55 IL-27, an IL-2 family cytokine, is a negative regulator of Th17 development.56 This cytokine also induces Tr1 cells, a Treg population characterized by IL-10 expression.57 IL-10 is also a negative regulator of Th17 development.58 Mice deficient in the IL-27 receptor, WSX-1, show exuberant Smoothened Agonist proliferation of Th17 cells in EAE suggesting that IL-27 inhibits the development of disease.59 These interactions help explain how relatively minor disruptions

in Treg homeostasis by inflammation in genetically susceptible animals initiated by a critical inflammatory trigger may precipitate autoimmunity through a default pathway, i.e. Th17 differentiation. The IL-17A receptor has recently been reported to be expressed on differentiated Th1 cells. In vitro experiments show that IL-17A is capable downregulating expression of the Th1 transcription factor, T-bet.60 These findings suggest that apart from its pleiotropic pro-inflammatory functions,

Th17 cells are capable of regulating pathogenic Th1-mediated tissue inflammation.61 In the absence of TGF-β and in the presence of IL-12 or IL-23, differentiated Th17 cells lose IL-17A and IL-17F secretion and become IFN-γ-producing cells.62 This switch is dependent on the Th1 transcriptions factors, STAT4 and T-bet, and suggests that Th17 cells are not terminally differentiated PD98059 but are capable of substantial plasticity. Direct evidence that Th17, as well as Th1 cells can induce proliferative GN has been published using a planted foreign antigen model, where ovalbumin is planted in glomeruli of Rag1−/− mice (deficient in T and B cells). Injection

Cetuximab manufacturer of either ovalbumin-specific Th1 or Th17 polarized cells induced proliferative GN.63 Th17 cell induced injury developed early and correlated with increased neutrophil recruitment, while Th1 cell-mediated GN was more delayed and featured enhanced macrophage activation. This system has the advantage of being able to definitively demonstrate that it is the Th cells as effectors that are directing the injury, without potential confounding effects of CD8+ cells, B cells or antibody. These findings support a model in which some forms of proliferative GN, where effectors of cell mediated immunity are prominent, may be Th17 cell predominant, while others are Th1 mediated. It suggests that Th17 cells might dominate glomerular diseases that are neutrophil rich, although other recent evidence in autoimmune renal disease64 (discussed below) suggests a role for Th17 in macrophage recruitment. Types of GN and its association with the Th17 cell subset are listed in Table 2. Anti-GBM GN disease has been believed to be Th1 mediated due to the presence of DTH effectors65 and the predominance of the Th1-associated IgG antibody subclasses (IgG1 and/or IgG3) deposited in the kidney.