CD72 negatively regulates signaling through the antigen receptor of B cells

PZR suppresses innate immune response to RNA viral infection by inhibiting MAVS activation in interferon signaling mediated by RIG-I and MDA5

RNA viral infections seriously endanger human health. Src homology 2 (SH2) domain-containing protein tyrosine phosphatase 2 (SHP2) suppresses innate immunity against influenza A virus, and pharmacological inhibition of SHP2 provokes hepatic innate immunity. SHP2 binds and catalyzes tyrosyl dephosphorylation of protein zero-related (PZR), but the regulatory effect of PZR on innate immune response to viral infection is unclear. In this study, the transcription and protein level of PZR in host cells were found to be decreased with RNA viral infection, and high level of PZR was uncovered to inhibit interferon (IFN) signaling mediated by RIG-I and MDA5. Through localizing in mitochondria, PZR targeted and interacted with MAVS (also known as IPS-1/VISA/Cardif), suppressing the aggregation and activation of MAVS. Specifically, Y263 residue in ITIM is critical for PZR to exert immunosuppression under RNA viral infection. Moreover, the recruited SHP2 by PZR that modified with tyrosine phosphorylation under RNA viral infection might inhibit phosphorylation activation of MAVS. In conclusion, PZR and SHP2 suppress innate immune response to RNA viral infection through inhibiting MAVS activation. This study reveals the regulatory mechanism of PZR-SHP2-MAVS signal axis on IFN signaling mediated by RIG-I and MDA5, which may provide new sight for developing antiviral drugs.

CD72, a new immune checkpoint molecule, is a novel prognostic biomarker for kidney renal clear cell carcinoma

BACKGROUND

The incidence and mortality of clear cell carcinoma of the kidney increases yearly. There are limited screening methods and advances in treating kidney renal clear cell carcinoma (KIRC). It is important to find new biomarkers to screen, diagnose and predict the prognosis of KIRC. Some studies have shown that CD72 influences the development and progression of colorectal cancer, nasopharyngeal cancer, and acute lymphoid leukemia. However, there is a lack of research on the role of CD72 in the pathogenesis of KIRC. This study aimed to determine whether CD72 is associated with the prognosis and immune infiltration of KIRC, providing an essential molecular basis for the early non-invasive diagnosis and immunotherapy of KIRC.

METHODS

Using TCGA, GTE, GEO, and ImmPort databases, we obtained the differentially expressed mRNA (DEmRNA) associated with the prognosis and immunity of KIRC patients. We used the Kruskal-Wallis test to identify clinicopathological parameters associated with target gene expression. We performed univariate and multivariate COX regression analyses to determine the effect of target gene expression and clinicopathological parameters on survival. We analyzed the target genes' relevant functions and signaling pathways through enrichment analysis. Finally, the correlation of target genes with tumor immune infiltration was explored by ssGSEA and Spearman correlation analysis.

RESULTS

The results revealed that patients with KIRC with higher expression of CD72 have a poorer prognosis. CD72 was associated with the Pathologic T stage, Pathologic stage, Pathologic M stage, Pathologic N stage, Histologic grade in KIRC patients, Laterality, and OS event. It was an independent predictor of the overall survival of KIRC patients. Functional enrichment analysis showed that CD72 was significantly enriched in oncogenic and immune-related pathways. According to ssGSEA and Spearman correlation analysis, CD72 expression was significantly associated with tumor immune cells and immune checkpoints.

CONCLUSION

Our study suggests that CD72 is associated with tumor immunity and may be a biomarker relevant to the diagnosis and prognosis of KIRC patients.

Hematopoietic stem and progenitor cells confer cross-protective trained immunity in mouse models

Recent studies suggest that infection reprograms hematopoietic stem and progenitor cells (HSPCs) to enhance innate immune responses upon secondary infectious challenge, a process called "trained immunity." However, the specificity and cell types responsible for this response remain poorly defined. We established a model of trained immunity in mice in response to Mycobacterium avium infection. scRNA-seq analysis revealed that HSPCs activate interferon gamma-response genes heterogeneously upon primary challenge, while rare cell populations expand. Macrophages derived from trained HSPCs demonstrated enhanced bacterial killing and metabolism, and a single dose of recombinant interferon gamma exposure was sufficient to induce similar training. Mice transplanted with influenza-trained HSPCs displayed enhanced immunity against M. avium challenge and vice versa, demonstrating cross protection against antigenically distinct pathogens. Together, these results indicate that heterogeneous responses to infection by HSPCs can lead to long-term production of bone marrow derived macrophages with enhanced function and confer cross-protection against alternative pathogens.

An inflammatory state remodels the immune microenvironment and improves risk stratification in acute myeloid leukemia

Acute myeloid leukemia (AML) is a hematopoietic malignancy with poor prognosis and limited treatment options. Here we provide a comprehensive census of the bone marrow immune microenvironment in adult and pediatric patients with AML. We characterize unique inflammation signatures in a subset of AML patients, associated with inferior outcomes. We identify atypical B cells, a dysfunctional B-cell subtype enriched in patients with high-inflammation AML, as well as an increase in CD8+GZMK+ and regulatory T cells, accompanied by a reduction in T-cell clonal expansion. We derive an inflammation-associated gene score (iScore) that associates with poor survival outcomes in patients with AML. Addition of the iScore refines current risk stratifications for patients with AML and may enable identification of patients in need of more aggressive treatment. This work provides a framework for classifying patients with AML based on their immune microenvironment and a rationale for consideration of the inflammatory state in clinical settings.

Autoantibodies elicited with SARS-CoV-2 infection are linked to alterations in double negative B cells

Double negative (DN) B cells (CD27-IgD-) comprise a heterogenous population of DN1, DN2, and the recently described DN3 and DN4 subsets. In autoimmune disease, DN2 cells are reported to be precursors to autoreactive antibody secreting cells and expansion of DN2 cells is linked to elevated interferon levels. Severe SARS-CoV-2 infection is characterized by elevated systemic levels of pro-inflammatory cytokines and serum autoantibodies and expansion of the DN2 subset in severe SARS-CoV-2 infection has been reported. However, the activation status, functional capacity and contribution to virally-induced autoantibody production by DN subsets is not established. Here, we validate the finding that severe SARS-CoV-2 infection is associated with a reduction in the frequency of DN1 cells coinciding with an increase in the frequency of DN2 and DN3 cells. We further demonstrate that with severe viral infection DN subsets are at a heightened level of activation, display changes in immunoglobulin class isotype frequency and have functional BCR signaling. Increases in overall systemic inflammation (CRP), as well as specific pro-inflammatory cytokines (TNFα, IL-6, IFNγ, IL-1β), significantly correlate with the skewing of DN1, DN2 and DN3 subsets during severe SARS-CoV-2 infection. Importantly, the reduction in DN1 cell frequency and expansion of the DN3 population during severe infection significantly correlates with increased levels of serum autoantibodies. Thus, systemic inflammation during SARS-CoV-2 infection drives changes in Double Negative subset frequency, likely impacting their contribution to generation of autoreactive antibodies.

SARS-CoV-2 infection relaxes peripheral B cell tolerance

Severe SARS-CoV-2 infection is associated with strong inflammation and autoantibody production against diverse self-antigens, suggesting a system-wide defect in B cell tolerance. BND cells are a B cell subset in healthy individuals harboring autoreactive but anergic B lymphocytes. In vitro evidence suggests inflammatory stimuli can breach peripheral B cell tolerance in this subset. We asked whether SARS-CoV-2-associated inflammation impairs BND cell peripheral tolerance. To address this, PBMCs and plasma were collected from healthy controls, individuals immunized against SARS-CoV-2, or subjects with convalescent or severe SARS-CoV-2 infection. We demonstrate that BND cells from severely infected individuals are significantly activated, display reduced inhibitory receptor expression, and restored BCR signaling, indicative of a breach in anergy during viral infection, supported by increased levels of autoreactive antibodies. The phenotypic and functional BND cell alterations significantly correlate with increased inflammation in severe SARS-CoV-2 infection. Thus, autoreactive BND cells are released from peripheral tolerance with SARS-CoV-2 infection, likely as a consequence of robust systemic inflammation.

