Abstract
BackgroundLepromatous leprosy caused by Mycobacterium leprae is associated with antigen specific T cell unresponsiveness/anergy whose underlying mechanisms are not fully defined. We investigated the role of CD25+FOXP3+ regulatory T cells in both skin lesions and M.leprae stimulated PBMC cultures of 28 each of freshly diagnosed patients with borderline tuberculoid (BT) and lepromatous leprosy (LL) as well as 7 healthy household contacts of leprosy patients and 4 normal skin samples.Methodology/Principle FindingsQuantitative reverse transcribed PCR (qPCR), immuno-histochemistry/flowcytometry and ELISA were used respectively for gene expression, phenotype characterization and cytokine levels in PBMC culture supernatants. Both skin lesions as well as in vitro antigen stimulated PBMC showed increased percentage/mean fluorescence intensity of cells and higher gene expression for FOXP3+, TGF-β in lepromatous (p<0.01) as compared to tuberculoid leprosy patients. CD4+CD25+FOXP3+ T cells (Tregs) were increased in unstimulated basal cultures (p<0.0003) and showed further increase in in vitro antigen but not mitogen (phytohemaglutinin) stimulated PBMC (iTreg) in lepromatous as compared to tuberculoid leprosy patients (p<0.002). iTregs of lepromatous patients showed intracellular TGF-β which was further confirmed by increase in TGF-β in culture supernatants (p<0.003). Furthermore, TGF-β in iTreg cells was associated with phosphorylation of STAT5A. TGF-β was seen in CD25+ cells of the CD4+ but not that of CD8+ T cell lineage in leprosy patients. iTregs did not show intracellular IFN-γ or IL-17 in lepromatous leprosy patients.Conclusions/SignificanceOur results indicate that FOXP3+ iTregs with TGF-β may down regulate T cell responses leading to the antigen specific anergy associated with lepromatous leprosy.
Highlights
The hall mark of leprosy caused by Mycobacterium leprae is involvement of the skin and peripheral nerves of man
Lepromatous leprosy is a generalized infectious disease caused by Mycobacterium leprae with the patients showing T cell mediated unresponsiveness to the pathogen and chronicity of lesions
The recent discovery of CD25+FOXP3+ cells with regulatory functions (Tregs) in mice and man have made it possible to study their role in the dampening of T cell responses in lepromatous leprosy
Summary
The hall mark of leprosy caused by Mycobacterium leprae is involvement of the skin and peripheral nerves of man. Leprosy patients present with varied clinic-pathological manifestations and bacterial load which are influenced by the host immune response. Tuberculoid leprosy, both polar (TT) and borderline forms (BT) show localized paucibacillary, hypo pigmented, hypo anesthetic patches and early nerve damage. In the 70 s a subset of suppressor T cells were first described as a distinct population that inhibited responses through soluble factors [2]. Lepromatous leprosy caused by Mycobacterium leprae is associated with antigen specific T cell unresponsiveness/anergy whose underlying mechanisms are not fully defined. We investigated the role of CD25+FOXP3+ regulatory T cells in both skin lesions and M.leprae stimulated PBMC cultures of 28 each of freshly diagnosed patients with borderline tuberculoid (BT) and lepromatous leprosy (LL) as well as 7 healthy household contacts of leprosy patients and 4 normal skin samples
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