CD45 regulates signal transduction and lymphocyte activation by specific association with receptor molecules on T or B cells

Protein Tyrosine Phosphatases: Mighty oaks from little acorns grow

In October 2020, we were finally able to gather for a celebration of Eddy Fischer's 100th birthday. As with many other events, COVID had disrupted and restricted preparations for the gathering, which ultimately was held via ZOOM. Nevertheless, it was a wonderful opportunity to share a day with Eddy, an exceptional scientist and true renaissance man, and to appreciate his stellar contributions to science. Eddy Fischer, together with Ed Krebs, was responsible for the discovery of reversible protein phosphorylation, which launched the entire field of signal transduction. The importance of this seminal work is now being felt throughout the biotechnology industry with the development of drugs that target protein kinases, which have transformed the treatment of a wide array of cancers. I was privileged to have worked with Eddy both as a postdoc and a junior faculty member, during which time we laid the foundations for our current understanding of the protein tyrosine phosphatase (PTP) family of enzymes and their importance as critical regulators of signal transduction. This tribute to Eddy is based upon the talk I presented at the event, giving a personal perspective on Eddy's influence on my career, our early research efforts together in this area, and how the field has developed since then.

The Mannose Receptor: From Endocytic Receptor and Biomarker to Regulator of (Meta)Inflammation

The mannose receptor is a member of the C-type lectin (CLEC) family, which can bind and internalize a variety of endogenous and pathogen-associated ligands. Because of these properties, its role in endocytosis as well as antigen processing and presentation has been studied intensively. Recently, it became clear that the mannose receptor can directly influence the activation of various immune cells. Cell-bound mannose receptor expressed by antigen-presenting cells was indeed shown to drive activated T cells towards a tolerogenic phenotype. On the other hand, serum concentrations of a soluble form of the mannose receptor have been reported to be increased in patients suffering from a variety of inflammatory diseases and to correlate with severity of disease. Interestingly, we recently demonstrated that the soluble mannose receptor directly promotes macrophage proinflammatory activation and trigger metaflammation. In this review, we highlight the role of the mannose receptor and other CLECs in regulating the activation of immune cells and in shaping inflammatory responses.

Origins and clinical relevance of proteoforms in pediatric malignancies

INTRODUCTION

Cancer changes the proteome in complex ways that reach well beyond simple changes in protein abundance. Genomic and transcriptional variations and post-translational protein modification create functional variants of a protein, known as proteoforms. Childhood cancers have fewer genomic alterations but show equally dramatic phenotypic changes as malignant cells in adults. Therefore, unraveling the complexities of the proteome is even more important in pediatric malignancies. Areas covered: In this review, the biological origins of proteoforms and technological advancements in the study of proteoforms are discussed. Particular emphasis is given to their implication in childhood malignancies and the critical role of cancer-specific proteoforms for the next generation of cancer therapies and diagnostics. Expert opinion: Recent advancements in technology have led to a better understanding of the underlying mechanisms of tumorigenesis. This has been critical for the development of more effective and less harmful treatments that are based on direct targeting of altered proteins and deregulated pathways. As proteome coverage and the ability to detect complex proteoforms increase, the most need for change is in data compilation and database availability to mediate high-level data analysis and allow for better functional annotation of proteoforms.

Non-thermal plasma induces immunogenic cell death in vivo in murine CT26 colorectal tumors

Immunogenic cell death is characterized by the emission of danger signals that facilitate activation of an adaptive immune response against dead-cell antigens. In the case of cancer therapy, tumor cells undergoing immunogenic death promote cancer-specific immunity. Identification, characterization, and optimization of stimuli that induce immunogenic cancer cell death has tremendous potential to improve the outcomes of cancer therapy. In this study, we show that non-thermal, atmospheric pressure plasma can be operated to induce immunogenic cell death in an animal model of colorectal cancer. In vitro, plasma treatment of CT26 colorectal cancer cells induced the release of classic danger signals. Treated cells were used to create a whole-cell vaccine which elicited protective immunity in the CT26 tumor mouse model. Moreover, plasma treatment of subcutaneous tumors elicited emission of danger signals and recruitment of antigen presenting cells into tumors. An increase in T cell responses targeting the colorectal cancer-specific antigen guanylyl cyclase C (GUCY2C) were also observed. This study provides the first evidence that non-thermal plasma is a bone fide inducer of immunogenic cell death and highlights its potential for clinical translation for cancer immunotherapy.

Mining the Complex Family of Protein Tyrosine Phosphatases for Checkpoint Regulators in Immunity

The family of protein tyrosine phosphatases (PTPs) includes 107 genes in humans that are diverse in their structures and expression profiles. The majority are present in immune cells and play various roles in either inhibiting or promoting the duration and amplitude of signaling cascades. Several PTPs, including TC-PTP (PTPN2) and SHP-1 (PTPN6), have been recognized as being crucial for maintaining proper immune response and self-tolerance, and have gained recognition as true immune system checkpoint modulators. This chapter details the most recent literature on PTPs and immunity by examining their known functions in regulating signaling from either established checkpoint inhibitors or by their intrinsic properties, as modulators of the immune response. Notably, we review PTP regulatory properties in macrophages, antigen-presenting dendritic cells, and T cells. Overall, we present the PTP gene family as a remarkable source of novel checkpoint inhibitors wherein lies a great number of new targets for immunotherapies.

A Simple, Versatile Antibody-Based Barcoding Method for Flow Cytometry

Barcoding of biological samples is a commonly used strategy to mark or identify individuals within a complex mixture. However, cell barcoding has not yet found wide use in flow cytometry that would benefit greatly from the ability to analyze pooled experimental samples simultaneously. This is due, in part, to technical and practical limitations of current fluorescent dye-based methods. In this study, we describe a simple, versatile barcoding strategy that relies on combinations of a single Ab conjugated to different fluorochromes and thus in principle can be integrated into any flow cytometry application. To demonstrate the efficacy of the approach, we describe the results of a variety of experiments using live cells as well as fixed and permeabilized cells. The results of these studies show that Ab-based barcoding provides a simple, practical method for identifying cells from individual samples pooled for analysis by flow cytometry that has broad applications in immunological research.

Receptor-type tyrosine phosphatase ligands: looking for the needle in the haystack

Reversible protein phosphorylation plays a pivotal role in intercellular communication. Together with protein tyrosine kinases, protein tyrosine phosphatases (PTPs) are involved in the regulation of key cellular processes by controlling the phosphorylation levels of diverse effectors. Among PTPs, receptor-like protein tyrosine phosphatases (RPTPs) are involved in important developmental processes, particularly in the formation of the nervous system. Until recently, few ligands had been identified for RPTPs, making it difficult to grasp the effects these receptors have on cellular processes, as well as the mechanisms through which their functions are mediated. However, several potential RPTP ligands have now been identified to provide us with unparalleled insights into RPTP function. In this review, we focus on the nature and biological outcomes of these extracellular interactions between RPTPs and their associated ligands.

