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

Identification of differences in CD4+ T-cell gene expression between people with asthma and healthy controls

Functional enrichment analysis of genome-wide association study (GWAS)-summary statistics has suggested that CD4+ T-cells play an important role in asthma pathogenesis. Despite this, CD4+ T-cells are under-represented in asthma transcriptome studies. To fill the gap, 3'-RNA-Seq was used to generate gene expression data on CD4+ T-cells (isolated within 2 h from collection) from peripheral blood from participants with well-controlled asthma (n = 32) and healthy controls (n = 11). Weighted Gene Co-expression Network Analysis (WGCNA) was used to identify sets of co-expressed genes (modules) associated with the asthma phenotype. We identified three modules associated with asthma, which are strongly enriched for GWAS-identified asthma genes, antigen processing/presentation and immune response to viral infections. Through integration of publicly available eQTL and GWAS summary statistics (colocalisation), and protein-protein interaction (PPI) data, we identified PTPRC, a potential druggable target, as a putative master regulator of the asthma gene-expression profiles. Using a co-expression network approach, with integration of external genetic and PPI data, we showed that CD4+ T-cells from peripheral blood from asthmatics have different expression profiles, albeit small in magnitude, compared to healthy controls, for sets of genes involved in immune response to viral infections (upregulated) and antigen processing/presentation (downregulated).

Protein Tyrosine Phosphatase CD45 As an Immunity Regulator and a Potential Effector of CAR-T therapy

The leukocyte common antigen CD45 is a receptor tyrosine phosphatase and one of the most prevalent antigens found on the surface of blood cells. CD45 plays a crucial role in the initial stages of signal transmission from receptors of various immune cell types. Immunodeficiency, autoimmune disorders, and oncological diseases are frequently caused by gene expression disorders and imbalances in CD45 isoforms. Despite extensive research into the structure and functions of CD45, the molecular mechanisms behind its role in transmitting signals from T-cell receptors and chimeric antigen receptors remain not fully understood. It is of utmost importance to comprehend the structural features of CD45 and its function in regulating immune system cell activation to study oncological diseases and the impact of CD45 on lymphocytes and T cells modified by chimeric antigen receptors.

Multiplexed Single-Cell Leukocyte Enzymatic Secretion Profiling from Whole Blood Reveals Patient-Specific Immune Signature

Enzymatic secretion of immune cells (leukocytes) plays a dominant role in host immune responses to a myriad of biological triggers, including infections, cancers, and cardiovascular diseases. Current tools to probe these leukocytes inadequately profile these vital biomarkers; the need for sample preprocessing steps of cell lysis, labeling, washing, and pipetting inevitably triggers the cells, changes its basal state, and dilutes the individual cell secretion in bulk assays. Using a fully integrated system for multiplexed profiling of native immune single-cell enzyme secretion from 50 μL of undiluted blood, we eliminate sample handling. With a total analysis time of 60 min, the integrated platform performs six tasks of leukocyte extraction, cell washing, fluorescent enzyme substrate mixing, single-cell droplet making, droplet incubation, and real-time readout for leukocyte secretion profiling of neutrophil elastase, granzyme B, and metalloproteinase. We calibrated the device, optimized the protocols, and tested the leukocyte secretion of acute heart failure (AHF) patients at admission and predischarge. This paper highlights the presence of single-cell enzymatic immune phenotypes independent of CD marker labeling, which could potentially elucidate the innate immune response states. We found that patients recovering from AHF showed a corresponding reduction in immune-cell enzymatic secretion levels and donor-specific enzymatic signatures were observed, which suggests patient-to-patient heterogeneous immune response. This platform presents opportunities to elucidate the complexities of the immune response from a single drop of blood and bridge the current technological, biological, and medical gap in understanding immune response and biological triggers.

Atypical chemokine receptor 1 on nucleated erythroid cells regulates hematopoiesis

Healthy individuals of African ancestry have neutropenia that has been linked with the variant rs2814778(G) of the gene encoding atypical chemokine receptor 1 (ACKR1). This polymorphism selectively abolishes the expression of ACKR1 in erythroid cells, causing a Duffy-negative phenotype. Here we describe an unexpected fundamental role for ACKR1 in hematopoiesis and provide the mechanism that links its absence with neutropenia. Nucleated erythroid cells had high expression of ACKR1, which facilitated their direct contact with hematopoietic stem cells. The absence of erythroid ACKR1 altered mouse hematopoiesis including stem and progenitor cells, which ultimately gave rise to phenotypically distinct neutrophils that readily left the circulation, causing neutropenia. Individuals with a Duffy-negative phenotype developed a distinct profile of neutrophil effector molecules that closely reflected the one observed in the ACKR1-deficient mice. Thus, alternative physiological patterns of hematopoiesis and bone marrow cell outputs depend on the expression of ACKR1 in the erythroid lineage, findings with major implications for the selection advantages that have resulted in the paramount fixation of the ACKR1 rs2814778(G) polymorphism in Africa.

