Luminita Pricop

Differential modulation of stimulatory and inhibitory Fc gamma receptors on human monocytes by Th1 and Th2 cytokines.

Immune complex-mediated inflammatory responses are initiated by FcγR on phagocytes. We report in this study that an inhibitory receptor, FcγRIIb2, is expressed on circulating human monocytes, and when co-cross-linked with stimulatory FcγR it down-regulates effector function. FcγRIIb2 expression is increased by IL-4 and decreased by IFN-γ, in contrast to the activating receptor, FcγRIIa, which is increased by IFN-γ and decreased by IL-4. Thus, Th1 and Th2 cytokines differentially regulate the opposing FcγR systems, altering the balance of activating and inhibiting FcγR. The detection and cytokine modulation of FcγRIIb2 in human myeloid cells provide evidence of a negative regulator of immune complex-mediated responses in human phagocytes and offer a new approach to limit Ab-triggered inflammation in autoimmune disease.

Human receptors for immunoglobulin G: Key elements in the pathogenesis of rheumatic disease

The structural diversity of Fc gammaR provides a mechanism by which IgG can elicit a broad range of cell responses. Fc gammaR vary in their affinity for IgG, their preference for IgG subclasses, the cell types in which they are expressed, and the intracellular signals which they elicit--stimulatory or inhibitory. Expansion in our knowledge of structure-function relationships among Fc gammaR has identified them as heritable risk factors for disease susceptibility and valuable targets for therapeutic modulation of the immune system.

Decreased transcription of the human FCGR2B gene mediated by the -343 G/C promoter polymorphism and association with systemic lupus erythematosus

The role for inhibitory Fc gamma receptors class IIb (FcγRIIb) in the onset, progression and severity of several animal models of autoimmune diseases is well established. By contrast, the pathogenic potential of FcγRIIb in human autoimmune diseases remains largely unknown. Here we report the identification of a polymorphism in the human FCGR2B promoter (dbSNP no. rs3219018) that is associated in homozygosity with systemic lupus erythematosus (SLE) phenotype in European-Americans (OR=11.1, P=0.003). Experimental evidence correlates the polymorphism (a G–C substitution at position –343 relative to the start of transcription) with altered FcγRIIb expression and function. The G–C substitution correlated with decreased transcription of the FCGR2B promoter, and resulted in decreased binding of the AP1 transcription complex to the mutant promoter sequence. The surface expression of FcγRIIb receptors was significantly reduced in activated B cells from (–343 C/C) SLE patients. These findings suggest that genetic defects may lead to deregulated expression of the FCGR2B gene in –343 C/C homozygous subjects, and may play a role in the pathogenesis of human SLE.

Paucity of Clinical Disease despite Serological Autoimmunity and Kidney Pathology in Lupus-Prone New Zealand Mixed 2328 Mice Deficient in BAFF

Constitutive overexpression of B cell-activating factor belonging to the TNF family (BAFF) promotes development of systemic lupus erythematosus (SLE), and treatment of SLE mice with BAFF antagonists ameliorates disease. To determine whether SLE can develop de novo in BAFF-deficient hosts, BAFF-deficient New Zealand Mixed (NZM) 2328 (NZM.Baff−/−) mice were generated. In NZM.Baff−/− mice, spleen B cells (including CD5+ B1a and CD5− B1b B cells), germinal centers, Ig-secreting cells, and T cells were reduced in comparison to NZM.Baff+/+ mice. Serum total Ig and autoantibody levels were reduced at 4–6 mo but approached wild-type levels with increasing age, indicating that autoreactive B cells can survive and secrete autoantibodies despite the complete absence of BAFF. At least some of these autoantibodies are nephrophilic in that glomerular deposition of total IgG and IgG1 (but not of IgG2a, IgG2b, or C3) was substantial in NZM.Baff−/− mice by 12–13 mo of age. Despite proliferative glomerulonephritis, highlighted by widespread glomerular hyaline thrombi, being common among NZM.Baff−/− mice by 6–7 mo of age, severe proteinuria and mortality were greatly attenuated. These results demonstrate that the lifelong absence of BAFF does not protect NZM 2328 mice from serological autoimmunity and renal pathology. Nevertheless, the character of the renal pathology is altered, and the mice are largely spared from clinically overt disease (severe proteinuria and premature death). These observations may have profound ramifications for the use of BAFF antagonists in human SLE and related diseases.