Comprehensive expression profiles of genes for protein tyrosine phosphatases in immune cells

The phosphorylation and dephosphorylation of signaling molecules play a crucial role in various cellular processes, including immune responses. To date, the global expression profile of protein tyrosine phosphatases (PTPs) in various immune cells has not been described. With the RefDIC (Reference Genomics Database of Immune Cells) database compiled by RIKEN (Rikagaku Kenkyusho), we examined the expression patterns of PTP-encoding genes in mice and identified between 57 and 64 PTP-encoding genes (depending on cutoff values) that were commonly expressed in immune cells. Cells of different lineages contained additional, unique PTP-encoding genes, which resulted in a total of 58 to 76 genes. Compared with cells from nonimmune tissues, immune cells exhibited enhanced expression of the genes encoding 8 PTP-encoding genes, including Ptprc, Ptpn6, and Ptpn22, but had barely detectable expression of 11 PTP-encoding genes, including Ptprd and Tns1. Each immune cell lineage had between 2 and 18 PTP-encoding genes expressed at relatively high or low extents relative to the average expression among immune cells; for example, Ptprj in B cells, Dusp3 in macrophages, Ptpro in dendritic cells, and Ptprg in mast cells. These PTPs potentially play important roles in each cell lineage, and our analysis provides insight for future functional studies.

Ethanol-induced CD3 and CD2 hyporesponsiveness of peripheral blood T lymphocytes

The functional relevance of a direct ethanol effect on the membrane structure of T lymphocytes and accessory cells (APC), as well as on signal transduction systems was studied in ten normal subjects. Ethanol incubation (80 mM for 24h) of highly purified T cells increased the number of CD4+/CD45RA+ lymphocytes. In contrast, ethanol exposure induced a drop in CD14+/LFA-3+ APC values. These changes were accompanied by faulty T-cell proliferation in response to anti-CD3 and anti-CD2 mAb and inhibition of CD3- and CD2-mediated rises in intracellular calcium and, to a lesser extent, inositol 1,4,5-triphosphate levels. These data clearly indicate that a membrane-specific ethanol interaction both modifies surface glycoproteic and/or glycolipidic structures and alters transmembrane transduction of the activation signals.

The cytoplasmic tail of CD45 is released from activated phagocytes and can act as an inhibitory messenger for T cells

CD45 is the prototypic transmembrane protein tyrosine phosphatase (PTP), which is expressed on all nucleated hematopoietic cells and plays a central role in the integration of environmental signals into immune cell responses. Here we report an alternative function for the intracellular domain of CD45. We dis-covered that CD45 is sequentially cleaved by serine/metalloproteinases and gamma-secretases during activation of human monocytes and granulocytes by fungal stimuli or phorbol 12-myristate 13-acetate but not by other microbial stimuli. Proteolytic processing of CD45 occurred upon activation of monocytes or granulocytes but not of T cells, B cells, or dendritic cells and resulted in a 95-kDa fragment of the cytoplasmic tail of CD45 (ct-CD45). ct-CD45 was released from monocytes and granulocytes upon activation-induced cell death. Binding studies with ct-CD45 revealed a counter-receptor on preactivated T cells. Moreover, T-cell proliferation induced by dendritic cells or CD3 antibodies was inhibited in the presence of ct-CD45. Taken together, the results of our study demonstrate that fragments of the intracellular domain of CD45 from human phagocytes can function as intercellular regulators of T-cell activation.

Bcl10 plays a divergent role in NK cell-mediated cytotoxicity and cytokine generation

Activating receptors such as NKG2D and Ly49D mediate a multitude of effector functions including cytotoxicity and cytokine generation in NK cells. However, specific signaling events that are responsible for the divergence of distinct effector functions have yet to be determined. In this study, we show that lack of caspase recruitment domain-containing protein Bcl10 significantly affected receptor-mediated cytokine and chemokine generation, but not cytotoxicity against tumor cells representing "missing-self" or "induced-self." Lack of Bcl10 completely abrogated the generation of GM-CSF and chemokines and it significantly reduced the generation of IFN-gamma (>75%) in NK cells. Commitment, development, and terminal maturation of NK cells were largely unaffected in the absence of Bcl10. Although IL-2-activated NK cells could mediate cytotoxicity to the full extent, the ability of the freshly isolated NK cells to mediate cytotoxicity was somewhat reduced. Therefore, we conclude that the Carma1-Bcl10-Malt1 signaling axis is critical for cytokine and chemokine generation, although it is dispensable for cytotoxic granule release depending on the activation state of NK cells. These results indicate that Bcl10 represents an exclusive "molecular switch" that links the upstream receptor-mediated signaling to cytokine and chemokine generations.

Tyrosine phosphatases and their possible interplay with tyrosine kinases

Protein tyrosine phosphatases represent a new family of intracellular and receptor-linked enzymes. They are totally specific toward tyrosyl residues in proteins, and, with specific activities 10-1000-fold greater than those of the protein tyrosine kinases, they can be expected to tightly control the level of phosphotyrosine within the cell. Most transmembrane forms contain two conserved intracellular catalytic domains, as displayed by the leukocyte common antigen CD45, but highly variable external segments. Some are related to the neuronal cell adhesion molecules (NCAMs) or fasciclin II and others contain fibronectin III repeats; this suggests that these enzymes might be involved in cell-cell interaction. The intercellular enzymes appear to contain a highly conserved catalytic core linked to a regulatory segment. Deletion of the regulatory domain alters both substrate specificity and cellular localization. Likewise, overexpression of the full-length and truncated enzymes affects cell cycle progression and actin filament stability, respectively. The interplay between tyrosine kinases and phosphatases is considered. A hypothesis is presented suggesting that in some systems phosphatases might act synergistically with the kinases and elicit a physiological response, irrespective of the state of phosphorylation of the target protein.

Regulation of Ly49D/DAP12 Signal Transduction by Src-Family Kinases and CD45

Activating, DAP12-coupled members of the Ly-49 family of NK cell receptors help control viral infections in mice. However, the kinases and/or phosphatases mediating tyrosine phosphorylation of Ly-49D-associated DAP12 have not been elucidated. In this study, we show for the first time that Src family tyrosine kinases are physically and functionally associated with Ly-49D/DAP12 signaling in murine NK cells. Specifically, we demonstrate the following: 1) inhibition of Src family kinases suppresses DAP12 phosphorylation and downstream DAP12 signals; 2) both Fyn and Lck are capable of phosphorylating DAP12; and 3) both kinases coimmunoprecipitate with the Ly-49D/DAP12 complex in NK cells. Although we detect enhanced phosphorylation of Fyn upon Ly-49D cross-linking in NK cells, Ly-49D-mediated events in both Fyn-/- and Fyn/Lck-/- mice appear normal, reinforcing the theme of redundancy in the ability of Src family kinases to initiate activation events. In contrast to disruption of specific Src family enzymes, Ly-49D/DAP12-mediated calcium mobilization and cytokine production by CD45 null NK cells are defective. Although others have ascribed the effects of CD45 mutation solely on the suppression of Src family activity, we demonstrate in this study that DAP12 is hyperphosphorylated in CD45 null NK cells, resulting in uncoordinated tyrosine-mediated signaling upon Ly-49D ligation. Therefore, although our data are consistent with a Src kinase activity proximally within DAP12 signaling, DAP12 also appears to be a substrate of CD45, suggesting a more complex role for this phosphatase than has been reported previously.