The Biology of CD45 and its Use as a Therapeutic Target

All mature hemopoietic lineage cells, with exclusion of platelets and mature erythrocytes, share the surface expression of a transmembrane phosphatase, the CD45 molecule. It is also present on hemopoietic stem cells and most leukemic clones and therefore presents as an appropriate target for immunotherapy with anti-CD45 antibodies. This short review details the biology of CD45 and its recent targeting for both treatment of malignant disorders and tolerance induction. In particular, the question of potential stem cell depletion for induction of central tolerance or depletion of malignant hemopoietic cells is addressed. Mechanisms underlying the effects downstream of CD45 binding to the cell surface are discussed.

Reduced expression of CD45 protein-tyrosine phosphatase provides protection against anthrax pathogenesis

The modulation of cellular processes by small molecule inhibitors, gene inactivation, or targeted knockdown strategies combined with phenotypic screens are powerful approaches to delineate complex cellular pathways and to identify key players involved in disease pathogenesis. Using chemical genetic screening, we tested a library of known phosphatase inhibitors and identified several compounds that protected Bacillus anthracis infected macrophages from cell death. The most potent compound was assayed against a panel of sixteen different phosphatases of which CD45 was found to be most sensitive to inhibition. Testing of a known CD45 inhibitor and antisense phosphorodiamidate morpholino oligomers targeting CD45 also protected B. anthracis-infected macrophages from cell death. However, reduced CD45 expression did not protect anthrax lethal toxin (LT) treated macrophages, suggesting that the pathogen and independently added LT may signal through distinct pathways. Subsequent, in vivo studies with both gene-targeted knockdown of CD45 and genetically engineered mice expressing reduced levels of CD45 resulted in protection of mice after infection with the virulent Ames B. anthracis. Intermediate levels of CD45 expression were critical for the protection, as mice expressing normal levels of CD45 or disrupted CD45 phosphatase activity or no CD45 all succumbed to this pathogen. Mechanism-based studies suggest that the protection provided by reduced CD45 levels results from regulated immune cell homeostasis that may diminish the impact of apoptosis during the infection. To date, this is the first report demonstrating that reduced levels of host phosphatase CD45 modulate anthrax pathogenesis.

Reactive oxygen and nitrogen species as signaling molecules regulating neutrophil function

As a cornerstone of the innate immune response, neutrophils are the archetypical phagocytic cell; they actively seek out, ingest, and destroy pathogenic microorganisms. To achieve this essential role in host defense, neutrophils deploy a potent antimicrobial arsenal that includes oxidants, proteinases, and antimicrobial peptides. Importantly, oxidants produced by neutrophils, referred to in this article as reactive oxygen (ROS) and reactive nitrogen (RNS) species, have a dual function. On one hand they function as potent antimicrobial agents by virtue of their ability to kill microbial pathogens directly. On the other hand, they participate as signaling molecules that regulate diverse physiological signaling pathways in neutrophils. In the latter role, ROS and RNS serve as modulators of protein and lipid kinases and phosphatases, membrane receptors, ion channels, and transcription factors, including NF-kappaB. The latter regulates expression of key cytokines and chemokines that further modulate the inflammatory response. During the inflammatory response, ROS and RNS modulate phagocytosis, secretion, gene expression, and apoptosis. Under pathological circumstances such as acute lung injury and sepsis, excess production of ROS may influence vicinal cells such as endothelium or epithelium, contributing to inflammatory tissue injury. A better understanding of these pathways will help identify novel targets for amelioration of the untoward effects of inflammation.

CD45 is required for type I IFN production by dendritic cells

CD45 is a leukocyte tyrosine phosphatase, essential for normal immune responses. We have studied the function of splenic dendritic cells of CD45(+/+), CD45(-/-), CD45RABC and CD45RO transgenic mice. We show that there are increased numbers of plasmacytoid dendritic cells in CD45(-/-) mice. DC of all mice are capable of responding to lymphocytic choriomeningitis virus (LCMV) infection by up-regulation of MHC and costimulatory molecules. DC of CD45(-/-) mice have an impaired capacity to produce type I interferons in response to LCMV infection in vivo. These data indicate that lack of CD45 expression in DC has a profound effect on their function. This is largely restored by CD45RABC or CD45RO transgenes.