CAR-T Cells Shoot for New Targets: Novel Approaches to Boost Adoptive Cell Therapy for B Cell-Derived Malignancies

Chimeric antigen receptor (CAR)-T cell therapy is undeniably a promising tool in combating various types of hematological malignancies. However, it is not yet optimal and a significant number of patients experience a lack of response or relapse after the treatment. Therapy improvement requires careful analysis of the occurring problems and a deeper understanding of the reasons that stand behind them. In this review, we summarize the recent knowledge about CAR-T products' clinical performance and discuss diversified approaches taken to improve the major shortcomings of this therapy. Especially, we prioritize the challenges faced by CD19 CAR-T cell-based treatment of B cell-derived malignancies and revise the latest insights about mechanisms mediating therapy resistance. Since the loss of CD19 is one of the major obstacles to the success of CAR-T cell therapy, we present antigens that could be alternatively used for the treatment of various types of B cell-derived cancers.

Single-cell Atlas of common variable immunodeficiency shows germinal center-associated epigenetic dysregulation in B-cell responses

Common variable immunodeficiency (CVID), the most prevalent symptomatic primary immunodeficiency, displays impaired terminal B-cell differentiation and defective antibody responses. Incomplete genetic penetrance and ample phenotypic expressivity in CVID suggest the participation of additional pathogenic mechanisms. Monozygotic (MZ) twins discordant for CVID are uniquely valuable for studying the contribution of epigenetics to the disease. Here, we generate a single-cell epigenomics and transcriptomics census of naïve-to-memory B cell differentiation in a CVID-discordant MZ twin pair. Our analysis identifies DNA methylation, chromatin accessibility and transcriptional defects in memory B-cells mirroring defective cell-cell communication upon activation. These findings are validated in a cohort of CVID patients and healthy donors. Our findings provide a comprehensive multi-omics map of alterations in naïve-to-memory B-cell transition in CVID and indicate links between the epigenome and immune cell cross-talk. Our resource, publicly available at the Human Cell Atlas, gives insight into future diagnosis and treatments of CVID patients.

Common variable immunodeficiency (CVID) is the most prevalent primary immunodeficiency. Here the authors perform single-cell omics analyses in CVID-discordant monozygotic twins and show epigenetic and transcriptional alterations associated with activation in memory B cells.

Neonatal Rhesus Macaques Have Distinct Immune Cell Transcriptional Profiles following HIV Envelope Immunization

HIV-1-infected infants develop broadly neutralizing antibodies (bnAbs) more rapidly than adults, suggesting differences in the neonatal versus adult responses to the HIV-1 envelope (Env). Here, trimeric forms of HIV-1 Env immunogens elicit increased gp120- and gp41-specific antibodies more rapidly in neonatal macaques than adult macaques. Transcriptome analyses of neonatal versus adult immune cells after Env vaccination reveal that neonatal macaques have higher levels of the apoptosis regulator BCL2 in T cells and lower levels of the immunosuppressive interleukin-10 (IL-10) receptor alpha (IL10RA) mRNA transcripts in T cells, B cells, natural killer (NK) cells, and monocytes. In addition, immunized neonatal macaques exhibit increased frequencies of activated blood T follicular helper-like (Tfh) cells compared to adults. Thus, neonatal macaques have transcriptome signatures of decreased immunosuppression and apoptosis compared with adult macaques, providing an immune landscape conducive to early-life immunization prior to sexual debut.

Use of gene expression profiling to identify candidate genes for pretherapeutic patient classification in acute appendicitis

Background

Phlegmonous and gangrenous appendicitis represent independent pathophysiological entities with different clinical courses ranging from spontaneous resolution to septic disease. However, reliable predictive methods for these clinical phenotypes have not yet been established. In an attempt to provide pathophysiological insights into the matter, a genomewide gene expression analysis was undertaken in patients with acute appendicitis.

Methods

Peripheral blood mononuclear cells were isolated and, after histological confirmation of PA or GA, analysed for genomewide gene expression profiling using RNA microarray technology and subsequent pathway analysis.

Results

Samples from 29 patients aged 7–17 years were included. Genomewide gene expression analysis was performed on 13 samples of phlegmonous and 16 of gangrenous appendicitis. From a total of 56 666 genes, 3594 were significantly differently expressed. Distinct interaction between T and B cells in the phlegmonous appendicitis group was suggested by overexpression of T cell receptor α and β subunits, CD2, CD3, MHC II, CD40L, and the B cell markers CD72 and CD79, indicating an antiviral mechanism. In the gangrenous appendicitis group, expression of genes delineating antibacterial mechanisms was found.

Conclusion

These results provide evidence for different and independent gene expression in phlegmonous and gangrenous appendicitis in general, but also suggest distinct immunological patterns for the respective entities. In particular, the findings are compatible with previous evidence of spontaneous resolution in phlegmonous and progressive disease in gangrenous appendicitis.

A Guillain-Barré syndrome-associated SIGLEC10 rare variant impairs its recognition of gangliosides

Guillain-Barré syndrome (GBS), including its variant Miller Fisher syndrome (MFS), is an acute peripheral neuropathy that involves autoimmune mechanisms leading to the production of autoantibodies to gangliosides; sialic acid-containing glycosphingolipids. Although association with various genetic polymorphisms in the major histocompatibility complex (MHC) is shown in other autoimmune diseases, GBS is an exception, showing no such link. No significant association was found by genome wide association studies, suggesting that GBS is not associated with common variants. To address the involvement of rare variants in GBS, we analyzed Siglec-10, a sialic acid-recognizing inhibitory receptor expressed on B cells. Here we demonstrate that two rare variants encoding R47Q and A108V substitutions in the ligand-binding domain are significantly accumulated in patients with GBS. Because of strong linkage disequilibrium, there was no patient carrying only one of them. Recombinant Siglec-10 protein containing R47Q but not A108V shows impaired binding to gangliosides. Homology modeling revealed that the R47Q substitution causes marked alteration in the ligand-binding site. Thus, GBS is associated with a rare variant of the SIGLEC10 gene that impairs ligand binding of Siglec-10. Because Siglec-10 regulates antibody production to sialylated antigens, our finding suggests that Siglec-10 regulates development of GBS by suppressing antibody production to gangliosides, with defects in its function predisposing to disease.

TFG is required for autophagy flux and to prevent endoplasmic reticulum stress in CH12 B lymphoma cells

Plasma cells depend on quality control of newly synthesized antibodies in the endoplasmic reticulum (ER) via macroautophagy/autophagy and proteasomal degradation. The cytosolic adaptor protein TFG (Trk-fused gene) regulates ER-Golgi transport, the secretory pathway and proteasome activity in non-immune cells. We show here that TFG is upregulated during lipopolysaccharide- and CpG-induced differentiation of B1 and B2 B cells into plasmablasts, with the highest expression of TFG in mature plasma cells. CRISPR-CAS9-mediated gene disruption of tfg in the B lymphoma cell line CH12 revealed increased apoptosis, which was reverted by BCL2 but even more by ectopic TFG expression. Loss of TFG disrupted ER structure, leading to an expanded ER and increased expression of ER stress genes. When compared to wild-type CH12 cells, tfg KO CH12 cells were more sensitive toward ER stress induced by tunicamycin, monensin and proteasome inhibition or by expression of an ER-bound immunoglobulin (Ig) μ heavy (µH) chain. CH12 tfg KO B cells displayed more total LC3, lower LC3-II turnover and increased numbers and size of autophagosomes. Tandem-fluorescent-LC3 revealed less accumulation of GFP-LC3 in starved and chloroquine-treated CH12 tfg KO B cells. The GFP:RFP ratio of tandem-fluorescent-LC3 was higher in tunicamycin-treated CH12 tfg KO B cells, suggesting less autophagy flux during induced ER stress. Based on these data, we suggest that TFG controls autophagy flux in CH12 B cells and propose that TFG is a survival factor that alleviates ER stress through the support of autophagy flux in activated B cells and mature plasma cells.Abbreviations: Ab, antibody; Ag, antigen; ASC, antibody-secreting cells; ATG, autophagy-related; BCR, B cell receptor; COPII, coat protein complex II; CpG, non-methylated CpG oligonucleotide; ER, endoplasmic reticulum; ERAD, ER-associated degradation; FO, follicular; GFP, green fluorescent protein; HC, heavy chain; Ig, immunoglobulin; IRES, internal ribosomal entry site; LC, light chain; MZ, marginal zone; NFKB, nuclear factor of kappa light polypeptide gene enhancer in B cells; TLR, toll-like receptor; UPR, unfolded protein response.

