Louis, MO). of FcRs involved in immune activation, inhibited IVIG-induced increases in IL-10 production, but not IL-12p70 decreases, whereas the anti-IL-10 antibody restored the decrease in IL-12p70 induced by IVIG. These findings suggest that IVIG induced the upregulation of IL-10 production through FcRI activation, and IL-10 was indispensable to the suppressing effect of IVIG on the production of IL-12p70 in LPS-stimulated BMDC. == 1. Introduction == Dendritic cells (DCs) are potent and specialized antigen presenting cells and important regulators of innate and adaptive immunity with the ability to induce T cell activation or its suppression. After the migration from peripheral tissues to the lymphoid organs, DCs trigger immune responses by secreting proinflammatory and anti-inflammatory cytokines to regulate T cell polarization [1,2]. Bone-marrow-derived mouse dendritic cells (BMDCs) produce proinflammatory cytokine IL-12p70 and anti-inflammatory cytokine IL-10 when stimulated with LPS [3]. Development and proliferation of type 1 effector helper T cells (Th1) is known to be under the influence of IL-12p70. IL-12p70 activates NK and T cells and its production is inhibited by IL-10 [4,5]. DC maturation is impaired by IL-10, and Th1-mediated immune responses are attenuated by immature DC [6,7]. It is thought to be an important role of DC to control the balance between the development of effector and regulatory helper T cells in determination of the direction toward efficient immunosuppression and immune activation. Intravenous immunoglobulin (IVIG) is a highly purified immunoglobulin (IgG) fraction prepared from pooled plasma of several thousand donors and, based on its immunoregulatory role, is Stigmastanol widely applied for the therapy of inflammatory and autoimmune diseases [8]. IgG consists of two major functional regions, Fab and Fc. The Fab region is mainly responsible for antigen binding including the blockade of certain receptors and neutralization of bacterial toxins, autoantibodies, or cytokines. The Fc Rabbit polyclonal to Cystatin C region couples the antibody to IgG receptors, named Fc gamma receptors (FcRs), of the innate immune effector cells, such as neutrophils, mast cells, macrophages, and dendritic Stigmastanol cells [8]. Although the precise mechanisms of the regulatory functions of IVIG in the immune system have not been cleared yet, several mechanisms of action have been proposed, such as the interaction of an anti-idiotypic antibody, modulation of cytokine production, inhibition of T-cell proliferation, and modulation of serum complement action on target cells [911]. Bayry et al. reported an interesting bidirectional effect of IVIG [12]. They showed that IVIG inhibited the production of IL-12p70 and stimulated the secretion of IL-10 in LPS-activated human monocyte-derived dendritic cells (mo-DC). As a consequence, in the presence of IVIG during mo-DC maturation or developmental stages, the T-cell stimulatory activity of mo-DC is impaired and its T-cell suppressive Stigmastanol function appears [12]. The mechanisms of this bidirectional effect of IVIG on cytokine production are not clear. To understand the immunoregulatory function of IVIG more clearly, we focused on the relationship between this modulatory effect of IVIG on cytokine production and its actions on the signaling pathway in mouse BMDC stimulated with LPS. LPS signal is mediated by the transmembrane receptor, Toll-like receptor 4 (TLR4), for the induction of cytokine production in immune cells [13]. The LPS-triggered TLR4 activation induces the phosphorylation of intracellular signaling proteins including transcription factor NF-B and members of the extracellular signal-regulated kinases (ERKs) family, ERK1/2, p38 MAPK, and c-Jun N-terminal kinase (JNK). Activation of TLR4 is necessary for the maturation and functional responses of BMDC including cytokine production, phagocytosis, antigen presentation, and T-cell activation/suppression [14,15]. Because IVIG contains a wide range of antibodies that harbor a broad repertoire of antigen binding variable regions present in normal serum, an LPS-binding fraction in IVIG is a possible factor that blocks TLR4 signaling and reduces cytokine production in DC stimulated with LPS [16]. However, it is difficult to explain that only an inhibition of TLR4 signaling results in the upregulation of cytokine production in these LPS-stimulated cells. BMDCs express two general classes of FcRs [17]. One is activation receptors, the high affinity receptor FcRI (CD64) and the low affinity receptor FcRIII (CD16), which mediate activating functions in immune responses. The-chain of these two activation receptors associates with the cell-signaling common-chain (FcR) subunit containing the immunoreceptor tyrosine-based activation motif (ITAM), and ITAM is indispensable in the immune responses after receptor activation. The other is the Stigmastanol inhibitory receptor FcRIIB (CD32B) containing the immunoreceptor tyrosine-based inhibitory motif (ITIM) within the sequence and it has been shown to be critical for its inhibitory function [17]. In the case of signal transduction by FcR after.