B-cell receptor reactivity against Rothia mucilaginosa in nodular lymphocyte-predominant Hodgkin lymphoma

Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) is a Hodgkin lymphoma expressing functional B-cell receptors (BCR). Recently, we described a dual stimulation model of IgD+ lymphocyte-predominant cells by Moraxella catarrhalis antigen RpoC and its superantigen MID/hag, associated with extralong CDR3 and HLA-DRB1*04 or HLADRB1* 07 haplotype. The aim of the present study was to extend the antigen screening to further bacteria and viruses. The fragment antibody-binding (Fab) regions of seven new and 15 previously reported cases were analyzed. The reactivity of non-Moraxella spp.-reactive Fab regions against lysates of Rothia mucilaginosa was observed in 5/22 (22.7%) cases. Galactofuranosyl transferase (Gltf) and 2,3-butanediol dehydrogenase (Bdh) of R. mucilaginosa were identified by comparative silver- and immuno-staining in two-dimensional gels, with subsequent mass spectrometry and validation by western blots and enzyme-linked immunosorbent assay. Both R. mucilaginosa Gltf and Bdh induced BCR pathway activation and proliferation in vitro. Apoptosis was induced by recombinant Gltf/ETA'-immunotoxin conjugates in DEV cells expressing recombinant R. mucilaginosa-reactive BCR. Reactivity against M. catarrhalis RpoC was confirmed in 3/7 newly expressed BCR (total 10/22 reactive to Moraxella spp.), resulting in 15/22 (68.2%) cases with BCR reactivity against defined bacterial antigens. These findings strengthen the hypothesis of bacterial trigger contributing to subsets of NLPHL.

Identification of molecular candidates which regulate calcium-dependent CD8+ T-cell cytotoxicity

Cytotoxic CD8⁺ T lymphocytes (CTL) eliminate infected cells or transformed tumor cells by releasing perforin-containing cytotoxic granules at the immunological synapse. The secretion of such granules depends on Ca²⁺-influx through store operated Ca²⁺ channels, formed by STIM (stromal interaction molecule)-activated Orai proteins. Whereas molecular mechanisms of the secretion machinery are well understood, much less is known about the molecular machinery that regulates the efficiency of Ca²⁺-dependent target cell killing. CTL killing efficiency is of high interest considering the number of studies on CD8⁺ T lymphocytes modified for clinical use. Here, we isolated total RNA from primary human cells: natural killer (NK) cells, non-stimulated CD8⁺ T-cells, and from Staphylococcus aureus enterotoxin A (SEA) stimulated CD8⁺ T-cells (SEA-CTL) and conducted whole genome expression profiling by microarray experiments. Based on differential expression analysis of the transcriptome data and analysis of master regulator genes, we identified 31 candidates which potentially regulate Ca²⁺-homeostasis in CTL. To investigate a putative function of these candidates in CTL cytotoxicity, we transfected either SEA-stimulated CTL (SEA-CTL) or antigen specific CD8⁺ T-cell clones (CTL-MART-1) with siRNAs specific against the identified candidates and analyzed the killing capacity using a real-time killing assay. In addition, we complemented the analysis by studying the effect of inhibitory substances acting on the candidate proteins if available. Finally, to unmask their involvement in Ca²⁺ dependent cytotoxicity, candidates were also analyzed under Ca²⁺-limiting conditions. Overall, we identified four hits, CCR5 (C-C chemokine receptor type five), KCNN4 (potassium calcium-activated channel subfamily N), RCAN3 (regulator of calcineurin) and BCL (B-cell lymphoma) 2 which clearly affect the efficiency of Ca²⁺ dependent cytotoxicity in CTL-MART-1 cells, CCR5, BCL2, and KCNN4 in a positive manner, and RCAN3 in a negative way.

