Fc receptor homologs: newest members of a remarkably diverse Fc receptor gene family

FCRL1 immunoregulation in B cell development and malignancy

Immunotherapeutic targeting of surface regulatory proteins and pharmacologic inhibition of critical signaling pathways has dramatically shifted our approach to the care of individuals with B cell malignancies. This evolution in therapy reflects the central role of the B cell receptor (BCR) signaling complex and its co-receptors in the pathogenesis of B lineage leukemias and lymphomas. Members of the Fc receptor-like gene family (FCRL1-6) encode cell surface receptors with complex tyrosine-based regulation that are preferentially expressed by B cells. Among them, FCRL1 expression peaks on naïve and memory B cells and is unique in terms of its intracellular co-activation potential. Recent studies in human and mouse models indicate that FCRL1 contributes to the formation of the BCR signalosome, modulates B cell signaling, and promotes humoral responses. Progress in understanding its regulatory properties, along with evidence for its over-expression by mature B cell leukemias and lymphomas, collectively imply important yet unmet opportunities for FCRL1 in B cell development and transformation. Here we review recent advances in FCRL1 biology and highlight its emerging significance as a promising biomarker and therapeutic target in B cell lymphoproliferative disorders.

Evidence for Extensive Duplication and Subfunctionalization of FCRL6 in Armadillo (Dasypus novemcinctus)

The control of infections by the vertebrate adaptive immune system requires careful modulation to optimize defense and minimize harm to the host. The Fc receptor-like (FCRL) genes encode immunoregulatory molecules homologous to the receptors for the Fc portion of immunoglobulin (FCR). To date, nine different genes (FCRL1-6, FCRLA, FCRLB and FCRLS) have been identified in mammalian organisms. FCRL6 is located at a separate chromosomal position from the FCRL1-5 locus, has conserved synteny in mammals and is situated between the SLAMF8 and DUSP23 genes. Here, we show that this three gene block underwent repeated duplication in Dasypus novemcinctus (nine-banded armadillo) resulting in six FCRL6 copies, of which five appear functional. Among 21 mammalian genomes analyzed, this expansion was unique to D. novemcinctus. Ig-like domains that derive from the five clustered FCRL6 functional gene copies show high structural conservation and sequence identity. However, the presence of multiple non-synonymous amino acid changes that would diversify individual receptor function has led to the hypothesis that FCRL6 endured subfunctionalization during evolution in D. novemcinctus. Interestingly, D. novemcinctus is noteworthy for its natural resistance to the Mycobacterium leprae pathogen that causes leprosy. Because FCRL6 is chiefly expressed by cytotoxic T and NK cells, which are important in cellular defense responses against M. leprae, we speculate that FCRL6 subfunctionalization could be relevant for the adaptation of D. novemcinctus to leprosy. These findings highlight the species-specific diversification of FCRL family members and the genetic complexity underlying evolving multigene families critical for modulating adaptive immune protection.

Fc receptor-like 1 (FCRL1) is a novel biomarker for prognosis and a possible therapeutic target in diffuse large B-cell lymphoma

BACKGROUND

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin's lymphoma, which can involve various types of mature B-cells. Considering that the incidence of DLBCL has increased, additional research is required to identify novel and effective prognostic and therapeutic molecules. Fc receptor-like 1 (FCRL1) acts as an activation co-receptor of human B-cells. Aberrant expression of this molecule has been reported in a number of B-cell-related disorders. Moreover, the clinical significance and prognosis value of FCRL1 in DLBCL are not completely identified.

METHODS

In this study, the expression levels of FCRL1 were determined in thirty patients with DLBCL and 15 healthy controls (HCs). In addition, the correlation between FCRL1 expressions with clinicopathological variables of DLBCL patients were examined. Then, the potential roles of FCRL1 in proliferation, apoptosis, and cell cycle distribution of B-cells from DLBCL patients were determined using flow cytometry analysis, after knockdown of this marker using retroviral short hairpin RNA interference. Quantitative real time-PCR, western blotting, and enzyme-linked immunosorbent assay were also used to identify the possible effects of FCRL1 knockdown on the expression levels of BCL-2, BID, BAX, intracellular signaling pathway PI3K/p-Akt, and p65 nuclear factor-kappa B (NF-κB) in the B-cells of DLBCL.

RESULTS

Statistical analysis revealed higher levels of FCRL1 expression in the B-cells of DLBCL patients compared to HCs at both protein and mRNA levels. A positive correlation was observed between the FCRL1 expression and some clinicopathological parameters of DLBCL patients. In addition, FCRL1 knockdown significantly decreased cell proliferation and stimulated apoptosis as well as G1 cell cycle arrest in the B-cells of DLBCL patients. The levels of p65 NF-κB and PI3K/p-Akt expressions were markedly reduced after knockdown of FCRL1 expression.

CONCLUSIONS

These results suggested that FCRL1 could be a potential novel biomarker for prognosis and/or a possible effective therapeutic target for treatment of patients with DLBCL.

Identification of multiple novel susceptibility genes associated with autoimmune thyroid disease

Background

Autoimmune thyroid disease (AITD) is induced by various factors, including inheritability, which regulates gene expression. Multiple loci correlated with AITD have been discovered utilizing genome-wide association studies (GWASs). Nevertheless, demonstrating the biological relevance and function of these genetic loci is difficult.

Methods

The FUSION software was utilized to define genes that were expressed differentially in AITD using a transcriptome-wide association study (TWAS) method in accordance with GWAS summary statistics from the largest genome-wide association study of 755,406 AITD individuals (30,234 cases and 725,172 controls) and levels of gene expression from two tissue datasets (blood and thyroid). Further analyses were performed such as colocalization, conditional, and fine-mapping analyses to extensively characterize the identified associations, using functional mapping and annotation (FUMA) to conduct functional annotation of the summary statistics of 23329 significant risk SNPs (P < 5 × 10^-8) recognized by GWAS, together with summary-data-based mendelian randomization (SMR) for identifying functionally related genes at the loci in GWAS.

Results

There were 330 genes with transcriptome-wide significant differences between cases and controls, and the majority of these genes were new. 9 of the 94 unique significant genes had strong, colocalized, and potentially causal correlations with AITD. Such strong associations included CD247, TPO, KIAA1524, PDE8B, BACH2, FYN, FOXK1, NKX2-3, and SPATA13. Subsequently, applying the FUMA approach, novel putative AITD susceptibility genes and involved gene sets were detected. Furthermore, we detected 95 probes that showed strong pleiotropic association with AITD through SMR analysis, such as CYP21A2, TPO, BRD7, and FCRL3. Lastly, we selected 26 genes by integrating the result of TWAS, FUMA, and SMR analysis. A phenome-wide association study (pheWAS) was then carried out to determine the risk of other related or co-morbid phenotypes for AITD-related genes.

