Dominant recognition of a cross‐reactive B‐cell epitope in Mycobacterium leprae 10 K antigen by immunoglobulin G1 antibodies across the disease spectrum in leprosy

Abstract

Mycobacterium leprae-specific immunoglobulin G1 (IgG1) antibodies in patients with leprosy show a direct correlation with bacterial load (rho=0.748; P<0002) suggesting that IgG1 B-cell responses may be surrogate markers of disease progression. To investigate if this upregulation was a general feature of IgG1 responses to all M. leprae (ML) antigens, we analysed responses to several recombinant purified ML heat-shock proteins (HSP). Three recombinant HSPs (ML10 K, ML 18 K and ML 65 K) were tested for their ability to induce various IgG subclasses in patients with either the lepromatous (LL/BL, n=26) or tuberculoid form (BT/TT, n=39) of the disease as well as in healthy households (HC, n=14) and endemic controls (EC=19). Our major findings were: (1) selective augmentation of IgG1 antibody responses to ML10 K; (2) recognition of a restricted number of epitopes across the disease spectrum and healthy controls by IgG1 antibodies; (3) dominant recognition of cross-reactive epitopes which were common to both ML and MT 10 K. This response was not related to contamination with endotoxin. Epitope mapping using 15-mer overlapping peptides spanning the ML 10 000 MW revealed an immunodominant IgG1 binding peptide (aa41-55) in patients as well as healthy controls. This peptide is a shared epitope with M. tuberculosis 10 K suggesting that postswitched IgG1 B cells recognizing this epitope rather than naive B cells are being expanded.

A role for interleukin‐5 in promoting increased immunoglobulin M at the site of disease in leprosy

“…The elevated levels of serum antibodies in patients with L-lep or disseminated disease, compared with the levels found in patients with the T-lep self-limited form, 13,14 and the antibodies shown in this study at the site of disease may contribute to host defence or immunopathology. The correlation of antibodies with the progressive infection suggests that they play no role in protection but some suggest an early role in leprosy and other mycobacterial infections.…”

“…The expression of IL-5 and B-cell markers and of functional genes in L-lep lesions is consistent with the overall T helper type 2 cytokine pattern in L-lep lesions compared with T-lep lesions, 3 as well as the elevated systemic humoral response that is prominent in L-lep patients. 13,14 The polar L-lep and T-lep clinical presentations correlate with the level of cell-mediated immunity against M. leprae, as well as the cytokine patterns in the skin lesions, with Th2 cytokines (IL-4, IL-5 and IL-10) expressed in L-lep lesions and Th1 cytokines (IL-2 and IFN-c) in T-lep lesions [2][3][4]. In fact, type 2 cytokines such as IL-4 and IL-10 have negative immunoregulatory roles in the context of infection [5,6], and antibody responses are greater in lepromatous patients, suggesting that humoral immunity is not protective.…”

Proposing Low-Similarity Peptide Vaccines againstMycobacterium tuberculosis

“…This is an important issue, particularly because the epitopic characterization of mycobacterial antigens advances slowly, antigen-by-antigen [12–14]. …”

Immune profiling of leprosy and tuberculosis patients to 15‐mer peptides of Mycobacterium leprae and M. tuberculosis GroES in a BCG vaccinated area: implications for development of vaccine and diagnostic reagents

“…Monoclonal antibodies specific for human IgG subclasses, HP 6001 (anti‐IgG1) and HP 6002 (anti‐IgG2), prepared at the Center for Disease Control, Atlanta, were a gift from the late Dr Charles Reimer. The specificity evaluation and performance characteristics of these antibodies are described in detail elsewhere 17 and antimouse IgG (H + L chain‐specific) antibodies conjugated to alkaline phosphatase was obtained commercially (Jackson Laboratories, NJ, USA) and diluted according to the manufacturer's recommendations.…”

“…M. leprae GroES has been shown to induce strong T cell responses in tuberculoid 14,15 as well as in exposed healthy contacts of leprosy patients, 16 and therefore this antigen has been the focus of study as a potential vaccine candidate. Paradoxically, we have shown that ML GroES also induces extremely high titres of IgG1 antibody in leprosy patients, 17 a response associated with disease progression. In leprosy, IgG1 antibodies also show significant negative association with interferon‐γ, 18 a critical T cell cytokine responsible for macrophage activation and intracellular killing of mycobacteria.…”