Dual regulation of BCR-mediated growth inhibition signaling by CD72

Updates on lymphoblastic leukemia/lymphoma classification and minimal/measurable residual disease analysis

Lymphoblastic leukemia/lymphoma (ALL/LBL), especially certain subtypes, continues to confer morbidity and mortality despite significant therapeutic advances. The pathologic classification of ALL/LBL, especially that of B-ALL, has recently substantially expanded with the identification of several distinct and prognostically important genetic drivers. These discoveries are reflected in both current classification systems, the World Health Organization (WHO) 5th edition and the new International Consensus Classification (ICC). In this article, novel subtypes of B-ALL are reviewed, including DUX4, MEF2D and ZNF384-rearranged B-ALL; the rare pediatric entity B-ALL with TLF3::HLF, now added to the classifications, is discussed; updates to the category of B-ALL with BCR::ABL1-like features (Ph-like B-ALL) are summarized; and emerging genetic subtypes of T-ALL are presented. The second half of the article details current approaches to minimal/measurable residual disease (MRD) detection in B-ALL and T-ALL and presents anticipated challenges to current approaches in the burgeoning era of antigen-directed immunotherapy.

Global MicroRNAs Expression Profile Analysis Reveals Possible Regulatory Mechanisms of Brain Injury Induced by Toxoplasma gondii Infection

Toxoplasma gondii (T. gondii) is an obligate intracellular parasitic protozoan that can cause toxoplasmosis in humans and other endotherms. T. gondii can manipulate the host gene expression profile by interfering with miRNA expression, which is closely associated with the molecular mechanisms of T. gondii-induced brain injury. However, it is unclear how T. gondii manipulates the gene expression of central nervous system (CNS) cells through modulation of miRNA expression in vivo during acute and chronic infection. Therefore, high-throughput sequencing was used to investigate expression profiles of brain miRNAs at 10, 25, and 50 days post-infection (DPI) in pigs infected with the Chinese I genotype T. gondii strain in this study. Compared with the control group 87, 68, and 135 differentially expressed miRNAs (DEMs) were identified in the infected porcine brains at 10, 25, and 50 DPI, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis showed that a large number significantly enriched GO terms and KEGG pathways were found, and were mostly associated with stimulus or immune response, signal transduction, cell death or apoptosis, metabolic processes, immune system or diseases, and cancers. miRNA–gene network analysis revealed that the crucial connecting nodes, including DEMs and their target genes, might have key roles in the interactions between porcine brain and T. gondii. These results suggest that the regulatory strategies of T. gondii are involved in the modulation of a variety of host cell signaling pathways and cellular processes, containing unfolded protein response (UPR), oxidative stress (OS), autophagy, apoptosis, tumorigenesis, and inflammatory responses, by interfering with the global miRNA expression profile of CNS cells, allowing parasites to persist in the host CNS cells and contribute to pathological damage of porcine brain. To our knowledge, this is the first report on miRNA expression profile in porcine brains during acute and chronic T. gondii infection in vivo. Our results provide new insights into the mechanisms underlying T. gondii-induced brain injury during different infection stages and novel targets for developing therapeutic agents against T. gondii.

A regulatory role for CD72 expression on B cells and increased soluble CD72 in primary Sjogren's syndrome

BACKGROUND

CD72, a co-receptor of B cell receptor (BCR), has been reported to have both positive and negative effects on B cell functions in several immunological diseases. The B cell plays an important role in the pathogenesis of primary Sjogren's syndrome (pSS). However, whether CD72 is involved in the process remains unknown. This study aimed to observe the possible role of CD72 in the pathogenesis of pSS.

RESULTS

A total of 60 cases who fulfilled the American-European Consensus Group (AECG) criteria for the diagnosis of pSS and 61 gender and age-matched healthy controls were recruited in this study. The percentage of CD72+ B cells was 85.31 ± 8.37% in pSS patients and 76.91 ± 8.50% in healthy controls(p < 0.001). The percentage of CD72+ B cells was correlated to serum IgG levels in patients [β = 0.018(0.001-0.036), p = 0.034]. The level of serum soluble CD72 was significantly higher in pSS patients than the one in healthy controls (0.41 (0.29) vs 0.07 (0.08) ng/mL, p < 0.001).

CONCLUSIONS

The percentage of CD72+ B cells was upregulated in pSS patients and was correlated to the serum IgG level, which revealed the hyperactivity of B cells in this disease. The serum soluble CD72 level was also increased in pSS patients. These results indicated a potential role of CD72 in the pathogenesis of pSS.

[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.

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.

Novel therapeutic targets at the platelet vascular interface

Platelet activation in vivo can be part of the hemostatic response to injury or a pathological response to disease. In either setting, platelets adhere to the vessel wall and to each other, forming a closely packed mass interspersed with fibrin. Recent studies have identified new molecules on the platelet surface and within platelets that support and regulate thrombus growth and stability, ensuring that platelet accumulation after injury is sufficient to stop bleeding, but not so exuberant that vascular occlusion occurs. An understanding of how this balance is achieved helps to illuminate the events of platelet activation and, at the same time, provides potential targets for new classes of antiplatelet agents.

