Cytokine-regulated expression and inhibitory function of FcgammaRIIB1 and -B2 receptors in human dendritic cells

The arachidonic acid-LTB4-BLT2 pathway enhances human B-CLL aggressiveness

Deregulation of the oxidative cascade of poly-unsaturated fatty acids (PUFAs) has been associated with several cancers, including chronic lymphocytic leukemia (B-CLL). Leukotriene B4 (LTB4), a metabolite of arachidonic acid (AA), is produced by B-CLL and contributes to their survival. The aim of the present study was to analyze the activity of the oxidative cascade of PUFAs in B-CLL. Purified B cells from patients and normal B CD5 positive cells were subjected to flow cytometry, Western-blot and RT-qPCR analyses. LTB4 plasma and intracellular concentrations were determined by ELISA. Our results showed that aggressive B-CLL tumor cells, i.e. cells with an annual proliferation index above 2, over-expressed calcium-dependent and calcium-independent phospholipases A2 (cPLA2-alpha and iPLA2-beta, respectively), 5-lipoxygenase (5LOX) and leukotriene A4 hydroxylase (LTA4H). Intracellular LTB4 levels were lower in the most aggressive cells than in cells with a smaller proliferation index, despite equivalent plasma levels, and lower expression of cytochrome P450 4F3A (CYP4F3A), one major enzyme involved in LTB4 inactivation. Since BLT2, a LTB4 membrane receptor was also more often expressed on aggressive tumor cells, and since a BLT2 inhibitor significantly impaired B-CLL viability in vitro, we propose that LTB4 was efficiently trapped onto BLT2 present on aggressive tumors, thereby eliciting an autocrine response. Taken together our results demonstrate a major deregulation of the pathway leading to LTB4 synthesis and degradation in B-CLL cells, and provide a framework for understanding how these modifications promote cell survival and proliferation, especially in the most aggressive BCLL.

The function of Fcγ receptors in dendritic cells and macrophages

Dendritic cells (DCs) and macrophages use various receptors to recognize foreign antigens and to receive feedback control from adaptive immune cells. Although it was long believed that all immunoglobulin Fc receptors are universally expressed by phagocytes, recent findings indicate that only monocyte-derived DCs and macrophages express high levels of activating Fc receptors for IgG (FcγRs), whereas conventional and plasmacytoid DCs express the inhibitory FcγR. In this Review, we discuss how the uptake, processing and presentation of antigens by DCs and macrophages is influenced by FcγR recognition of immunoglobulins and immune complexes in the steady state and during inflammation.

Multiple mechanisms mediate enhanced immunity generated by mAb-inactivated F. tularensis immunogen

We have previously demonstrated that immunization with inactivated Francisella tularensis, a Category A intracellular mucosal pathogen, combined with IgG2a anti-F. tularensis monoclonal antibody, enhances protection against subsequent F. tularensis challenge. To understand the mechanism(s) involved, we examined the binding, internalization, presentation, and in vivo trafficking of inactivated F. tularensis in the presence and absence of opsonizing monoclonal antibody. We found that when inactivated F. tularensis is combined with anti-F. tularensis monoclonal antibody, presentation to F. tularensis-specific T cells is enhanced, this enhancement is Fc receptor-dependent, and requires a physical linkage between the monoclonal antibody and the inactivated F. tularensis immunogen. This enhanced presentation is due, in part, to enhanced binding and internalization of inactivated F. tularensis by antigen presenting cells, and involves interactions with multiple Fc receptor types. Furthermore, targeting inactivated F. tularensis to Fc receptors enhances dendritic cell maturation and extends the time period over which antigen presenting cells stimulate T cells. In vivo trafficking studies reveal enhanced transport of inactivated F. tularensis immunogen to the Nasal Associated Lymphoid Tissue in the presence of monoclonal antibody, which is FcRn-dependent. In summary, these are the first comprehensive studies using a single vaccine protection model/immunogen to establish the array of mechanisms involved in enhanced immunity/protection mediated by an Fc receptor-targeted mucosal immunogen. These results demonstrate that multiple cellular/immune mechanisms contribute to Fc receptor-enhanced immunity.

Regulation of allograft survival by inhibitory FcγRIIb signaling

Fcγ receptors (FcγR) provide important immunoregulation. Targeting inhibitory FcγRIIb may therefore prolong allograft survival, but its role in transplantation has not been addressed. FcγRIIb signaling was examined in murine models of acute or chronic cardiac allograft rejection by transplanting recipients that either lacked FcγRIIb expression (FcγRIIb(-/-)) or overexpressed FcγRIIb on B cells (B cell transgenic [BTG]). Acute heart allograft rejection occurred at the same tempo in FcγRIIb(-/-) C57BL/6 (B6) recipients as wild type recipients, with similar IgG alloantibody responses. In contrast, chronic rejection of MHC class II-mismatched bm12 cardiac allografts was accelerated in FcγRIIb(-/-) mice, with development of more severe transplant arteriopathy and markedly augmented effector autoantibody production. Autoantibody production was inhibited and rejection was delayed in BTG recipients. Similarly, whereas MHC class I-mismatched B6.K(d) hearts survived indefinitely and remained disease free in B6 mice, much stronger alloantibody responses and progressive graft arteriopathy developed in FcγRIIb(-/-) recipients. Notably, FcγRIIb-mediated inhibition of B6.K(d) heart graft rejection was abrogated by increasing T cell help through transfer of additional H2.K(d)-specific CD4 T cells. Thus, inhibitory FcγRIIb signaling regulates chronic but not acute rejection, most likely because the supra-optimal helper CD4 T cell response in acute rejection overcomes FcγRIIb-mediated inhibition of the effector B cell population. Immunomodulation of FcγRIIb in clinical transplantation may hold potential for inhibiting progression of transplant arteriopathy and prolonging transplant survival.