Conclusions

The current work provides further insight into widespread changes in AITD at the transcriptomic level, as well as characterized the genetic component of gene expression in AITD by validating identified genes, establishing new correlations, and uncovering novel susceptibility genes. Our findings indicate that the genetic component of gene expression plays a significant part in AITD.

Fc Receptor-Like Gene Expression in Renal Transplantation Patients

Background:

It has been well-documented that the Fc receptor-like (FCRL) molecule contributes to the pathogenesis of certain autoimmune disorders. FCRL molecules belong to the immunoglobulin superfamily produced by B cells. Also, these molecules induce activating or inhibitory signals of B cells. According to this information and also considering the critical role of immune reactions in organ transplantation, the following experiment was performed to analyze the gene expression level of FCRLs in peripheral blood mononuclear cells of kidney transplant recipients.

Materials and Methods:

Blood samples were obtained from 32 renal transplant patients on days 1, 3, and 7 post-transplantations. Patients were divided into two groups according to the presence or absence of rejection. Also, 24 age-matched healthy subjects were enrolled as control group. After total RNA extraction from peripheral blood mononuclear cells (PBMC) and cDNA synthesis, the gene expression levels of FCRL1, FCRL2, and FCRL4 in each group were measured by real-time polymerase chain reaction.

Results:

Our results showed that FCRL1 expression levels in kidney transplant patients were significantly less than healthy controls. The overall FCRL2 expression level was not significantly different between them. However, at days 1 and 7, following transplantation in the non-rejected group FCRL2 level was significantly higher than the control group. Comparing the FCRL4 gene expression levels of both groups with healthy controls showed a significant decrease in the third and seventh days post-transplantation.

Conclusion:

It can be concluded that mononuclear cells, mainly B cells, have an essential role to play in kidney transplantation.

Evolution of Fc Receptor-Like Scavenger in Mammals

Fc receptor-like (FCRL) molecules comprise a large family of receptors, homologous to the receptors for the Fc portion of immunoglobulins (FCR). Within this family, an unusual gene known to exist in mice, rats and dogs, termed FCRLS, encodes a chimeric protein with both Ig-like FCRL and type B scavenger-receptor cysteine-rich (SRCR)-like domains. In mice, FCRLS is located next to the CD5L and KIRREL1 genes. Here, we show that the curious FCRLS gene is actually present across major mammalian groups, but its annotation is generally incorrect or absent. Anchored on mouse FCRLS and FCRL2 genomic sequence alignments, phylogenetic analyses demonstrated that many mammalian sequences currently annotated as FCRL2 cluster with FCRLS, supported by a conserved genetic synteny among organisms. This analysis shows that FCRLS is present in Rodentia, some Carnivora (Canidae and Ursidae), Chiroptera, Arctiodactyla, Proboscidae, and some Primata. Thus, the FCRLS most likely originated in a eutherian mammal ancestor since it is not present in Monotremata or Marsupialia. FCRLS has a peculiar distribution pattern across mammalian lineages, being present in some species, but absent in others from the same family, as in carnivores for example. The most parsimonious hypothesis to explain this FCRLS evolution is that it was convergently lost in several independent mammalian lineages. Analyses of branch-specific nucleotide evolutionary rates, show that FCRL2 and FCRLS have similar ranges of rates across mammals, suggesting that both genes have crucial, but separate functions in the immune system. Bayesian estimates of evolutionary rates for FCRLS in mammalian lineages revealed that carnivores display the highest mutation rate after rodents. Additionally, positive diversifying selection was detected for both FCRL2 and FCRLS. Our results show that the presence of the FCRLS gene is older and more widespread across mammals than previously thought and appears to be functional, being under positive selection. Its precise physiologic role should thus be investigated.

Identification of distinct LRC- and Fc receptor complex-like chromosomal regions in fish supports that teleost leukocyte immune-type receptors are distant relatives of mammalian Fc receptor-like molecules

Leukocyte immune-type receptors (LITRs) are a large family of immunoregulatory receptor-types originally identified in the channel catfish (Ictalurus punctatus (Ip)LITRs). Phylogenetic analyses of LITRs show that they share distant evolutionary relationships with important mammalian immunoregulatory receptors belonging to the Fc receptors family and the leukocyte receptor complex (LRC), but their syntenic relationships with these immunoglobulin superfamily members have not been investigated. To further examine the possible evolutionary connections between teleost LITRs and various mammalian immunoregulatory receptor-types, we surveyed the genomic databases of representative vertebrate taxa and our results show that teleost LITRs generally exist in large genomic clusters, which are linked to vangl2, arhgef11, and slam family genes, features that are also shared by amphibian and mammalian Fc receptor-like molecules (FCRLs). Moreover, detailed phylogenetic comparisons between the individual Ig-like domains of LITRs and mammalian FCRLs shows that these receptors share related Ig-like domains indicative of their common ancestry. However, contrary to our previous reports, no supportive evidence for phylogenetic relationships between the Ig-like domains of LITRs with the Ig-like domains of LRC-encoded mammalian immunoregulatory receptors was found. We also identified an LRC-like region in the zebrafish genome, but no expanded litr-related genes were located in this region. Similarly, no lilr-related genes were found in spotted gar, a representative basal ray-finned fish. Finally, two distantly related fcrls and an LRC-like gene were identified in the elephant shark genome, suggesting that the loss of an immunoregulatory receptor-containing LRC region may be unique to ray-finned fish.

Roles for the FCRL6 Immunoreceptor in Tumor Immunology

Members of the Fc receptor-like (FCRL1-6) gene family encode transmembrane glycoproteins that are preferentially expressed by B cells and generally repress responses via cytoplasmic tyrosine-based regulation. Given their distribution and function, there is a growing appreciation for their roles in lymphoproliferative disorders and as immunotherapeutic targets. In contrast to FCRL1-5, FCRL6 is distinctly expressed outside the B lineage by cytotoxic T and NK lymphocytes. Its restricted expression by these orchestrators of cell-mediated immunity, along with its inhibitory properties and extracellular interactions with MHCII/HLA-DR, represent a newly appreciated axis with relevance in tolerance and cancer defense. The significance of FCRL6 in this arena has been recently demonstrated by its upregulation in HLA-DR⁺ tumor samples from melanoma, breast, and lung cancer patients who relapsed following PD-1 blockade. These findings imply a potential mechanistic role for FCRL6 in adaptive evasion to immune checkpoint therapy. Here we review these new developments in the FCRL field and identify new evidence for the prognostic significance of FCRL6 in malignancies that collectively indicate its potential as a biomarker and therapeutic target.

