Antigen presentation, but not antibody secretion, by B cells drives CNS autoimmunity induced by immunization with human MOG.

Objective Clinical studies indicate that anti-CD20 B cell depletion may be an effective multiple sclerosis therapy. We investigated mechanisms of its immune modulation using two paradigms of experimental autoimmune encephalomyelitis (EAE). Methods Murine EAE was induced by either recombinant myelin oligodendrocyte glycoprotein (rMOG), a model in which B cells are considered to contribute pathogenically, or MOG peptide (p)35–55, a model that does not require B cells. Results In EAE induced by rMOG, B cells became activated and, when serving as antigen presenting cells (APC), promoted differentiation of proinflammatory MOG-specific Th1 and Th17 cells. B cell depletion prevented or reversed established rMOG-induced EAE, which was associated with less CNS inflammation, elimination of meningeal B cells, and reduction of MOG-specific Th1 and Th17 cells. In contrast, in EAE induced by MOG p35–55, B cells did not become activated or efficiently polarize proinflammatory MOG-specific T cells, similar to naïve B cells. In this EAE setting, anti-CD20 treatment exacerbated EAE, and did not impede development of Th1 or Th17 cells. Irrespective of the EAE model used, B cell depletion reduced the frequency of regulatory T cells, and increased the capacity of remaining APC to promote development of encephalitogenic T cells. Interpretation Our study highlights distinct roles for B cells in pathogenesis and regulation of CNS autoimmune disease. Clinical benefit from depletion of antigen-activated B cells may relate primarily to abrogation of proinflammatory B cell APC function. However, in certain clinical settings, elimination of unactivated B cells, which participate in regulation of T cells and other APC, may be undesirable.

Mechanisms of action as well as cellular targets of glatiramer acetate (GA) in multiple sclerosis (MS) are still not entirely understood. IL-1␤ is present in CNS-infiltrating macrophages and microglial cells and is an important mediator of inflammation in experimental autoimmune encephalitis (EAE), the MS animal model. A natural inhibitor of IL-1␤, the secreted form of IL-1 receptor antagonist (sIL-1Ra) improves EAE disease course. In this study we examined the effects of GA on the IL-1 system. In vivo, GA treatment enhanced sIL-1Ra blood levels in both EAE mice and patients with MS, whereas IL-1␤ levels remained undetectable. In vitro, GA per se induced the transcription and production of sIL-1Ra in isolated human monocytes. Furthermore, in T cell contactactivated monocytes, a mechanism relevant to chronic inflammation, GA strongly diminished the expression of IL-1␤ and enhanced that of sIL-1Ra. This contrasts with the effect of GA in monocytes activated upon acute inflammatory conditions. Indeed, in LPSactivated monocytes, IL-1␤ and sIL-1Ra production were increased in the presence of GA. These results demonstrate that, in chronic inflammatory conditions, GA enhances circulating sIL-1Ra levels and directly affects monocytes by triggering a bias toward a less inflammatory profile, increasing sIL-1Ra while diminishing IL-1␤ production. This study sheds light on a mechanism that is likely to participate in the therapeutic effects of GA in MS.experimental autoimmune encephalitis ͉ cellular contact ͉ inflammation ͉ autoimmune disease

Laquinimod is a novel oral drug that is currently being evaluated for the treatment of relapsing-remitting (RR) multiple sclerosis (MS). Using the animal model for multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), we examined how laquinimod promotes immune modulation. Oral laquinimod treatment reversed established RR-EAE and was associated with reduced central nervous system (CNS) inflammation, decreased Th1 and Th17 responses, and an increase in regulatory T cells (Treg). In vivo laquinimod treatment inhibited donor myelin-specific T cells from transferring EAE to naive recipient mice. In vivo laquinimod treatment altered subpopulations of myeloid antigen presenting cells (APC) that included a decrease in CD11c+CD11b+CD4+ dendritic cells (DC) and an elevation of CD11bhiGr1hi monocytes. CD11b+ cells from these mice exhibited an anti-inflammatory type II phenotype characterized by reduced STAT1 phosphorylation, decreased production of IL-6, IL-12/23 and TNF, and increased IL-10. In adoptive transfer, donor type II monocytes from laquinimod-treated mice suppressed clinical and histologic disease in recipients with established EAE. As effects were observed in both APC and T cell compartments, we examined whether T cell immune modulation occurred as a direct effect of laquinimod on T cells, or as a consequence of altered APC function. Inhibition of Th1 and Th17 differentiation was observed only when type II monocytes or DC from laquinimod-treated mice were used as APC, regardless of whether myelin-specific T cells were obtained from laquinimod-treated or untreated mice. Thus, laquinimod modulates adaptive T cell immune responses via its effects on cells of the innate immune system, and may not influence T cells directly.