Integrative Analysis of Long Noncoding RNAs in Patients with Graft-versus-Host Disease

BACKGROUND

Chronic graft-versus-host disease (cGVHD) remains a major cause of late non-recurrence mortality despite remarkable improvements in the field of allogeneic hematopoietic stem cell transplantation. Although recent studies have found that B-cell receptor (BCR)-activated B cells contribute to pathogenesis in cGVHD, the specific molecular mechanisms of B cells in this process remain unclear.

METHODS

In our study, human long noncoding RNA (lncRNA) microarrays and bioinformatic analysis were performed to identify different expressions of lncRNAs in peripheral blood B cells from cGVHD patients compared with healthy ones. The differential expression of lncRNA was confirmed in additional samples by quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

The microarray analysis revealed that 106 of 198 differentially expressed lncRNAs were upregulated and 92 were downregulated in cGVHD patients compared with healthy controls. Intergenic lncRNAs accounted for the majority of differentially expressed lncRNAs. A KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis showed that the differentially expressed mRNAs, which were coexpressed with lncRNA, between the cGVHD group and the healthy group were significantly enriched in the BCR signaling pathway. Further analysis of the BCR signaling pathway and its coexpression network identified three lncRNAs with the strongest correlation with BCR signaling and cGVHD, as well as a series of protein-coding genes and transcription factors associated with them. The three candidate lncRNAs were further validated in another group of cGVHD patients by qRT-PCR.

CONCLUSIONS

This is the first study on the correlation between lncRNA and cGVHD using lncRNA microarray analysis. Our study provides novel enlightenment in exploring the molecular pathogenesis of cGVHD.

CD22 and CD72 contribute to the development of scleroderma in a murine model

BACKGROUND

Systemic sclerosis (SSc) is a systemic autoimmune disease that is characterized by excessive fibrosis. CD22 and CD72 are B cell-specific cell surface molecules that negatively regulate B cell function.

OBJECTIVE

The aim of the present study was to investigate the roles of CD22 and CD72 in a murine scleroderma model.

METHODS

The experimental fibrosis model was generated by subcutaneous injection of bleomycin or hypochlorous acid (HOCL) into wild-type (WT), CD22-deficient (CD22^-/-), CD72-deficient (CD72^-/-) and CD22 and CD72 double-deficient (CD22^-/-/CD72^-/-) mice. We histologically assessed skin fibrosis and inflammatory cell infiltration. Cytokine and chemokine expression levels were measured by real-time polymerase chain reaction.

RESULTS

The severity of fibrosis in the skin and lung was significantly less in CD22^-/-, CD72^-/-, and CD22^-/-/CD72^-/- mice than in WT mice in the bleomycin-induced model. In the skin of bleomycin-treated mice, the numbers of CD3⁺ T cells, CD8⁺ T cells, and F4/80⁺ macrophages were significantly lower in CD22^-/-, CD72^-/-, and CD22^-/-/CD72^-/- mice than in WT mice. The expression levels of mRNAs for IL-6, TNF-α, TGF-β, CTGF, IL-1β, IL-13, CXCL2, and ICAM-1 were significantly lower in CD22^-/-, CD72^-/-, and CD22^-/-/CD72^-/- mice than in WT mice. In the HOCL-induced model, both skin and lung fibrosis were ameliorated in CD22^-/-, CD72^-/- and CD22^-/-/CD72^-/- mice compared to WT mice.

CONCLUSION

These results indicate that CD22 and CD72 likely play crucial roles in skin and lung fibrosis. Moreover, the inhibition of CD22 and CD72 function has potential as a therapeutic approach to SSc.

Recent BCR stimulation induces a negative autoregulatory loop via FBXO10 mediated degradation of HGAL

Regulating B-cell receptor (BCR) signaling after antigenic stimulation is essential to properly control immune responses. Currently known mechanisms of inhibiting BCR signaling are via co-receptor stimulation and downstream immunoreceptor tyrosine-based inhibition motif (ITIM) phosphorylation. Herein we demonstrate that BCR stimulation induces rapid and reversible palmitoylation of the SCF-FBXO10 ubiquitin E3 ligase. This results in FBXO10 relocation to the cell membrane, where it targets the human germinal center-associated lymphoma (HGAL) protein for ubiquitylation and degradation, leading to decreases in both BCR-induced calcium influx and phosphorylation of proximal BCR effectors. Importantly, FBXO10 recognition and degradation of HGAL is phosphorylation independent and instead relies on a single evolutionarily conserved HGAL amino acid residue (H91) and FBXO10 relocalization to the cytoplasmic membrane. Together our findings demonstrate the first evidence of negative BCR signaling regulation from direct BCR stimulation and define the temporospatial functions of the FBXO10-HGAL axis. FBXO10 is infrequently mutated in DLBCL but some of these mutations deregulate BCR signaling. These observations may have important implications on lymphomagenesis and other immune processes.

Coordinated roles for glycans in regulating the inhibitory function of CD22 on B cells

CD22 is an inhibitory B cell co-receptor that recognizes sialic acid-containing glycoconjugates as ligands. Interactions with its glycan ligands are key to regulating the ability of CD22 to modulate B cell function, the most widely explored of which is antagonizing B cell receptor (BCR) signaling. Most importantly, interactions of CD22 with ligands on the same cell (cis) control the organization of CD22 on the cell surface, which minimizes co-localization with the BCR. In contrast with the modest ability of CD22 to intrinsically dampen BCR signaling, glycan ligands presented on another cell (trans) along with an antigen drawn CD22 and the BCR together within an immunological synapse, strongly inhibiting BCR signaling. New concepts are emerging for how CD22 controls B cell function, such as changes in glycosylation at different stages of B cell differentiation, specifically on GC B cells. Related to these changes, new players, such galectin-9, have been discovered that regulate cell surface nanoclusters of CD22. Roles of glycan ligands in controlling CD22 are the primary focus of this review as we highlight the ability of CD22 to modulate B cell function.

