients with different clinical forms of leprosy, 36 lepromatous (LL), 33 tuberculoid (TL), and 22 dimorphic (DL), and 31 healthy volunteer donors were included in this study. Total complement system (CS) activity was assessed by hemolytic methods, whereas individual components were quantified by the enzyme-linked immunosorbent assay. Under conditions allowing initiation of cascade by the classic pathway (CP) but not alternative pathway (AP) activation, significant CS consumption was detected only in sera from patients with LL. In this group of patients, C4 but not factor B (fB) or C3 was significantly reduced, whereas mannose-binding lectin (MBL) serum levels were significantly higher. These results indicate that the CP is involved in CS activation in patients infected with Mycobacterium leprae manifesting LL clinical form of leprosy. An association is likely between circulating immune complexes and MBL high serum levels for initiation of CS activation in patients with LL form of leprosy.

Cloning and sequencing of a Bordetella pertussis serum resistance locus.

We have characterized a new virulence factor in Bordetella pertussis: serum resistance. Compared with Escherichia coli HB101, wild-type B. pertussis was relatively resistant to classical-pathway, complement-dependent killing by normal human serum. However, a mutant of B. pertussis (BPM2041) which is less virulent in mice and which has Tn5 lac inserted in a previously uncharacterized bvg-regulated gene was found to be at least 10-fold more susceptible to serum killing than the wild type. We have named this locus brk, for Bordetella resistance to killing. We have cloned and sequenced the brk locus, and it encodes two divergently transcribed open reading frames (ORFs), termed BrkA and BrkB. Both ORFs are necessary for serum resistance. Within the 300 bases which separate the two ORFs and upstream of each ORF are putative sites for BvgA binding. BrkA shows 29% identity to pertactin and has two RGD motifs in addition to a conserved proteolytic processing site and an outer membrane targeting signal. Like pertactin, BrkA is involved in adherence and invasion. Despite the similarities, a pertactin mutant was found to be not as sensitive to serum killing as the BrkA or BrkB mutants. BrkB is similar to ORFs in E. coli and Mycobacterium leprae and displays domains of homology to various transporters. On the basis of its hydropathy profile, BrkB is predicted to be a cytoplasmic membrane protein. By Southern blot, brk sequences were found in Bordetella bronchiseptica and Bordetella parapertussis but not in Bordetella avium.

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)

Inhibition of complement activity in murine leprosy.

NIH mice infected with Mycobacterium lepraemurium (MLM) show a marked depression in their levels of hemolytic complement that is proportional to the degree of infection. The defect affects more the activation of complement through the classical pathway (CPW) than the activation of complement through the alternative pathway. Although this low activity of CPW-complement may be due to different causes (complement consumption by the infecting microorganism, lack of biosynthesis of complement components, or the presence of complement inhibitory factors), our results seem to support the last possibility. The generation of factors in the infected animals that inhibit the autologous activity of complement as the infection goes on reduces the risk of complement-mediated tissue damage and prolongs the survival time of the host, a wise strategy on the part of the MLM to assure its own survival as a parasite.

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

The activation of the complement system by phenolic glycolipid 1 (PGL) from Mycobacterium leprae was studied. It was found that PGL consumed haemolytic complement through both the classical and the alternative pathways. This was further studied at the level of C3. Although the activation was independent of anti-PGL antibodies present in normal human serum, the addition of antibody augmented the activation of complement by PGL. The uptake of C3 through the classical pathway was enhanced predominantly by IgM antibody whereas, IgG antibody against PGL was responsible for the augmentation of the alternative pathway activation. Furthermore, it was found that both the disaccharide and trisaccharide components of PGL were able to activate the complement system.

Comprehensive evaluation of complement components in the course of type I (Lepra) and type II (ENL) reactions.

Complement components C1q and C4 of classic pathway; C3d, a breakdown product of C3, and factor B of alternate pathway: and C3, a component both of classic and alternate pathways, were studied in 35 patients, comprising 18 type I (Lepra) and 17 type II (ENL) reactions. There was a significant decrease in C3 and factor B with a concomitant rise of C3d during ENL. These changes indicate their preeminent role in immunogenesis of type II (ENL) reaction. The changes in the classic pathway components, on the other hand, were insignificant, apparently suggesting its limited involvement in ENL. Furthermore, reversion of factor B and C3d after subsidence of reaction is intriguing and may indicate that they are not substantially affected even with contemporary treatment. Complement components, of both classic and alternate pathways, showed no significant alterations either during type I (Lepra) reaction or after its amelioration.

Reduced complement-mediated immune complex solubilization in leprosy patients.

The ability of sera from leprosy patients to solubilize immune precipitates in vitro through the complement system was studied. The solubilizing capacity of sera from patients who did not have any reactions during 2 years or more after starting chemotherapy was comparable with that of normal laboratory volunteers. On the other hand, sera from borderline tuberculoid and lepromatous leprosy patients in reaction had markedly decreased levels of solubilization. Their total and the alternative pathway haemolytic levels did not show a corresponding decrease. Although the circulating immune complexes and serum C3d of these patients came down after the subsidence of reaction, their solubilization remained consistently low during a 3 month follow-up period.