Imbalance in cytokine homeostasis plays an important part in the pathogenesis of chronic inflammatory diseases such as multiple sclerosis and rheumatoid arthritis. We demonstrated that T cells might exert a pathological effect through direct cellular contact with human monocytes/macrophages, inducing a massive up-regulation of the prototypical proinflammatory cytokines IL-1beta and TNF. This mechanism that might be implicated in chronic inflammation is specifically inhibited by high-density lipoproteins (HDL). Like many other stimuli, besides proinflammatory cytokines, the contact-mediated activation of monocytes induces the production of cytokine inhibitors such as the secreted form of the IL-1 receptor antagonist (sIL-1Ra). The present study demonstrates that stimulated T cells generate microparticles (MP) that induce the production of TNF, IL-1beta, and sIL-1Ra in human monocytes; the production of TNF and IL-1beta but not that of sIL-1Ra is inhibited in the presence of HDL. The results were similar when monocytes were stimulated by whole membranes of T cells or soluble extracts of the latter. This suggests that MP carry similar monocyte-activating factors to cells from which they originate. Thus, by releasing MP, T cells might convey surface molecules similar to those involved in the activation of monocytes by cellular contact. By extension, MP might affect the activity of cells, which are usually not in direct contact with T cells at the inflammatory site. Furthermore, this study demonstrates that HDL exert an anti-inflammatory effect in nonseptic activation of human monocytes, not only by inhibiting the production of IL-1beta and TNF but also, by leaving sIL-1Ra production unchanged.

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The unbalanced production of IL-1β and its natural, specific inhibitor, the secreted IL-1R antagonist (sIL-1Ra), plays an important role in chronic/sterile inflammation. Relevant to this condition is direct cellular contact with stimulated T cells which is a potent inducer of cytokine production in human monocytes/macrophages. We previously demonstrated that activation of PI3Ks is a prerequisite of the transcription of the sIL-1Ra gene in human monocytes activated by IFN-β. In this study, we addressed the question of PI3K involvement in the production of IL-1β and sIL-1Ra in monocytes activated by cellular contact with stimulated T cells (mimicked by CHAPS-solubilized membranes of stimulated T cells (CEsHUT)), and a crude preparation of LPS, to compare stimuli relevant to chronic/sterile and acute/infectious inflammation, respectively. In monocytes activated by either CEsHUT or LPS, the inhibition of PI3Ks abrogated sIL-1Ra transcript expression and sIL-1Ra production, demonstrating that PI3Ks control the induction of sIL-1Ra gene transcription. In contrast, PI3K inhibition increased the production of IL-1β protein in both CEsHUT- and LPS-activated monocytes, the enhancement being drastically higher in the former. This was not due to changes in IL-1β mRNA steady-state levels or transcript stability, but to the involvement of PI3Ks in the repression of IL-1β secretion. The downstream PI3K effector, Akt, was implicated in this process. The present results demonstrate that PI3Ks are involved in the inhibition of IL-1β secretion and in the induction of sIL-1Ra production in human blood monocytes by controlling different mechanisms in conditions mimicking chronic/sterile (CEsHUT) and acute/infectious (LPS) inflammation.

Autoimmune neuroinflammation, including multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE), a prototype for T cell–mediated autoimmunity, is believed to result from immune tolerance dysfunction leading to demyelination and substantial neurodegeneration. We previously showed that CNS-restricted expression of hepatocyte growth factor (HGF), a potent neuroprotective factor, reduced CNS inflammation and clinical deficits associated with EAE. In this study, we demonstrate that systemic HGF treatment ameliorates EAE through the development of tolerogenic dendritic cells (DCs) with high expression levels of glucocorticoid-induced leucine zipper (GILZ), a transcriptional repressor of gene expression and a key endogenous regulator of the inflammatory response. RNA interference–directed neutralization of GILZ expression by DCs suppressed the induction of tolerance caused by HGF. Finally, adoptive transfer of HGF-treated DCs from wild-type but not GILZ gene–deficient mice potently mediated functional recovery in recipient mice with established EAE through effective modulation of autoaggressive T cell responses. Altogether, these results show that by inducing GILZ in DCs, HGF reproduces the mechanism of immune regulation induced by potent immunomodulatory factors such as IL-10, TGF-β1, and glucocorticoids and therefore that HGF therapy may have potential in the treatment of autoimmune dysfunctions.