Natural and inducible regulatory B cells are widely distributed in ovine lymphoid tissues

Regulatory B cells that produce IL-10 are now recognized as an important component of the immune system. We previously confirmed that IL-10 secreting CD21⁺ regulatory B cells (B_reg cells) were present in ovine jejunal Peyer's patches (JPP) and this IL-10 production suppressed IL-12 and IFN-γ secretion. It is not known, however, whether ovine B_reg cells are restricted to JPP or are present in other lymphoid tissues. Therefore, CD21⁺ B cells were purified from sheep JPP and from a variety of mucosal and systemic lymphoid tissues using magnetic cell sorting. Purified CD21⁺ B cells were stimulated with a TLR9-agonist, CpG oligodeoxynucleotide (CpG ODN), and the frequency of spontaneous and inducible (i) IL-10-secreting B cells was evaluated by ELISPOT. Spontaneous IL-10 secreting CD21⁺ B cells were present in mucosal (jejunal PP, parabronchial lymph nodes (LN), mesesnteric LN, and palatine tonsils) and systemic (spleen and blood) lymphoid tissues. Mucosal lymphoid tissues (parabronchial and mesenteric LNs and JPP) had the highest frequency of cells spontaneously secreting IL-10 while tonsils had the lowest. The frequency of B cells spontaneously secreting IL-10 was lowest in blood and spleen. There was large inter-animal variation in the frequency of CD21⁺ B cells spontaneously secreting IL-10 and no significant difference was detected following CpG ODN stimulation. When comparing within individual animals there was, however, a consistent increase in the frequency of CD21⁺ cells secreting IL-10 following CpG ODN stimulation versus stimulation with GpC control ODN. The presence of inducible (i)B_reg cells in ovine mucosal tissues supports previous evidence from mice indicating that B cells have the capacity to modulate inflammatory responses. The presence of iB_reg cells in ruminants may also provide a novel therapeutic target for both immunomodulatory drugs and vaccines designed to control antigen-specific mucosal inflammation.

Signalling circuits that direct early B-cell development

In mammals, the B-cell lineage arises from pluripotent progenitors in the bone marrow. During their development, B-cells undergo lineage specification and commitment, followed by expansion and selection. These processes are mediated by regulated changes in gene expression programmes, rearrangements of immunoglobulin (Ig) genes, and well-timed rounds of proliferation and apoptosis. Many of these processes are initiated by environmental factors including cytokines, chemokines, and cell-cell contacts. Developing B-cells process these environmental cues into stage-specific functions via signalling pathways including the PI3K, MAPK, or JAK-STAT pathway. The cytokines FLT3-Ligand and c-Kit-Ligand are important for the early expansion of the B-cell precursors at different developmental stages and conditions. Interleukin 7 is essential for commitment to the B-cell lineage and for orchestrating the Ig recombination machinery. After rearrangement of the immunoglobulin heavy chain, proliferation and apoptosis, and thus selection, are mediated by the clonal pre-B-cell receptor, and, following light chain rearrangement, by the B-cell receptor.

CD72 is a Negative Regulator of B Cell Responses to Nuclear Lupus Self-antigens and Development of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is the prototypic systemic autoimmune disease characterized by production of autoantibodies to various nuclear antigens and overexpression of genes regulated by IFN-I called IFN signature. Genetic studies on SLE patients and mutational analyses of mouse models demonstrate crucial roles of nucleic acid (NA) sensors in development of SLE. Although NA sensors are involved in induction of anti-microbial immune responses by recognizing microbial NAs, recognition of self NAs by NA sensors induces production of autoantibodies to NAs in B cells and production of IFN-I in plasmacytoid dendritic cells. Among various NA sensors, the endosomal RNA sensor TLR7 plays an essential role in development of SLE at least in mouse models. CD72 is an inhibitory B cell co-receptor containing an immunoreceptor tyrosine-based inhibition motif (ITIM) in the cytoplasmic region and a C-type lectin like-domain (CTLD) in the extracellular region. CD72 is known to regulate development of SLE because CD72 polymorphisms associate with SLE in both human and mice and CD72^−/− mice develop relatively severe lupus-like disease. CD72 specifically recognizes the RNA-containing endogenous TLR7 ligand Sm/RNP by its extracellular CTLD, and inhibits B cell responses to Sm/RNP by ITIM-mediated signal inhibition. These findings indicate that CD72 inhibits development of SLE by suppressing TLR7-dependent B cell response to self NAs. CD72 is thus involved in discrimination of self-NAs from microbial NAs by specifically suppressing autoimmune responses to self-NAs.

CD72/CD100 and PD-1/PD-L1 markers are increased on T and B cells in HIV-1+ viremic individuals, and CD72/CD100 axis is correlated with T-cell exhaustion

In our work, we analyzed the role of the CD100/CD72 and PD-1/PD-L1 axes in immune response dysfunction in human immunodeficiency virus (HIV)-1 infection in which high expressions of PD-1 and PD-L1 were associated with an immunosuppressive state via limitation of the HIV-1-specific T-cell responses. CD100 was demonstrated to play a relevant role in immune responses in various pathological processes and may be responsible for immune dysregulation during HIV-1 infection. We investigated the function of CD72/CD100, and PD-1/PDL-1 axes on T and B cells in HIV-infected individuals and in healthy individuals. We analyzed the frequencies and fluorescence intensities of these four markers on CD4+, CD8+ T and B cells. Marker expressions were increased during active HIV-1 infection. CD100 frequency on T cells was positively associated with the expression of PD-1 and PD-L1 on T cells from HIV-infected treatment-naïve individuals. In addition, the frequency of CD72-expressing T cells was associated with interferon gamma (IFN-γ) production in HIV-infected treatment-naïve individuals. Our data suggest that the CD72/CD100 and PD-1/PD-L1 axes may jointly participate in dysregulation of immunity during HIV-1 infection and could partially explain the immune systems' hyper-activation and exhaustion.

Trib1 Is Overexpressed in Systemic Lupus Erythematosus, While It Regulates Immunoglobulin Production in Murine B Cells

Systemic lupus erythematosus (SLE) is a severe and heterogeneous autoimmune disease with a complex genetic etiology, characterized by the production of various pathogenic autoantibodies, which participate in end-organ damages. The majority of human SLE occurs in adults as a polygenic disease, and clinical flares interspersed with silent phases of various lengths characterize the usual evolution of the disease in time. Trying to understand the mechanism of the different phenotypic traits of the disease, and considering the central role of B cells in SLE, we previously performed a detailed wide analysis of gene expression variation in B cells from quiescent SLE patients. This analysis pointed out an overexpression of TRIB1. TRIB1 is a pseudokinase that has been implicated in the development of leukemia and also metabolic disorders. It is hypothesized that Trib1 plays an adapter or scaffold function in signaling pathways, notably in MAPK pathways. Therefore, we planned to understand the functional significance of TRIB1 overexpression in B cells in SLE. We produced a new knock-in model with B-cell-specific overexpression of Trib1. We showed that overexpression of Trib1 specifically in B cells does not impact B cell development nor induce any development of SLE symptoms in the mice. By contrast, Trib1 has a negative regulatory function on the production of immunoglobulins, notably IgG1, but also on the production of autoantibodies in an induced model. We observed a decrease of Erk activation in BCR-stimulated Trib1 overexpressing B cells. Finally, we searched for Trib1 partners in B cells by proteomic analysis in order to explore the regulatory function of Trib1 in B cells. Interestingly, we find an interaction between Trib1 and CD72, a negative regulator of B cells whose deficiency in mice leads to the development of autoimmunity. In conclusion, the overexpression of Trib1 could be one of the molecular pathways implicated in the negative regulation of B cells during SLE.

Negative regulation of B cell responses and self-tolerance to RNA-related lupus self-antigen

The antibody response to RNA-related antigens such as Sm/RNP requires the endosomal RNA sensor TLR7, and this process is crucial in the development of systemic lupus erythematosus at least in animal models. The inhibitory B cell receptor CD72 is unique because it recognizes Sm/RNP and specifically inhibits the activation of Sm/RNP-reactive B cells by activating SH2-containing protein tyrosine phosphatase 1 (SHP-1). In the normal immune system, Sm/RNP-reactive B cells are tolerized by a unique mechanism that probably involves SHP-1. These self-reactive B cells appear in the peripheral lymphoid organs, differentiate into marginal zone B cells, and then undergo apoptosis without further maturation into plasma cells. Thus, CD72 is involved in the suppression of TLR7-mediated response to RNA in complexes with nuclear proteins that are resistant to nucleases, whereas free RNAs are degraded by nucleases before they encounter the endosomal RNA sensor.

