Expression of functional activating and inhibitory Fcgamma receptors on human B cells

Isotype-specific outcomes in Fc gamma receptor targeting of PspA using fusion proteins as a vaccination strategy against Streptococcus pneumoniae infection

Streptococcus pneumoniae (Spn) remains a considerable threat to public health despite the availability of antibiotics and polysaccharide conjugate vaccines. The lack of mucosal immunity in addition to capsular polysaccharide diversity, has proved to be problematic in developing a universal vaccine against Spn. Targeting antigen to Fc receptors is an attractive way to augment both innate and adaptive immunity against mucosal pathogens, by promoting interactions with activating Fcγ receptors (FcγR) that mediate diverse immunomodulatory functions. The effect of targeting FcγR is highly influenced by the IgG subclass, which bares differential affinities for activating and inhibitory FcγR. In the current study we demonstrate targeting activating FcγR with fusion proteins consisting of PspA and IgG2a Fc enhance PspA-specific immune responses, and effectively protect against mucosal Spn challenge. Specifically, targeting PspA to FcγR polarized alveolar macrophage to the AM1 phenotype and increased conventional dendritic cell subsets in the lung in addition to augmenting Th1 cytokines and PspA-specific IgG and IgA. In contrast, fusion proteins consisting of PspA fused to the IgG1 Fc provided minimal benefit over administration of PspA alone, as a result of interaction with the inhibitory FcγRIIB. Protective efficacy of the IgG1 fusion protein was significantly enhanced in animals deficient for FcγRIIB accompanied by increased B cell maturation and proliferation levels in these animals. These studies demonstrate FcγR targeting is an effective strategy for inducing potent cellular and humoral responses via mucosal immunization with Fc fusion proteins, however, careful consideration of the Fc region utilized is required since Fc isotype subclass heavily influenced immunization induced effector functions and survival against lethal Spn challenge. Fc-engineering with specific attention to FcγRIIB engagement presents a valuable vaccine strategy for protecting against Spn infection.

Low doses of IgG from atopic individuals can modulate in vitro IFN-γ production by human intra-thymic TCD4 and TCD8 cells: An IVIg comparative approach

The regulatory effect of allergic responses induced by IgG antibodies on human intra-thymic cells has not been reported in the literature. The aim of this study was to evaluate the possible differential effect of purified IgG from atopic and non-atopic individuals on human intra-thymic αβT cell cytokine production. Thymic tissues were obtained from 14 patients who were less than 7 d old. Additionally, blood samples were collected from atopic and non-atopic volunteers. Thymocytes and peripheral blood mononuclear cells were cultured with purified atopic or non-atopic IgG, and intracellular cytokine production was assessed. Purified IgG did not influence the frequency or viability of human intra-thymic αβT cells. Purified non-atopic IgG induced greater IFN-γ production by intra-thymic CD4+CD8+ T cells than did the mock treatment and atopic IgG. A similar effect of purified non-atopic IgG on TCD8 cells was observed compared with the mock treatment. Atopic IgG inhibited IFN-γ and TGF-β production by intra-thymic TCD4 cells. Treatment with intravenous immunoglobulin resulted in intermediate levels of IFN-γ and TGF-β in intra-thymic TCD4 cells compared with treatment with atopic and non-atopic IgG. Peripheral TCD4 cells from non-atopic individuals produced IFN-γ only in response to atopic IgG. This report describes novel evidence revealing that IgG from atopic individuals may influence intracellular IFN-γ production by intra-thymic αβT cells in a manner that may favor allergy development.

Preconception allergen sensitization can induce B10 cells in offspring: a potential main role for maternal IgG

Background

The mechanisms through which allergies can be inhibited after preconception immunization with allergens are not fully understood. We aimed to evaluate whether maternal immunization can induce a regulatory B (B10) cell population in offspring in concert with allergy inhibition.

Methods

C57BL/6 females were or were not immunized with OVA and were mated with normal WT males. Their offspring were evaluated at 3 days of age or 20 days after neonatal immunization. Human peripheral B cells from atopic and non-atopic individuals were also evaluated.

Results

Preconception OVA immunization induced B10 cells in offspring, and IL-10 production appeared to be critical for FcγRIIB upregulation in offspring B cells. Murine and human IL-10-producing B cells responded in vitro to IgG according to the atopic repertoire of the cells.