Flow cytometric expression of common antigens CD18/CD45 in blood from dogs with lymphoid malignancies: A semi-quantitative study

Flow cytometry is useful to study lymphoid malignancies since it allows both immunophenotyping of neoplastic cells and quantification of antigen expression. CD18 and CD45 are commonly exposed membrane antigens with different levels of expression on blood leukocyte and neoplastic cells. The aim of this retrospective study was to semi-quantitatively evaluate the expression of CD18 and CD45 in dogs with different lymphoid malignancies with blood involvement and to compare results with those from healthy dogs and dogs with reactive diseases. Blood samples from 13 dogs with precursor lymphoid malignancies, 20 with mature neoplasms (either chronic lymphocytic leukaemia or lymphoma), of different immunophenotypes, were compared with 24 healthy dogs and 12 dogs with different reactive diseases. The median fluorescence intensity (MFI) for CD18 and CD45 was recorded on lymphoid and granulocytic populations using dual colour flow cytometry, and the ratio between MFI for lymphoid and granulocytic populations (L/N ratio) was calculated to compare the results obtained in different sessions using an internal control (granulocyte fluorescence intensity). Significant decreases in the L/N ratio were detected in neoplastic samples for both CD18 (either precursors or mature versus controls) and CD45 (either precursors or mature versus control), while using MFI only slight differences were detectable in CD45 between precursors and controls. Neoplastic cells often exhibited lower expression of the L/N ratio for CD18, and mainly for CD45, most likely due to a less mature pattern than normal cells and/or to an aberrant quantitative expression of surface antigen. Moreover, more than 50% of neoplastic lymphoid cells exhibited L/N ratios that were not within the values observed in controls for at least one antigen. Altered L/N ratios, in particular decreases of CD45, were mainly observed in precursor neoplasms and in T-cell neoplasms. Detection of altered expression of common antigens, and in particular a L/N ratio for CD45 lower than a value of 103% may be useful as a confirmation of pseudo-clonality thus helping in differentiating reactive and neoplastic lymphocyte expansions.

Altered CD45 expression and disease

CD45, the leucocyte common antigen, is a haemopoietic cell-specific tyrosine phosphatase. Many isoforms are generated by alternative splicing, but their function remains obscure. The extracellular domain of CD45 is highly polymorphic in all vertebrates. Importantly, human polymorphic variants that alter CD45 isoform expression are associated with autoimmune and infectious diseases, establishing CD45 as an important immunomodulator with a significant influence on disease burden. Here, we discuss the new opportunities provided by the human variants for investigating and understanding how CD45 regulates antigen receptor signalling, cytokine responses and apoptosis.

The protein tyrosine phosphatase CD45 is required for interleukin 6 signaling in U266 myeloma cells

The objective of this study was to examine whether CD45 mediates interleukin 6 (IL-6) signaling in human multiple myeloma (MM) cells. We chose U266 MM cells as a study model and isolated cells into CD45+ and CD45- subpopulations. CD45+ and CD45- U266 cells were cocultured with bone marrow stromal cells (BMSCs). IL-6-induced proliferation in CD45+ U266 cells was inhibited by vanadate, a potent protein tyrosine phosphatase inhibitor. However, IL-6-independent CD45- U266 cell growth was not affected by vanadate. CD45+ U266 cells, but not CD45- U266 cells, have the capability of cell adhesion concomitant with actin filament polymerization at the adherent cells. Adhesion of CD45+ U266 cells to BMSCs was impaired by vanadate. We clarified the signaling differences between CD45+ and CD45- U266 cells in response to IL-6. In CD45+ U266 cells, IL-6 increased tyrosine phosphorylation of gp130 and STAT3 and stimulated the level of Mcl-1 protein expression. An association between CD45 and the Src-family protein tyrosine kinase, Lyn, was maintained in the presence of IL-6; the formation of the CD45/Lyn complex was impaired by vanadate. Additionally, IL-6-induced Lyn kinase activity in CD45+ U266 cells was increased by the cross-linking of CD45, and this increase was due to the dephosphorylation of Tyr507 at Lyn. In conclusion, IL-6-dependent MM cells require CD45 to initiate IL-6 signaling and to maintain Lyn kinase activity, both of which are essential for cell proliferation and cell adhesion.

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.