Intracellular Phospho-Flow cytometry reveals novel insights into TCR proximal signaling events. A comparison with Western blot

β2-Adrenergic Receptor Expression and Intracellular Signaling in B Cells Are Highly Dynamic during Collagen-Induced Arthritis

The sympathetic nervous system (SNS) has either a pro-inflammatory or anti-inflammatory effect, depending on the stage of arthritis. In the past, treatment of arthritic B cells with a β2-adrenergic receptor (β2-ADR) agonist has been shown to attenuate arthritis. In this study, the expression and signaling of β2-ADR in B cells during collagen-induced arthritis (CIA) were investigated to provide an explanation of why only B cells from arthritic mice are able to improve CIA. Splenic B cells were isolated via magnetic-activated cell sorting (MACS). Adrenergic receptors on B cells and intracellular β2-ADR downstream molecules (G protein-coupled receptor kinase 2 (GRK-2), β-Arrestin 2, p38 MAPK, extracellular signal-regulated kinase 1/2 (ERK1/2) and cAMP response element-binding protein (CREB)) were analyzed at different time points in naïve and arthritic B cells with and without stimulation of β2-ADR agonist terbutaline by flow cytometry. β2-ADR-expressing B cells increase during CIA without a change in receptor density. Moreover, we observed a profound downregulation of GRK-2 shortly after induction of arthritis and an increase in β-Arrestin 2 only at late stage of arthritis. The second messengers studied (p38, ERK1/2 and CREB) followed a biphasic course, characterized by a reduction at onset and an increase in established arthritis. Stimulation of CIA B cells with the β-ADR agonist terbutaline increased pp38 MAPK independent of the timepoint, while pERK1/2 and pCREB were enhanced only in the late phase of arthritis. The phosphorylation of p38 MAPK, ERK1/2 and CREB in the late phase of arthritis was associated with increased IL-10 produced by B10 cells. The change of β2-ADR expression and signaling during sustained inflammation might be an integral part of the switch from pro- to anti-inflammatory action of sympathetic mechanisms in late arthritis.

The Quest for Anti-α-Synuclein Antibody Specificity-Lessons Learnt From Flow Cytometry Analysis

The accumulation of alpha-synuclein (aSyn) is the hallmark of a group of neurodegenerative conditions termed synucleopathies. Physiological functions of aSyn, including those outside of the CNS, remain elusive. However, a reliable and reproducible evaluation of aSyn protein expression in different cell types and especially in low-expressing cells is impeded by the existence of a huge variety of poorly characterized anti-aSyn antibodies and a lack of a routinely used sensitive detection methods. Here, we developed a robust flow cytometry-based workflow for aSyn detection and antibody validation. We test our workflow using three commercially available antibodies (MJFR1, LB509, and 2A7) in a variety of human cell types, including induced pluripotent stem cells, T lymphocytes, and fibroblasts, and provide a cell- and antibody-specific map for aSyn expression. Strikingly, we demonstrate a previously unobserved unspecificity of the LB509 antibody, while the MJFR1 clone revealed specific aSyn binding however with low sensitivity. On the other hand, we identified an aSyn-specific antibody clone 2A7 with an optimal sensitivity for detecting aSyn in a range of cell types, including those with low aSyn expression. We further utilize our workflow to demonstrate the ability of the 2A7 antibody to distinguish between physiological differences in aSyn expression in neuronal and non-neuronal cells from the cortical organoids, and in neural progenitors and midbrain dopaminergic neurons from healthy controls and in patients with Parkinson's disease who have aSyn gene locus duplication. Our results provide a proof of principle for the use of high-throughput flow cytometry-based analysis of aSyn and highlight the necessity of rigorous aSyn antibody validation to facilitate the research of aSyn physiology and pathology.

