Aberrant T-cell activation underlies many autoimmune disorders, yet most attempts to induce T-cell tolerance have failed. Building on previous strategies for tolerance induction that exploited natural mechanisms for clearing apoptotic debris, we show that antigen-decorated microparticles (500-nm diameter) induce long-term T-cell tolerance in mice with relapsing experimental autoimmune encephalomyelitis. Specifically, intravenous infusion of either polystyrene or biodegradable poly(lactide-co-glycolide) microparticles bearing encephalitogenic peptides prevents the onset and modifies the course of the disease. These beneficial effects require microparticle uptake by marginal zone macrophages expressing the scavenger receptor MARCO and are mediated in part by the activity of regulatory T cells, abortive T-cell activation and T-cell anergy. Together these data highlight the potential for using microparticles to target natural apoptotic clearance pathways to inactivate pathogenic T cells and halt the disease process in autoimmunity.

In a lethal West Nile virus (WNV) model, central nervous system infection triggered a threefold increase in CD45 int /CD11b + /CD11c ؊ microglia at days 6 -7 postinfection (p.i.). Few microglia were proliferating, suggesting that the increased numbers were derived from a migratory precursor cell. Depletion of " circulating " (Gr1 ؊ (Ly6C lo )CX3CR1 + ) and " infl ammatory " (Gr1 hi /Ly6C hi /CCR2 + ) classical monocytes during infection abrogated the increase in microglia. C57BL/6 chimeras reconstituted with cFMS -enhanced green fl uorescent protein (EGFP) bone marrow (BM) showed large numbers of peripherally derived (GFP + ) microglia expressing GR1 + (Ly6C + ) at day 7 p.i., suggesting that the infl ammatory monocyte is a microglial precursor. This was confi rmed by adoptive transfer of labeled BM (Ly6C hi /CD115 + ) or circulating infl ammatory monocytes that traffi cked to the WNV-infected brain and expressed a microglial phenotype. CCL2 is a chemokine that is highly expressed during WNV infection and important in infl ammatory monocyte traffi cking. Neutralization of CCL2 not only reduced the number of GFP + microglia in the brain during WNV infection but prolonged the life of infected animals. Therefore, CCL2-dependent infl ammatory monocyte migration is critical for increases in microglia during WNV infection and may also play a pathogenic role during WNV encephalitis.

Inflammatory monocyte-derived effector cells play an important role in the pathogenesis of numerous inflammatory diseases. However, no treatment option exists that is capable of modulating these cells specifically. We show that infused negatively charged, immune-modifying microparticles (IMPs), derived from polystyrene, microdiamonds, or biodegradable poly(lactic-co-glycolic) acid, were taken up by inflammatory monocytes, in an opsonin-independent fashion, via the macrophage receptor with collagenous structure (MARCO). Subsequently, these monocytes no longer trafficked to sites of inflammation; rather, IMP infusion caused their sequestration in the spleen through apoptotic cell clearance mechanisms and, ultimately, caspase-3–mediated apoptosis. Administration of IMPs in mouse models of myocardial infarction, experimental autoimmune encephalomyelitis, dextran sodium sulfate–induced colitis, thioglycollate-induced peritonitis, and lethal flavivirus encephalitis markedly reduced monocyte accumulation at inflammatory foci, reduced disease symptoms, and promoted tissue repair. Together, these data highlight the intricate interplay between scavenger receptors, the spleen, and inflammatory monocyte function and support the translation of IMPs for therapeutic use in diseases caused or potentiated by inflammatory monocytes.

Targeted immune tolerance is a coveted therapy for the treatment of a variety of autoimmune diseases, as current treatment options often involve nonspecific immunosuppression. Intravenous (iv) infusion of apoptotic syngeneic splenocytes linked with peptide or protein autoantigens using ethylene carbodiimide (ECDI) has been demonstrated to be an effective method for inducing peripheral, antigen-specific tolerance for treatment of autoimmune disease. Here, we show the ability of biodegradable poly(lactic-co-glycolic acid) (PLG) nanoparticles to function as a safe, cost-effective, and highly efficient alternative to cellular carriers for the induction of antigen-specific T cell tolerance. We describe the formulation of tolerogenic PLG particles and demonstrate that administration of myelin antigen-coupled particles both prevented and treated relapsing-remitting experimental autoimmune encephalomyelitis (R-EAE), a CD4 T cell-mediated mouse model of multiple sclerosis (MS). PLG particles made on-site with surfactant modifications surpass the efficacy of commercially available particles in their ability to couple peptide and to prevent disease induction. Most importantly, myelin antigen-coupled PLG nanoparticles are able to significantly ameliorate ongoing disease and subsequent relapses when administered at onset or at peak of acute disease, and minimize epitope spreading when administered during disease remission. Therapeutic treatment results in significantly reduced CNS infiltration of encephalitogenic Th1 (IFN-γ) and Th17 (IL-17a) cells as well as inflammatory monocytes/macrophages. Together, these data describe a platform for antigen display that is safe, low-cost, and highly effective at inducing antigen-specific T cell tolerance. The development of such a platform carries broad implications for the treatment of a variety of immune-mediated diseases.

