Ligation of human Fc receptor like-2 by monoclonal antibodies down-regulates B-cell receptor-mediated signalling

Silencing of FCRLB by shRNA ameliorates MuSK-induced EAMG in mice

INTRODUCTION

Muscle specific kinase (MuSK) antibody positive myasthenia gravis (MG) often presents with a severe disease course and resistance to treatment. Treatment-refractory patients may respond to B cell depleting treatment methods. Our aim was to investigate whether inhibition of Fc receptor-like B (FCRLB) could effectively suppress autoimmunity without diminishing B cell counts in animal model of MG, a classical antibody-mediated autoimmune disease.

METHODS

Experimental autoimmune MG was induced in Balb/C mice with two s.c. immunizations with recombinant human MuSK in complete Freund's adjuvant. FCRLB was silenced with a lentiviral particle transported shRNA in myasthenic mice with a single i.p. injection during second MuSK-immunization. Control immunized mice received scrambled shRNA or saline. Mice were observed for clinical parameters for 28 days and at termination, anti-MuSK IgG, neuromuscular junction (NMJ) deposits, muscle AChR expression and lymph node B and T cell ratios were assessed by ELISA, immunofluorescence, immunoblotting and flow cytometry, respectively.

RESULTS

FCRLB shRNA-treated mice showed no muscle weakness or weight loss at termination. Also, they exhibited higher grip strength and muscle AChR levels, lower anti-MuSK IgG and NMJ IgG/C3 levels than control mice. Flow cytometry analysis showed that ratios of major effector lymph node B and T cell populations were not altered by FCRLB silencing. However, regulatory T and CD19 + CD5+ B cell ratios were decreased in FCRLB shRNA-group.

CONCLUSION

Our results provide evidence regarding involvement and therapeutic value of FCRLB in MuSK-MG. Silencing of FCRLB appears to substantially inhibit antibody production without interfering with survival of major lymphocyte populations.

FCRL1 Regulates B Cell Receptor-Induced ERK Activation through GRB2

Regulation of BCR signaling has important consequences for generating effective Ab responses to pathogens and preventing production of autoreactive B cells during development. Currently defined functions of Fc receptor-like (FCRL) 1 include positive regulation of BCR-induced calcium flux, proliferation, and Ab production; however, the mechanistic basis of FCRL1 signaling and its contributions to B cell development remain undefined. Molecular characterization of FCRL1 signaling shows phosphotyrosine-dependent associations with GRB2, GRAP, SHIP-1, and SOS1, all of which can profoundly influence MAPK signaling. In contrast with previous characterizations of FCRL1 as a strictly activating receptor, we discover a role for FCRL1 in suppressing ERK activation under homeostatic and BCR-stimulated conditions in a GRB2-dependent manner. Our analysis of B cells in Fcrl1 -/- mice shows that ERK suppression by FCRL1 is associated with a restriction in the number of cells surviving splenic maturation in vivo. The capacity of FCRL1 to modulate ERK activation presents a potential for FCRL1 to be a regulator of peripheral B cell tolerance, homeostasis, and activation.

Expression profile of Fc receptor-like molecules in patients with IgA nephropathy

BACKGROUND

Fc receptor-like (FCRL) molecules were considered to play a role in the pathogenesis of certain autoimmune diseases. Nonetheless, the clinical significance of FCRLs in IgA nephropathy (IgAN) remains unclear.

OBJECTIVE

This study is aimed at investigating the expression levels of FCRLs molecules in IgAN patients and determining its relevance to disease activity.

METHODS

The mRNA expression levels of FCRLs were determined in peripheral blood mononuclear cells (PBMCs) of 42 IgAN patients and 48 healthy controls by quantitative real-time PCR (qRT-PCR). FCRLs proteins expression in B cells of 25 IgAN patients, 14 patients with non-IgAN glomerulonephritis, and 29 healthy controls were detected by Flow cytometry. The Spearman correlation test was used to assess the correlation of FCRLs expression with clinical parameters of IgAN patients.

RESULTS

Our results indicated significant down-regulation of FCRL2 and FCRL3 mRNA levels in IgAN patients compared to healthy subjects. Surface protein expression of FCRLs molecules confirmed the qRT-PCR results. But FCRL2 and FCRL3 protein levels did not correlate with clinicopathologic phenotypes of IgAN patients. However, we found a significant positively correlation of FCRL2 and FCRL3 mRNA expression with the core 1 β1,3-galactosyltransferase (C1GALT1) and its molecular chaperone (Cosmc) mRNA levels in IgAN patients.

CONCLUSIONS

FCRL2 and FCRL3 expression levels in IgAN patients are significantly decreased and correlated with CIGALT1 and Cosmc mRNA expression.