Pregnancy probabilistically augments potential precursors to chronic, immune-mediated or autoimmune lacrimal gland infiltrates

PURPOSE

This study asked whether pregnancy, a risk factor for dry eye disease associated with both chronic, immune-mediated- and autoimmune etiologies, augments development of clusters of coordinately functioning cells (CCFC) that may be precursors to pathological lacrimal gland infiltrates.

METHODS

Lacrimal glands were from six virgin- and six term-pregnant rabbits of the same age and environmental exposure history. Seventy-two immune response-related gene transcripts were assayed by real time RT-PCR. Principal component (PC) analysis identified transcript signatures of CCFC contributing negative (^⊖) or positive (^⊕) PC loadings and determined gland PC projections, which reflect levels of CCFC development.

RESULTS

Three CCFC were of interest as potential precursors to pathological infiltrates. CCFC 1^⊖ was suggestive of an ectopic lymphoid structure with resting T cells and B cells. CCFC 1^⊕ was suggestive of an immune-mediated infiltrate with T_H1 cells and mature, cytotoxic B cells. CCFC 2^⊖ was suggestive of an ectopic lymphoid structure with activated T cells, mature B cells, germinal center, and plasmacytes. CCFC 4^⊖ and CCFC 5^⊖ also included plasmacytes. Pregnancy augmented CCFC 1^⊖ in some glands; augmented CCFC 1^⊕ in others; and augmented CCFC 2^⊖, CCFC 4^⊖, and CCFC 5^⊖ different combinations.

CONCLUSIONS

Potential precursors of pathological infiltrates form in the lacrimal glands by the time of sexual maturity. Pregnancy augments lacrimal gland plasmacyte populations, and it can augment development of potential precursors to either chronic, immune-mediated infiltrates or autoimmune infiltrates of various phenotypes. Systemic and strictly local, probabilistic phenomena interact with pregnancy to determine which combinatorial phenotypes are favored.

Low levels of the immunoregulator Semaphorin 4D (CD100) in sera of HIV patients

INTRODUCTION

Semaphorin-4D (CD100), generated by CD4/CD8 T-cells and its receptor on B cells - CD72, play a role in immune regulation. Both have soluble forms - sCD100/sCD72.

METHODS

sCD100 and sCD72 levels were determined by ELISA (MyBioSource, USA).

RESULTS

28 chronic HIV patients and 50 matched healthy volunteers participated in our study. Before treatment, CD4 T-cells counts were 267 ± 216 cells/mcl and viral load (VL) was 586,675 ± 1897,431 copies/ml. Two years following HAART, CD4 T-cells counts rose to 475 ± 264 cells/mcl and VL dropped to 2050 ± 10,539 copies/ml. CD8 T-cells counts were stable. sCD72 levels prior (4.13 ± 2.03 ng/ml) and following HAART (3.53 ± 2.01 ng/ml) were similar to control levels (4.51 ± 2.66 ng/ml). sCD100 levels before (40.47 ± 31.4 ng/ml) and following HAART (37.68 ± 29.44 ng/ml) were significantly lower compared to controls (99.67 ± 36.72 ng/ml) despite the significant increase in CD4 T-cells counts.

CONCLUSIONS

The permanent low levels of the immunoregulator sCD100 suggest a role for CD100 in the immune dysfunction and T cells exhaustion of HIV.

CD11c+ T-bet+ memory B cells: Immune maintenance during chronic infection and inflammation?

CD11c+ T-bet+ B cells have now been detected and characterized in different experimental and clinical settings, in both mice and humans. Whether such cells are monolithic, or define subsets of B cells with different functions is not yet known. Our studies have identified CD11c+ IgM+ CD19^hi splenic IgM memory B cells that appear at approximately three weeks post-ehrlichial infection, and persist indefinitely, during low-level chronic infection. Although the CD11c+ T-bet+ B cells we have described are distinct, they appear to share many features with similar cells detected under diverse conditions, including viral infections, aging, and autoimmunity. We propose that CD11c+ T-bet+ B cells as a group share characteristics of memory B cells that are maintained under conditions of inflammation and/or low-level chronic antigen stimulation. In some cases, these cells may be advantageous, by providing immunity to re-infection, but in others may be deleterious, by contributing to aged-associated autoimmune responses.

CD72 negatively regulates B lymphocyte responses to the lupus-related endogenous toll-like receptor 7 ligand Sm/RNP

Akatsu and colleagues show that CD72 specifically recognizes Sm/RNP, a lupus-related self-antigen and an endogenous TLR7 ligand, and inhibits B cell responses to Sm/RNP. In mice, CD72 prevents production of anti-Sm/RNP antibodies crucial for lupus development.

Toll-like receptor 7 (TLR7) plays an essential role in development of systemic lupus erythematosus by co-stimulating B cells reactive to the endogenous TLR7 ligand Sm/ribonucleoprotein (RNP), a crucial lupus self-antigen. However, how the TLR7-mediated autoimmune response is regulated is not yet known. In this study, we demonstrate that CD72, an inhibitory B cell co-receptor known to prevent development of lupus, recognizes Sm/RNP at the extracellular C-type lectin-like domain (CTLD) and specifically inhibits B cell response to Sm/RNP. Moreover, the CTLD of CD72^c, a lupus-susceptible allele, binds to Sm/RNP less strongly than that of lupus-resistant CD72^a. Reduced binding of CD72^c is supported by x-ray crystallographic analysis that reveals a considerable alteration in charge at the putative ligand-binding site. Thus, CD72 appears to specifically inhibit B cell response to the endogenous TLR7 ligand Sm/RNP through CTLD-mediated recognition of Sm/RNP, thereby preventing production of anti-Sm/RNP antibody crucial for development of lupus.

Evidence for the existence of regulatory and effector B cell populations in Peyer's patches of sheep

IL-10 secreting CD21(+) B cells exist in sheep Peyer's patches (PP). It's not known however, whether all PP B cells are regulatory or whether an effector population also exists in this tissue. To further characterize the subpopulations of B cells in PP's, highly purified B cells were negatively sorted from jejunal PP and fractionated according to co-expression of CD72(+)CD21(+)or CD72(+)CD21(-) molecules and then stimulated with the TLR9-agonist, CpG ODN. IL-10, IL-12, IFN-γ, and IgM production were then assayed. We observed that only highly purified CD72(+)CD21(+) B cells spontaneously secreted high levels of IL-10, but they did not produce any IL-12, IFN-γ or IgM suggesting that this cell population contains regulatory B cells. In contrast, CD72(+)CD21(-) B cells did not secrete IL-10, but secreted IL-12, IFN-γ, and IgM, suggesting they include effector cells. In addition, B cells expressing surface IgA, IgM and IgG1 all secreted similar levels of IL-10. We further confirmed that only B cells produce IL-10, while other cells in the PP including DCs and T cells do not. Our investigations may provide evidence for the existence of two sub-populations in sheep PP; IL-10 secreting regulatory (CD72(+)CD21(+)) cells, and IL-12/IFN-γ/IgM-secreting effector (CD72(+)CD21(-)) cells.

The role of Sema4D/CD100 as a therapeutic target for tumor microenvironments and for autoimmune, neuroimmune and bone diseases

INTRODUCTION

Semaphorin 4D (Sema4D), also known as CD100, has been implicated in physiologic roles in the immune and nervous systems. However, the interaction of Sema4D with its high affinity receptor, Plexin-B1, reveals a novel role for Sema4D produced by the tumor microenvironment in tumor angiogenesis and metastasis.