Antibody-induced transplantation tolerance that is dependent on thymus-derived regulatory T cells

Targeting of the CD45RB isoform by mAb (anti-CD45RB) effectively induces donor-specific tolerance to allografts. The immunological mechanisms underlying the tolerant state remain unclear although some studies have suggested the involvement of regulatory T cells (T-regs). Although their generative pathway remains undefined, tolerance promoting T-regs induced by systemic anti-CD45RB treatment have been assumed to originate in the peripheral immune system. We demonstrate herein that separable effects on the peripheral and central immune compartments mediate graft survival induced by anti-CD45RB administration. In the absence of the thymus, anti-CD45RB therapy is not tolerogenic though it retains peripheral immunosuppressive activity. The thymus is required for anti-CD45RB to produce indefinite graft survival and donor-specific tolerance, and this effect is accomplished through thymic production of donor-specific T-regs. These data reveal for the first time an Ab-based tolerance regimen that relies on the central tolerance pathway.

Protein tyrosine phosphatases and the immune response

Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism for numerous important aspects of eukaryotic physiology and is catalysed by kinases and phosphatases. Together, cells of the immune system express at least half of the 107 protein tyrosine phosphatase (PTP) genes in the human genome, most of which encode multidomain proteins that contain protein- and phospholipid-interaction domains. Here, we discuss the diverse but specific, and important, roles that PTPs have in immune cells, focusing mainly on T and B cells, and we highlight recent evidence that even subtle alterations in PTPs can cause immune dysfunction and human disease.

Recruitment of intestinal CD45RA+ and CD45RC+ cells induced by a candidate oral vaccine against porcine post-weaning colibacillosis

To assess the influence of a live attenuated oral vaccine against porcine post-weaning colibacillosis (PWC) induced by enterotoxigenic Escherichia coli (ETEC) on mucosal lymphoid cell CD45 isoforms expression, experimental group of weaned pigs (n=6) was immunized orally with F4ac+ non-ETEC strain (day 0) and challenged with F4ac+ ETEC strain 7 days latter. Non-immunized ETEC-infected pigs (n=6) served as control. All pigs were killed on post-challenge day 7. The small intestine was excised for isolation of jejunal lamina propria (JLP) and ileal Peyer's patch (IPP) lymphocytes and immunohistochemical studies. The results obtained by immunophenotyping of isolated cells show that the proportion of CD45RA+ and CD45RC+ JLP, but not IPP, cells were higher in the non-ETEC-immunized ETEC-infected pigs versus non-immunized infected. Additionally, while CD45RA+ JLP cells increased only slightly, the expression of CD45RC isoform on the JLP cells was significantly higher (P< or =0.01) in the experimental than in the control group. The results of the quantitative phenotypic analysis of isolated lymphocytes were not confirmed by immunohistochemical in situ staining. The majority of intestinal immune cells was found to express CD45RA antigen in situ, but no differences were observed between the two groups of weaned pigs neither in CD45RA+ nor in CD45RC+ cells. Our overall evidence indicates that the increased expression of CD45RC isoform was in fact induced in a limited number of JLP T cells in the vaccinated pigs. This was accompanied with the impaired protection of the vaccinated pigs from challenge-induced PWC.

Anti-CD45 isoform antibodies enhance phagocytosis and gene expression of IL-8 and TNF-alpha in human neutrophils by differential suppression on protein tyrosine phosphorylation and p56lck tyrosine kinase

To determine the biological functions of membrane expressed CD45 isoforms on polymorphonuclear neutrophils (PMN), the monoclonal IgG F(ab')2 antibody against CD45, CD45RA or CD45RO was used as surrogate ligand for binding with these molecules on PMN. We found 99.5 +/- 3.2%, 42.3 +/- 5.8% and 96.7 +/- 2.6% PMN expressed CD45, CD45RA and CD45RO molecules on the cell surface, respectively. The interaction of CD45, CD45RA or CD45RO with its specific antibody on PMN enhanced phagocytosis markedly (34-83% increase), mainly via increased expression of complement receptor type 3 (CR3, CD11b) on the cells. The production of IL-8 by PMN was also increased significantly after binding with antibodies (anti-CD45 > anti-CD45RO > anti-CD45RA). Anti-CD45RA and anti-CD45RO, but not anti-CD45, enhanced TNF-alpha mRNA expression and decreased protein tyrosine phosphorylation of PMN. However, only anti-CD45RO suppressed Src family protein tyrosine kinase p56lck expression in the cells. These results suggest that the cross-linking of CD45 isoforms by their specific antibodies stimulated different PMN activities by differential suppression on protein tyrosine phosphorylation and Src family tyrosine kinase p56lck.

Negative regulation of the NFAT1 factor by CD45: implication in HIV-1 long terminal repeat activation

HIV-1 gene regulation is greatly dependent on the presence of the -104/-81 enhancer region which is regulated by both NF-kappaB and NFAT transcription factors. We have found that a greater induction in HIV-1 long terminal repeat-driven gene expression was observed upon PMA/ionomycin (Iono) stimulation of a CD45-deficient cell line (J45.01) in comparison to the parental Jurkat cells. Unlike NF-kappaB which was not affected by the absence of CD45, NFAT showed a much greater augmentation in nuclear translocation and transcriptional activity in J45.01 cells upon PMA/Iono stimulation. PMA/Iono-induced NFAT activation, NFAT translocation and calcium influx peaked at similar time points for both Jurkat and J45.01 cell lines. The NFAT-dependent promoters from the IL-2 and TNF-alpha genes were also more potently activated by PMA/Iono in J45.01 cells. Interestingly, higher levels of intracellular calcium were consistently demonstrated in PMA/Iono-induced CD45-deficient cell lines (J45.01 and HPB45.0). Furthermore, PMA/Iono induction of calcium mobilization in both Jurkat and J45.01 cell lines was observed to be EGTA-sensitive. Mechanistic studies revealed that CD3zeta and ZAP-70 were more heavily tyrosine phosphorylated in J45.01 cells than Jurkat cells. Analysis of the HIV-1 enhancer by EMSAs demonstrated that the bound NFAT complex was present at higher levels in J45.01 nuclear extracts and that the NFAT1 member was predominant. In conclusion, our results indicate that NFAT activation by stimuli acting in a more distal fashion from the TCR-mediated signaling pathway can be down-regulated by CD45 and that this CD45-dependent regulation in turn affects HIV-1 long terminal repeat activation.