Conclusions

Our results reveal that maternal immunization induces allergen-specific B10 cells in offspring and a pivotal role for the IgG repertoire in IL-10 production by murine and human B cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s13223-017-0195-8) contains supplementary material, which is available to authorized users.

FcγRIIb expression in early stage chronic lymphocytic leukemia

In normal B-cells, B-cell antigen receptor (BCR) signaling can be negatively regulated by the low-affinity receptor FcγRIIb (CD32b). To better understand the role of FcγRIIb in chronic lymphocytic leukemia (CLL), we correlated its expression on 155 samples from newly-diagnosed Binet A patients with clinical characteristics and outcome. FcγRIIb expression was similar in normal B-cells and leukemic cells, this being heterogenous among patients and within CLL clones. FcγRIIb expression did not correlate with well known prognostic markers [disease stage, serum beta-2 microglobulin (B2M), IGHV mutational status, expression of ZAP-70 and CD38, and cytogenetics] except for a weak concordance with CD49d. Moreover, patients with low FcγRIIb expression (69/155, 44.5%) required therapy earlier than those with high FcγRIIb expression (86/155, 55.5%) (median 151.4 months vs. not reached; p=.071). These results encourage further investigation on the role of FcγRIIb in CLL biology and prognostic significance in larger series of patients.

B cells interactions in lipid immune responses: implications in atherosclerotic disease

Atherosclerosis is considered as an inflammatory and chronic disorder with an important immunologic component, which underlies the majority of cardiovascular diseases; condition that belongs to a group of noncommunicable diseases that to date and despite of prevention and treatment approaches, they remain as the main cause of death worldwide, with 17.5 million of deaths every year. The impact of lipids in human health and disease is taking center stage in research, due to lipotoxicity explained by elevated concentration of circulating lipids, in addition to altered adipose tissue metabolism, and aberrant intracellular signaling. Immune response and metabolic regulation are highly integrated systems and the proper function of each one is dependent on the other. B lymphocytes express a variety of receptors that can recognize foreign, endogenous or modified self-antigens, among them oxidized low density lipoproteins, which are the main antigens in atherosclerosis. Mechanisms of B cells to recognize, remove and present lipids are not completely clear. However, it has been reported that B cell can recognize/remove lipids through a range of receptors, such as LDLR, CD1d, FcR and SR, which might have an atheroprotector or proatherogenic role during the course of atherosclerotic disease. Pertinent literature related to these receptors was examined to inform the present conclusions.

Allergen-specific IgG as a mediator of allergy inhibition: Lessons from mother to child

Allergen-specific IgG produced by immune mothers is associated with less predisposition to allergy development in their children. This finding has been described by several groups over the last few decades, but the mechanisms by which maternal IgG can inhibit allergy development are still not fully understood. With the purpose of summarizing past investigations, we review the literature on murine models of maternal immunization with allergens and on immune regulation in humans after passive therapy with purified IgG. Based on our review, a new hypothesis about these mechanisms is presented, which may provide a foundation for the future development of therapies to inhibit allergy development.

FcgammaRIIb inhibits allergic lung inflammation in a murine model of allergic asthma

Allergic asthma is characterized by airway eosinophilia, increased mucin production and allergen-specific IgE. Fc gamma receptor IIb (FcγRIIb), an inhibitory IgG receptor, has recently emerged as a negative regulator of allergic diseases like anaphylaxis and allergic rhinitis. However, no studies to date have evaluated its role in allergic asthma. Our main objective was to study the role of FcγRIIb in allergic lung inflammation. We used a murine model of allergic airway inflammation. Inflammation was quantified by BAL inflammatory cells and airway mucin production. FcγRIIb expression was measured by qPCR and flow cytometry and the cytokines were quantified by ELISA. Compared to wild type animals, FcγRIIb deficient mice mount a vigorous allergic lung inflammation characterized by increased bronchoalveolar lavage fluid cellularity, eosinophilia and mucin content upon ragweed extract (RWE) challenge. RWE challenge in sensitized mice upregulated FcγRIIb in the lungs. Disruption of IFN-γ gene abrogated this upregulation. Treatment of naïve mice with the Th1-inducing agent CpG DNA increased FcγRIIb expression in the lungs. Furthermore, treatment of sensitized mice with CpG DNA prior to RWE challenge induced greater upregulation of FcγRIIb than RWE challenge alone. These observations indicated that RWE challenge upregulated FcγRIIb in the lungs by IFN-γ- and Th1-dependent mechanisms. RWE challenge upregulated FcγRIIb on pulmonary CD14+/MHC II+ mononuclear cells and CD11c+ cells. FcγRIIb deficient mice also exhibited an exaggerated RWE-specific IgE response upon sensitization when compared to wild type mice. We propose that FcγRIIb physiologically regulates allergic airway inflammation by two mechanisms: 1) allergen challenge mediates upregulation of FcγRIIb on pulmonary CD14+/MHC II+ mononuclear cells and CD11c+ cells by an IFN-γ dependent mechanism; and 2) by attenuating the allergen specific IgE response during sensitization. Thus, stimulating FcγRIIb may be a therapeutic strategy in allergic airway disorders.

