T cell tolerance in the modulation of autoimmune anti-myeloperoxidase ANCA-associated glomerulonephritis

Autoimmune ANCA-associated glomerulonephritis (GN) is the most common of the severe crescentic forms of GN. It is closely associated with systemic small vessel vasculitis and autoimmunity to myeloperoxidase (MPO). The mechanisms of the breakdown of tolerance to MPO and the subsequent development of renal injury remain to be established. Nevertheless, the cause of autoimmunity is likely to be associated with the failure of central and peripheral tolerance mechanisms to prevent the development of autoimmunity. In the efforts to understand the development of MPO autoimmunity, this thesis studies the contributions of central and peripheral tolerance in modulating tolerance to MPO and explored ways in which MPO autoimmunity and autoimmune MPO-ANCA-associated GN can be inhibited. This thesis first studies the importance of central tolerance in MPO autoimmunity. MPO mRNA expression was found in medullary thymic epithelial cells expressing MHC II and the transcriptional regulator AIRE. The role of central tolerance in establishing MPO tolerance was demonstrated in MPO-/- mice after MPO immunization significantly enhanced frequencies of IL-17A- and IFNγ-producing autoreactive anti-MPO T cells and ANCA titres. The detection of MPO protein by immunostaining in murine and human thymii tissue sections revealed that MPO is localized in neutrophils and macrophages which may be associated with the clearance of apoptotic cells in the central deletion process. In assessing the role of regulatory T cells (Tregs; CD4+CD25+Foxp3+) in peripheral tolerance, immunodeletion of Tregs in MPO-intact naïve C57BL/6 mice was associated with enhanced frequency of IL-17A- and IFNγ-producing anti-MPO T cells and enhanced ANCA titres. In addition, there was a marked increase in the severity of focal/segmental necrotizing GN triggered by sub-nephritogenic dose of anti-GBM antibody to induce glomerular neutrophil degranulation and MPO deposition in MPO-immunized mice. This thesis then accesses the ability of nasal administration of an immunogenic MPO peptide 409-428 (MPO409-428) to induce MPO tolerance hence preventing the development of autoimmune MPO-ANCA-associated GN. MPO tolerization by the nasal delivery of MPO409-428 without adjuvant in a dose-dependent manner successfully inhibited the induction of cellular and humoral MPO autoimmunity to subsequent immunization in contrast to mice tolerized with control peptide (OVA323-339). In accessing renal injury, there was a marked decrease in the severity of focal/segmental necrotizing GN triggered by sub-nephritogenic dose of anti-GBM antibody. Finally, bone marrow-derived dendritic cells (BMDCs) from naïve C57BL/6 and CD40-/- mice were used to assess the ability of aberrant MPO presentation in the protection of MPO autoimmunity and renal injury. Recipient naïve C57BL/6 of CD40-/- MPO-pulsed BMDCs were protected from cellular and humoral MPO autoimmunity induced by immunization with MPO. These mice were also protected from glomerular focal/segmental necrotizing renal injury triggered by sub-nephritogenic dose of anti-GBM antibody. This thesis thus demonstrated the contributions of central tolerance and peripheral Tregs in the maintenance of tolerance to MPO. In addition, the induction of nasal tolerance and the use of CD40-/- tolerogenic BMDCs can confer protection from the development of autoimmune MPO-ANCA-associated GN. The findings contribute significantly to a greater understanding of tolerance mechanisms to MPO and further identify potential new therapies.