Interdependence of sequential cytotoxic T lymphocyte and natural killer cell cytotoxicity against melanoma cells

Cytotoxic T lymphocytes (CTL) and natural killer (NK) cells recognize and eliminate cancer cells. However, immune evasion, downregulation of immune function by the tumour microenvironment and resistance of cancer cells are major problems. Although CTL and NK cells are both important to eliminate cancer, most studies address them individually. We quantified sequential primary human CTL and NK cell cytotoxicity against the melanoma cell line SK-Mel-5. At high effector-to-target ratios, NK cells or melan-A (MART-1)-specific CTL eliminated all SK-Mel-5 cells within 24 h, indicating that SK-Mel-5 cells are not resistant initially. However, at lower effector-to-target ratios, which resemble numbers of the immune contexture in human cancer, a substantial number of SK-Mel-5 cells survived. Pre-exposure to CTL induced resistance in surviving SK-Mel-5 cells to subsequent CTL or NK cell cytotoxicity, and pre-exposure to NK cells induced resistance in surviving SK-Mel-5 cells to NK cells. Higher human leucocyte antigen class I expression or interleukin-6 levels were correlated with resistance to NK cells, whereas reduction in MART-1 antigen expression was correlated with reduced CTL cytotoxicity. The CTL cytotoxicity was rescued beyond control levels by exogenous MART-1 antigen. In contrast to the other three combinations, CTL cytotoxicity against SK-Mel-5 cells was enhanced following NK cell pre-exposure. Our assay allows quantification of sequential CTL and NK cell cytotoxicity and might guide strategies for efficient CTL-NK cell anti-melanoma therapies. KEY POINTS: Cytotoxic T lymphocytes (CTL) and natural killer (NK) cells eliminate cancer cells. Both CTL and NK cells attack the same targets, but most studies address them individually. In a sequential cytotoxicity model, the interdependence of antigen-specific CTL and NK cell cytotoxicity against melanoma is quantified. High numbers of antigen-specific CTL and NK cells eliminate all melanoma cells. However, lower numbers induce resistance if secondary CTL or NK cell exposure follows initial CTL exposure or if secondary NK cell exposure follows initial NK cell exposure. On the contrary, if secondary CTL exposure follows initial NK cell exposure, cytotoxicity is enhanced. Alterations in human leucocyte antigen class I expression and interleukin-6 levels are correlated with resistance to NK cells, whereas a reduction in antigen expression is correlated with reduced CTL cytotoxicity; CTL cytotoxicity is rescued beyond control levels by exogenous antigen. This assay and the results on interdependencies will help us to understand and optimize immune therapies against cancer.

B‐cell receptors of EBV‐negative Burkitt lymphoma bind modified isoforms of autoantigens

Burkitt lymphoma (BL) represents the most aggressive B‐cell‐lymphoma. Beside the hallmark of IG‐MYC‐translocation, surface B‐cell receptor (BCR) is expressed, and mutations in the BCR pathway are frequent. Coincidental infections in endemic BL, and specific extra‐nodal sites suggest antigenic triggers. To explore this hypothesis, BCRs of BL cell lines and cases were screened for reactivities against a panel of bacterial lysates, lysates of Plasmodium falciparum, a custom‐made virome array and against self‐antigens, including post‐translationally modified antigens.

An atypically modified, SUMOylated isoform of Bystin, that is, SUMO1‐BYSL was identified as the antigen of the BCR of cell line CA46. SUMO1‐BYSL was exclusively expressed in CA46 cells with K139 as site of the SUMOylation. Secondly, an atypically acetylated isoform of HSP40 was identified as the antigen of the BCR of cell line BL41. K104 and K179 were the sites of immunogenic acetylation, and the acetylated HSP40 isoform was solely present in BL41 cells. Functionally, addition of SUMO1‐BYSL and acetylated HSP40 induced BCR pathway activation in CA46 and BL41 cells, respectively. Accordingly, SUMO1‐BYSL‐ETA’ immunotoxin, produced by a two‐step intein‐based conjugation, led to the specific killing of CA46 cells. Autoantibodies directed against SUMO1‐BYSL were found in 3 of 14 (21.4%), and autoantibodies against acetylated HSP40 in 1/14(7.1%) patients with sporadic Burkitt‐lymphoma. No reactivities against antigens of the infectious agent spectrum could be observed.

