The cellular uptake, intracellular processing, and presentation of foreign antigen are crucial processes for eliciting an effective adaptive host response to the majority of pathogens. The effective ...recognition of antigen by T cells requires that it is first processed and then presented on MHC molecules that are expressed on other cells. A critical step leading to the presentation of antigen is delivering the foreign cargo to an intracellular compartment where the antigen can be processed and loaded onto MHC molecules. Fc-gamma receptors (FcγRs) recognize IgG-coated targets, such as opsonized pathogens or immune complexes (ICs). Cross-linking leads to internalization of the cargo with associated activation of down-stream signaling cascades. FcγRs vary in their affinity for IgG and intracellular trafficking, and therefore have an opportunity to regulate antigen presentation by controlling the shuttling and processing of their cargos. In this way, they critically influence physiological and pathophysiological adaptive immune cell functions. In this review, we will cover the contribution of FcγRs to antigen-presentation with a focus on the intracellular trafficking of IgG-ICs and the pathways that support this function. We will also discuss genetic evidence linking FcγR biology to immune cell activation and autoimmune processes as exemplified by systemic lupus erythematosus (SLE).
Cytotoxic T lymphocyte antigen 4 (CTLA-4) is an essential negative regulator of T cell immune responses whose mechanism of action is the subject of debate. CTLA-4 shares two ligands (CD80 and CD86) ...with a stimulatory receptor, CD28. Here, we show that CTLA-4 can capture its ligands from opposing cells by a process of trans-endocytosis. After removal, these costimulatory ligands are degraded inside CTLA-4—expressing cells, resulting in impaired costimulation via CD28. Acquisition of CD86 from antigen-presenting cells is stimulated by T cell receptor engagement and observed in vitro and in vivo. These data reveal a mechanism of immune regulation in which CTLA-4 acts as an effector molecule to inhibit CD28 costimulation by the cell-extrinsic depletion of ligands, accounting for many of the known features of the CD28—CTLA-4 system.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
CD28 and CTLA-4 (CD152) play essential roles in regulating T cell immunity, balancing the activation and inhibition of T cell responses, respectively. Although both receptors share the same ligands, ...CD80 and CD86, the specific requirement for two distinct ligands remains obscure. In the present study, we demonstrate that, although CTLA-4 targets both CD80 and CD86 for destruction via transendocytosis, this process results in separate fates for CTLA-4 itself. In the presence of CD80, CTLA-4 remained ligand bound, and was ubiquitylated and trafficked via late endosomes and lysosomes. In contrast, in the presence of CD86, CTLA-4 detached in a pH-dependent manner and recycled back to the cell surface to permit further transendocytosis. Furthermore, we identified clinically relevant mutations that cause autoimmune disease, which selectively disrupted CD86 transendocytosis, by affecting either CTLA-4 recycling or CD86 binding. These observations provide a rationale for two distinct ligands and show that defects in CTLA-4-mediated transendocytosis of CD86 are associated with autoimmunity.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The immune suppressive protein CTLA-4 is constitutively expressed by Tregs and induced in effector T cells upon activation. Its crucial role in adaptive immunity is apparent from the fatal autoimmune ...pathology seen in CTLA-4 knockout mice. However, little is known regarding factors that regulate CTLA-4 expression and their effect upon its function to remove CD80 and CD86 from antigen presenting cells by transendocytosis. Th17 cells are emerging as significant players in autoimmunity as well as other diseases. Therefore, in this study we have examined the effects of Th17 polarising conditions on CTLA-4 expression and function in human T cells and show that Th17 conditions can suppress the expression of CTLA-4 and its transendocytic function. In contrast to Th17 cells, vitamin D is inversely associated with autoimmune disease. We have previously shown a striking ability of 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) to enhance CTLA-4, however, its effects upon B7 transendocytosis and its activity in the context of inflammation remained unknown. Here we show that induction of CTLA-4 by 1,25(OH)2D3 can actually be enhanced in the presence of Th17 polarising cytokines. Furthermore, its transendocytic function was maintained such that T cells generated in the presence of Th17 conditions and 1,25(OH)2D3 were highly effective at capturing CTLA-4 ligands from antigen presenting cells and suppressing T cell division. Taken together, these data reveal an inhibitory effect of Th17 polarising conditions upon CTLA-4-mediated regulation and show that 1,25(OH)2D3 counteracts this effect. Given the importance of CTLA-4-mediated suppression in the control of autoimmune diseases, our novel data highlight the importance of vitamin D in inflammatory settings.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
1,25-Dihydroxyvitamin D3 1,25(OH)2D3, the active form of vitamin D, exerts potent effects on several tissues including cells of the immune system, where it affects T cell activation, ...differentiation and migration. The circulating, inactive form of vitamin D, 25(OH)D3, is generally used as an indication of vitamin D status. However, use of this precursor depends on its uptake by cells and subsequent conversion by the enzyme 25(OH)D3-1α-hydroxylase (CYP27B1) into active 1,25(OH)2D3. Using human T cells, we show in this study that addition of inactive 25(OH)D3 is sufficient to alter T cell responses only when dendritic cells (DCs) are present. Mechanistically, CYP27B1 is induced in DCs upon maturation with LPS or upon T cell contact, resulting in the generation and release of 1,25(OH)2D3, which subsequently affects T cell responses. In most tissues, vitamin D binding protein acts as a carrier to enhance the use of vitamin D. However, we show that vitamin D binding protein modulates T cell responses by restricting the availability of inactive 25(OH)D3 to DC. These data indicate that the level of free 25(OH)D3 available to DCs determines the inflammatory/regulatory balance of ensuing T cell responses.