Accelerated pathological and clinical nephritis in systemic lupus erythematosus-prone New Zealand Mixed 2328 mice doubly deficient in TNF receptor 1 and TNF receptor 2 via a Th17-associated pathway.

TNF-α has both proinflammatory and immunoregulatory functions. Whereas a protective role for TNF administration in systemic lupus erythematosus (SLE)-prone (New Zealand Black × New Zealand White)F1 mice has been established, it remains uncertain whether this effect segregates at the individual TNFR. We generated SLE-prone New Zealand Mixed 2328 mice genetically deficient in TNFR1, in TNFR2, or in both receptors. Doubly-deficient mice developed accelerated pathological and clinical nephritis with elevated levels of circulating IgG anti-dsDNA autoantibodies and increased numbers of CD4+ T lymphocytes, especially activated memory (CD44highCD62Llow) CD4+ T cells. We show that these cells expressed a Th17 gene profile, were positive for IL-17 intracellular staining by FACS, and produced exogenous IL-17 in culture. In contrast, immunological, pathological, and clinical profiles of mice deficient in either TNFR alone did not differ from those in each other or from those in wild-type controls. Thus, total ablation of TNF-α-mediated signaling was highly deleterious to the host in the New Zealand Mixed 2328 SLE model. These observations may have profound ramifications for the use of TNF and TNFR antagonists in human SLE and related autoimmune disorders, as well as demonstrate, for the first time, the association of the Th17 pathway with an animal model of SLE.

Inhibition of Interleukin 10 Signaling after Fc Receptor Ligation and during Rheumatoid Arthritis

Interleukin-10 (IL-10) is a potent deactivator of myeloid cells that limits the intensity and duration of immune and inflammatory responses. The activity of IL-10 can be suppressed during inflammation, infection, or after allogeneic tissue transplantation. We investigated whether inflammatory factors suppress IL-10 activity at the level of signal transduction. Out of many factors tested, only ligation of Fc receptors by immune complexes inhibited IL-10 activation of the Jak-Stat signaling pathway. IL-10 signaling was suppressed in rheumatoid arthritis joint macrophages that are exposed to immune complexes in vivo. Activation of macrophages with interferon-γ was required for Fc receptor–mediated suppression of IL-10 signaling, which resulted in diminished activation of IL-10–inducible genes and reversal of IL-10–dependent suppression of cytokine production. The mechanism of inhibition involved decreased cell surface IL-10 receptor expression and Jak1 activation and was dependent on protein kinase C delta. These results establish that IL-10 signaling is regulated during inflammation and identify Fc receptors and interferon-γ as important regulators of IL-10 activity. Generation of macrophages refractory to IL-10 can contribute to pathogenesis of inflammatory and infectious diseases characterized by production of interferon-γ and immune complexes.

Cytokine-mediated regulation of activating and inhibitory Fcγ receptors in human monocytes

Fcγ receptors (FcγR) trigger inflammatory reactions in response to immunoglbulin‐opsonized pathogens and antigen‐antibody complexes. The coordinate expression of activating and inhibitory FcγR ensures the homeostasis of immune complex‐driven inflammatory responses. In this study, we used antibodies with preferential binding for activating FcγRIIa and inhibitory FcγRIIb receptors to investigate the expression and regulation of FcγRII isoforms in human monocytes. Cross‐linking of FcγRIIa triggered phagocytosis and cytokine production. Cross‐linking of FcγRIIb was associated with phosphorylation of the immunoreceptor tyrosine‐based inhibitory motif and with a marked reduction in monocyte effector functions. Our study revealed that tumor necrosis factor α (TNF‐α), interleukin (IL)‐10, and IL‐13 altered the transcriptional activity of the FcγRIIB promoter in transfected cell lines and skewed the balance of activating versus inhibitory FcγR in human monocytes. TNF‐α decreased the expression of inhibitory FcγRIIb. IL‐10 up‐regulated all classes of FcγR and induced alternative activation in monocytes, an effect that was synergistic with that of TNF‐α. In contrast, IL‐4 and IL‐13, in combination with TNF‐α, decreased the expression of activating FcγR and markedly down‐regulated FcγR‐mediated function. Our findings suggest that the cytokine milieu can induce changes in the relative expression of FcγR with opposing function and thus, may regulate the amplitude of FcγR‐mediated uptake and inflammation.