Fc Receptor-Like 6 (FCRL6) Discloses Progenitor B Cell Heterogeneity That Correlates With Pre-BCR Dependent and Independent Pathways of Natural Antibody Selection

B-1a cells produce "natural" antibodies (Abs) to neutralize pathogens and clear neo self-antigens, but the fundamental selection mechanisms that shape their polyreactive repertoires are poorly understood. Here, we identified a B cell progenitor subset defined by Fc receptor-like 6 (FCRL6) expression, harboring innate-like defense, migration, and differentiation properties conducive for natural Ab generation. Compared to FCRL6- pro B cells, the repressed mitotic, DNA damage repair, and signaling activity of FCRL6+ progenitors, yielded VH repertoires with biased distal Ighv segment accessibility, constrained diversity, and hydrophobic and charged CDR-H3 sequences. Beyond nascent autoreactivity, VH11 productivity, which predominates phosphatidylcholine-specific B-1a B cell receptors (BCRs), was higher for FCRL6+ cells as was pre-BCR formation, which was required for Myc induction and VH11, but not VH12, B-1a development. Thus, FCRL6 revealed unexpected heterogeneity in the developmental origins, regulation, and selection of natural Abs at the pre-BCR checkpoint with implications for autoimmunity and lymphoproliferative disorders.

Fc Receptor-Like 1 as a Promising Target for Immunotherapeutic Interventions of B-Cell-Related Disorders

BACKGROUND

Human B-cell responses are regulated through synergy between a collection of activation and inhibitory receptors. Fc receptor-like (FCRL) molecules have recently been identified as co-receptors that are preferentially expressed in human B-cells, which may also play an important role in the regulation of human B-cell responses. FCRL1 is a member of the FCRL family molecules with 2 immunoreceptor tyrosine-based activation motifs (ITAMs) in its cytoplasmic tail. This study aimed to investigate the regulatory roles of FCRL1 in human B-cell responses.

MATERIALS AND METHODS

The regulatory potential of FCRL1 in human B-cell through knockdown of FCRL1 expression in the Ramos and Daudi Burkitt lymphoma (BL) cell lines by using the retroviral-based short hairpin ribonucleic acid (shRNA) delivery method. The functional consequences of FCRL1 knockdown were assessed by measuring the proliferation, apoptosis, and the expression levels of Bcl-2, Bid, and Bax genes as well as phosphoinositide-3 kinase/-serine-threonine kinase AKT (PI3K/p-AKT) pathway in the BL cells, using the quantitative real-time polymerase chain reaction (PCR) and flow cytometry analysis. The NF-κB activity was also measured by the enzyme-linked immunosorbent assay (ELISA).

RESULTS

FCRL1 knockdown significantly decreased cell proliferation and increased apoptotic cell death in the BL cells. There was a significant reduction in the extent of the Bcl-2 gene expression in the treated BL cells compared with control cells. On the contrary, FCRL1 knockdown increased the expression levels of Bid and Bax genes in the treated BL cells when compared with control cells. In addition, the extent of the PI3K/p-AKT expression and phosphorylated-p65 NF-κB activity was significantly decreased in the treated BL cells compared with control cells.

CONCLUSIONS

These results suggest that FCRL1 can play a key role in the activation of human B-cell responses and has the potential to serve as a target for immunotherapy of FCRL1 positive B-cell-related disorders.

Prognostic significance of Fc receptor-like 1 in patients with chronic lymphocytic leukemia, hairy cell leukemia, and various B-cell non-Hodgkin's lymphoma

Fc receptor-like 1 (FCRL1) positively regulates B-cell responses and may involve in the pathogenesis of B-cell malignancies. This study examined the expression pattern of FCRL1 in B-cell non-Hodgkin's lymphoma patients using real-time PCR and flow cytometry. The results revealed higher levels of FCRL1 expression in diffuse large B-cell lymphoma, hairy cell leukemia, and Burkitt lymphoma patients compared with control groups. There was a significant reduction in the levels of FCRL1 expression in chronic lymphocytic leukemia and mantle cell lymphoma patients compared with healthy individuals. These findings suggest FCRL1 as an excellent marker for the prognosis or immunotherapy of B-cell malignancies.

Update on Fc receptor-like (FCRL) family: new immunoregulatory players in health and diseases

INTRODUCTION

Fc receptor-like (FCRL) molecules, as recently identified members of the immunoglobulin superfamily (IgSF), are preferentially expressed by B-cells. They have variable number of extracellular immunoglobulin-like domains and cytoplasmic activating ITAMs and/or inhibitory ITIMs. FCRL1-5 are dominantly expressed in different stages of B-cells development. But, FCRL6 is preferentially expressed in different subsets of T-cells and NK cells. FCRL1-5 could regulate different features of B-cell evolution such as development, differentiation, activation, antibody secretion and isotype switching. Areas covered: Improved understanding of FCRL expression may grant B-cells and finally its signaling pathways, alone or in cooperation with other signaling molecules, as interesting new targets for diagnostic, monitoring and immunotherapeutic modalities; although further investigations remain to be defined. Recent investigations on different family members of FCRL proteins have substantiated their differential expression on different tissues, malignancies, immune related disease and infectious diseases. Expert opinion: FCRLs restricted expressions in normal B-cells and T-cell subsets accompanied with their overexpression in B-cell malignancies introduce them as logical candidates for the development of antibody- and cell-based immunotherapy approaches in B-cell malignancies, immune-mediated and infectious diseases. FCRLs would be applied as attractive and specific targets for immunodiagnostic approaches, clinical prognosis as well as disease monitoring of relevant patients.

Analysis of the association between Fc receptor family gene polymorphisms and ocular Behçet's disease in Han Chinese

Fc receptors are known to have a pivotal role in the initiation and regulation of many immunological and inflammatory processes. This study aimed to investigate the association of Fc receptor family gene polymorphisms with ocular Behçet's disease (BD) in Han Chinese. A two stage case-control study was performed in 1022 BD cases and 1803 healthy controls. Twenty-three SNPs were genotyped using the MassARRAY system (Sequenom), TaqMan SNP Genotyping Assay and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. The expression of FCGR3A was examined by real-time PCR and cytokine production was measured by enzyme linked immunosorbent assay (ELISA). A significantly higher frequency of the FCGR3A/rs428888 CT genotype (Pc = 1.96 × 10^-7, OR = 1.897) and a lower frequencies of CC genotype and C allele (Pc = 1.96 × 10^-7, OR = 0.527; Pc = 7.22 × 10^-7, OR = 0.554 respectively) were found in ocular BD as compared with controls. Functional experiments showed an increased FCGR3A expression (P = 0.005) and increased cytokine protein expressions of MCP-1, IL-1β and TNF-α by LPS stimulated PBMCs in CT carriers of FCGR3A rs428888 compared to CC carriers (P = 0.034; P = 0.025; P = 0.04; respectively). Our findings demonstrate that FCGR3A/rs428888 confers genetic susceptibility for ocular BD in Han Chinese.