Comparison of Acalabrutinib, A Selective Bruton Tyrosine Kinase Inhibitor, with Ibrutinib in Chronic Lymphocytic Leukemia Cells

Purpose: Ibrutinib inhibits Bruton tyrosine kinase (BTK) by irreversibly binding to the Cys-481 residue in the enzyme. However, ibrutinib also inhibits several other enzymes that contain cysteine residues homologous to Cys-481 in BTK. Patients with relapsed/refractory or previously untreated chronic lymphocytic leukemia (CLL) demonstrate a high overall response rate to ibrutinib with prolonged survival. Acalabrutinib, a selective BTK inhibitor developed to minimize off-target activity, has shown promising overall response rates in patients with relapsed/refractory CLL. A head-to-head comparison of ibrutinib and acalabrutinib in CLL cell cultures and healthy T cells is needed to understand preclinical biologic and molecular effects.Experimental Design: Using samples from patients with CLL, we compared the effects of both BTK inhibitors on biologic activity, chemokine production, cell migration, BTK phosphorylation, and downstream signaling in primary CLL lymphocytes and on normal T-cell signaling to determine the effects on other kinases.Results: Both BTK inhibitors induced modest cell death accompanied by cleavage of PARP and caspase-3. Production of CCL3 and CCL4 chemokines and pseudoemperipolesis were inhibited by both drugs to a similar degree. These drugs also showed similar inhibitory effects on the phosphorylation of BTK and downstream S6 and ERK kinases. In contrast, off-target effects on SRC-family kinases were more pronounced with ibrutinib than acalabrutinib in healthy T lymphocytes.Conclusions: Both BTK inhibitors show similar biological and molecular profile in primary CLL cells but appear different on their effect on normal T cells. Clin Cancer Res; 23(14); 3734-43. ©2016 AACR.

IL-10 Production in Macrophages Is Regulated by a TLR-Driven CREB-Mediated Mechanism That Is Linked to Genes Involved in Cell Metabolism

IL-10 is produced by macrophages in diverse immune settings and is critical in limiting immune-mediated pathology. In helminth infections, macrophages are an important source of IL-10; however, the molecular mechanism underpinning production of IL-10 by these cells is poorly characterized. In this study, bone marrow-derived macrophages exposed to excretory/secretory products released by Schistosoma mansoni cercariae rapidly produce IL-10 as a result of MyD88-mediated activation of MEK/ERK/RSK and p38. The phosphorylation of these kinases was triggered by TLR2 and TLR4 and converged on activation of the transcription factor CREB. Following phosphorylation, CREB is recruited to a novel regulatory element in the Il10 promoter and is also responsible for regulating a network of genes involved in metabolic processes, such as glycolysis, the tricarboxylic acid cycle, and oxidative phosphorylation. Moreover, skin-resident tissue macrophages, which encounter S. mansoni excretory/secretory products during infection, are the first monocytes to produce IL-10 in vivo early postinfection with S. mansoni cercariae. The early and rapid release of IL-10 by these cells has the potential to condition the dermal microenvironment encountered by immune cells recruited to this infection site, and we propose a mechanism by which CREB regulates the production of IL-10 by macrophages in the skin, but also has a major effect on their metabolic state.

ZAP-70, CTLA-4 and proximal T cell receptor signaling in cows infected with Mycobacterium avium subsp. paratuberculosis

Paratuberculosis is a chronic intestinal disease of ruminant animals caused by Mycobacterium avium subsp. paratuberculosis (MAP). A hallmark of paratuberculosis is a transition from a cell-mediated Th1 type response to a humoral Th2 response with the progression of disease from a subclinical to clinical state. The objective of this study was to investigate the expression of two crucial molecules in T cell function, ZAP-70 (zeta-chain-associated protein of 70 kDa) and CTLA-4 (cytotoxic T-lymphocyte antigen-4), in cows naturally infected with MAP. Peripheral blood mononuclear cells (PBMCs) isolated from control non-infected cows (n=5), and cows in subclinical (n=6) and clinical stages of paratuberculosis (n=6) were cultured alone (medium only), and with concanavalin A, and a whole cell sonicate of MAP for 24, 72 and 144 h to measure the dynamic changes of ZAP-70 and CTLA-4 expression on CD4, CD8, and gamma delta (γδ) T cells. Flow cytometry was also performed to measure ZAP-70 phosphorylation to examine proximal T cell receptor signaling in animals of different disease status. The surface expression of CTLA-4 was increased in animals in subclinical stage of infection while levels of ZAP-70 were decreased in CD4+ T cells of both subclinical and clinical animals, indicating a change in T cell phenotype with disease state. Interestingly, proximal T cell receptor signaling was not altered in infected animals. This study demonstrated changes in crucial signaling molecules in animals infected with MAP, thereby elucidating T cell alterations associated with disease progression.