Protein tyrosine phosphatases in higher plants

Reversible protein phosphorylation is the most common mechanism for cellular regulation in eukaryotic systems. Indeed, approximately 5% of the Arabidopsis genome encodes protein kinases and phosphatases. Among the thousands of such enzymes, only a small fraction has been examined experimentally. Studies have demonstrated that Ser/Thr phosphorylation and dephosphorylation play a key role in the regulation of plant physiology and development. However, function of tyrosine phosphorylation, despite the overwhelming importance in animals, has not been systematically studied in higher plants. As a result, it is still controversial whether tyrosine phosphorylation is important in plant signal transduction. Recently, the first two protein tyrosine phosphatases (PTPs) from a higher plant were characterized. A diverse group of genes encoding putative PTPs have been identified from the Arabidopsis genome sequence databases. Genetic analyses of various PTPs are underway and preliminary results have provided evidence that these PTPs serve critical functions in plant responses to stress signals and in plant development.

CD45 tyrosine phosphatase controls common gamma-chain cytokine-mediated STAT and extracellular signal-related kinase phosphorylation in activated human lymphoblasts: inhibition of proliferation without induction of apoptosis

The objective of this study was to test whether CD45 signals can influence signaling processes in activated human lymphoblasts. To this end, we generated lymphoblasts which proliferate in response to common gamma-chain cytokines, but readily undergo apoptosis after cytokine withdrawal. In experiments with the CD45R0 mAb UCHL-1, but not control CD45 mAbs, we found significant inhibition of proliferation. Interestingly, the pan-CD45 mAb GAP8.3, which is most effective in inhibition of OKT-3-mediated proliferation in quiescent lymphocytes, was ineffective in lymphoblasts. Addition of CD3 mAb OKT-3 had no influence on IL-2-mediated proliferation (with or without UCHL-1). In contrast, after addition of OKT-3 to IL-4- and IL-7-stimulated proliferation assays, UCHL-1 signals could not significantly alter cellular proliferation. We did not find induction of apoptosis following CD45R0 signaling. In Western blots using mAbs detecting phosphorylated STAT-3, STAT-5, STAT-6, or extracellular signal-related kinase 1/2, we found that CD45R0 signaling could effectively diminish phosphorylation of these intracellular signaling components. Using RT-PCR, we found that CD45R0 signaling inhibited IL-2 mRNA production without major influence on IL-13, IL-5, or IFN-gamma mRNA levels. Costimulation with OKT-3 and IL-2 optimally induced secretion of IFN-gamma, TNF-alpha, and IL-5, which was not decreased by CD45 signals. In conclusion, we illustrate that CD45R0 signals control early cytokine receptor-associated signaling processes and mRNA and DNA synthesis in activated human lymphoblasts. Furthermore, we show the existence of CD45 epitopes (GAP8.3), which are active and critical for signaling in quiescent lymphocytes, but are nonfunctional in activated human lymphoblasts.

Do immune complexes formed with autoantibodies have a role in the maintenance of immune homeostasis through interaction with FC receptors

Natural autoantibodies play an important regulatory role in the maintenance of immune homeostasis. They act as a first line of defense against environmental pathogens like toxins, bacteria and erythrocytes. In humans they are mainly produced by CD5+ B cells that are under the control of a regulatory T cell population. Fc-gamma receptors are involved in antigen recognition and signal transduction and tuning, and some of the members of the FcR family have structural similarity to MHC molecules; they may interact with multiple Ig ligands and with non-Ig ligands. We discuss the interactions between immune-complexes formed with natural autoantibodies and Fc-gamma receptors and suggest that such interactions may affect self-recognition in the thymus and regulate immune homeostasis.

Effects of the protein tyrosine phosphatase CD45 on FcgammaRIIa signaling and neutrophil function

OBJECTIVE

Neutrophil receptors for the Fc portion of IgG (FcgammaR) trigger immune responses following cross-linking by IgG-coated foreign particles or immune complexes. Membrane-associated CD45, a protein tyrosine phosphatase termed leukocyte common antigen, has been shown to be essential for antigen receptor kinase mediated signaling in lymphocytes, and we hypothesized that CD45 may play a similar role in FcgammaR-mediated signaling and immune function in human neutrophils.

METHODS

The experimental approach was that of cell surface molecule ligation via cross-linking with specific antibodies. Antibody dependent cellular cytotoxicity (ADCC) was assessed using a single-cell plaque assay and IL-6 production measured using ELISA. Tyrosine phosphorylation levels were assessed with anti-phospho-tyrosine blots and F-actin polymerization by flow cytometry and confocal microscopy.

RESULTS

Neutrophils pretreated with anti-CD45 had a reduced ability to perform ADCC compared to untreated neutrophils. FcgammaRIIa cross-linking resulted in significantly increased concentrations of secreted IL-6 compared to untreated neutrophils, and IL-6 production was further enhanced by cocross-linking CD45 with FcgammaRIIa. Cross-linking CD45 alone also induced IL-6 production. FcgammaRIIa cross-linking resulted in increased protein tyrosine phosphorylation and F-actin polymerization in neutrophils. Cocross-linking CD45 with FcgammaRIIa resulted in abrogation of FcgammaRIIa mediated tyrosine phosphorylation and F-actin polymerization.

CONCLUSIONS

These data provide evidence that CD45 can regulate or enhance the stimulation and function of human neutrophils mediated through FcgammaR(s). In addition, CD45 ligation may play an essential role in cytokine induction pathways that lead to inflammatory reactions in vivo.

Emerging issues in receptor protein tyrosine phosphatase function: lifting fog or simply shifting?

Transmembrane (receptor) tyrosine phosphatases are intimately involved in responses to cell-cell and cell-matrix contact. Several important issues regarding the targets and regulation of this protein family are now emerging. For example, these phosphatases exhibit complex interactions with signaling pathways involving SRC family kinases, which result from their ability to control phosphorylation of both activating and inhibitory sites in these kinases and possibly also their substrates. Similarly, integrin signaling illustrates how phosphorylation of a single protein, or the activity of a pathway, can be controlled by multiple tyrosine phosphatases, attesting to the intricate integration of these enzymes in cellular regulation. Lastly, we are starting to appreciate the roles of intracellular topology, tyrosine phosphorylation and oligomerization among the many mechanisms regulating tyrosine phosphatase activity.

The role of lipid rafts in T cell antigen receptor (TCR) signalling

Plasma membranes of many cell types contain domains enriched in specific lipids and cholesterol, called lipid rafts. In T lymphocytes, key T cell antigen receptor (TCR) signalling molecules associate with rafts, and disrupting raft-association of certain of these abrogates TCR signalling. The TCR itself associates with lipid rafts, and TCR cross-linking causes aggregation of raft-associated proteins. Furthermore, raft aggregation promotes tyrosine phosphorylation and recruitment of signalling proteins, but excludes the tyrosine phosphatase CD45. Together the data suggest that lipid rafts are important in controlling appropriate protein interactions in resting and activated T cells, and that aggregation of rafts following receptor ligation may be a general mechanism for promoting immune cell signalling.