Trisomy 21 causes changes in the circulating proteome indicative of chronic autoinflammation

Trisomy 21 (T21) causes Down syndrome (DS), but the mechanisms by which T21 produces the different disease spectrum observed in people with DS are unknown. We recently identified an activated interferon response associated with T21 in human cells of different origins, consistent with overexpression of the four interferon receptors encoded on chromosome 21, and proposed that DS could be understood partially as an interferonopathy. However, the impact of T21 on systemic signaling cascades in living individuals with DS is undefined. To address this knowledge gap, we employed proteomics approaches to analyze blood samples from 263 individuals, 165 of them with DS, leading to the identification of dozens of proteins that are consistently deregulated by T21. Most prominent among these proteins are numerous factors involved in immune control, the complement cascade, and growth factor signaling. Importantly, people with DS display higher levels of many pro-inflammatory cytokines (e.g. IL-6, MCP-1, IL-22, TNF-α) and pronounced complement consumption, resembling changes seen in type I interferonopathies and other autoinflammatory conditions. Therefore, these results are consistent with the hypothesis that increased interferon signaling caused by T21 leads to chronic immune dysregulation, and justify investigations to define the therapeutic value of immune-modulatory strategies in DS.

Immune Monitoring of Trans-endothelial Transport by Kidney-Resident Macrophages

Small immune complexes cause type III hypersensitivity reactions that frequently result in tissue injury. The responsible mechanisms, however, remain unclear and differ depending on target organs. Here, we identify a kidney-specific anatomical and functional unit, formed by resident macrophages and peritubular capillary endothelial cells, which monitors the transport of proteins and particles ranging from 20 to 700 kDa or 10 to 200 nm into the kidney interstitium. Kidney-resident macrophages detect and scavenge circulating immune complexes "pumped" into the interstitium via trans-endothelial transport and trigger a FcγRIV-dependent inflammatory response and the recruitment of monocytes and neutrophils. In addition, FcγRIV and TLR pathways synergistically "super-activate" kidney macrophages when immune complexes contain a nucleic acid. These data identify a physiological function of tissue-resident kidney macrophages and a basic mechanism by which they initiate the inflammatory response to small immune complexes in the kidney.

Fc Receptor-Like Proteins in Pathophysiology of B-cell Disorder

Members of the family of Fc receptor-like (FcRL) proteins, homologous to FcγRI, have been identified by multiple research groups. Consequently, they have been described using multiple nomenclatures including Fc receptor homologs (FcRH), immunoglobulin superfamily receptor translocation-associated genes (IRTA), immunoglobulin-Fc-gp42-related genes (IFGP), Src homology 2 domain-containing phosphatase anchor proteins (SPAP), and B cell cross-linked by anti-immunoglobulin M-activating sequences (BXMAS). They are now referred to under a unified nomenclature as FCRL. Eight different human FCRL genes have been identified, all of which appear to be related to the genes of the immunoglobulin superfamily (IgSF) of cellular adhesion molecules. These type 1 transmembrane glycoproteins are composed of different combinations of 5 types of immunoglobulin-like domains, with each protein consisting of 3 to 9 domains, and no individual domain type conserved throughout all of the FCRL proteins. Ligands for the majority of the FCRLs remain unknown. In general, FCRL expression is restricted to lymphocytes and is primarily expressed in B-lymphocytes, supporting FCRL’s involvement in a variety of immune disorders. Most FCRLs functionally repress B-cell activation; however, they might have dual roles in lymphocyte functions as these proteins often possess immunoreceptor tyrosine activation (ITAM) and inhibitory (ITIM) motif elements. The biological functions of these newly recognized FCRL proteins are just beginning to emerge, and might provide the insight necessary for understanding pathophysiology of lymphocyte disorders and treating different immune diseases.

Fc Receptors and Fc Receptor-Like Molecules within the Immunoreceptor Family

Receptors for the Fc portion of immunoglobulins (FcRs) account for most cell-mediated biological activities of antibodies. The majority of FcRs are encoded by a set of genes, clustered in the fcr locus, on chromosome 1 in humans and on chromosome 1 and 3 in mice. Eight (in humans) and six (in mice) new genes were found, intermixed with FcR genes in corresponding fcr loci, which encode FcR-like molecules (FcRLs). FcRs and FcRLs are genetically, phylogenetically, structurally, and functionally related. FcRs and FcRLs, however, markedly differ by their ligands, their tissue distribution, and, therefore, by the biological functions they control. A systematic comparison of their biological properties leads to the conclusion that FcRLs are not like FcRs. They altogether form a single family within the immunoreceptor family, whose members fulfill distinct but complementary roles in immunity by differentially controlling innate and adaptive responses.

Role of IgA receptors in the pathogenesis of IgA nephropathy

Immunoglobulin A nephropathy (IgAN) or Berger's disease is the most common form of primary glomerulonephritis in the world and one of the first causes of end-stage renal failure. IgAN is characterized by the accumulation of immune complexes containing polymeric IgA1 in mesangial areas. The pathogenesis of this disease involves the deposition of polymeric and hypogalactosylated IgA1 (Gd-IgA1) in the mesangium. Quantitative and structural changes of Gd-IgA1 play a key role in the development of the disease due to functional abnormalities of two IgA receptors: the FcαRI (CD89) expressed by blood myeloid cells and the transferrin receptor (CD71) on mesangial cells. Abnormal Gd-IgA1 induces release of soluble CD89, which participates in the formation of circulating IgA1 complexes. These complexes are trapped by CD71 that is overexpressed on mesangial cells in IgAN patients together with the crosslinking enzyme transglutaminase 2 allowing pathogenic IgA complex formation in situ and mesangial cell activation. A humanized mouse model expressing IgA1 and CD89 develops IgAN in a similar manner as patients. In this model, a food antigen, the gliadin, was shown to be crucial for circulating IgA1 complex formation and deposition, which could be prevented by a gluten-free diet. Identification of these new partners opens new therapeutic prospects for IgAN treatment.