These results indicate a pathogenic role of autoreactivity evoked by immunogenic post‐translational modifications in a subgroup of sporadic BL including two EBV‐negative BL cell lines.

Unspecific CTL Killing Is Enhanced by High Glucose via TNF-Related Apoptosis-Inducing Ligand

TNF-related apoptosis inducing ligand (TRAIL) is expressed on cytotoxic T lymphocytes (CTLs) and TRAIL is linked to progression of diabetes. However, the impact of high glucose on TRAIL expression and its related killing function in CTLs still remains largely elusive. Here, we report that TRAIL is substantially up-regulated in CTLs in environments with high glucose (HG) both in vitro and in vivo. Non-mitochondrial reactive oxygen species, NFκB and PI3K/Akt are essential in HG-induced TRAIL upregulation in CTLs. TRAIL^high CTLs induce apoptosis of pancreatic beta cell line 1.4E7. Treatment with metformin and vitamin D reduces HG-enhanced expression of TRAIL in CTLs and coherently protects 1.4E7 cells from TRAIL-mediated apoptosis. Our work suggests that HG-induced TRAIL^high CTLs might contribute to the destruction of pancreatic beta cells in a hyperglycemia condition.

Cytotoxic Efficiency of Human CD8+ T Cell Memory Subtypes

Immunological memory is important to protect humans against recurring diseases. Memory CD8⁺ T cells are required for quick expansion into effector cells but also provide immediate cytotoxicity against their targets. Whereas many functions of the two main cytotoxic subtypes, effector memory CD8⁺ T cells (T_EM) and central memory CD8⁺ T cells (T_CM), are well defined, single T_EM and T_CM cell cytotoxicity has not been quantified. To quantify cytotoxic efficiency of T_EM and T_CM, we developed a FRET-based single cell fluorescent assay with NALM6 target cells which allows analysis of target cell apoptosis, secondary necrosis following apoptosis, and primary necrosis after T_EM- or T_CM-target cell contact. Both, single cell and population cytotoxicity assays reveal a higher cytotoxic efficiency of T_EM compared to T_CM, as quantified by target cell apoptosis and secondary necrosis. Perforin, granzyme B, FasL, but not TRAIL expression are higher in T_EM compared to T_CM. Higher perforin levels (likely in combination with higher granzyme levels) mediate higher cytotoxic efficiency of T_EM compared to T_CM. Both, T_EM and T_CM need the same time to find their targets, however contact time between CTL and target, time to induce apoptosis, and time to induce secondary necrosis are all shorter for T_EM. In addition, immune synapse formation in T_EM appears to be slightly more efficient than in T_CM. Defining and quantifying single T_EM and T_CM cytotoxicity and the respective mechanisms is important to optimize future subset-based immune therapies.

Targeting the Microtubule-Network Rescues CTL Killing Efficiency in Dense 3D Matrices

Efficacy of cytotoxic T lymphocyte (CTL)-based immunotherapy is still unsatisfactory against solid tumors, which are frequently characterized by condensed extracellular matrix. Here, using a unique 3D killing assay, we identify that the killing efficiency of primary human CTLs is substantially impaired in dense collagen matrices. Although the expression of cytotoxic proteins in CTLs remained intact in dense collagen, CTL motility was largely compromised. Using light-sheet microscopy, we found that persistence and velocity of CTL migration was influenced by the stiffness and porosity of the 3D matrix. Notably, 3D CTL velocity was strongly correlated with their nuclear deformability, which was enhanced by disruption of the microtubule network especially in dense matrices. Concomitantly, CTL migration, search efficiency, and killing efficiency in dense collagen were significantly increased in microtubule-perturbed CTLs. In addition, the chemotherapeutically used microtubule inhibitor vinblastine drastically enhanced CTL killing efficiency in dense collagen. Together, our findings suggest targeting the microtubule network as a promising strategy to enhance efficacy of CTL-based immunotherapy against solid tumors, especially stiff solid tumors.

