This may be consistent with the hypothesis that naturally occurring CD4+CD25+ Tregs play a role in the induction and differentiation of Tr1 cells, which are induced upon Ag exposure under certain tolerogenic conditions [48C50]. comparison to treatment with IVIg. M045 treatment had profound effects on the clinical course of EAMG, accompanied by down-modulation of pathogenic antibody responses. These effects were associated with reduced B cell activation and T cell proliferative responses to AChR, an expansion in the population of FoxP3+ regulatory T cells, and Memantine hydrochloride enhanced production of suppressive cytokines, such as IL-10. Treatment was at least as effective as IVIg in suppressing EAMG, even at doses 25C30 fold lower. Multimeric Fc molecules offer the advantages of being recombinant, homogenous, available in unlimited quantity, free of risk from infection and effective at significantly reduced protein loads, and may represent a viable therapeutic alternative to polyclonal IVIg. Keywords: IgG, Fc, IVIg, multimers, EAMG, T cells, Regulatory T cells, B cells, Dendritic cells 1. Introduction Myasthenia gravis (MG) is an autoimmune disorder characterized in most cases by T cell and antibody (Ab) responses to the skeletal muscle nicotinic acetylcholine receptor (AChR). High-affinity, anti-AChR Abs bind to the muscle endplate leading to AChR dysfunction or loss via activation of complement, cross-linking of AChR receptors, or direct blockade of acetylcholine binding sites [1,2]. MG is typically managed with acetylcholinesterase inhibitors and immunosuppressive medications, but acute exacerbations are treated using either therapeutic plasma exchange or intravenous immune globulin (IVIg). The effectiveness of IVIg in MG has been demonstrated in a randomized clinical trial [3], and it is often preferred due to its ease of administration, although it has definite limitations due to its expense, potential side effects, and the high volume load of a therapeutic dose [4]. Although the mode of action of IVIg in MG is still not clear, several possibilities have been proposed, including actions related to the Fc portion of IgG. In fact, recent studies suggest that the anti-inflammatory and anti-autoimmune effects of IVIg reside primarily in the Fc fragment [5C7]. While Memantine hydrochloride the exact mechanisms of Fc-mediated immune tolerance are controversial, it is likely that Fc interactions with Fc gamma receptors (FcRs) are critically involved. FcRs play an essential role in antibody-mediated effector functions, and blocking of activating FcRs results in the abrogation of antibody activity in autoimmune models [7]. It is also well-known that the majority of FcRs are low-affinity receptors, binding Fc bearing immune Memantine hydrochloride aggregates more efficiently than homodimeric Fc fragments that comprise normal IVIg [7]. Along these lines, aggregated IgG fragments have been shown to be required for suppression of inflammation in immune thrombocytopenic purpura (ITP) and inflammatory arthritis animal models [8C11]. Fc-based fusion protein therapeutics have recently emerged as a significant class of highly efficient pharmaceuticals, in which the Fc region of an antibody of the IgG isotype is joined to a different protein [12,13]. Moreover, their effectiveness is commonly believed to be due to their interaction with specific effector proteins, such as the neonatal Fc receptor (FcRn), which increases IgG serum half-life and prolongs therapeutic activity [14,15]. Fc fragments have also been tested along with adjuvants for the stimulation of protective immunity or induction of tolerance against specific antigens due to their ability to activate specific FCRs[16]. However, current approaches that use Fc fragments to deliver Ag to immune cells have a major disadvantage in that the stalk from their monomeric structure are unable to cross-link multiple FcRs required for enhanced cell signaling [17]. Thus, it has been a long-sought goal to develop a Mouse monoclonal to Ractopamine strategy to couple homodimeric IgG Fc-fusion proteins efficiently into polymeric immune complexes. Murine IgG2a is the homologue of human IgG1, and both molecules have a high affinity for FcRI [18,19], share the ability to fix complement and bind to protein antigens [20,21]. The IgG1 is the most abundant human immunoglobulin and thus the major component of IVIG [22C24]. Therefore, to develop a platform for clinical translation, fully recombinant Fc molecules consisting of multimerized murine IgG2a Fc (termed M045) were developed and shown to bind with high affinity to canonical FcRs, and to effectively ameliorate collagen-induced arthritis and murine immune thrombocytopenic purpura [25]. In the present study, we sought to compare the therapeutic efficacy of M045 with that of IVIg in a murine model of autoimmune myasthenia gravis (EAMG). Our findings show that M045 effectively down-modulated ongoing EAMG, and these clinical effects were accompanied by lowered serum autoantibody levels, reduced splenic B.