FCRL3 gene polymorphisms confer risk for sudden sensorineural hearing loss in a Chinese Han Population

Fc receptor-like 3 (FCRL3) has recently been associated with susceptibility to several immune-related diseases. In this study, we evaluated the potential association of FCRL3 polymorphisms with sudden sensorineural hearing loss (SSNHL) in a Chinese Han population. Five single-nucleotide polymorphisms (SNPs) in FCRL3-rs945635, rs3761959, rs7522061, rs10489678, and rs7528684-were genotyped in 630 patients with SSNHL and 600 healthy controls by using a PCR-restriction fragment length polymorphism assay. The allele, genotype, and haplotype frequencies in the patients and the controls were compared using a χ(2) test. Moreover, we performed haplotype analysis by using the online software platform SHEsis. The results revealed a significant association between three SNPs-rs7528684, rs3761959, and rs7522061-and SSNHL in the studied Chinese Han population. Furthermore, the AGT and GAC haplotypes were associated with a significantly higher prevalence of SSNHL than were the GAT, GGC and GGT haplotypes. However, no significant differences were detected in either the genotype or allele frequencies of the other two SNPs, rs945635 and rs10489678, between the SSNHL and control groups. Overall, this study has identified an association between FCRL3 polymorphisms and increased risk of SSNHL in a Chinese Han population.

Association of FCRL3 Genetic Polymorphisms With Endometriosis-Related Infertility Risk: An Independent Study in Han Chinese

The Fc receptor-like 3 (FCRL3) gene was reported to be linked to a variety of autoimmune diseases, including endometriosis-related infertility. However, this linkage has not been studied in Chinese population and there has been no meta-analysis on the interrelationship of FCRL3 gene and endometriosis-related infertility. The aim of the study was to investigate the association between FCRL3 genetic polymorphisms and the risk of endometriosis-related infertility in Han Chinese, and a further meta-analysis was conducted to confirm our results.Four single nucleotide polymorphisms (SNPs) (rs7528684 [FCRL3_3], rs11264799 [FCRL3_4], rs945635 [FCRL3_5], and rs3761959 [FCRL3_6]) on FCRL3 gene were genotyped in a case-control cohort composed of 217 patients suffering from endometriosis-related infertility and 220 healthy controls using cleaved amplification polymorphism sequence-tagged sites (polymerase chain reaction-restriction fragment length polymorphism, PCR-RFLP). Odds ratio (OR) and its 95% confidence interval (CI) was used to evaluate the association quantitatively. Furthermore, a meta-analysis of previous studies including the present study was implemented through Stata 11.0 (Stata Corporation, College Station, TX).We found an approximately 1.4-fold significantly increased frequency of the FCRL3_3 variant in women with endometriosis-related infertility over the controls (OR = 1.41 [95% CI = 1.08-1.84], P = 0.013). However, no significant difference was found between women with endometriosis-related infertility and controls for FCRL3_4, FCRL3_5, and FCRL3_6. Regardless of the symptoms and the revised classification of the American Society of Reproductive Medicine (rASRM) stage of endometriosis, there was a significant association between FCRL3_3 variant and an increased risk of endometriosis-related infertility. Meta-analysis of previous studies combined with the present study further confirmed the association between FCRL3_3 and the risk of endometriosis-related infertility.In summary, the present study suggested that FCRL3_3 variant was associated with an increased risk of endometriosis-related infertility, regardless of symptoms, and rASRM stage of the patients. Meta-analysis of previous studies combined with the present study further confirmed our results. Further large-scale studies in the future are warranted to explore the association between FCRL3 genetic polymorphisms and endometriosis-related infertility, as well as other human diseases, in Asian and other ethnicities.

FCRL3 gene polymorphisms confer autoimmunity risk for allergic rhinitis in a Chinese Han population

Background

Heredity and environmental exposures may contribute to a predisposition to allergic rhinitis (AR). Autoimmunity may also involve into this pathologic process. FCRL3 (Fc receptor-like 3 gene), a novel immunoregulatory gene, has recently been reported to play a role in autoimmune diseases.

Objective

This study was performed to evaluate the potential association of FCRL3 polymorphisms with AR in a Chinese Han population.

Methods

Five single-nucleotide polymorphisms of FCRL3, rs945635, rs3761959, rs7522061, rs10489678 and rs7528684 were genotyped in 540 AR patients and 600 healthy controls using a PCR-restriction fragment length polymorphism assay. Allele, genotype and haplotype frequencies were compared between patients and controls using the χ2 test. The online software platform SHEsis was used to analyze their haplotypes.

Results

This study identified three strong risk SNPs rs7528684, rs10489678, rs7522061 and one weak risk SNP rs945635 of FCRL3 in Chinese Han AR patients. For rs7528684, a significantly increased prevalence of the AA genotype and A allele in AR patients was recorded. The frequency of the GG genotype and G allele of rs10489678 was markedly higher in AR patients than those in controls. For rs7522061, a higher frequency of the TT genotype, and a lower frequency of the CT genotype were found in AR patients. Concerning rs945635, a lower frequency of the CC genotype, and a higher frequency of G allele were observed in AR patients. According to the analysis of the three strong positive SNPs, the haplotype of AGT increased significantly in AR cases (AR = 38.8%, Controls = 24.3%, P = 8.29×10-14, OR [95% CI] 1.978 [1.652~2.368]).

Conclusions

This study found a significant association between the SNPs in FCRL3 gene and AR in Chinese Han patients. The results suggest these gene polymorphisms might be the autoimmunity risk for AR.

Significant Association Between Fc Receptor-Like 3 Polymorphisms (-1901A>G and -658C>T) and Neuromyelitis Optica (NMO) Susceptibility in the Chinese Population

Neuromyelitis optica (NMO) is an autoimmune disorder. In pathogenesis, NMO-immunoglobulin G (NMO-IgG) selectively binds to aquaporin-4 (AQP4) and resulted in neuritis, myelitis, and brain lesion. Fc receptor-like 3 (FCRL3) gene encodes a member of the immunoglobulin receptor superfamily, which plays an important part in regulating immune activities. This study aimed at investigating the association between FCRL3 polymorphisms and NMO susceptibility and, hopefully, to contribute to the development of novel methods for diagnosis and treatment of NMO. We selected 150 NMO patients and 300 healthy controls from the Chinese population. Tag single nucleotide polymorphisms (SNPs) were identified with reference to CBI-dbSNP and HapMap databases. DNA were extracted and amplified. Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was applied to determine the polymorphisms. χ (2), odds ratio (OR), and 95 % confidence interval (95 % CI) were presented to evaluate genotype distribution and association between SNPs and NMO susceptibility. Six out of 15 SNPs were selected according to the filter. No significant altered genotype distribution was observed concerning -11G>C, -166C>T, -219G>C, and -1629C>G polymorphisms. The G allele of -1901A>G variation was demonstrated to be more frequent in patients compared with controls (P < 0.001). The T allele of -658C>T polymorphism was significantly more prevalent in NMO patients than controls (P = 0.009). In summary, the study revealed that the G allele in -1901A>G polymorphism and T allele in -658C>T polymorphism are genetic risk factors for NMO in the Chinese population. Further research is needed to account for different ethnicities and clarify the mechanisms behind, which might contribute to the elucidation of novel diagnosis methods.