High Glucose Enhances Cytotoxic T Lymphocyte-Mediated Cytotoxicity

Cytotoxic T lymphocytes (CTLs) are key players to eliminate tumorigenic or pathogen-infected cells using lytic granules (LG) and Fas ligand (FasL) pathways. Depletion of glucose leads to severely impaired cytotoxic function of CTLs. However, the impact of excessive glucose on CTL functions still remains largely unknown. Here we used primary human CD8+ T cells, which were stimulated by CD3/CD28 beads and cultured in medium either containing high glucose (HG, 25 mM) or normal glucose (NG, 5.6 mM). We found that in HG-CTLs, glucose uptake and glycolysis were enhanced, whereas proliferation remained unaltered. Furthermore, CTLs cultured in HG exhibited an enhanced CTL killing efficiency compared to their counterparts in NG. Unexpectedly, expression of cytotoxic proteins (perforin, granzyme A, granzyme B and FasL), LG release, cytokine/cytotoxic protein release and CTL migration remained unchanged in HG-cultured CTLs. Interestingly, additional extracellular Ca2+ diminished HG-enhanced CTL killing function. Our findings suggest that in an environment with excessive glucose, CTLs could eliminate target cells more efficiently, at least for a certain period of time, in a Ca2+-dependent manner.

Interorganelle Tethering to Endocytic Organelles Determines Directional Cytokine Transport in CD4+ T Cells

Delivery of vesicles to their desired destinations plays a central role in maintaining proper cell functionality. In certain scenarios, depending on loaded cargos, the vesicles have spatially distinct destinations. For example, in T cells, some cytokines (e.g., IL-2) are polarized to the T cell-target cell interface, whereas the other cytokines are delivered multidirectionally (e.g., TNF-α). In this study, we show that in primary human CD4⁺ T cells, both TNF-α⁺ and IL-2⁺ vesicles can tether with endocytic organelles (lysosomes/late endosomes) by forming membrane contact sites. Tethered cytokine-containing vesicle (CytV)-endocytic organelle pairs are released sequentially. Only endocytic organelle-tethered CytVs are preferentially transported to their desired destination. Mathematical models suggest that endocytic organelle tethering could regulate the direction of cytokine transport by selectively attaching different microtubule motor proteins (such as kinesin and dynein) to the corresponding CytVs. These findings establish the previously unknown interorganelle tethering to endocytic organelles as a universal solution for directional cytokine transport in CD4⁺ T cells. Modulating tethering to endocytic organelles can, therefore, coordinately control directionally distinct cytokine transport.

High glucose distinctively regulates Ca2+ influx in cytotoxic T lymphocytes upon target recognition and thapsigargin stimulation

In CTLs: High glucose-culture enhances thapsigargin-induced SOCE but decreases target recognition-induced Ca²⁺ influx. High glucose-culture regulates expression of ORAIs and STIMs without affecting glucose uptake. More high glucose-cultured CTLs are prone to necrosis after execution of killing.

miR-34a: a new player in the regulation of T cell function by modulation of NF-κB signaling

NF-κB functions as modulator of T cell receptor-mediated signaling and transcriptional regulator of miR-34a. Our in silico analysis revealed that miR-34a impacts the NF-κB signalosome with miR-34a binding sites in 14 key members of the NF-κB signaling pathway. Functional analysis identified five target genes of miR-34a including PLCG1, CD3E, PIK3CB, TAB2, and NFΚBIA. Overexpression of miR-34a in CD4⁺ and CD8⁺ T cells led to a significant decrease of NFΚBIA as the most downstream cytoplasmic NF-κB member, a reduced cell surface abundance of TCRA and CD3E, and to a reduction of T cell killing capacity. Inhibition of miR-34a caused an increase of NFΚBIA, TCRA, and CD3E. Notably, activation of CD4⁺ and CD8⁺ T cells entrails a gradual increase of miR-34a. Our results lend further support to a model with miR-34a as a central NF-κB regulator in T cells.

