Simon Freeley

Animal models of anti‐neutrophil cytoplasmic antibody‐associated vasculitis

OTHER ARTICLES PUBLISHED ON ANCA IN THIS ISSUE

Transferred Antigen-Specific TH17 but not TH1 Cells Induce Crescentic Glomerulonephritis in Mice

To explore the role of antigen-specific CD4(+) T cells in glomerulonephritis, we administered ovalbumin 323-339 peptide conjugated to glomerular-binding polyclonal antibody and induced disease in RAG1(-/-) mice with CD4(+) T cells from OT2 × RAG1(-/-) mice. These OT2 × RAG1(-/-) mice have a transgenic T-cell receptor specific for this peptide. When CD4(+) T cells were primed in vivo, crescentic glomerulonephritis developed after 21 days in mice given peptide-conjugated glomerular-binding antibody but not unconjugated antibody control. We then investigated the relative roles of T(H)1 and T(H)17 cells, using Fab(2) fragments of glomerular-binding antibody to exclude a role for antibody in this model. T cells from OT2 × RAG1(-/-) mice were polarized in vitro, and T(H)1 or T(H)17 cell lines were injected into mice that were also given peptide-conjugated Fab(2) or unconjugated Fab(2) control, giving four experimental groups. After 21 days crescentic glomerulonephritis was seen in mice receiving T(H)17 cells and peptide-conjugated Fab(2) but in none of the other three groups. These results suggest that T(H)17 but not T(H)1 cells can induce crescentic glomerulonephritis.

Granulocyte colony stimulating factor exacerbates antineutrophil cytoplasmic antibody vasculitis

Objectives Granulocyte colony stimulating factor (GCSF) is important in mobilising neutrophils from the bone marrow but also has a range of proinflammatory effects. We therefore decided to investigate the role of GCSF in antineutrophil cytoplasmic antibody (ANCA) vasculitis. Methods We measured GCSF levels in the serum of 38 patients with active ANCA vasculitis compared with 31 age-matched controls, and assessed the effect of GCSF priming on the response of human neutrophils to ANCA. We also examined the effect of exogenous GCSF administration in a murine model of antimyeloperoxidase (anti-MPO) vasculitis, and the effect of GCSF on murine neutrophil activation. Results The serum levels of GCSF in patients with active ANCA vasculitis were significantly higher than those of age matched healthy controls (mean 38.04 vs 18.35 pg/ml, p<0.001). Furthermore, we demonstrated that GCSF primed human neutrophils in vitro for a respiratory burst in response to anti-MPO ANCA. In an anti-MPO antibody transfer model, mice given GCSF had more crescents (mean 29.1% vs 5.8% per glomerular cross section, p<0.05), more macrophages (mean 3.2 vs 1.2 per glomerular cross-section, p<0.01), higher serum creatines (mean 13.6 vs 8.3 μmol/l, p<0.05) and more haematuria (p<0.05) compared with controls. In vivo administration of GCSF with lipopolysaccharide (LPS), but not LPS alone, led to upregulation of CD11c on murine neutrophils. Conclusions These data suggest that GCSF, which is raised in patient serum, may play an important role in exacerbating disease in ANCA vasculitis. In addition, GCSF therapy for neutropenia should be used with caution in these patients.

Humanised mice have functional human neutrophils

The differences between murine and human neutrophils mean that findings in mice may not translate to humans, and therefore an in vivo model with human neutrophils would be an important methodological advance. We generated humanised mice by injecting human cord blood derived CD34+ stem cells into irradiated NOD-scid-γc(-/-) mice. At least 3 months after engraftment, treatment of mice with GCSF mobilised circulating human neutrophils, which comprised 2.6% of human leukocytes, and led to L-selectin shedding and upregulation of CD66b, CD11b and CD63. Subsequent in vivo LPS treatment led to further downregulation of L-selectin with upregulation of CD66b and CD63, and also resulted in human neutrophil sequestration in the lungs. Furthermore, human neutrophils from these mice were capable of robust functional responses. They were shown to undergo a respiratory burst, and to degranulate with upregulation of CD63 and CD66b, in response to fMLP and Escherichia coli. These data show that functional human neutrophils develop from CD34+ cord blood stem cells in NOD-scid-γc(-/-) mice. They suggest that this approach may facilitate the in vivo study of human neutrophils in clinically relevant models of infection and autoimmunity.