B cells from rheumatoid arthritis patients show important alterations in the expression of CD86 and FcgammaRIIb, which are modulated by anti-tumor necrosis factor therapy

Introduction

Several molecules help preserve peripheral B cell tolerance, but when altered, they may predispose to autoimmunity. This work studied the expression of the costimulatory molecule CD86 and the inhibitory receptor for IgG immune complexes FcγRIIb (CD32b), on B cells from rheumatoid arthritis (RA) patients, and the influence of anti-tumor necrosis factor (TNF) therapy.

Methods

Peripheral B cells from 18 RA patients and 13 healthy donors were characterized using flow cytometry. Eleven patients who underwent a six-month adalimumab therapy were further assessed for phenotypic changes on their B cells.

Results

RA patients exhibited a high percentage of naïve and memory B cells expressing CD86. In contrast, expression of FcγRIIb was significantly reduced on RA memory B cells and plasmablasts as compared to healthy donors, probably due to downregulation of this receptor when differentiating from naïve to memory cells. These alterations on FcγRIIb were associated with high levels of anti-citrullinated vimentin autoantibodies. In addition, treatment with adalimumab normalized the expression of CD86 on memory B cells and reduced the expression of FcγRIIb, mainly on naïve B cells.

Conclusions

Our findings show that peripheral B cells from RA patients have an altered expression of key molecules, such as CD86 and FcγRIIb. Because this latter receptor is required for feedback inhibition, a deficient expression might contribute to humoral autoimmune responses. Furthermore, these molecules are likely to be influenced by inflammatory factors, since they were modulated by TNF inhibition.

Regulation of hematopoietic cell function by inhibitory immunoglobulin G receptors and their inositol lipid phosphatase effectors

Numerous autoimmune and inflammatory disorders stem from the dysregulation of hematopoietic cell activation. The activity of inositol lipid and protein tyrosine phosphatases, and the receptors that recruit them, is critical for prevention of these disorders. Balanced signaling by inhibitory and activating receptors is now recognized to be an important factor in tuning cell function and inflammatory potential. In this review, we provide an overview of current knowledge of membrane proximal events in signaling by inhibitory/regulatory receptors focusing on structural and functional characteristics of receptors and their effectors Src homology 2 (SH2) domain-containing tyrosine phosphatase 1 and SH2 domain-containing inositol 5-phosphatase-1. We review use of new strategies to identify novel regulatory receptors and effectors. Finally, we discuss complementary actions of paired inhibitory and activating receptors, using Fc gammaRIIA and Fc gammaRIIB regulation human basophil activation as a prototype.

Hypoxia skews dendritic cells to a T helper type 2-stimulating phenotype and promotes tumour cell migration by dendritic cell-derived osteopontin

It is well recognized that tissue microenvironments are involved in regulating the development and function of dendritic cells (DC). Oxygen supply, which varies in different tissues, has been accepted as an important microenvironmental factor in regulating the biological functions of several immune cells and as being involved in tumour progression and metastasis. However, little is known about the effect of hypoxia on the biological functions of DC and the effect of these hypoxia-conditioned DC on tumour metastasis. In this study, we analysed the transcriptional profiles of human monocyte-derived immature DC (imDC) and mature DC (mDC) cultured under normoxia and hypoxia by microarray, and found a body of potential targets regulating the functions of DC during hypoxia. In addition, the phagocytic ability of hypoxic imDC markedly decreased compared with that of normoxic imDC. Importantly, hypoxic DC poorly induced the proliferation of allogeneic T cells, but polarized allogeneic CD4(+) naive T cells into a T helper type 2 (Th2) response. Moreover, hypoxic DC secreted large amounts of osteopontin, which were responsible for the enhanced migration of tumour cells. Therefore, our study provides new insights into the biological functions of DC under hypoxic conditions and one of mechanisms underlying tumour immune escape during hypoxia.

A novel Fc gamma receptor ligand augments humoral responses by targeting antigen to Fc gamma receptors

Generating efficient antibody (Ab) responses against weak antigens remains challenging. Ab responses require antigen (Ag) uptake by antigen-presenting cells (APC), followed by presentation of processed Ag to T cells. Limited uptake of antigenic peptides by APC constrains Ab responses. Here we improve vaccine efficacy by targeting Ag to Fcgamma receptors (FcgammaR) using R4, a recombinant FcgammaR ligand. R4 has four repeats per chain of the hinge region and CH2 domain (HCH2) of human IgG1. HCH2 encompasses the FcgammaR binding site. The repeats are linked to the human IgG1 framework. To test R4 in augmenting Ag uptake, we expressed human serum albumin domain 1 (HSA1) at the N terminus of R4 to produce HSA1R4. HSA1R4 (50 microg) administered to mice in Ribi adjuvant induces up to 1100-fold higher HSA1-specific IgG titers than HSA1 (p<0.001). HSA1R4 (250 ng) induces up to 130 times more anti-HSA1 Ab than HSA1Fc, a protein with HSA1 linked to the IgG1 framework (p<0.001). HSA-reactive T cells proliferate more briskly to HSA1R4 than to HSA1Fc (p<0.008). Immunization with HSA1R4 yields greater T cell reactivity to HSA1 ex vivo than immunization with HSA1Fc (p<0.004). Linking antigenic peptides to linear HCH2 polymers may facilitate vaccine development.