AREAS COVERED

The ligation of Sema4D/CD100 with CD72 on immune and inflammatory cells is known to stimulate immune responses and regulation. Because CD100 and CD72 are expressed on lung immune and nonimmune cells, as well as on mast cells, the CD100/CD72 interaction plays another important role in allergic airway inflammation and mast cell functions. A better understanding of Sema4D-mediated cell signaling in physiological and pathological processes may be crucial for crafting new Sema4D-based therapeutics for human disease and tumor microenvironments. Strategies to achieve effective management through treatment with Sema4D include special siRNAs, neutralizing antibodies and knockdown.

EXPERT OPINION

This review focuses on the links between Sema4D and human diseases such as cancer, bone metabolism, immune responses and organ development. The current knowledge regarding the expression of Sema4D and its receptors and its functional roles is systemically reviewed to explore Sema4D as both a target and a therapeutic in human diseases.

Suppression of cell division-associated genes by Helicobacter pylori attenuates proliferation of RAW264.7 monocytic macrophage cells

Helicobacter pylori at multiplicity of infection (MOI ≥ 50) have been shown to cause apoptosis in RAW264.7 monocytic macrophage cells. Because chronic gastric infection by H. pylori results in the persistence of macrophages in the host's gut, it is likely that H. pylori is present at low to moderate, rather than high numbers in the infected host. At present, the effect of low-MOI H. pylori infection on macrophage has not been fully elucidated. In this study, we investigated the genome-wide transcriptional regulation of H. pylori-infected RAW264.7 cells at MOI 1, 5 and 10 in the absence of cellular apoptosis. Microarray data revealed up- and down-regulation of 1341 and 1591 genes, respectively. The expression of genes encoding for DNA replication and cell cycle-associated molecules, including Aurora-B kinase (AurkB) were down-regulated. Immunoblot analysis verified the decreased expression of AurkB and downstream phosphorylation of Cdk1 caused by H. pylori infection. Consistently, we observed that H. pylori infection inhibited cell proliferation and progression through the G1/S and G2/M checkpoints. In summary, we suggest that H. pylori disrupts expression of cell cycle-associated genes, thereby impeding proliferation of RAW264.7 cells, and such disruption may be an immunoevasive strategy utilized by H. pylori.

A regulatory role for CD72 expression on B cells in systemic lupus erythematosus

BACKGROUND

B regulatory cells and their regulatory products/markers, such us semaphorin 3A (sema3A) and its receptor NP-1, FcγIIB, IL-10, and others, act at the very base of self-tolerance, maintenance, and prevention of autoimmune disease development.

OBJECTIVES

The aim of the present study was to assess the involvement of CD72, a regulatory receptor on B cells, in systemic lupus erythematosus (SLE). In addition, the potential of soluble sema3A in enhancing the expression of CD72 on B cells of SLE patients was investigated.

RESULTS

CD72 expression on activated B cells of SLE patients was significantly lower than that of normal controls. This lower expression of CD72 in SLE patients correlated inversely with SLE disease activity and was associated with lupus nephritis, the presence of anti-dsDNA antibodies, and low levels of complement. Co-culture of purified B cells from healthy controls with condition-media containing recombinant sema3A resulted in significant enhancement of CD72. Similar enhancement of CD72 on activated B cells from SLE patients, though significant, was still lower than in normal individuals.

CONCLUSIONS

The lower expression of CD72 on activated B cells from SLE patients correlates with SLE disease activity, lupus nephritis, the presence of anti-dsDNA antibodies, and low levels of complement. The improvement of CD72 expression following the addition of soluble semaphorin 3A suggests that CD72 may be useful as a biomarker to be followed during the treatment of SLE.

CD72 Stimulation Modulates Anti-IgM Induced Apoptotic Signaling through the Pathway of NF-κB, c-Myc and p27Kip1

Engagement of mIgM induces G1 arrest and apoptosis in immature B cells. The biochemical mechanism(s) regulating the cell death process are poorly understood. Cross-linking of CD72 (a B cell co-receptor) with anti-CD72 antibody was shown to protect B cells from apoptosis. We investigated the molecular mechanism involved in apoptosis preventing signaling mediated by CD72 ligation using a derivative (WEHIdelta) of the WEHI231 cell line which is representative of immature B cells. Apoptotic WEHIdelta cells following cross-linking of mIgM demonstrate a dramatic loss of c-Myc protein after transient up-regulation. In contrast, pre-ligation of CD72 was able to sustain c-Myc expression after transient up-regulation. Cross-linking of mIgM of WEHIdelta cells causes accumulation of the Cdk inhibitor, p27(Kip1). CD72 pre-ligation was shown to inhibit the accumulation of p27(Kip1) protein. Moreover, NF-kappaB activity was not suppressed in WEHIdelta cells after mIgM cross-linking when the cells were pre-treated with anti-CD72 antibody. These results strongly suggest that the apoptosis preventing signal evoked by CD72 ligation is delivered through the pathway of NF-kappaB, c-Myc, p27(Kip1) and cyclin.

The Myc-miR-17-92 axis amplifies B-cell receptor signaling via inhibition of ITIM proteins: a novel lymphomagenic feed-forward loop

The c-Myc oncoprotein regulates >15% of the human transcriptome and a limited number of microRNAs (miRNAs). Here, we establish that in a human B-lymphoid cell line, Myc-repressed, but not Myc-stimulated, genes are significantly enriched for predicted binding sites of Myc-regulated miRNAs, primarily those comprising the Myc-activated miR-17~92 cluster. Notably, gene set enrichment analysis demonstrates that miR-17∼92 is a major regulator of B-cell receptor (BCR) pathway components. Many of them are immunoreceptor tyrosine inhibitory motif (ITIM)-containing proteins, and ITIM proteins CD22 and FCGR2B were found to be direct targets of miR-17∼92. Consistent with the propensity of ITIM proteins to recruit phosphatases, either MYC or miR-17~92 expression was necessary to sustain phosphorylation of spleen tyrosine kinase (SYK) and the B-cell linker protein (BLNK) upon ligation of the BCR. Further downstream, stimulation of the BCR response by miR-17-92 resulted in the enhanced calcium flux and elevated levels of Myc itself. Notably, inhibition of the miR-17~92 cluster in diffuse large B-cell lymphoma (DLBCL) cell lines diminished the BCR response as measured by SYK and BLNK phosphorylation. Conversely, human DLBCLs of the BCR subtype express higher Myc and mir17hg transcript levels than other subtypes. Hence, the Myc-miR-17-92-BCR axis, frequently affected by genomic rearrangements, constitutes a novel lymphomagenic feed-forward loop.

Cd72(c) is a modifier gene that regulates Fas(lpr)-induced autoimmune disease

Although modifier genes are extensively studied in various diseases, little is known about modifier genes that regulate autoimmune diseases. Autoimmune disease caused by the Fas(lpr) mutation depends on the genetic background of mouse strains, suggesting a crucial role of modifier genes. MRL/MpJ-Fas(lpr) (MRL/lpr) and AKR/lpr mice develop severe and mild lupus-like autoimmune disease, respectively, whereas this mutation does not cause disease on C57BL/6 (B6) or C3H background. Both MRL and AKR carry the same haplotype of the Cd72 gene encoding an inhibitory BCR coreceptor (CD72(c)), and CD72(c) contains several amino acid substitutions and a deletion in the extracellular region compared with CD72(a) and CD72(b). To address the role of Cd72(c) locus in the regulation of Fas(lpr)-induced autoimmune disease, we generated B6.CD72(c)/lpr and MRL.CD72(b)/lpr congenic mice. Introduction of the chromosomal interval containing Cd72(c) did not cause disease in B6 mice by itself, but caused development of lupus-like disease in the presence of Fas(lpr) on B6 background, clearly demonstrating that this interval contains the modifier gene that regulates Fas(lpr)-induced autoimmune disease. Conversely, MRL.CD72(b)/lpr congenic mice showed milder disease compared with MRL/lpr mice. We further demonstrated that Cd72(c) is a hypofunctional allele in BCR signal inhibition and that CD72 deficiency induces severe autoimmune disease in the presence of Fas(lpr). These results strongly suggest that the Cd72(c) is a crucial modifier gene that regulates Fas(lpr)-induced autoimmune disease due to its reduced activity of B cell signal regulation.