Members of the novel UBASH3/STS/TULA family of cellular regulators suppress T-cell-driven inflammatory responses in vivo

The UBASH3/STS/TULA family consists of two members sharing substantial homology and a similar multi-domain architecture, which includes a C-terminal histidine phosphatase domain capable of dephosphorylating phosphotyrosine-containing substrates. TULA-family proteins act as downregulators of receptor-induced activation in several cell types, including T cells and platelets. Deletion of both family members in mice has been shown to result in hyperresponsiveness of T cells to T-cell receptor (TCR)/CD3 complex engagement, but little is known about the biological consequences of double knockout (dKO) and especially of either single KO (sKO). We elucidated the biological consequences of the lack of TULA-family proteins in dKO and TULA and TULA-2 sKO animals. In order to do so, we examined immune responses in Trinitrobenzene sulfonic acid (TNBS)-induced colitis, a mouse model of human inflammatory bowel disease, which is characterized by the involvement of multiple cell types, of which T cells have a crucial role, in the development of a pathological inflammatory condition. Our data indicate that TNBS treatment upregulates T-cell responses in all KO mice studied to a significantly higher degree than in wild-type mice. Although the lack of either TULA-family member exacerbates inflammation and T-cell responses in a specific fashion, the lack of both TULA and TULA-2 in dKO exerts a higher effect than the lack of a single family member in TULA and TULA-2 sKO. Analysis of T-cell responses and TCR-mediated signaling argues that the proteins investigated affect T-cell signaling by regulating phosphorylation of Zap-70, a key protein tyrosine kinase.

Label-free monitoring of T cell activation by the impedance-based xCELLigence system

T cells play a critical role in maintaining the normal function of the adaptive immune response, with their dysfunction resulting in a variety of autoimmune and immunodeficiency diseases. Efficient and accurate detection of T cell function is therefore crucial to clinical diagnosis and development of immunomodulators. A variety of in vitro cellular systems are currently employed for analyzing T cell activation, yet all suffer from some combination of low throughput, unnatural conditions and long assay times. Label-free technologies are capable of detecting phenotypic responses to treatments under physiological conditions, thereby potentially accelerating drug discovery by facilitating the use of disease-relevant cell models for functional assessment and clinical diagnosis. The xCELLigence system is an impedance based label-free platform that allows for dynamic monitoring of subtle morphological and adhesive changes in cells, such as those induced during T cell activation. Here we describe the development and validation of a T cell activation assay based upon electrical impedance. Co-activation of Jurkat cells with anti-CD28 and anti-CD3 functional antibodies led to impedance changes that were rapidly and sensitively recorded (within 30 minutes). This phenomenon was also observed in human peripheral blood mononuclear cells. These changes reflect morphological and adhesive alterations correlated with cytoskeletal reorganization as verified by microscopy. They were functionally dependent on canonical T cell signaling pathways, including calcium-mediated signals and Src family kinases because relevant inhibitors impaired T cell activation. Our results provide a convenient approach to measure T cell activation in real-time and to elucidate the underlying mechanisms of action through probing with small molecules.