Inhibition of B cell-mediated antigen presentation by intravenous immunoglobulins (IVIg)

Previous work from our laboratory revealed that IVIg interacted with intracellular proteins involved in antigen presentation in B cells, suggesting that IVIg might interfere with the process of antigen presentation in these cells. In the present work, we used an in vitro assay with ovalbumin as model antigen and showed that IVIg inhibited both BCR-dependent and BCR-independent antigen presentation. The inhibition could not be explained by a modulation of expression of MHC II molecules expressed on B cells and was shown to occur in an FcgammaRIIb-independent manner, suggesting that the events responsible for the inhibitory effect occur at the intracellular level. This was supported by the observation of a direct correlation between the level of spontaneous internalization of two different proteins (IVIg and HSA) and their inhibitory potential. The inhibition of B cell-mediated antigen presentation reported here may help explain some of the anti-inflammatory effects of IVIg observed in treated patients, such as a decrease in autoantibody production.

T cell responses to steroid cytochrome P450 21-hydroxylase in patients with autoimmune primary adrenal insufficiency

CONTEXT

Autoimmune Addison's disease is thought to result from T cell mediated autoimmunity. Autoantibodies against the steroidogenic cytochrome P450 enzyme 21-hydroxylase (21OH) are found in most patients, and 21OH is therefore a likely target for antigen-specific T cells.

OBJECTIVE

The aim was to study cellular immunity to 21OH and its associations with 21OH autoantibodies and human leukocyte antigen alleles in autoimmune Addison's disease.

DESIGN/PATIENTS

Peripheral blood mononuclear cells were collected from 33 patients with autoimmune Addison's disease and 21 controls. Cellular proliferation and production of cytokines in response to stimulation with 21OH or 21OH-derived peptides were tested.

RESULTS

Cellular proliferation (P = 0.0009) and secretion of interferon-gamma (P < 0.0001) in response to 21OH was significantly higher in patients compared to healthy controls and associated with the presence of 21OH autoantibodies (P = 0.0052). Furthermore, the 21OH-specific production of interferon-gamma was enhanced in the presence of 21OH autoantibodies. This effect was partially inhibited by antibodies against the Fc receptor for IgG, CD32. Moreover, mature dendritic cells proved superior to the other antigen-presenting cells in invoking cellular responses to 21OH. An association between cellular immunity to 21OH and the high-risk HLA genotype for Addison's disease, DRB1*0301-DQ2/DRB1*0404-DQ8, was observed (P = 0.0089). Finally, a significant association between the DRB1*0404-DQ8 haplotype and cellular responses to a 21OH-derived peptide predicted to bind to DRB1*0404 was detected (P = 0.0055).

CONCLUSION

Patients with autoimmune Addison's disease have circulating 21OH-specific T cells, with amino acids 342-361 of 21OH possibly constituting a disease-specific epitope presented by HLA-DRB1*0404.

Current immunological approaches for management of allergic rhinitis and bronchial asthma

A large population world over is affected with allergic diseases and asthma. Pharmacotherapy for allergic diseases and asthma is effective in controlling symptoms but on discontinuation of medication, symptoms reoccur. In contrast, immunotherapy modifies and corrects the underlying pathological immune responses in an antigen-specific manner. Immunotherapy shows an increase in IgG (blocking antibody) that competes with IgE for allergen, inhibiting the release of inflammatory mediators. Recent studies suggest that immunotherapy acts by modifying CD4+ T-cell responses either by immune deviation, T-cell anergy and/or both. Current immunological approaches for management of allergies and asthma involve immunization with native allergen, modified allergen, peptides/cDNA of allergen, anti-IgE, adjuvants coupled allergen, including immunostimulatory DNA sequences, cytokines, and bacterial products. These approaches modulate the immune response and are intended to give long-term benefit.