Human FcR polymorphism and disease

Fc receptors play a central role in maintaining the homeostatic balance in the immune system. Our knowledge of the structure and function of these receptors and their naturally occurring polymorphisms, including single nucleotide polymorphisms and/or copy number variations, continues to expand. Through studies of their impact on human biology and clinical phenotype, the contributions of these variants to the pathogenesis, progression, and/or treatment outcome of many diseases that involve immunoglobulin have become evident. They affect susceptibility to bacterial and viral pathogens, constitute as risk factors for IgG or IgE mediated inflammatory diseases, and impact the development of many autoimmune conditions. In this chapter, we will provide an overview of these genetic variations in classical FcγRs, FcRLs, and other Fc receptors, as well as challenges in achieving an accurate and comprehensive understanding of the FcR polymorphisms and genomic architecture.

Emerging roles for the FCRL family members in lymphocyte biology and disease

Members of the extended Fc receptor-like (FCRL) family in humans and mice are preferentially expressed by B cells and possess tyrosine-based immunoregulatory function. Although the majority of these proteins repress B cell receptor-mediated activation, there is an emerging evidence for their bifunctionality and capacity to counter-regulate adaptive and innate signaling pathways. In light of these findings, the recent discovery of ligands for several of these molecules has begun to reveal exciting potential for them in normal lymphocyte biology and is launching a new phase of FCRL investigation. Importantly, these fundamental developments are also setting the stage for defining their altered roles in the pathogenesis of a growing number of immune-mediated diseases. Here we review recent advances in the FCRL field and highlight the significance of these intriguing receptors in normal and perturbed immunobiology.

Association between functional Fc receptor-like 3 (FCRL3) -169 C/T polymorphism and susceptibility to seropositive rheumatoid arthritis in Asians: a meta-analysis

OBJECTIVE

The aim of this study was to determine whether the functional Fc receptor like-3 (FCRL3) -169 C/T polymorphism confers susceptibility to rheumatoid arthritis (RA).

METHODS

A meta-analysis was conducted on the associations between the FCRL3 -169 C/T polymorphism and RA.

RESULTS

A total of 17 comparison studies including 11,170 patients and 11,142 controls were considered in the meta-analysis. The meta-analysis showed no association between RA and the FCRL3 -169 C allele in study subjects (OR = 1.046, 95% CI = 0.997-1.098, p = 0.068). Stratification by ethnicity indicated an association between the FCRL3 -169 C allele and RA in Asians (OR = 1.101, 95% CI = 1.035-1.174, p = 0.002), but not in Europeans. Stratification of patients according to the presence of rheumatoid factor (RF) revealed a different significant association between the C allele and RA in RF-positive and RF-negative RA patients. Stratification by ethnicity indicated an association between the FCRL3 -169 C allele and RF-positive RA in Asians (OR = 1.093, 95% CI = 1.004-1.189, p = 0.040), but not in Europeans.

CONCLUSIONS

This meta-analysis demonstrates that the FCRL3 -169 C/T polymorphism may confer susceptibility to seropositive RA in Asians.

Fc receptor-like 3 (FCRL3) -169 C/T polymorphism and systemic lupus erythematosus: a meta-analysis

Our aim was to determine whether the Fc receptor-like 3 (FCRL3) -169 C/T (rs7528684) polymorphism confers susceptibility to systemic lupus erythematosus (SLE). A meta-analysis was conducted on the associations between the FCRL3 -169 C/T polymorphism and the SLE. A total of nine sets of comparisons containing 3,628 patients and 6,490 controls were considered. The meta-analysis showed no association between the SLE and the FCRL3 -169 C allele in all study patients (odds ratio [OR] = 0.999, 95 % confidence interval [CI] = 0.925-1.080, p = 0.986). Stratification by ethnicity indicated no association between the C allele and the SLE in neither Europeans nor Asians (OR = 1.058, 95 % CI = 0.925-1.250, p = 0.414; OR = 0.981, 95 % CI = 0.884-1.088, p = 0.715). Furthermore, analysis using the recessive model, the dominant model, and the homozygote contrast showed the same pattern for the C allele in European and Asian groups, showing no association between the FCRL3 -169 C/T polymorphism and the SLE. Even after excluding studies whose controls were not in Hardy-Weinberg equilibrium, we found that this did not materially affect the meta-analysis results. However, the single Latin American study did show an association between the FCRL3 polymorphism and the SLE under homozygote contrast (OR for CC vs. TT = 2.689, 95 % CI = 1.152-1.277, p = 0.022). This meta-analysis of published studies including 2,544 patients and 3,913 controls demonstrates that the FCRL3 -169 C/T polymorphism does not confer susceptibility to SLE in Europeans or Asians.

Association of FCRL4 polymorphisms on disease susceptibility and severity of ankylosing spondylitis in Chinese Han population

Previous studies have found that the Fc receptor-like (FCRL) molecule, involved in controlling B cell signaling, may contribute to the autoimmune disease process. Many studies have reported the relation of FCRL gene family with SLE and RA. We hypothesized that FCRL4 may be a key gene for ankylosing spondylitis (AS) development. To test this hypothesis, we screened FCRL4 polymorphisms in the Chinese Han population. Five tag single nucleotide polymorphisms (SNPs), including rs14335, rs849826, rs10489674, rs2778003, and rs2777963, were selected. Using a case-control study, five tag SNPs, which captured the majority of known common variation within FCRL4 gene, were selected and genotyped by Multiplex Snapshot technique. We analyzed 299 patients and 300 controls from China. The genotype analysis demonstrated that one of the FCRL4 tag SNPs rs2777963 TT genotype may be a risk factor of AS (χ(2) = 7.374, p = 0.024). The haplotype analysis indicated that there were no significant differences between AS cases and controls. Patients with AS who had rs14335 AA genotype had a significantly declined visual analogue scale patient's global assessment scores compared to those with the GG genotype (31.21 ± 26.25 vs 40.54 ± 25.40, p = 0.035) and GA genotype (38.29 ± 24.94 vs 40.54 ± 25.40, p = 0.044), and in locus rs10489674, TT genotype had significantly increased Bath Ankylosing Spondylitis Disease Activity Index scores compared to those with the CC genotype (4.73 ± 2.43 vs 3.15 ± 1.61, p = 0.003) and CT genotype (4.73 ± 2.43 vs 2.97 ± 1.71, p = 0.001). The FCRL4 polymorphisms may play an important role in the susceptibility and severity of AS in the Chinese Han population.