Human CD72 splicing isoform responsible for resistance to systemic lupus erythematosus regulates serum immunoglobulin level and is localized in endoplasmic reticulum

BACKGROUND

CD72 is an inhibitory co-receptor expressed on B cells. We previously demonstrated significant association of the polymorphism of the CD72 gene with susceptibility to human systemic lupus erythematosus (SLE) in individuals carrying a SLE-susceptible FCGR2B genotype (FCGR2B-232Thr/Thr). The human CD72 locus generates a splicing isoform that lacks exon 8 (CD72Δex8) as well as full-length CD72 (CD72fl), and the CD72 polymorphism regulates exon 8 skipping.

RESULTS

Here we demonstrated that individuals carrying the disease-protective CD72 genotype exhibit significantly lower serum immunoglobulin levels than do individuals carrying other CD72 genotypes (P < 0.05). Although expression level of CD72fl in the peripheral blood B cells was similar regardless of CD72 genotype, the protein level of CD72Δex8 was increased in individuals carrying the disease-protective CD72 genotype, suggesting a crucial role of CD72Δex8 in regulation of antibody production. By expressing these human CD72 isoforms in mouse cell lines, we further demonstrated that CD72Δex8 is accumulated in endoplasmic reticulum (ER) and fails to regulate BCR signaling whereas human CD72fl is efficiently transported to the cell surface and inhibits signaling through the B cell antigen receptor (BCR), as is the case for mouse CD72.

CONCLUSION

Human CD72 polymorphism appears to regulate antibody production as well as susceptibility to SLE by regulating expression of ER-localizing CD72Δex8.

Biology and function of neuroimmune semaphorins 4A and 4D

Semaphorins belong to a family of membrane-bound and secreted molecules that regulate the functional activity of axons in the nervous system. Sema4A and Sema4D were the first semaphorins also found to be expressed in immune cells and were, therefore, termed "immune semaphorins". It is known that Sema4A has three functional receptors, namely Plexin D1, Plexin B1, and Tim-2, whereas Sema4D binds to Plexin B1 and CD72. Recent studies suggest that immune semaphorins play critical roles in many physiological and pathological processes and such. In this review, we summarize the current knowledge on the biology of neuroimmune semaphorins and their corresponding receptors, their distribution in organs and tissues, function in the immune response, and critical regulatory roles in various diseases.

[Evaluation of percentage of lymphocytes B with expression of co-receptors CD 40, CD22 and CD72 in hypertrophied adenoid at children with otitis media with effusion]

INTRODUCTION

In hypertrophied adenoid lymphocytes B make up about 60% all lymphocytes. When the lymphocytes B come in interaction with antigens this membranes signal be passed through their receptor (BCR) to interior of cell. This signal affect modulation on gene expression, activation from which depends activation, anergy or apoptosis of lymphocyte B. Accompany BCR co-receptors regulate his functions influence stimulate or inhibitive. To the most important co-receptors stepping out on lymphocyte B belong: CD40, CD22, CD72.

AIM OF STUDY

The aim of study was evaluation of lymphocytes B (CD19) with co-expression with CD72 and CD40 receptors in hypertrophied adenoid with at children with otitis media with effusion.

MATERIAL

An investigation was executed in hypertrophied adenoids with or without otitis media with effusion.

METHODS

By flow cytometry percentage of lymphocytes B with co-receptors CD 40, CD22 and CD72 in was analyzed.

RESULTS

The percentages of CD19+CD72+ lymphocytes in the group of children with adenoid hypertrophy and exudative otitis media were lower as compared to the reference group. However, the percentages of CD19+CD22+, CD19+CD40+ in the study group was approximate to the reference group.

CONCLUSIONS

The lower percentage of lymphocytes B CD72 + near approximate percentages of lymphocytes B CD40+ and BCD22+ at children with otitis media with effusion can be the cause of incorrect humoral response in hypertrophied adenoid at children. Maybe it is cause reduced spontaneous production IgA and IgG through lymphocyte at children with otitis media with effusion.

CD72 negatively regulates KIT-mediated responses in human mast cells

KIT activation, through binding of its ligand, stem cell factor, is crucial for normal mast cell growth, differentiation, and survival. Furthermore, KIT may also contribute to mast cell homing and cytokine generation. Activating mutations in KIT lead to the dysregulated mast cell growth associated with the myeloproliferative disorder, mastocytosis. We investigated the potential of downregulating such responses through mast cell inhibitory receptor activation. In this study, we report that the B cell-associated ITIM-containing inhibitory receptor, CD72, is expressed in human mast cells. Ligation of CD72 with the agonistic Ab, BU40, or with recombinant human CD100 (rCD100), its natural ligand, induced the phosphorylation of CD72 with a resulting increase in its association with the tyrosine phosphatase SH2 domain-containing phosphatase-1. This, in turn, resulted in an inhibition of KIT-induced phosphorylation of Src family kinases and extracellular-regulated kinases (ERK1/2). As a consequence of these effects, KIT-mediated mast cell proliferation, chemotaxis, and chemokine production were significantly reduced by BU40 and rCD100. Furthermore, BU40 and rCD100 also downregulated the growth of the HMC1.2 human mast cell line. Thus, targeting CD72 may provide a novel approach to the suppression of mast cell disease such as mastocytosis.

B cell abnormality and autoimmune disorders

Various abnormalities have been described in B cells from patients with systemic autoimmune diseases such as systemic lupus erythematosus (SLE) and lupus-prone mice. Many of the abnormalities do not appear to be connected with the pathogenesis of the disease. However, various animal models developing lupus-like disease including both spontaneous mutans such as (NZB x NZW)F1 and MRL/lpr and mice generated by transgenic or knockout technology such as Bim-deficient and CD40L-transgenic mice show defect in apoptosis of mature B cells induced by ligation of the B cell antigen receptor (BCR). BCR-mediated apoptosis appears to be involved in deletion of self-reactive B cells. Thus, defect in BCR-mediated apoptosis is a widely observed B cell abnormality in lupus-prone mice and may play a role in the pathogenesis of systemic autoimmune diseases by abrogating deletion of self-reactive B cells.

CD72, a coreceptor with both positive and negative effects on B lymphocyte development and function

INTRODUCTION

B lymphocytes remain in a resting state until activated by antigenic stimuli through interaction with the B cell receptor (BCR). Coreceptors on B cells can modulate the thresholds for signaling through the BCR for growth and differentiation. CD72 is a B cell coreceptor that has been shown to interact with CD100, a semaphorin, and to enhance BCR signaling.

DISCUSSION

CD72 ligation induces a variety of early signaling events such as activation of the Src kinases Blk and Lyn and the non-src kinase Btk leading to activation of the mitogen-activated protein (MAP) kinases, events usually associated with positive signaling. CD72 signals can enable Btk-deficient B cells to overcome their unresponsiveness to BCR signaling. On the other hand, BCR-mediated signals are enhanced in CD72-deficient cells but are reduced in CD100 null cells. The dual effects of CD72 on B cells can be explained by its association with positive and negative signaling molecules. Thus, CD72 interacts with SHP-1, an SH2-domain containing protein tyrosine phosphatase, a negative regulator of signaling, and Grb2, an adaptor protein associated with the Ras/MAPK pathway. Ligation of CD72 also triggered its association with CD19, a positive modulator of B cell receptor signaling. We propose a dual signaling hypothesis to explain the growth and differentiation promoting properties of CD72. Deficiency in either CD72 or CD100 leads to autoimmunity in mouse models. CD72 expression and polymorphisms exhibit some association with autoimmune diseases such as lupus, Sjogren's syndrome, and type 1 diabetes.