CD45-induced tumor necrosis factor alpha production in monocytes is phosphatidylinositol 3-kinase-dependent and nuclear factor-kappaB-independent

The pro-inflammatory cytokine tumor necrosis factor (TNF)-alpha plays a pivotal role in the pathogenesis of rheumatoid arthritis. The mechanisms involved in regulating monocyte/macrophage TNFalpha production are not yet fully understood but are thought to involve both soluble factors and cell/cell contact with other cell types. Ligation of certain cell surface receptors, namely CD45, CD44, and CD58, can induce the production of TNFalpha in monocytes. In this paper, we investigate further the signaling pathways utilized by cell surface receptors (specifically CD45) to induce monocyte TNFalpha and compare the common/unique pathways involved with that of lipopolysaccharide. The results indicate that monocyte TNFalpha induced upon CD45 ligation or lipopolysaccharide stimulation is differentially modulated by phosphatidylinositol 3-kinase and nuclear factor-kappaB but similarly regulated by p38 mitogen-activated protein kinase. These results demonstrate that both common and unique signaling pathways are utilized by different stimuli for the induction of TNFalpha. These observations may have a major bearing on approaches to inhibiting TNFalpha production in disease where the cytokine has a pathogenic role.

Aggregation of lipid rafts accompanies signaling via the T cell antigen receptor

The role of lipid rafts in T cell antigen receptor (TCR) signaling was investigated using fluorescence microscopy. Lipid rafts labeled with cholera toxin B subunit (CT-B) and cross-linked into patches displayed characteristics of rafts isolated biochemically, including detergent resistance and colocalization with raft-associated proteins. LCK, LAT, and the TCR all colocalized with lipid patches, although TCR association was sensitive to nonionic detergent. Aggregation of the TCR by anti-CD3 mAb cross-linking also caused coaggregation of raft-associated proteins. However, the protein tyrosine phosphatase CD45 did not colocalize to either CT-B or CD3 patches. Cross-linking of either CD3 or CT-B strongly induced tyrosine phosphorylation and recruitment of a ZAP-70(SH2)(2)-green fluorescent protein (GFP) fusion protein to the lipid patches. Also, CT-B patching induced signaling events analagous to TCR stimulation, with the same dependence on expression of key TCR signaling molecules. Targeting of LCK to rafts was necessary for these events, as a nonraft- associated transmembrane LCK chimera, which did not colocalize with TCR patches, could not reconstitute CT-B-induced signaling. Thus, our results indicate a mechanism whereby TCR engagement promotes aggregation of lipid rafts, which facilitates colocalization of LCK, LAT, and the TCR whilst excluding CD45, thereby triggering protein tyrosine phosphorylation.

CD148, a new membrane tyrosine phosphatase involved in leukocyte function

Protein tyrosine phosphatases play an essential role in the control of leucocyte cell growth an differentiation. Recently a new receptor type membrane tyrosine phosphatase named CD148 has been identified. This molecule is present on the membrane of all the hematopoietic lineages as well as on several other cell types, mainly epithelial cells and its expression increases after cell activation. This molecule is able to act as a transducing molecule. Moreover, CD148 is able to modulate the signal transduction through the TCR/CD3 complex, in a manner similar to CD45. It has also been suggested that CD148 could be involved in mechanisms of differentiation and inhibition of cell growth. In addition, CD148 seems to be associated with a serine/threonine kinase in certain epithelial cell lines and leucocytes. Here, we review recent data on the expression and function of CD148 in both human, mouse and rat.

Eendenburg JDH, Eggermont AMM, Fleuren GJ, Kuppen PJK. The Regulatory Role of CD45 on Rat NK Cells in Target Cell Lysis

To investigate the role of CD45 in rat NK cell function, we developed new mAbs directed against rat CD45. mAb ANK12 binds to a high molecular isoform of CD45 and mAb ANK74 binds to the common part on all known CD45 isoforms, as has been described for the anti-rat CD45 mAb OX1. The ability of these mAbs to affect NK cell-mediated lysis was tested using the Fc receptor-positive target cell line P815. mAb ANK12 was found to significantly enhance the lysis of P815, whereas ANK74 and the anti-CD45 mAb OX1 did not. In addition, cross-linking of the CD45 isoform by ANK12 induced tyrosine phosphorylation of specific proteins in NK cells. Subsequently, the involvement of CD45 in the negative signaling after “self” MHC class I recognition by rat NK cells was investigated. The anti-CD45 mAbs were found to affect NK cell-mediated lysis of syngeneic tumor cell lines, depending upon the expression level of MHC class I on target cells. mAbs ANK74 and OX1 only inhibited lysis of the syngeneic tumor cell lines that expressed low levels of MHC class I. Furthermore, both mAbs caused an inhibition of NK cell-mediated lysis of these tumor cell lines when MHC class I molecules on the tumor cell lines were masked by an Ab. These results suggest that CD45 regulates the inhibitory signal pathway after self MHC class I recognition, supposedly by dephosphorylation of proteins.

CDw150 Associates with Src-Homology 2-Containing Inositol Phosphatase and Modulates CD95-Mediated Apoptosis

CDw150, a receptor up-regulated on activated T or B lymphocytes, has a key role in regulating B cell proliferation. Patients with X-linked lymphoproliferative disease have mutations in a gene encoding a protein, DSHP/SAP, which interacts with CDw150 and is expressed in B cells. Here we show that CDw150 on B cells associates with two tyrosine-phosphorylated proteins, 59 kDa and 145 kDa in size. The 59-kDa protein was identified as the Src-family kinase Fgr. The 145-kDa protein is the inositol polyphosphate 5′-phosphatase, SH2-containing inositol phosphatase (SHIP). Both Fgr and SHIP interact with phosphorylated tyrosines in CDw150’s cytoplasmic tail. Ligation of CDw150 induces the rapid dephosphorylation of both SHIP and CDw150 as well as the association of Lyn and Fgr with SHIP. CD95/Fas-mediated apoptosis is enhanced by signaling via CDw150, and CDw150 ligation can override CD40-induced rescue of CD95-mediated cell death. The ability of CDw150 to regulate cell death does not correlate with serine phosphorylation of the Akt kinase, but does correlate with SHIP tyrosine dephosphorylation. Thus, the CDw150 receptor may function to regulate the fate of activated B cells via SHIP as well as via the DSHP/SAP protein defective in X-linked lymphoproliferative disease patients.

Adoptively transferable tolerance induced by CD45RB monoclonal antibody

The phenomenon of rejection remains the most serious problem in transplantation. The ultimate goal in transplant immunology is to develop therapeutic strategies that lead to tolerance. It has been shown that two injections of a monoclonal antibody to CD45RB leads to indefinite acceptance of renal allografts in mice. Moreover, the CD45RB monoclonal antibody reverses acute rejection and still induces tolerance. The purpose of this study was to assess mechanisms that could underlie this therapeutic benefit. It was shown that splenic lymphocytes from tolerant animals augmented proliferation in allogeneic mixed lymphocyte reactions against donor alloantigens, and the serum of tolerant mice contained donor-specific antibodies, mainly of the IgG1 isotype, suggesting the presence of TH2 cytokines. Tolerance could not be broken by interleukin-2 infusion, but tolerance could be adoptively transferred by transfusion of tolerant mouse CD4+ splenic lymphocytes into naive allografted animals. These data suggest that an active immunoregulatory mechanism is partly responsible for the therapeutic effect. CD45RB-directed therapy may find clinical application in organ transplantation in human patients.