Ligation of Fc gamma receptor IIB enhances levels of antiviral cytokine in response to PRRSV infection in vitro

PRRSV infection ADE facilitates the attachment and internalization of the virus onto its host cells, such as monocytes and macrophages, through Fc receptor-mediated endocytosis. FcγRIIB is the only inhibitory receptor with a tyrosine-based inhibitory motif (ITIM) in its cytoplasmic tail, where counters the "ITAM triggered" activation signals and down-regulates phagocytosis. However, porcine FcγRIIB's role in the antiviral immune response to PRRSV infection has not been studied. In this study, our results indicated that selective activation of porcine FcγRIIB in PAM cells up-regulated significantly mRNA levels of IFN-α and TNF-α at any time point post-pretreatment, suggesting that porcine FcγRIIB signal can enhance the innate antiviral response of host cells. PRRSV infection assay mediated by FcγRIIB indicated that selective activation of porcine FcγRIIB in PAM cells enhanced mRNA levels of antiviral cytokine (IFN-α and TNF-α) and repressed mRNA levels of IL-10 in response to PRRSV infection, suggesting that FcγRIIB ligation can enhance the antiviral immune response to PRRSV infection. In addition, FcγRIIB ligation to infection indicated that PRRSV replication in PAM was not positive correlation with increasing of IFN-α mRNA levels and decreasing of IL-10 mRNA levels, suggesting that there is complex viral replication mechanism in immune cells such as PAM for PRRSV.

Cutting edge: human FcRL4 and FcRL5 are receptors for IgA and IgG

Fc receptor-like (FcRL) proteins are a family of cellular receptors homologous to FcγRI and are predominantly expressed by B cells. They function to costimulate or inhibit BCR signaling through consensus ITAMs and ITIMs; however, the extracellular ligands of these receptors remain unknown or controversial. In this study, we tested the ability of human FcRL proteins to bind Igs and found FcRL4 and FcRL5 to be bona fide Fc receptors. In cellular binding assays, FcRL4 bound efficiently to IgA and FcRL5 binds all IgG isotypes with varied efficiency. Additionally, we generated mAbs capable of specifically blocking these interactions. Given their expression on activated B cells and potential for inhibitory signaling, FcRL4 and FcRL5 are likely to be important for immune complex-dependent human B cell regulation, and they represent novel therapeutic targets for receptor blockade therapies.

Fc receptor like 3 in Chinese patients of Han nationality with Guillain-Barré syndrome

Fc receptor like 3 gene (FcRL3) has been associated with some autoimmune diseases. Here, its role in Guillain-Barré syndrome (GBS) was evaluated by studying nine FcRL3 gene SNPs in a Chinese cohort of GBS patients. The frequencies of FcRL3-3-169C, FcRL3-6 intron3A, and FcRL3-8 exon15G alleles were significantly increased in GBS patients compared with healthy controls. The frequency of FcRL3-1→9 CCTGGAGAA haplotype was significantly increased, and the frequencies of FcRL3-1→9 CCTACAAAA,CCCACGAAA, and CCTGCGGAA haplotypes were significantly decreased compared with healthy controls. These results suggest that FcRL3 is associated with GBS incidence.

Genetic polymorphism studies in periodontitis and Fcγ receptors

Periodontitis is a complex chronic subgingival plaque-induced inflammatory disease influenced by multiple factors, including genetics, behavior and the environment. Many genetic association studies have been conducted in periodontology. One of the most extensively investigated gene families is the Fcγ receptor gene family, which plays a key role in regulating host immune responses to bacteria. Unlike other genetic polymorphisms reported in periodontology, most Fcγ receptor polymorphisms reported not only have established biological functions but are reported to associate with other autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus. There are, however, few recent reviews summarizing the association of this gene family with periodontitis. This article critically reviews the current understanding of genetic polymorphism studies in periodontitis, then summarizes the research status of Fcγ receptor polymorphisms and periodontitis and also of other genes involved in the regulatory network of Fcγ receptors, with special reference to their anticipated biological roles. Moreover, some possible future research directions in the related area are discussed.

Susceptibility loci for the defective foreign protein-induced tolerance in New Zealand Black mice: implication of epistatic effects of Fcgr2b and Slam family genes

In contrast to normal mice, autoimmune-prone New Zealand Black (NZB) mice are defective in susceptibility to tolerance induced by deaggregated bovine γ globulin (DBGG). To examine whether this defect is related to the loss of self-tolerance in autoimmunity, susceptibility loci for this defect were examined by genome-wide analysis using the F(2) intercross of nonautoimmune C57BL/6 (B6) and NZB mice. One NZB locus on the telomeric chromosome 1, designated Dit (Defective immune tolerance)-1, showed a highly significant linkage. This locus overlapped with a locus containing susceptibility genes for autoimmune disease, namely Fcgr2b and Slam family genes. To investigate the involvement of these genes in the defective tolerance to DBGG, we took advantage of two lines of Fcgr2b-deficient B6 congenic mice: one carries autoimmune-type, and the other carries B6-type, Slam family genes. Defective tolerance was observed only in Fcgr2b-deficient mice with autoimmune-type Slam family genes, indicating that epistatic effects of both genes are involved. Thus, common genetic mechanisms may underlie the defect in foreign protein antigen-induced tolerance and the loss of self-tolerance in NZB mouse-related autoimmune diseases.

Disease Phenotypes and Gender Association of FCRL3 Single-Nucleotide Polymorphism −169T/C in Taiwanese Patients with Systemic Lupus Erythematosus and Rheumatoid Arthritis

Objective.

To investigate the association of the functional FCRL3 single-nucleotide polymorphism (SNP) −169T/C with disease phenotypes and susceptibility to systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) in Taiwanese.

Methods.

FCRL3 SNP −169T/C was genotyped in 573 patients with SLE, 670 patients with RA, and 758 controls. Genotype distributions and allele frequencies were compared among the 3 groups as aggregates or as stratified by clinical characteristics, autoantibody profile, and sex within patient groups.

Results.

Overall, FCRL3 SNP −169T/C was not associated with susceptibility to either SLE or RA. However, −169CC genotype was significantly reduced in leukopenia-positive SLE patients as compared to the leukopenia-negative SLE patients (CC vs CT+TT, p = 6 × 10−4, OR 0.444, 95% CI 0.279–0.708) and controls (p = 6.1 × 10−3, OR 0.583, 95% CI 0.396–0.857). On the other hand, −169TT genotypes were significantly more numerous in RA patients with non-destructive disease as compared with patients with destructive disease (CC+CT vs TT: p = 0.007, OR 1.672, 95% CI 1.149–2.432). The −169T allele frequency was also significantly increased in non-destructive RA compared with patients with destructive disease (C vs T: p = 0.010, OR 1.423, 95% CI 1.089–1.859). FCRL3 SNP −169TT homozygous donors were significantly more numerous among female cyclic citrullinated peptide (CCP)-negative RA patients versus female CCP-positive RA patients (CC+CT vs TT: p = 0.019, OR 1.64, 95% CI 1.085–2.479).

