PI3-Kinase p110α Deficiency Modulates T Cell Homeostasis and Function and Attenuates Experimental Allergic Encephalitis in Mature Mice

Class I phosphoinositide 3-kinases (PI3K) are involved in the development of normal and autoimmune responses, including Experimental Autoimmune Encephalomyelitis (EAE), a mouse model for human multiple sclerosis (MS). Here, the role of the ubiquitously expressed class IA PI3K p110α catalytic subunits in EAE has been analyzed using a model of Cre/flox mediated T cell specific deletion of p110α catalytic chain (p110αΔT). Comparison of two month-old (young) and six month-old (mature) p110αΔT mice and their wild type (WT) counterparts indicated loss of spleen CD4+ T cells that increased with age, indicating a role of p110α in their homeostasis. In contrast, CD4+ T regulatory (Treg) cells were enhanced in mature p110αΔT mice when compared to WT mice. Since Myelin Oligodendrocyte Glycoprotein (MOG) peptide-induced EAE is dependent on, or mediated by CD4+ T cells and CD4+ T cell-derived cytokines and controlled by Treg cells, development of EAE in young and mature WT or p110αΔT mice was analyzed. EAE clinical symptoms and disease scores in six month p110αΔT mice were significantly lower than those of mature WT, or young WT and p110αΔT mice. Furthermore, ex vivo antigen activation of lymph node cells from MOG immunized mature p110αΔT mice induced significantly lower levels of IFN-γ and IL-17A than young p110αΔT or young and mature WT mice. Other cytokines including IL-2, IL-10 or TNF-α showed no significant differences between p110αΔT and WT mature mice. Our data show a lower incidence of MOG-induced EAE in mature p110αΔT mice linked to altered T cell homeostasis and lower secretion of inflammatory cytokines.

Anacardic acid induces IL-33 and promotes remyelination in CNS

Given the known neuroreparative actions of IL-33 in experimental models of central nervous system (CNS) injury, we predicted that compounds which induce IL-33 are likely to promote remyelination. We found anacardic acid as a candidate molecule to serve as a therapeutic agent to promote remyelination. Addition of anacardic acid to cultured oligodendrocyte precursor cells (OPCs) rapidly increased expression of myelin genes and myelin proteins, suggesting a direct induction of genes involved in myelination by anacardic acid. Also, when added to OPCs, anacardic acid resulted in the induction of IL-33. In vivo, treatment of with anacardic acid in doses which ranged from 0.025 mg/kg to 2.5 mg/kg,improved pathologic scores in experimental allergic encephalitis (EAE) and in the cuprizone model of demyelination/remyelination. Electron microscopic studies performed in mice fed with cuprizone and treated with anacardic acid showed lower g-ratio scores when compared to controls, suggesting increased remyelination of axons. In EAE, improvement in paralytic scores was seen when the drug was given prior to or following the onset of paralytic signs. In EAE and in the cuprizone model, areas of myelin loss, which are likely to remyelinate, was associated with a greater recruitment of IL-33–expressing OPCs in mice which received anacardic acid when compared to controls.

Ocular nerve growth factor administration (oNGF) affects disease severity and inflammatory response in the brain of rats with experimental allergic encephalitis (EAE)

The rat acute experimental autoimmune encephalomyelitis (EAE) model was used to investigate the effects of ocularly administered nerve growth factor (oNGF) on disease development and brain inflammation. It was found that oNGF affects clinical scores. However, EAE rats receiving oNGF treatment showed reduced expression of pro-inflammatory cytokines and chemokines in the cerebellum and the hippocampus, but not in the frontal cortex. These data confirm the ability of oNGF to counteract the effects of EAE in the brain and suggest a role for oNGF in the regulation of local inflammatory responses observed in the acute phase of EAE.

GM-CSF mediates autoimmunity by enhancing IL-6–dependent Th17 cell development and survival

Granulocyte macrophage–colony stimulating factor (GM-CSF) is critically involved in development of organ-related autoimmune inflammatory diseases including experimental allergic encephalitis and collagen-induced arthritis. Roles of GM-CSF in the initiation and in the effector phase of the autoimmune response have been proposed. Our study was designed to investigate the mechanisms of GM-CSF in autoimmunity using a model of autoimmune heart inflammatory disease (myocarditis). The pathological sequel after immunization with heart myosin has been shown previously to depend on IL-1, IL-6, IL-23, and IL-17. We found that innate GM-CSF was critical for IL-6 and IL-23 responses by dendritic cells and generation of pathological Th17 cells in vivo. Moreover, GM-CSF promoted autoimmunity by enhancing IL-6–dependent survival of antigen specific CD4+ T cells. These results suggest a novel role for GM-CSF in promoting generation and maintenance of Th17 cells by regulation of IL-6 and IL-23 in vivo.

A GMCSF/Interleukin-15 Fusokine Leads to the Generation of a Novel Type of CD2/MHCII Immune Regulatory Cell with Potent Immune Suppressive Properties as Demonstrated in the EAE Mouse Model of Multiple Sclerosis.

Multiple sclerosis (MS) is an autoimmune disease characterised by the infiltration of autoreactive T-cell causing damages to the central nervous system. So far, interferon-β and glatiramer acetate are the only two immunomodulatory coumpounds that have been approved as non-curative disease managing strategies. Therefore, there is an urgent need for the development of novel efficient therapies that can be both safe and potent in inhibiting MS progression and promote reversal of disease state. We have recently published a report describing a novel synthetic GMCSF and IL15 Fusion Transgene (GIFT15) and have described its paradoxical and potent immune suppressive properties in vivo [Rafei et al., Blood (March 2007)]. Its mechanism of action relies on STAT3 hyperactivation arising from aberrant signalling taking place downstream of the IL15 receptor. We have now further studied the effect of GIFT15 on mouse spleen cells in vitro and here demonstrate that it leads to the conversion of murine T-cells to a novel suppressive regulatory cell type. Indeed, GIFT15-treated splenocytes (hereafter GIFT15 regs) shed their TCR and loose expression of CD3, CD4 and CD8, retain CD2 expression and acquire expression of MHC II. Distinct to classic T-regulatory cells, GIFT15 regs do not express CD25 or FOXP3. GIFT15 regs were able to suppress an in vitro two-way MLR by a contact-dependent mechanism as well as by the contemporaneous production of interleukin (IL)-10. Furthermore, GIFT15 regs were able to block antigen-specific activation of CD4-T-cells in response to autologous macrophage stimulation. As a proof-of-principle in vivo study, GIFT15 regs were injected intravenously in mice with pre-established experimental allergic encephalitis (EAE) and disease score was monitored over time. Interestingly, mice recovered significantly faster than controls following administration GIFT15 regs and a blockade in EAE progression was also noticed over time. In conclusion, our data suggests that GIFT15 can be used as a method to ex vivo generate suppressor cells of a new type which are distinct from classic Tregs or Tr1 cells. We propose that GIFT15 regs derived from autologous lymphocytes may be exploited for the treatment of autoimmune disease such as MS and may also be of use for other autoimmune ailments as well.