Prevention of experimental allergic encephalomyelitis by an antibody to CD45RB

CD45 is involved in the regulation of lymphocyte activation, and it has been demonstrated that ligation of CD45 induces apoptosis of T and B lymphocytes. Recently anti-CD45RB antibody therapy was shown to block acute allograft rejection in a mouse model of transplantation. Therefore, we wanted to examine the effects of anti-CD45RB antibody treatment on the course of an autoimmune disorder, experimental allergic encephalomyelitis (EAE), a Th1-mediated process. Mice immunized with myelin basic protein and treated with anti-CD45RB antibody did not develop EAE. Histologically, there was no evidence of lymphocytic infiltrates in the central nervous system. T cell proliferation and TNF-alpha production were significantly decreased in anti-CD45RB-treated mice. Furthermore, there was a significant reduction in the production of other Th1 cytokines including interferon-gamma and IL-2, but not IL-4 or IL-6. However, levels of a number of adhesion markers or markers of activation such as VLA-4 and LFA-1 on T cells were no different in treated versus control animals. Thus, anti-CD45RB can prevent EAE and appears to do so by altering T cell proliferation and cytokine production.

CD45 partially mediates heterotypic adhesion between murine leukemia/lymphoma cell line L5178Y and marrow stromal cells

We raised mAbs to whole L5178Y leukemia/lymphoma (LL) cells to identify adhesion proteins involved in adherence between LL cells and marrow stromal cells. One mAb, 4C, and its subclones 4C.1 and 4C.2 inhibited adherence of L5178Y LL cells to MLT. a nontransformed murine marrow stromal cell line. These MoAbs are directed against CD45RA. Control anti-CD45 mAbs and isotype mAbs were non-inhibitory. Other anti-CD45 mAbs, M1/9.3, RA3-3A1/6.1 and RA3-2C2/1 do not compete with mAb 4C.1 for binding to the L5178Y cell surface, but mAb 4C.1 competes for binding of mAb RA3-2C2/1. Effects of mAb 4C on tyrosine-phosphatase activity of CD45 in L5178Y cells are minimal, suggesting direct involvement of CD45 as an adhesion protein.

Epitope-specific signaling through CD45 on T lymphocytes leads to cAMP synthesis in monocytes after ICAM-1-dependent cellular interaction

We recently demonstrated that different CD45 monoclonal antibodies (mAb) are able to induce cellular aggregation in human peripheral blood mononuclear cells (PBMC) through LFA-1/ICAM-1 interactions. Such interactions could be down-modulated by protein kinase (PK) A/G inhibitors, but were unaffected by inhibitors of PKC, suggesting the involvement of PKA or PKG in CD45 mAb-induced adhesion. In this study we show that after incubation of PBMC with several (but not all) mAb to CD45, CD45RO and CD45RA, intracellular cAMP, but not cGMP concentrations readily increase, reaching a maximum 30 min after start of activation. As evidenced by several lines of investigation cAMP accumulation was independent of Fc receptor-associated signaling as well as tyrosine phosphatase activity of CD45. In highly pure T lymphocytes, CD45 mAb were unable to induce cAMP synthesis, but readily did so after addition of autologous monocytes. After paraformaldehyde fixation of both quiescent or IFN-gamma/TNF-alpha-preactivated monocytes, cAMP production was no longer detectable, suggesting monocytes as the cell of origin for the increased cAMP synthesis. Further, cAMP accumulation in monocytes occurred after reconstitution to T lymphocytes preincubated with CD45 mAb and extensively washed. Importantly, pretreatment of T lymphocyte/monocyte mixtures with LFA-1 mAb and/or ICAM-1 mAb down-regulated CD45 mAb-induced cAMP synthesis. Finally, we demonstrate that CD45 mAb are not only capable of inducing cAMP production, but also of directly stimulating PKA enzyme activity. Based on the data presented, we propose that CD45 signaling in T lymphocytes subsequently activates cAMP accumulation and PKA activation in monocytes via LFA-1/ICAM-1-dependent cellular interactions.

Molecular characterization of a tyrosine-specific protein phosphatase encoded by a stress-responsive gene in Arabidopsis

Protein tyrosine kinases and phosphatases play a vital role in the regulation of cell growth and differentiation in animal systems. However, none of these enzymes has been characterized from higher plants. In this study, we isolated a cDNA encoding a putative protein tyrosine phosphatase (PTPase) from Arabidopsis (referred to as AtPTP1). The expression level of AtPTP1 is highly sensitive to environmental stresses. High-salt conditions increased AtPTP1 mRNA levels, whereas cold treatment rapidly eliminated the AtPTP1 transcript. The recombinant AtPTP1 protein specifically hydrolyzed phosphotyrosine, but not phosphoserine/threonine, in protein substrates. Site-directed mutagenesis defined two highly conserved amino acids, cysteine-265 and aspartate-234, as being essential for the phosphatase activity of the AtPTP1 protein, suggesting a common catalytic mechanism for PTPases from all eukaryotic systems. In summary, we have identified AtPTP1 as a tyrosine-specific protein phosphatase that may function in stress responses of higher plants.

CD148 Is a Membrane Protein Tyrosine Phosphatase Present in All Hematopoietic Lineages and Is Involved in Signal Transduction on Lymphocytes

Evidence is presented showing that a protein tyrosine phosphatase different from CD45 is present on the membrane of human hematopoietic cells. The molecule recognized by the monoclonal antibody 143-41, which has been classified as CD148 in the VI International Workshop on Leukocyte Differentiation Antigens, was immunopurified and sequenced. The sequence obtained from N-terminus as well as from two different CNBr-digested peptides showed a close identity with a previously described tyrosine phosphatase named HPTP-η/DEP-1. CD148 is present on all hematopoietic lineages, being expressed with higher intensity on granulocytes than on monocytes and lymphocytes. Interestingly, whereas it is clearly present on peripheral blood lymphocytes, it is poorly expressed on different lymphoid cell lines of T and B origin. When this protein tyrosine phosphatase was cocrosslinked with CD3, an inhibition of the normally observed calcium mobilization was observed. This inhibition correlates with a decrease in phospholipase C-γ (PLC-γ) phosphorylation and is similar to the one observed with CD45. In addition, it is shown that the crosslinking of the CD148 alone is also able to induce an increase in [Ca2+]i. This increase is abolished in the presence of genistein and by cocrosslinking with CD45. These data, together with the induction of tyrosine phosphorylation on several substrates, including PLC-γ, after CD148 crosslinking, suggest the involvement of a tyrosine kinase-based signaling pathway in this process. In conclusion, the data presented show that CD148 corresponds to a previously described protein tyrosine phosphatase HPTP-η/DEP-1 and that this molecule is involved in signal transduction in lymphocytes.