Regulated Expression of FcγR in Human Dendritic Cells Controls Cross-Presentation of Antigen-Antibody Complexes

Receptors for IgG (FcγR) expressed in dendritic cells (DCs) influence the initiation of Ab-mediated immunity. Dynamic variations in FcγR expression allow DCs to adjust their capacity to capture Ab-opsonized Ag. The current paradigm predicts a progressive decline in FcγR-mediated phagocytic function upon DC maturation. Surprisingly, we find that expression of the phagocytic receptor FcγRIIa is preserved in immature and mature DCs at comparable levels with macrophages. Moreover, phagocytosis of antigenic peptides directed to FcγRIIa on DCs leads to dramatic increases in Ag cross-presentation and T cell activation. In immature DCs, high expression of inhibitory FcγRIIb correlates with decreased uptake and cross-presentation of Ab-Ag complexes. In contrast, engagement of FcγRIIb is not associated with changes in cross-presentation in mature DCs. We provide evidence that FcγRIIb expression is patently reduced in mature DCs, an effect that is modulated by treatment with cytokines. The regulated expression of activating and inhibitory FcγRs in DCs emerges as a critical checkpoint in the process of Ag uptake and cross-presentation

Inhibitory Fc Gamma Receptors: From Gene to Disease

Multiple lines of evidence have revealed a key role for inhibitory Fc gamma receptors class IIb (FcγRIIb) as negative modulators of innate and adaptive immune responses. Acquired and genetic factors regulate the expression of FcγRIIb receptors and modify their inhibitory potential. Recent advances have highlighted the importance of FcγRIIb receptors in influencing the development of cancer and autoimmunity. The association of increased FcγRIIb expression with tumor development is believed to operate at effector cell level resulting in inhibition of antitumor cytotoxicity. In autoimmune diseases, FcγRIIb receptors play a major role in controlling the amplitude of antibody- and immune complex-mediated reactions. Generally, FcγRIIb deficiency is associated with increased susceptibility and severity to organ-specific and systemic autoimmunity. This article discusses the proposed mechanisms for FcγRIIb deregulation associated with malignant and autoimmune pathology in animal models and human diseases.

Infliximab treatment shifts the balance between stimulatory and inhibitory Fcγ receptor type II isoforms on neutrophils in patients with rheumatoid arthritis

OBJECTIVE Human neutrophils express both activating and inhibitory Fcgamma receptors (FcgammaR), and their relative expression determines the inflammatory response to immune complexes. Tumor necrosis factor alpha (TNFalpha) up-regulates the expression of stimulatory FcgammaRIIa on neutrophils in vitro, and amplifies immune complex-induced activation of neutrophils in vivo. This study was undertaken to determine whether TNFalpha blockade in patients with rheumatoid arthritis (RA) alters the balance of activating FcgammaR and inhibitory FcgammaR and thereby decreases inflammation. METHODS We used fluorescence-activated cell sorting and Western blotting to examine FcgammaR expression on neutrophils in 24 patients with RA, preceding their first infusion of infliximab and immediately prior to >or=3 subsequent infusions. RESULTS In 13 of 24 patients (54.2%), there was a decrease in the expression of the predominant activating FcgammaR, FcgammaRIIa, after treatment with infliximab, an effect that persisted over >or=3 months of treatment. Although prior to initiation of infliximab therapy the inhibitory FcgammaR, FcgammaRIIb, was undetectable in neutrophils from 23 of 24 patients with RA, FcgammaRIIb protein was detected by Western blotting in 9 patients (37.5%) at the time of the third infliximab infusion. The induction of inhibitory FcgammaRIIb was always associated with decreased levels of FcgammaRIIa, and improvement following infliximab therapy, measured using the Health Assessment Questionnaire, was significantly associated with down-regulation of FcgammaRIIa. CONCLUSION Our findings indicate that TNFalpha inhibition may reduce inflammation in patients with RA by restoring the balance of activating and inhibitory FcgammaR and thereby raising the threshold for immune complex-mediated activation of neutrophils.