NKG2D triggers cytotoxicity in murine epidermal γδ T cells via PI3K-dependent, Syk/ZAP70-independent signaling pathway

Murine epidermal γδ T cells, known as dendritic epidermal T cells (DETCs), survey tissue stress through the invariant T-cell receptor (TCR) and non-clonotypic receptors such as NKG2D. NKG2D signaling via the DAP10-phosphatidylinositol 3-kinase (PI3K) pathway directly stimulates cytotoxicity in natural killer (NK) cells and costimulates CD8(+) T cells to augment TCR signals. In activated murine NK cells, NKG2D signals also via the DAP12-Syk/ZAP70 pathway that triggers both cytotoxicity and cytokine production. It remains controversial whether NKG2D on DETCs is a primary activating receptor or functions only as a costimulatory receptor, and signaling pathways initiated by NKG2D ligation in DETCs have not been analyzed. We show that stimulation of short-term DETC lines with recombinant NKG2D ligands triggers degranulation (exocytosis of cytotoxic granules) via the PI3K-dependent signaling pathway, but does not induce cytokine production or Syk/ZAP70 activation. Coengagement of TCR or Syk/ZAP70 signaling was not crucial for DETC-mediated killing of NKG2D ligand-expressing target cells. Thus, NKG2D can function as a coactivating stress receptor that directly triggers cytotoxicity in DETCs, at least after priming, via the PI3K-dependent, Syk/ZAP70-independent signaling pathway.

The membrane adaptor LAT is proteolytically cleaved following Fas engagement in a tyrosine phosphorylation-dependent fashion

Engagement of the TCR (T-cell receptor) induces tyrosine phosphorylation of the LAT (linker for the activation of T-cells) adaptor, and thereby it recruits several cytosolic mediators for downstream signalling pathways. The Fas protein is essential for T-lymphocyte apoptosis, and following Fas engagement, many proteins are proteolytically cleaved, including several molecules that are important for the transduction of TCR intracellular signals. In the present study, we demonstrate that the adaptor LAT is also subject to a proteolytic cleavage in mature T-lymphocytes and thymocytes in response to Fas engagement, and also on TCR stimulation, and we identify three aspartic acid residues at which LAT is cleaved. Interestingly, these aspartic acid residues are located in proximity to several functionally important tyrosine residues of LAT, raising the possibility that their phosphorylation could modulate LAT cleavage. Consistent with that hypothesis, we show that induction of phosphorylation by pervanadate or H2O2 in Jurkat cells and thymocytes inhibits Fas-mediated cleavage of LAT. Moreover, we show that LAT proteolysis is also enhanced during anergy induction of primary human T-cells, suggesting that LAT cleavage may act as a regulator of TCR-mediated activation of T-cells and not only as a transducer of cell death promoting stimuli.

Antibody constant region peptides can display immunomodulatory activity through activation of the Dectin-1 signalling pathway

We previously reported that a synthetic peptide with sequence identical to a CDR of a mouse monoclonal antibody specific for difucosyl human blood group A exerted an immunomodulatory activity on murine macrophages. It was therapeutic against systemic candidiasis without possessing direct candidacidal properties. Here we demonstrate that a selected peptide, N10K, putatively deriving from the enzymatic cleavage of the constant region (Fc) of human IgG₁, is able to induce IL-6 secretion and pIkB-α activation. More importantly, it causes an up-regulation of Dectin-1 expression. This leads to an increased activation of β-glucan-induced pSyk, CARD9 and pIkB-α, and an increase in the production of pro-inflammatory cytokines such as IL-6, IL-12, IL-1β and TNF-α. The increased activation of this pathway coincides with an augmented phagocytosis of non opsonized Candida albicans cells by monocytes. The findings suggest that some Fc-peptides, potentially deriving from the proteolysis of immunoglobulins, may cause an unexpected immunoregulation in a way reminiscent of innate immunity molecules.

Increased sensitivity to antigen in high avidity CD8(+) T cells results from augmented membrane proximal T-cell receptor signal transduction

The functional avidity of a cytotoxic T lymphocyte (CTL) is known to be a critical determinant of the efficacy with which it clears pathogens. High avidity cells, which are by definition highly sensitive to peptide antigen, are superior for elimination of viruses and tumours. Our studies have established the ability of T cells to undergo avidity modulation as a result of antigen encounter. High and low avidity cells established in this manner exhibit significant differences in the amount of peptide required to elicit effector function. However, how signalling is regulated in these cells as it relates to the control of peptide sensitivity remains to be defined. To address this question, we compared T-cell receptor (TCR) signal transduction events in high and low avidity CTL generated from OT-I(rag2-) TCR transgenic mice. Our data suggest that divergent signalling is initiated at the TCR-associated CD3ζ, with low avidity CTL requiring higher amounts of pMHC to achieve threshold levels of phosphorylated CD3ζ compared with high avidity CTL. Further, this difference is transduced further downstream to mitogen-activated protein kinase and Ca(2+) signalling pathways. These results suggest that regulated control of the initiation of TCR signalling in high versus low avidity cells determines the amount of peptide required for T-cell activation.