Signalling initiated with CD4-TCR or TCR-TCR interactions: comparison of tyrosine phosphorylation patterns and CD45 effects

Antigen-triggered response in T cells is mediated by the T cell receptor (TCR)/CD3-complex. This signalling, however, is modulated by a number of other surface molecules. Among the most important of these is the CD4/CD8 molecule which associates with the TCR/CD3-complex and binds to the MHC complex. The molecular mechanisms involved in interactions between TCR-TCR and TCR-CD4 are not fully understood. We have earlier described an experimental model that allows us to dissect signals involving CD4-TCR interactions and those involving TCR-TCR interactions using a mouse CD4-CD8- T cell hybridoma cell-line transfected either with the TCR from a mouse T-helper 2 cell-line (D10) alone or with both the TCR and the CD4 molecule. To further characterize these two different modes of signalling in T lymphocytes we have studied the tyrosine phosphorylation patterns resulting from these interactions. In addition, we have studied the modulatory effect of the CD45 molecule on these interactions. In contrast to some earlier reports, we found that both the patterns of induced tyrosine phosphorylation and the effects of CD45 modulation were essentially similar in the CD4-TCR and the TCR-TCR signal transduction cascades. The results are consistent with a purely synergistically amplifying function for CD4 on the TCR-mediated signalling.

The structure and function of CD26 in the T-cell immune response

CD26 is a widely distributed 110 kD cell-surface glycoprotein with known dipeptidyl-peptidase IV (DPP-IV) activity in its extracellular domain. This ecto-enzyme is capable of cleaving amino terminal dipeptides from polypeptides with either L-proline or L-alanine in the penultimate position. On human T cells, CD26 expression appears late in thymic differentiation and is preferentially restricted to the CD4+ helper/memory population, and CD26 can deliver a potent co-stimulatory T-cell activation signal. The cDNA sequence of CD26 predicts a type II membrane protein with only 6 amino acids in its cytoplasmic region, suggesting that, in addition to DPP-IV enzyme activity, other signal-inducing molecules may be associated with CD26. Considerable evidence exists that CD26 interacts, presumably in its extracellular domain, with both CD45, a protein tyrosine phosphatase, and adenosine deaminase (ADA), each of which is capable of functioning in a signal transduction pathway. In addition, CD26 is the receptor for ADA, and ADA on the cell surface is involved in an important immunoregulatory mechanism by which released ADA binds to the cell-surface ADA. This multifunctional molecule may be involved in cell migration and the HIV-1-associated loss of CD4+ cells through the process of programmed cell death. Thus, CD26 appears to play a key role in a number of aspects of lymphocyte function.

Co-localization of Fyn with CD3 complex, CD45 or CD28 depends on different mechanisms

The Src family protein tyrosine kinase Fyn (p59fyn) plays an important role in thymocyte development and T cell receptor (TCR) signal transduction. Fyn has been shown to associate with the TCR-CD3 complex, the protein tyrosine phosphatase CD45 and several co-receptors such as CD28 which are crucial for initiating T cell activation and proliferation. The molecular basis of how Fyn is associated with these transmembrane proteins is largely unknown. To investigate the Fyn association with the TCR-CD3 complex, CD45 and CD28 at the molecular level, various Fyn/beta-galactosidase fusion proteins were constructed and expressed in Jurkat cells. Co-localization experiments applying antibody-induced co-capping and double immunofluorescence staining techniques were used to study the association of these fusion proteins with the TCR-CD3 complex, CD45 and CD28. Our results revealed that co-localization of Fyn with the TCR-CD3 complex requires the unique N terminus whereas co-localization with CD45 depends on the unique N terminus, the Src homology (SH)3- and a functional SH2 domain. CD28 co-localizes with Fyn molecules that contain the N terminus and a functional SH2 domain. These results suggest that Fyn association with the TCR-CD3 complex, CD45 and CD28 is mediated by different molecular mechanisms.

CD148, a membrane protein tyrosine phosphatase, is able to induce tyrosine phosphorylation on human lymphocytes

CD148 is a new cluster of differentiation defined in the VI International Workshop on Leucocyte Differentiation Antigens. It has been identified as the hematopoietic form of a formerly described membrane protein tyrosine phosphatase called HPTP eta/ DEP-1. Previous data have demonstrated that this molecule is able to give rise to [Ca2+]i increase. In the present work we show its capability to induce protein tyrosine phosphorylation in human lymphocytes in spite of its intrinsic protein tyrosine phosphatase activity. The induction of kinase activity suggests the involvement of some protein tyrosine kinase based signaling pathway. The activation of this postulated kinase could be carried out through a direct association or via an adapter molecule.

Regulation of cell signaling by the protein tyrosine phosphatases, CD45 and SHP-1

An equilibrium between positive and negative regulation of immunoreceptor signaling leads to the proper execution of lymphocyte activation. Tyrosine phosphorylation is the initial event in antigen receptor-induced lymphocyte activation. It is generally accepted that protein tyrosine kinases are involved in positive regulation, whereas protein tyrosine phosphatases are important for the negative regulation of tyrosine phosphorylation-dependent processes. However, the interaction between protein tyrosine kinases and protein tyrosine phosphatases is complex. This article discusses the role of two protein tyrosine phosphatases. CD45 and SHP-1, in the regulation of immunoreceptor signaling. SHP-1 acts as a negative regulator for several immunoreceptors, including those for T- and B-cell antigen receptors. The major role of CD45 is in the positive regulation of T- and B-cell antigen receptor signaling.

CD45 isoforms on human CD4+ T-cell subsets

We have examined the level of surface expression and functional properties of leukocyte function associated antigen-1, very late antigen-4, and CD45 isoforms on a panel of human CD4+ T-cell clones representative of TH0, TH1, and TH2 cells. There were no qualitative differences in the expression of these antigens among the three types of CD4+ T-cell clones. However, CD45RB was the only CD45 isoform that provided a costimulatory signal in a solid-phase antibody-induced cellular proliferation assay. Additionally, the antigen-induced proliferative response of T-cell clones was inhibited by soluble anti-CD45RO and anti-CD45RB antibodies. Our results suggest that CD45 isoforms differentially provide costimulatory signals to T cells. However, the ability of each CD45 isoform to provide a costimulatory signal does not differ among the TH0, TH1, or TH2 T-cell populations.