This study examined the effect of danger on consolidation of neutral information in two regions of the rat (male and female) medial temporal lobe: the perirhinal cortex (PRh) and basolateral amygdala ...complex (BLA). The neutral information was the association that forms between an auditory stimulus and a visual stimulus (labeled S2 and S1) across their pairings in sensory preconditioning. We show that, when the sensory preconditioning session is followed by a shocked context exposure, the danger shifts consolidation of the S2-S1 association from the PRh to the BLA; and does so by interacting with processes involved in encoding of the S2-S1 pairings. Specifically, we show that the initial S2-S1 pairing in sensory preconditioning is encoded in the BLA and not the PRh; whereas the later S2-S1 pairings are encoded in the PRh and not the BLA. When the sensory preconditioning session is followed by a context alone exposure, the BLA-dependent trace of the early S2-S1 pairings decays and the PRh-dependent trace of the later S2-S1 pairings is consolidated in memory. However, when the sensory preconditioning session is followed by a shocked context exposure, the PRh-dependent trace of the later S2-S1 pairings is suppressed and the BLA-dependent trace of the initial S2-S1 pairing is consolidated in memory. These findings are discussed with respect to mutually inhibitory interactions between the PRh and BLA, and the way that these regions support memory in other protocols, including recognition memory in people.
The perirhinal cortex (PRh) and basolateral amygdala complex (BLA) process the pairings of neutral auditory and visual stimuli in sensory preconditioning. The involvement of each region in this processing is determined by the novelty/familiarity of the stimuli as well as events that occur immediately after the preconditioning session. Novel stimuli are represented in the BLA; however, as these stimuli are repeatedly presented without consequence, they come to be represented in the PRh. Whether the BLA- or PRh-dependent representation is consolidated in memory depends on what happens next. When nothing of significance occurs, the PRh-dependent representation is consolidated and the BLA-dependent representation decays; but when danger is encountered, the PRh-dependent representation is inhibited and the BLA-dependent representation is selected for consolidation.
The active form of vitamin D, 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), has potent immunomodulatory properties that have promoted its potential use in the prevention and treatment of infectious ...disease and autoimmune conditions. A variety of immune cells, including macrophages, dendritic cells, and activated T cells express the intracellular vitamin D receptor and are responsive to 1,25(OH)(2)D(3.) Despite this, how 1,25(OH)(2)D(3) regulates adaptive immunity remains unclear and may involve both direct and indirect effects on the proliferation and function of T cells. To further clarify this issue, we have assessed the effects of 1,25(OH)(2)D(3) on human CD4(+)CD25(-) T cells. We observed that stimulation of CD4(+)CD25(-) T cells in the presence of 1,25(OH)(2)D(3) inhibited production of proinflammatory cytokines including IFN- gamma, IL-17, and IL-21 but did not substantially affect T cell division. In contrast to its inhibitory effects on inflammatory cytokines, 1,25(OH)(2)D(3) stimulated expression of high levels of CTLA-4 as well as FoxP3, the latter requiring the presence of IL-2. T cells treated with 1,25(OH)(2)D(3) could suppress proliferation of normally responsive T cells, indicating that they possessed characteristics of adaptive regulatory T cells. Our results suggest that 1,25(OH)(2)D(3) and IL-2 have direct synergistic effects on activated T cells, acting as potent anti-inflammatory agents and physiologic inducers of adaptive regulatory T cells.