Antigen-specific tolerance is a highly desired therapy for immune-mediated diseases. Intravenous infusion of protein/peptide antigens linked to syngeneic splenic leukocytes with ethylene carbodiimide (Ag-SP) has been demonstrated to be a highly efficient method for inducing peripheral, antigen-specific T cell tolerance for treatment of autoimmune disease. However, little is understood about the mechanisms underlying this therapy. Here, we show that apoptotic Ag-SP accumulate in the splenic marginal zone where their uptake by F4/80+ macrophages induces production of IL-10 which upregulates the expression of the immunomodulatory costimulatory molecule PD-L1 which is essential for Ag-SP tolerance induction. Ag-SP infusion also induces Tregs which are dispensable for tolerance induction, but required for long-term tolerance maintenance. Collectively, these results indicate that Ag-SP tolerance recapitulates how tolerance is normally maintained in the hematopoietic compartment and highlight the interplay between the innate and adaptive immune systems in the induction of Ag-SP tolerance. We show for the first time that tolerance results from the synergistic effects of two distinct mechanisms – PD-L1-dependent T cell-intrinsic unresponsiveness and the activation of Tregs. These findings are particularly relevant as this tolerance protocol is currently being tested in a Phase I/IIa clinical trial in new-onset relapsing-remitting MS.

A major challenge for human allogeneic islet transplantation is the development of effective methods to induce donor-specific tolerance to obviate the need for life-long immunosuppression that is toxic to the insulin-producing ␤ cells and detrimental to the host. We developed an efficient donor-specific tolerance therapy that utilizes infusions of ethylene carbodiimide (ECDI)-treated donor splenic antigen-presenting cells that results in indefinite survival of allogeneic islet grafts in the absence of immunosuppression. Furthermore, we show that induction of tolerance is critically dependent on synergistic effects between an intact programmed death 1 receptorprogrammed death ligand 1 signaling pathway and CD4 ؉ CD25 ؉ Foxp3 ؉ regulatory T cells. This highly efficient antigen-specific therapy with a complete avoidance of immunosuppression has significant therapeutic potential in human islet cell transplantation.anergy ͉ programmed death-1 ͉ regulatory T cells ͉ transplantation ͉ islet transplantation

Summary As a group of disorders, autoimmunity ranks as the third most prevalent cause of morbidity and mortality in the Western World. However, the etiology of most autoimmune diseases remains unknown. Although genetic linkage studies support a critical underlying role for genetics, the geographic distribution of these disorders as well as the low concordance rates in monozygotic twins suggest that a combination of other factors including environmental ones are involved. Virus infection is a primary factor that has been implicated in the initiation of autoimmune disease. Infection triggers a robust and usually well-coordinated immune response that is critical for viral clearance. However, in some instances, immune regulatory mechanisms may falter, culminating in the breakdown of self-tolerance, resulting in immune-mediated attack directed against both viral and self-antigens. Traditionally, cross-reactive T-cell recognition, known as molecular mimicry, as well as bystander T-cell activation, culminating in epitope spreading, have been the predominant mechanisms elucidated through which infection may culminate in an T-cell-mediated autoimmune response. However, other hypotheses including virus-induced decoy of the immune system also warrant discussion in regard to their potential for triggering autoimmunity. In this review, we discuss the mechanisms by which virus infection and antiviral immunity contribute to the development of autoimmunity.

The chemokine receptor CXCR3 promotes the trafficking of activated T and NK cells in response to three ligands, CXCL9, CXCL10, and CXCL11. Although these chemokines are produced in the CNS in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE), their role in the pathogenesis of CNS autoimmunity is unresolved. We examined the function of CXCR3 signaling in EAE using mice that were deficient for CXCR3 (CXCR3−/−). The time to onset and peak disease severity were similar for CXCR3−/− and wild-type (WT) animals; however, CXCR3−/− mice had more severe chronic disease with increased demyelination and axonal damage. The inflammatory lesions in WT mice consisted of well-demarcated perivascular mononuclear cell infiltrates, mainly in the spinal cord and cerebellum. In CXCR3−/− mice, these lesions were more widespread throughout the CNS and were diffused and poorly organized, with T cells and highly activated microglia/macrophages scattered throughout the white matter. Although the number of CD4+ and CD8+ T cells infiltrating the CNS were similar in CXCR3−/− and WT mice, Foxp3+ regulatory T cells were significantly reduced in number and dispersed in CXCR3−/− mice. The expression of various chemokine and cytokine genes in the CNS was similar in CXCR3−/− and WT mice. The genes for the CXCR3 ligands were expressed predominantly in and/or immediately surrounding the mononuclear cell infiltrates. We conclude that in EAE, CXCR3 signaling constrains T cells to the perivascular space in the CNS and augments regulatory T cell recruitment and effector T cell interaction, thus limiting autoimmune-mediated tissue damage.