Single-cell analysis of human B cell maturation predicts how antibody class switching shapes selection dynamics

Protective humoral memory forms in secondary lymphoid organs where B cells undergo affinity maturation and differentiation into memory or plasma cells. Here, we provide a comprehensive roadmap of human B cell maturation with single-cell transcriptomics matched with bulk and single-cell antibody repertoires to define gene expression, antibody repertoires, and clonal sharing of B cell states at single-cell resolution, including memory B cell heterogeneity that reflects diverse functional and signaling states. We reconstruct gene expression dynamics during B cell activation to reveal a pre-germinal center state primed to undergo class switch recombination and dissect how antibody class-dependent gene expression in germinal center and memory B cells is linked with a distinct transcriptional wiring with potential to influence their fate and function. Our analyses reveal the dynamic cellular states that shape human B cell-mediated immunity and highlight how antibody isotype may play a role during their antibody-based selection.

Expression profiling of genes in rheumatoid fibroblast-like synoviocytes regulated by tumor necrosis factor-like ligand 1A using cDNA microarray analysis

Rheumatoid arthritis (RA) is an autoimmune disease that causes chronic inflammation in synovial tissues. Hyperplasia of synovial tissue leads to the formation of pannus, which invades joint cartilage and bone resulting in joint destruction. Tumor necrosis factor-like ligand 1A (TL1A), a member of the tumor necrosis factor superfamily (TNFSF15), contributes to the pathogenesis of autoimmune diseases, including RA. In the present study, a cDNA microarray was used to search for genes whose expression in rheumatoid fibroblast-like synoviocytes (RA-FLS) were regulated by TL1A. Four individual lines of primary cultured RA-FLS were incubated either with recombinant human TL1A protein or phosphate-buffered saline, as an unstimulated control, for 12 h. Gene expression was then detected through the microarray assay. The results revealed the expression profiles of genes in RA-FLS regulated by TL1A. The present study also demonstrated the functions of those genes whose expression in RA-FLS was regulated by TL1A. Among the genes in this profile, the present study focused on the following genes: Spectrin repeat-containing nuclear envelope 1, Fc receptor-like 2, PYD (pyrin domain)-containing 1, cell division cycle 45 homolog, signal transducer and activator of transcription 5B, and interferon regulatory factor 4. These genes may affect the pathogenesis of RA, including proliferation, regulation of B cells and T cells, inflammation, and cytokine processing. The present study revealed for the first time, to the best of our knowledge, the expression profile of genes in RA-FLS regulated by TL1A. The data indicate that TL1A may regulate the gene expression of various key molecules in RA-FLS, thus affecting the pathogenesis of RA. Further investigations of the genes detected in the current profiles may provide a deeper understanding of the pathogenesis and a novel target for the treatment of RA.

1q23.1 homozygous deletion and downregulation of Fc receptor-like family genes confer poor prognosis in chronic lymphocytic leukemia

The identification of chromosome 1 translocations and deletions is a rare and poorly investigated event in chronic lymphocytic leukemia (CLL). Nevertheless, the identification of novel additional molecular alterations is of great interest, opening to new prognostic and therapeutic strategies for such heterogeneous hematological disease. We here describe a patient affected by CLL with a mutated IGHV status, showing a balanced t(1;3)(q23.1;q21.3) translocation and a der(18)t(1;18)(q24.2;p11.32), accompanying the recurrent 13q14 heterozygous deletion in all analyzed cells at onset. By combining whole-genome sequencing, SNP array, RNA sequencing, and FISH analyses, we defined a 1q23.1 biallelic minimally deleted region flanking translocations breakpoints at both derivative chromosome 1 homologues. The deletion resulted in the downregulation of the Fc receptor-like family genes FCRL1, FCRL2, and FCRL3 and in the lack of expression of FCRL5, observed by RT-qPCR. The mutational status of TP53, NOTCH1, SF3B1, MYD88, FBXW7, and XPO1 was investigated by targeted next-generation sequencing, detecting a frameshift deletion within NOTCH1 (c.7544_7545delCT). We hypothesize a loss of tumor suppressor function for FCRL genes, cooperating with NOTCH1 mutation and 13q14 genomic loss in our patient, both conferring a negative prognosis, independently from the known biological prognostic factors of CLL.

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.

Targeted Therapies in Adult B-Cell Malignancies

B-lymphocytes are programmed for the production of immunoglobulin (Ig) after antigen presentation, in the context of T-lymphocyte control within lymphoid organs. During this differentiation/activation process, B-lymphocytes exhibit different restricted or common surface markers, activation of cellular pathways that regulate cell cycle, metabolism, proteasome activity, and protein synthesis. All molecules involved in these different cellular mechanisms are potent therapeutic targets. Nowadays, due to the progress of the biology, more and more targeted drugs are identified, a situation that is correlated with an extended field of the targeted therapy. The full knowledge of the cellular machinery and cell-cell communication allows making the best choice to treat patients, in the context of personalized medicine. Also, focus should not be restricted to the immediate effects observed as clinical endpoints, that is, response rate, survival markers with conventional statistical methods, but it should consider the prediction of different clinical consequences due to other collateral drug targets, based on new methodologies. This means that new reflection and new bioclinical follow-up have to be monitored, particularly with the new drugs used with success in B-cell malignancies. This review discussed the principal aspects of such evident bioclinical progress.