CD72 polymorphism associated with child-onset of idiopathic thrombocytopenic purpura in Chinese patients

Idiopathic thrombocytopenic purpura (ITP) is a disease putatively relating to abnormal immune function and auto-antiplatelet immunoglobulin. We examined whether polymorphism of CD72, an inhibitory receptor of B cells, affect the susceptibility to ITP, or associated with the clinical characteristics of ITP. A case-control study was carried out in 206 Chinese ITP patients and 169 healthy controls. The detection of variable number of tandem repeats in CD72 intron 8 was performed by polymerase chain reaction and subsequent analysis with polyacrylamide gel electrophoresis. We did not find direct association between CD72 genotypes and susceptibility to ITP. The haplotype that contained one repeat of 13 nucleotides in intron 8 (designated as *1, and haplotype containing two repeat of 13 nucleotides in intron 8 is designated as *2) was significantly associated with early first onset age (< or = 14) in ITP patients (P = 0.03). ITP patients with CD72*1\*1 and *1\*2 genotype had a 3.09-fold [95% confidence interval (CI), 1.32-7.25] and 1.98-fold (95% CI, 0.92-4.25) increased risk of appearing ITP manifestation at their childhood respectively. The haplotype CD72*1 is apparently a risk allele, whereas CD72*2 a protective allele for child-onset of ITP disease.

Conformational plasticity and navigation of signaling proteins in antigen-activated B lymphocytes

Over the past two decades our view of the B cell antigen receptor (BCR) has fundamentally changed. Being initially regarded as a mute antibody orphan of the B cell surface, the BCR turned out to be a complex multimolecular machine monitoring almost all stages of B cell development, selection, and activation through a plethora of ubiquitously and cell-type-specific effector proteins. A comprehensive understanding of the many BCR signaling facets is still out but a few common biochemical principles outlined in this review operate at the level of receptor activation and orchestrate specific wiring of intracellular transducer cascades. First, initiation and processing of antigen-induced signal transduction relies on transient conformational changes in the signaling proteins to trigger their physical interaction with downstream elements. Second, this dynamic assembly of signalosomes occurs at distinct subcellular locations, most prominently the plasma membrane, which requires dynamic relocalization of one or more of the engaged molecules. For both, precise complex formation and efficient subcellular targeting, B cell signaling components are equipped with a variety of protein interaction domains. Here we provide an overview on how these simple rules are applied by a limited number of transmembrane and cytosolic proteins to convert BCR ligation into Ca(2+) mobilization and Ras activation in an adjustable manner.

Natural phosphorylation of CD5 in chronic lymphocytic leukemia B cells and analysis of CD5-regulated genes in a B cell line suggest a role for CD5 in malignant phenotype

Chronic lymphocytic leukemia (CLL) results in the accumulation of B cells, presumably reflecting the selection of malignant cell precursors with Ag combined with complex alterations in protein activity. Repeated BCR stimulation of normal B cells leads to anergy and CD5 expression, both of which are features of CLL. Because CD5 is phosphorylated on tyrosine following BCR engagement and negatively regulates BCR signaling in normal B cells, we investigated its phosphorylation status and found it to be naturally phosphorylated on tyrosine but not on serine residues in CLL samples. To analyze the role of CD5, we established a B cell line in which CD5 is phosphorylated. Gene profiling of vector vs CD5-transfected B cells pointed out gene groups whose expression was enhanced: Apoptosis inhibitors (BCL2), NF-kappaB (RELB, BCL3), Wnt, TGFbeta, VEGF, MAPKs, Stats, cytokines, chemokines (IL-10, IL-10R, IL-2R, CCL-3, CCL-4, and CCR7), TLR-9, and the surface Ags CD52, CD54, CD70, and CD72. Most of these gene groups are strongly expressed in CLL B cells as compared with normal B cells. Unexpectedly, metabolic pathways, namely cholesterol synthesis and adipogenesis, are also enhanced by CD5. Conversely, CD5 inhibited genes involved in RNA splicing and processing, ribosome biogenesis, proteasome, and CD80 and CD86 Ags, whose expression is low in CLL. Comparison of CD5- vs tailless CD5-transfected cells further demonstrated the role of CD5 phosphorylation in the regulation of selected genes. These results support a model where CLL cells are chronically stimulated, leading to CD5 activation and cell survival. In addition to CD5 itself, we point to several CD5-induced genes as potential therapeutic targets.

Ca(2+) signaling in antigen receptor-activated B lymphocytes

B cells respond to antigen stimulation with mobilization of the Ca(2+) second messenger in two phases operated by two distinct sets of effector proteins. First, an antigen receptor-specific Ca(2+) initiation complex is assembled, activated, and targeted to the plasma membrane to trigger the transient release of Ca(2+) from intracellular stores of the endoplasmic reticulum. Second, more ubiquitously expressed Ca(2+) channels of the plasma membrane are opened to allow for sustained Ca(2+) influx from the extracellular medium. Depending on the developmental stage of the B cell, the kinetics and profile of the two phases are adjusted at multiple levels of positive and negative regulation. A molecular basis for the Ca(2+) signaling plasticity is provided by cytosolic and transmembrane adapter proteins. They act as signal organizers, which control enzyme/substrate interactions by directing the different signaling modules into specific subcellular compartments. These arrangements orchestrate a graduated activation of Ca(2+)-sensitive downstream pathways, which ultimately determine appropriate cellular responses, namely elimination of autoreactive B cells or proliferation and differentiation of immunocompetent B cells into antibody-secreting plasma cells.

Various domains of the B-cell regulatory molecule CD72 has diverged at different rates in mammals: cloning, transcription and mapping of porcine CD72

We report the cloning of the porcine B-cell co-receptor CD72, as well as genomic mapping and examination of transcription. The B-cell receptor (BCR) complex mediates signalling upon antigen recognition by the membrane bound BCR. Several co-receptors modulate this signal positively or negatively. CD72 has been shown to be a negatively regulating BCR co-receptor. We isolated and sequenced three porcine CD72 transcript variants. Using a pig radiation hybrid panel we found the porcine CD72 gene to be located on chromosome 1q21-28 in a region syntenic to human chromosome 9. The porcine CD72 gene is highly transcribed in lymph node, thymus and lung tissues as well as in pulmonary alveolar macrophages. The predicted porcine CD72 polypeptide shows conservation of immunoreceptor tyrosine-based inhibitory motifs and an extracellular C-type lectin domain. Compared to CD72 sequences from other mammals as well as from chicken, the polypeptide is highly conserved in the intracellular part and much less conserved in the extracellular part. We suggest that this difference might be due to the different nature of ligands and the constrains on these to co-evolve.

Increased mutations of CD72 transcript in B-lymphocytes from adolescent patients with systemic lupus erythematosus

Recent studies have shown that B cells play a central role in the pathogenesis of systemic lupus erythematosus (SLE). Abnormal expression of molecules engaging in B-cell receptor (BCR) signaling and resultant hyperactivity of B cells has been reported in both mouse models of lupus and patients with SLE. CD72 on B cells is unique in that it regulates BCR signaling both positively and negatively. We analyzed the expression of CD72 protein and mRNA in peripheral blood B cells from adolescent patients with SLE. The expression level of CD72 on B cells of the patients was decreased compared with that on B cells of controls. Sequence analysis of CD72 mRNA showed significantly increased nucleotide mutations, including both nucleotide substitutions and deletions. Almost all (95.6%) of the CD72 transcripts from the patients had different nucleotide sequences from those of the wild type. About half (41.3%) of the mutations were point mutations located close to the sequence of the immunoreceptor tyrosine-based inhibitory motif (ITIM), which negatively regulates BCR signaling. These results indicate that increased nucleotide mutation of CD72 mRNA accounts for the decreased expression level of CD72 in B cells, and it might be related to hyperactivity of B cells in patients with SLE.