Inhibition of T cell mitogenesis by a novel anti-CD45R monoclonal antibody

CD45 consists of a major family of membrane glycoproteins which have protein tyrosine phosphatase activity and regulate early activation events, progression and maturation signals in leucocytes. Various isoforms of CD45 (Mr 180-240 kDa) regulate sets of intermolecular associations between different surface receptors, and appear to be differentially expressed on B and T cells (namely CD45RA, B or CD45RO). We describe a novel IgG2a mAb directed against restricted and unique CD45R modified epitopes expressed preferentially on peripheral blood T cells. This anti-CD45R antibody (I(2)4c) at concentrations of 50 and 200 ng/mL inhibited mitogenic T cell lectin and anti-CD3-stimulated lymphocyte proliferation and blocked associated IL-2 secretion in vitro. Phorbol ester-stimulated mitogenesis was unaltered suggesting that the inhibition occurs independent of protein kinase C-mediated pathways. Western blotting and immunoprecipitation of purified cell lysates reveals that I(2)4c preferentially binds the higher Mr bands of CD45 expressed on T cells. Following T cell activation in vitro, the 190 kDa band became more predominant and an additional 130 kDa protein, possibly a proteolytic fragment was recognized. I(2)4c may inhibit T cell mitogenesis by direct effects on CD45R alone or by preventing interaction with other membrane-associated proteins and hence adhesive interactions with monocytes. Such interactions may however inhibit the initiation of signal transduction and, as a consequence, alter cellular activation by mitogenic lectins and anti-CD3 in vitro.

Lineage-specific induction of B cell apoptosis and altered signal transduction by the phosphotyrosine phosphatase inhibitor bis(maltolato)oxovanadium(IV)

Protein tyrosine phosphorylation is known to play key roles in lymphocyte signal transduction, and phosphotyrosine phosphatases (PTP) can act as both positive and negative regulators of these lymphocyte signals. We sought to examine the role of PTP further in these processes by characterizing the effects of bis(maltolato)-oxovanadium(IV) (BMLOV), previously known to be a nontoxic insulin mimetic agent in vivo. BMLOV was found to be a potent phosphotyrosine phosphatase inhibitor. BMLOV induced cellular tyrosine phosphorylation in B cells in a pattern similar to that observed following antigen receptor stimulation, whereas little tyrosine phosphorylation was induced in T cells. In B cells, BMLOV treatment resulted in tyrosine phosphorylation of Syk and phospholipase C gamma 2, while sIgM-induced signals were inhibited. By contrast, T cell receptor signals were moderately increased by BMLOV, and the cells displayed greater induction of IL-2 receptor without toxicity. The compound selectively induced apoptosis in B cell lymphoma and myeloid leukemia cell lines, but not in T cell leukemia or colon carcinoma cells. Interleukin-4 plus anti-CD40 antibody treatment of normal human peripheral B cells rescued the cells from BMLOV-induced death. These results suggest that phosphotyrosine phosphatase inhibitors can activate B cell signal pathways in a lineage-specific manner, resulting in desensitization of receptor-mediated signaling and induction of apoptosis.

Gene expressions of protein tyrosine phosphatases in regenerating rat liver and rat ascites hepatoma cells

mRNA levels for ten protein tyrosine phosphatases (PTPs), PTP-S, PTPH1, PTP-1, GLEPP1, LRP, PTP1D, PTPG1, PTP gamma, PTP delta, and LAR, were determined during regeneration of rat liver, and mRNA levels for 5 PTPs, PTP-S, PTP-1, PTP gamma, PTP delta, and LRP, were determined in three lines of rat ascites hepatoma cells. In regenerating rat liver, the expression patterns of PTP genes after partial hepatectomy could be classified into four groups. In group 1 (PTP-S and PTPH1), the mRNA levels increased rapidly, reached a maximum 7 h after partial hepatectomy, remained at a plateau for 1-2 days and then decreased gradually. In group 2 (PTP-1, GLEPP1, and LRP), the mRNA levels showed two peaks on days 1 and 5, and then decreased gradually. In group 3 (PTP1D and PTPG1), the mRNA levels increased rapidly, reached a maximum at 7 h, remained high for several days, and then did not decrease but rather increased after day 7. In group 4 (PTP gamma, PTP delta, and LAR), the mRNA levels remained constant for the first 5 days and increased over the control levels after day 7. In rat ascites hepatomas, gene expression of non-receptor-like PTPs (PTP-S and PTP-1) showed various neoplastic alterations, whereas mRNAs of receptor-like PTPs (PTP gamma, PTP delta, and LRP) were lost or drastically decreased.

Effects of monoclonal antibody against CD45RB on peripheral blood mononuclear cell proliferation and on HLA-DR and adhesion molecule expression on thyrocytes of patients with autoimmune thyroid disease

To evaluate the role of CD45 (especially that of the ectodomain region B) on immunocyte-thyrocyte signaling in patients with autoimmune thyroid disease (AITD), we have examined the in vitro and in vivo effects of a monoclonal antibody (mAb) against with CD45RB, termed MT3. MT3 was added to cultured peripheral blood mononuclear cells (PBMC) from patients with AITD and was additionally injected into severe combined immunodeficient (SCID) mice to which Graves' thyroid cells and intrathyroidal lymphocytes were engrafted. MT3 stimulated proliferation of PBMC when cultured for 2 to 3 days in patients with Hashimoto's thyroiditis (HT) and Graves' disease (GD) and in normal controls (NC). However, when cultured for 7 days, the stimulation index [SI: counts per minute (cpm) with mAb/cpm without mAb] was lowered by MT3 in NC and GD patients. However, the mean SI was not lowered in patients with HT. In SCID mice, the concentrations of human immunoglobulin G, antithyroglobulin and antithyroperoxidase antibodies in sera were not significantly changed by injecting MT3. The expression of human leukocyte antigen (HLA)-DR and intercellular adhesion molecule (ICAM)-1 on engrafted human thyrocytes decreased after the tissues were engrafted into the control mice to which vehicle alone was injected. However, in the mice injected with MT3, HLA-DR and ICAM-1 expression remained high or up-regulated by the injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Tyrosine phosphorylation pathway is involved in interferon-gamma (IFN-gamma) production; effect of sodium ortho vanadate

The molecular mechanisms regulating IFN-gamma production have yet to be well characterized. We describe here how treatment of activated cultures of peripheral blood mononuclear cells (PBMC) with the phosphotyrosine phosphatases (PTP) inhibitor sodium ortho vanadate results in greatly enhanced IFN-gamma production. Conversely, cellular proliferation of the same cultures is profoundly inhibited by treatment with vanadate, while the expression of IL-2R and DR molecules on activated lymphocytes remains substantially unmodified. Increased IFN-gamma production, but not inhibition of cellular proliferation, was also observed in mitogen-activated vanadate-treated Jurkat cells. On the other hand, IFN-gamma production induced in cultures of PBMC treated or not with vanadate, was strongly inhibited by incubation with the protein tyrosine kinase (PTK) inhibitor herbimycin A. As a result of the inhibited phosphatase activity, substrates for PTK become hyperphosphorylated on tyrosine residues, as shown by Western blot analysis of cell lysates from cultures of PBMC treated with vanadate. We suggest that the tyrosine phosphorylation pathway plays a role in regulating IFN-gamma production.