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.

Investigations into the regulation and function of the SH2 domain-containing protein-tyrosine phosphatase, SHP-1

Our laboratory is interested in identifying genes relevant to diseases. Our approach is to use spontaneous mouse mutants with immunological defects and decipher the molecular basis of the phenotypes. In the early 1990s, our attention was focused on the motheaten and viable motheaten mouse mutants. We used these mutant mice as a model system for elucidating the genetic and cellular events contributing to expression of normal hematopoietic and immune function. Our initial goal was to identify the gene responsible for the motheaten and viable motheaten phenotype. In 1993, we and others reported that both motheaten and viable motheaten mice have mutations in the SHP-1 gene. Currently, there are more than 600 publications involving SHP-1. In this review, rather than summarizing all these studies, we highlight work involving SHP-1 that were/are carried out in our and our collaborators' laboratories.

CD72 down-modulates BCR-induced signal transduction and diminishes survival in primary mature B lymphocytes

CD72, a 45-kDa type II transmembrane glycoprotein carrying an ITIM motif, is believed to be an inhibitory coreceptor of the BCR. Mature B cells lacking CD72 show enhanced Ca(2+) mobilization and are hyperproliferative in response to BCR ligation. However, the signal transduction pathways downstream of BCR signaling that transmit the inhibitory effect of CD72 in mature B cells remain unknown. To address this question, we used hen egg lysozyme-specific BCR transgenic mice to elucidate the differential cell signaling between wild-type and CD72-deficient B cells in response to hen egg lysozyme Ag stimulation. Our results demonstrate that CD72 predominantly down-regulates the major signal transduction pathways downstream of the BCR, including NF-AT, NF-kappaB, ERK, JNK, p38-MAPK, and PI3K/Akt in mature B cells. CD72 ligation with anti-CD72 Ab (K10.6), which mimics the binding of CD100 (a natural ligand for CD72) to release the inhibitory function of CD72, augments cell proliferation, Ca(2+) flux, IkappaBalpha activation, and ERK MAPK activity upon Ag stimulation in wild-type B cells. In addition, we show direct evidence that CD72 promotes cell cycle arrest and apoptosis after Ag stimulation in mature B cells. Taken together, our findings conclude that CD72 plays a dominant role as a negative regulator of BCR signaling in primary mature B lymphocytes.

A novel avian homologue of CD72, chB1r, down modulates BCR-mediated activation signals

The avian B cell differentiation antigen chB1 is a C-type lectin membrane protein most homologous to mammalian CD72. Here, we report a new chB1-related gene, chB1r, that is located 18 kb away the chB1 gene. The cytoplasmic domain of chB1r protein contains two immunoreceptor tyrosine-based inhibitory motifs (ITIMs: ITIM1 and 2), which are identical to those found in CD72, whereas chB1 lacks the second ITIM2. Although chB1 expression is restricted to the bursa and an immature B cell line, chB1r is highly expressed in the bursa, spleen and both immature and mature B cell lines, a pattern that parallels CD72 expression. SHP-1 and Grb2 interact with phosphorylated tyrosine residues within chB1r ITIM1 and ITIM2, respectively. By contrast, ITIM1 of chB1 does not interact with SHP-1. Functional characterization using chB1r/chB1 double-deficient DT40 B cells demonstrated that ITIM1 in chB1r transduces a negative signal for BCR-mediated nuclear factor of activated T cells (NF-AT) activation and that ITIM2 attenuates this negative signal. This study has established chB1r as the genuine avian homologue of mammalian CD72, and revealed an opposing role for the two ITIMs through binding with SHP-1 and Grb2 for regulation of BCR-mediated NF-AT activation.

Contact-dependent signaling events that promote thrombus formation

There is increasing evidence that formation of a stable hemostatic plug requires adhesive and signaling events that continue beyond the onset of platelet aggregation. These events are facilitated and, in some cases, made possible, by the persistent close contacts between platelets that can only occur when platelets begin to aggregate. Participants include integrins and other cell adhesion molecules, secreted agonists, receptor tyrosine kinases, and protein fragments that are shed from the surface of activated platelets. Collectively, these molecules promote the continued growth and stability of the hemostatic plug.

Minding the gaps to promote thrombus growth and stability

Efforts to understand the role of platelets in hemostasis and thrombosis have largely focused on the earliest events of platelet activation, those that lead to aggregation. Although much remains to be learned about those early events, this Review examines a later series of events: the interactions between platelets that can only occur once aggregation has begun, bringing platelets into close contact with each other, creating a protected environment in the gaps between aggregated platelets, and fostering the continued growth and stability of the hemostatic plug.