Tyramide signal amplification for analysis of kinase activity by intracellular flow cytometry

Intracellular flow cytometry permits quantitation of diverse molecular targets at the single-cell level. However, limitations in detection sensitivity inherently restrict the method, sometimes resulting in the inability to measure proteins of very low abundance or to differentiate cells expressing subtly different protein concentrations. To improve these measurements, an enzymatic amplification approach called tyramide signal amplification (TSA) was optimized for assessment of intracellular kinase cascades. First, Pacific Blue, Pacific Orange, and Alexa Fluor 488 tyramide reporters were shown to exhibit low nonspecific binding in permeabilized cells. Next, the effects of antibody concentration, tyramide concentration, and reaction time on assay resolution were characterized. Use of optimized TSA resulted in a 10-fold or greater improvement in measurement resolution of endogenous Erk and Stat cell signaling pathways relative to standard, nonamplified detection. TSA also enhanced assay sensitivity and, in conjunction with fluorescent cell barcoding, improved assay performance according to a metric used to evaluate high-throughput drug screens. TSA was used to profile Stat1 phosphorylation in primary immune system cells, which revealed heterogeneity in various populations, including CD4+ FoxP3+ regulatory T cells. We anticipate the approach will be broadly applicable to intracellular flow cytometry assays with low signal-to-noise ratios.

Flow cytometric analysis of cell signaling proteins

In recent years, techniques that combine the use of phospho-specific antibodies and multiparameter flow cytometry have been developed for the detection of protein phosphorylation at the single cell level. Flow cytometry is uniquely suited for this type of analysis, as it can measure functional and phenotypic markers in the context of complex cell populations. Phosphorylation can be assessed simultaneously in multiple cell subsets, and due to the small sample sizes required, and the rapid analyses of large numbers of cells in this approach, rare cell analysis is possible without the ex vivo expansion of cells.In this chapter, we detail flow cytometric protocols for the detection of intracellular phospho-proteins in samples derived from whole blood and peripheral blood mononuclear cell preparations. These protocols define steps for cell activation, fixation, permeabilization, and staining by phospho-specific and phenotyping antibodies. We discuss technical difficulties inherent to this technique and suggest solutions to commonly encountered problems. Additionally, we show examples of phospho-protein detection in lymphocyte subsets, dendritic cells, and monocytes activated with various stimuli, including mitogens, cytokines, and superantigens. Finally, we highlight a potential clinical trial application for this flow cytometric assay as a platform for pharmacodynamic monitoring of kinase inhibitors.

Role of CD45 signaling pathway in galactoxylomannan-induced T cell damage

Previously, we reported that Galactoxylomannan (GalXM) activates the extrinsic and intrinsic apoptotic pathways through an interaction with the glycoreceptors on T cells. In this study we establish the role of the glycoreceptor CD45 in GalXM-induced T cell apoptosis, using CD45(+/+) and CD45(-/-) cell lines, derived from BW5147 murine T cell lymphoma. Our results show that whereas CD45 expression is not required for GalXM association by the cells, it is essential for apoptosis induction. In CD45(+/+) cells, CD45 triggering by GalXM reduces the activation of Lck, ZAP70 and Erk1/2. Conversely, in CD45(-/-) cells, Lck was hyperphosphorylated and did not show any modulation after GalXM stimulation. On the whole, our findings provide evidence that the negative regulation of Lck activation occurs via CD45 engagement. This appears to be related to the capacity of GalXM to antagonize T cell activation and induce T cell death. Overall this mechanism may be responsible for the immune paralysis that follows GalXM administration and could explain the powerful immunosuppression that accompanies cryptococcosis.