Toll-Like Receptor 2 or Toll-Like Receptor 4 Deficiency Does Not Modify Lupus in MRLlpr Mice

Systemic lupus erythematosus is an autoimmune disease with a high morbidity and nephritis is a common manifestation. Previous studies in murine lupus models have suggest a role for Toll-like receptor 2 and 4. We examined the role of these molecules in MRL lpr mice which is one of the most established and robust murine models. We compared disease parameters in Toll-like receptor 2 or Toll-like receptor 4 deficient mice with their littermate controls. We found no difference in the severity of glomerulonephritis as assessed by histology, serum creatinine and albuminuria when Toll-like receptor 2 or Toll-like receptor 4 deficient MRLlpr mice were compared with Toll-like receptor sufficient controls. We also found similar levels of anti-dsDNA and anti-ssDNA antibodies. These results show that Toll-like receptor 2 and Toll-like receptor 4 do not play a significant role in MRLlpr mice, and therefore they may not be important in human lupus.

Human plasma C3 is essential for the development of memory B, but not T, lymphocytes

To the Editor: Primary C3 deficiency is an extremely rare autosomalrecessive disease, with fewer than 50 families described worldwide. Plasma and intracellular C3 are considered B-cell receptor (BCR) and T-cell receptor (TCR) costimulators, respectively, but their contribution to lymphocyte biology remains obscure, particularly in humans. Reduced plasma C3 can be caused not only by primary C3 deficiency, due to loss-of-function C3 mutations, but also by secondary C3 deficiency or C3 consumption, due to gain-of-function C3 mutations or due to mutations in C3 regulators such as complement Factor I (CFI). We reasoned that comparing Band T-cell differentiation and function in primary and secondary plasma C3 deficiency might help to understand the role of plasma and intracellular C3 in adaptive immunity. We report the immunological features of lymphocytes from 9 individuals with low plasma C3 belonging to 6 families, with mutations causing primary or secondary C3 deficiency and, in some cases, chronic kidney disease stages 1 to 3 (see Fig E1,A, and Tables E1 and E3 in this article’s Online Repository at www.jacionline.org).

Experimentally-induced anti-myeloperoxidase vasculitis does not require properdin, MASP-2 or bone marrow-derived C5.

Anti‐neutrophil cytoplasmic antibody vasculitis is a systemic autoimmune disease with glomerulonephritis and pulmonary haemorrhage as major clinical manifestations. The name reflects the presence of autoantibodies to myeloperoxidase and proteinase‐3, which bind to both neutrophils and monocytes. Evidence of the pathogenicity of these autoantibodies is provided by the observation that injection of anti‐myeloperoxidase antibodies into mice causes a pauci‐immune focal segmental necrotizing glomerulonephritis which is histologically similar to the changes seen on renal biopsy in patients. Previous studies in this model have implicated the alternative pathway of complement activation and the anaphylatoxin C5a. Despite this progress, the factors that initiate complement activation have not been defined. In addition, the relative importance of bone marrow‐derived and circulating C5 is not known. This is of interest given the recently identified roles for complement within leukocytes. We induced anti‐myeloperoxidase vasculitis in mice and confirmed a role for complement activation by demonstrating protection in C3‐deficient mice. We showed that neither MASP‐2‐ nor properdin‐deficient mice were protected, suggesting that alternative pathway activation does not require properdin or the lectin pathway. We induced disease in bone marrow chimaeric mice and found that circulating and not bone marrow‐derived C5 was required for disease. We have therefore excluded properdin and the lectin pathway as initiators of complement activation and this means that future work should be directed at other potential factors within diseased tissue. In addition, in view of our finding that circulating and not bone marrow‐derived C5 mediates disease, therapies that decrease hepatic C5 secretion may be considered as an alternative to those that target C5 and C5a.