GM-CSF-Producing Th Cells in Rats Sensitive and Resistant to Experimental Autoimmune Encephalomyelitis

Given that granulocyte macrophage colony-stimulating factor (GM-CSF) is identified as the key factor to endow auto-reactive Th cells with the potential to induce neuroinflammation in experimental autoimmune encephalomyelitis (EAE) models, the frequency and phenotype of GM-CSF-producing (GM-CSF+) Th cells in draining lymph nodes (dLNs) and spinal cord (SC) of Albino Oxford (AO) and Dark Agouti (DA) rats immunized for EAE were examined. The generation of neuroantigen-specific GM-CSF+ Th lymphocytes was impaired in dLNs of AO rats (relatively resistant to EAE induction) compared with their DA counterparts (susceptible to EAE) reflecting impaired CD4+ lymphocyte proliferation and less supportive of GM-CSF+ Th cell differentiation dLN cytokine microenvironment. Immunophenotyping of GM-CSF+ Th cells showed their phenotypic heterogeneity in both strains and revealed lower frequency of IL-17+ IFN-gamma+, IL-17+ IFN-gamma-, and IL-17-IFN-gamma+ cells accompanied by higher frequency of IL-17-IFN-gamma- cells among them in AO than in DA rats. Compared with DA, in AO rats was also found (i) slightly lower surface density of CCR2 (drives accumulation of highly pathogenic GM-CSF+ IFN-gamma+ Th17 cells in SC) on GM-CSF+ IFN-gamma+ Th17 lymphocytes from dLNs, and (ii) diminished CCL2 mRNA expression in SC tissue, suggesting their impaired migration into the SC. Moreover, dLN and SC cytokine environments in AO rats were shown to be less supportive of GM-CSF+ IFN-gamma+ Th17 cell differentiation (judging by lower expression of mRNAs for IL-1 beta, IL-6 and IL-23/p19). In accordance with the (i) lower frequency of GM-CSF+ Th cells in dLNs and SC of AO rats and their lower GM-CSF production, and (ii) impaired CCL2 expression in the SC tissue, the proportion of proinflammatory monocytes among peripheral blood cells and their progeny (CD45(hi) cells) among the SC CD11b+ cells were reduced in AO compared with DA rats. Collectively, the results indicate that the strain specificities in efficacy of several mechanisms controlling (auto) reactive CD4+ lymphocyte expansion/differentiation into the cells with pathogenic phenotype and migration of the latter to the SC contribute to AO rat resistance to EAE

Th17 cytokines and arthritis

Th17 cells are implicated in human autoimmune diseases, such as rheumatoid arthritis (RA), although it has not been established whether this persistent destructive arthritis is driven by Th1 and/or Th17 cells. Interleukin-17A (IL-17A) contributes to the pathogenesis of arthritis as has been shown in several experimental arthritis models. Importantly, recent data from first clinical trials with anti-IL-17A antibody treatment in psoriatic arthritis patients and RA patients looks promising. This review summarizes the findings about the role of Th17 cells in arthritis and discusses the impact of the different Th17 cytokines in the pathogenesis of this disease. However, further studies are needed to unravel the interplay between IL-17A and other Th17 cytokines such as IL-17F, IL-22, and IL-21 in the pathoimmunological process of this crippling disease, in particular, whether regulating Th17 cell activity or specific combinations of Th17 cytokines will have additional value compared to neutralizing IL-17A activity alone. Moreover, tumor necrosis factor-positive Th17 cells are discussed as potential dangerous cells in driving persistent arthritis in human early RA

RORγt drives production of the cytokine GM-CSF in helper T cells, which is essential for the effector phase of autoimmune neuroinflammation

Although the role of the T(H)1 and T(H)17 subsets of helper T cells as disease mediators in autoimmune neuroinflammation remains a subject of some debate, none of their signature cytokines are essential for disease development. Here we report that interleukin 23 (IL-23) and the transcription factor RORγt drove expression of the cytokine GM-CSF in helper T cells, whereas IL-12, interferon-γ (IFN-γ) and IL-27 acted as negative regulators. Autoreactive helper T cells specifically lacking GM-CSF failed to initiate neuroinflammation despite expression of IL-17A or IFN-γ, whereas GM-CSF secretion by Ifng(-/-)Il17a(-/-) helper T cells was sufficient to induce experimental autoimmune encephalomyelitis (EAE). During the disease effector phase, GM-CSF sustained neuroinflammation via myeloid cells that infiltrated the central nervous system. Thus, in contrast to all other known helper T cell-derived cytokines, GM-CSF serves a nonredundant function in the initiation of autoimmune inflammation regardless of helper T cell polarization