Conclusion.

The functional FCRL3 SNP −169T/C appears to play important roles in the development of certain phenotypes such as SLE leukopenia and RA disease severity in Taiwanese patients with SLE and RA.

The role of IgA and IgA Fc receptors as anti-inflammatory agents

MATERIALS AND METHODS

Serum monomeric immunoglobulin A (IgA) has powerful immunomodulatory roles in its ability to suppress immune responses. Monomeric IgA acts through FcalphaRI, which plays a significant role in vivo in maintaining the integrity of immune responses by an inhibitory immunoreceptor tyrosine-based activation motif-mediated process and powerful inhibitory cellular effector mechanisms elicited by the IgA system.

RESULTS

Triggering of FcalphaRI-mediated inhibitory function by Fab anti-FcalphaRI-mediated inhibitory function is able to inhibit several inflammatory and autoimmune diseases including asthma and glomerulonephritis.

CONCLUSION

The use of monomeric IgA as a therapeutic tool in human inflammatory diseases may offer much potential.

Clinical associations of the genetic variants of CTLA-4, Tg, TSHR, PTPN22, PTPN12 and FCRL3 in patients with Graves' disease

OBJECTIVE

Graves' disease (GD) is an organ-specific autoimmune disorder. Both immune-modulating genes and thyroid-specific genes are involved in its genetic pathogenesis. It remains unclear, however, how the interactions of various susceptibility genes contribute to the pathogenesis and clinical severity of the disease. The purpose of this study was to investigate the relationships between GD and single nucleotide polymorphisms (SNPs) from CTLA-4, PTPN22, PTPN12, FCRL3 (general autoimmunity genes regulating T and B cells) and the TSHR and Tg genes (disease-specific genes). Furthermore, we evaluated the influences these SNPs have on the risk and severity of GD.

DESIGN AND METHODS

This cross-sectional clinical study was performed in 436 GD patients and 316 healthy, gender-matched individuals. Twenty-eight SNPs from CTLA-4, PTPN22, PTPN12, FCRL3, TSHR and Tg genes were genotyped and their associations with the risk and severity of GD were analysed.

RESULTS

The CTLA-4 rs231779, Tg rs2069550 and PTPN22 rs3789604 SNPs were associated with GD, with additive risk effects present in rs231779 and rs2069550. The ACACC and ACGCT haplotypes, composed of five SNPs in the CTLA-4 gene (rs4553808, rs5472909, rs231775, rs231777 and rs231779), were protective and risk haplotypes respectively. The AA genotype of PTPN22 rs3789604 and AA genotype of FCRL3 rs7528684 were correlated with a reduced risk of GD, while the CC genotype of TSHR rs2239610 was associated with higher serum concentrations of FT4 and TRAb. Logistic analysis confirmed the contribution of CTLA-4 rs231779 to the development of GD.

CONCLUSIONS

These preliminary results demonstrate that the immune-regulatory gene CTLA-4 and the thyroid-specific gene Tg contribute to the risk of Graves' disease with additive effects, while PTPN22 rs3789604 and FCRL3 rs7528684 polymorphisms are protective against the disease. In addition, the TSHR rs2239610 SNP is related to the severity of Graves' disease.

Both FcgammaRIV and FcgammaRIII are essential receptors mediating type II and type III autoimmune responses via FcRgamma-LAT-dependent generation of C5a

FcgammaRIV is a relatively new IgG Fc receptor (FcgammaR) that is reported to contribute to the pathogenesis of autoimmune diseases, although its specific role in relation to FcgammaRIII, complement and IgG2 subclasses remains uncertain. Here we define FcgammaRIV on macrophages as a receptor for soluble IgG2a/b complexes but not for cellular bound IgG2a and show that simultaneous activation of FcgammaRIV and FcgammaRIII is critical to mediate certain type II/III autoimmune responses. FcgammaRIII-deficient mice display compensatory enhanced FcgammaRIV expression, are protected from lung inflammation after deposition of IgG complexes, and show reduced sensitivity to IgG2a/b-mediated hemolytic anemia, indicating that increased FcgammaRIV alone is not sufficient to trigger these diseases in the absence of FcgammaRIII. Importantly, however, blockade of FcgammaRIV is also effective in inhibiting phagocytosis and cytokine production in IgG2b-induced anemia and acute lung injury, processes that display a further dependence on C5a anaphylatoxin receptor. Using gene deletion and functional inhibition studies, we found that FcgammaRIII and FcgammaRIV are each essential to trigger an FcRgamma-linker for activation of T-cell-dependent signal that drives C5a production in the Arthus reaction. Together, the results demonstrate a combined requirement for FcgammaRIII and FcgammaRIV in autoimmune injury, and identify the linker for activation of T cells adaptor as an integral component of linked FcgammaR and C5a anaphylatoxin receptor activation to generate inflammation.

Mechanisms of anti-D action in the prevention of hemolytic disease of the fetus and newborn: what can we learn from rodent models?

PURPOSE OF REVIEW

Hemolytic disease of the fetus and newborn can be effectively prevented by administration of anti-D to the mother. In this setting, the IgG purified from the plasma of D-alloimmunized donors prevents the maternal immune response to D-positive red blood cells (RBC). Several monoclonal anti-D antibodies have recently been developed for potential use in the setting of hemolytic disease of the fetus and newborn; the functional assays used to assess the potential success of these antibodies have often assumed antigen clearance as the predominant mechanism of anti-D. Unfortunately, the in-vivo success of these monoclonal antibodies has thus far been limited. A similar inhibitory effect of IgG has been observed in animal models with a vast array of different antigens, referred to as antibody-mediated immune suppression (AMIS). Here, studies of AMIS are reviewed and the relevance of these findings for anti-D-mediated immunoprophylaxis is discussed.

RECENT FINDINGS

In animal models of AMIS, IgG-mediated antigen clearance was not sufficient for prevention of the antibody response to RBC. Furthermore, anti-RBC IgG inhibited B-cell priming to foreign RBC, but failed to prevent a T-cell response and immunological memory.

SUMMARY

The applicability of AMIS models for determining the true mechanism of anti-D, though uncertain, may nevertheless provide knowledge as to potential mechanisms of action of anti-RBC antibodies.