CD32B is highly expressed on clonal plasma cells from patients with systemic light-chain amyloidosis and provides a target for monoclonal antibody-based therapy

Despite advances in therapy, many patients with systemic light-chain amyloidosis (AL) die within 3 years from diagnosis. The humanized 2B6 monoclonal antibody (MoAb) is specific for the low-affinity IgG Fc receptor CD32B and effective in a human CD32B+ B-cell lymphoma murine xenograft model. Because MoAb therapy could improve outcomes in AL, we studied CD32B expression by clonal plasma cells obtained from 48 patients with AL. Transcript profiling showed that expression of CD32B was significantly higher than expression of all other Fc receptor family members. Reverse-transcriptase polymerase chain reaction (RT-PCR) using double-enriched CD138+ plasma cells showed uniform expression of the stable cell surface CD32B1 isoform at diagnosis and relapse, and flow cytometry showed intense CD32B cell surface staining on 99% of CD138+ plasma cells at diagnosis and relapse. These data provide a rationale for the novel therapeutic targeting of CD32B using the humanized 2B6 MoAb in patients with systemic AL-amyloidosis.

Possible therapeutic applications of single-chain antibodies in systemic autoimmune diseases

B cells participate in the induction and maintenance of systemic autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus, via production of pathogenic autoantibodies, contributing to the formation of immune complexes. Immune complex deposition in the kidney and joints causes inflammation and organ destruction, and chemokine production enhances T cell activation and tissue damage. The development of the disorder depends on several factors, for example, genetic susceptibility, environmental factors or immune dysregulation. Traditional therapies, which aimed at the alleviation of symptoms, are giving way to biological therapies with the potential of disrupting disease progression. This article focuses on antibody therapies, especially on the applications of single-chain antibodies, as new biological agents for the treatment of systemic autoimmune disorders.

A dominant role for FcgammaRII in antibody-enhanced dengue virus infection of human mast cells and associated CCL5 release

Dengue virus is a major mosquito-borne human pathogen with four known serotypes. The presence of antidengue virus antibodies in the serum of individuals prior to dengue virus infection is believed to be an important risk factor for severe dengue virus disease as a result of the phenomenon of antibody-dependent enhancement operating on Fc receptor (FcR)-bearing cells. In addition to blood monocytes, mast cells are susceptible to antibody-enhanced dengue virus infection, producing a number of inflammatory mediators including IL-1, IL-6, and CCL5. Using the human mast cell-like lines KU812 and HMC-1 as well as primary cultures of human cord blood-derived mast cells (CBMC), we aimed to identify the participating FcRs in antibody-enhanced mast cell dengue virus infection, as FcRs represent a potential site for therapeutic intervention. CBMC expressed significant levels of FcgammaRI, FcgammaRII, and FcgammaRIII, and mast cell-like HMC-1 and KU812 cells expressed predominantly FcgammaRII. All four serotypes of dengue virus showed antibody-enhanced binding to KU812 cells. Specific FcgammaRII blockade with mAb IV.3 was found to significantly abrogate dengue virus binding to KU812 cells and CBMC in the presence of dengue-specific antibody. Dengue virus infection and the production of CCL5 by KU812 cells were also inhibited by FcgammaRII blockade.

Human lupus autoantibody-DNA complexes activate DCs through cooperation of CD32 and TLR9

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by pathogenic autoantibodies against nucleoproteins and DNA. Here we show that DNA-containing immune complexes (ICs) within lupus serum (SLE-ICs), but not protein-containing ICs from other autoimmune rheumatic diseases, stimulates plasmacytoid DCs (PDCs) to produce cytokines and chemokines via a cooperative interaction between Toll-like receptor 9 (TLR9) and FcgammaRIIa (CD32). SLE-ICs transiently colocalized to a subcellular compartment containing CD32 and TLR9, and CD32+, but not CD32-, PDCs internalized and responded to SLE-ICs. Our findings demonstrate a novel functional interaction between Fc receptors and TLRs, defining a pathway in which CD32 delivers SLE-ICs to intracellular lysosomes containing TLR9, inducing a signaling cascade leading to PDC activation. These data demonstrate that endogenous DNA-containing autoantibody complexes found in the serum of patients with SLE activate the innate immune system and suggest a novel mechanism whereby these ICs contribute to the pathogenesis of this autoimmune disease.