Elimination of the binding of immunoglobulin Fc to Fc gamma receptors (FcγR) is highly desirable for the avoidance of unwanted inflammatory responses to therapeutic antibodies and fusion proteins. ...Many different approaches have been described in the literature but none of them completely eliminates binding to all of the Fcγ receptors. Here we describe a set of novel variants having specific amino acid substitutions in the Fc region at L234 and L235 combined with the substitution G236R. They show no detectable binding to Fcγ receptors or to C1q, are inactive in functional cell-based assays and do not elicit inflammatory cytokine responses. Meanwhile, binding to FcRn, manufacturability, stability and potential for immunogenicity are unaffected. These variants have the potential to improve the safety and efficacy of therapeutic antibodies and Fc fusion proteins.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
CTLA‐4 is an essential regulator of T‐cell immune responses whose intracellular trafficking is a hallmark of its expression. Defects in CTLA‐4 trafficking due to LRBA deficiency cause profound ...autoimmunity in humans. CTLA‐4 rapidly internalizes via a clathrin‐dependent pathway followed by poorly characterized recycling and degradation fates. Here, we explore the impact of manipulating Rab GTPases and LRBA on CTLA‐4 expression to determine how these proteins affect CTLA‐4 trafficking. We observe that CTLA‐4 is distributed across several compartments marked by Rab5, Rab7 and Rab11 in both HeLa and Jurkat cells. Dominant negative (DN) inhibition of Rab5 resulted in increased surface CTLA‐4 expression and reduced internalization and degradation. We also observed that constitutively active (CA) Rab11 increased, whereas DN Rab11 decreased CTLA‐4 surface expression via an impact on CTLA‐4 recycling, indicating CTLA‐4 shares similarities with other recycling receptors such as EGFR. Additionally, we studied the impact of manipulating both LRBA and Rab11 on CTLA‐4 trafficking. In Jurkat cells, LRBA deficiency was associated with markedly impaired CTLA‐4 recycling and increased degradation that could not be corrected by expressing CA Rab11. Moreover LRBA deficiency reduced CTLA‐4 colocalization with Rab11, suggesting that LRBA is upstream of Rab11. These results show that LRBA is required for effective CTLA‐4 recycling by delivering CTLA‐4 to Rab11 recycling compartments, and in its absence, CTLA‐4 fails to recycle and undergoes degradation.
Correct trafficking of CTLA‐4 is required for its function and mutations in proteins such as LRBA lead to CTLA‐4 deficiency disorders. Here we detail the intracellular pathways involved in CTLA‐4 trafficking using constitutively active and dominant negative Rab GTPases to probe the relationship between CTLA‐4 and LRBA. Our data show CTLA‐4 recycling is strongly dependent on Rab11 activity and that LRBA function is likely upstream of Rab11.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
The cytolytic ionotropic ATP receptor P2X 7 has several important roles in immune cell regulation, such as cytokine release, apoptosis, and microbial killing. Although
P2X 7 receptors are frequently ...coexpressed with another subtype of P2X receptor, P2X 4 , they are believed not to form heteromeric assemblies but to function only as homomers. Both receptors play a role in neuropathic
pain; therefore, understanding how they coordinate the cellular response to ATP is important for the development of effective
pain therapies. Here, we provide biochemical and electrophysiological evidence for an association between P2X 4 and P2X 7 that increases the diversity of receptor currents mediated via these two subtypes. The heterologously expressed receptors
were coimmunoprecipitated from human embryonic kidney (HEK) 293 cells, and the endogenous P2X 4 and P2X 7 receptors were similarly coimmunoprecipitated from bone marrow-derived macrophages. In HEK293 cells, the fraction of P2X 4 receptors biotinylated at the plasma membrane increased 2-fold in the presence of P2X 7 although there was no change in overall expression. Coexpression of a dominant-negative P2X 4 mutant (C353W) with P2X 7 , inhibited P2X 7 receptor mediated currents by greater than 2-fold, whereas a nonfunctional but nonâdominant-negative mutant (S341W) did not.
Coexpression of P2X 4 S341W with P2X 7 produced a current that was potentiated by ivermectin and inhibited by 2â²,3â²- O -(2,4,6-trinitrophenyl) adenosine 5-triphosphate (TNP-ATP), whereas expression of P2X 7 alone produced a current that was insensitive to both of these compounds at the concentrations used. These results demonstrate
a structural and functional interaction between P2X 4 and P2X 7 , which suggests that they associate to form heteromeric receptors.
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