Quantity, quality, and functionality of peripheral blood cells derived from residual blood of different apheresis kits

BACKGROUND

Research with primary human white blood cell (WBC) subpopulations requires high quantity, quality, and functionality of peripheral blood mononuclear cells (PBMCs) as a source to further characterize cellular subpopulations such as T and B lymphocytes, monocytes, or natural killer cells. Apart from buffy coats derived from whole blood, residual blood from preparative hemapheresis kits are used as a source for PBMCs, but knowledge on the yield and functionality of cells from different devices is limited.

STUDY DESIGN AND METHODS

We evaluated quantity and quality of PBMCs isolated from apheresis kits of two apheresis devices (AMICUS, Fenwal; and Trima Accel, Terumo BCT), the latter being our standard source for many years. PBMCs derived from Trima or AMICUS were tested for yield and subtype composition by flow cytometry. Functionality was assessed by cytokine induction of CD4⁺ and CD8⁺ T cells and by degranulation. Moreover, cytotoxic activity of natural killer cells was quantified by a real-time killing assay.

RESULTS

Mean numbers of isolated cells were 5.5 ± 2.4 × 10⁸ for AMICUS, and 10.3 ± 6.4 × 10⁸ for Trima Accel, respectively. The proportion of WBC subtypes corresponded to well-known numbers from whole blood, with minor differences between the two apheresis systems. Likewise, minor differences in cytokine induction were found in stimulated CD4⁺ or CD8⁺ T cells. Finally, PBMCs derived from the two systems showed comparable cytotoxic activity.

CONCLUSION

PBMC derived from residual blood of the AMICUS and Trima Accel apheresis devices serve as an economic and easily accessible source for functional PBMCs with comparable quantity and quality to PBMCs derived from whole blood.

A calcium optimum for cytotoxic T lymphocyte and natural killer cell cytotoxicity

KEY POINTS

Cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells are required to eliminate cancer cells. We analysed the Ca²⁺ dependence of CTL and NK cell cytotoxicity and found that in particular CTLs have a very low optimum of [Ca²⁺ ]_i (between 122 and 334 nm) and [Ca²⁺ ]_o (between 23 and 625 μm) for efficient cancer cell elimination, well below blood plasma Ca²⁺ levels. As predicted from these results, partial down-regulation of the Ca²⁺ channel Orai1 in CTLs paradoxically increases perforin-dependent cancer cell killing. Lytic granule release at the immune synapse between CTLs and cancer cells has a Ca²⁺ optimum compatible with this low Ca²⁺ optimum for efficient cancer cell killing, whereas the Ca²⁺ optimum for CTL migration is slightly higher and proliferation increases monotonously with increasing [Ca²⁺ ]_o . We propose that a partial inhibition of Ca²⁺ signals by specific Orai1 blockers at submaximal concentrations could contribute to tumour elimination.

ABSTRACT

Cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells are required to protect the human body against cancer. Ca²⁺ is a key metabolic factor for lymphocyte function and cancer homeostasis. We analysed the Ca²⁺ dependence of CTL and NK cell cytotoxicity against cancer cells and found that CTLs have a bell-shaped Ca²⁺ dependence with an optimum for cancer cell elimination at rather low [Ca²⁺ ]_o (23-625 μm) and [Ca²⁺ ]_i (122-334 nm). This finding predicts that a partial inhibition of Orai1 should increase (rather than decrease) cytotoxicity of CTLs at [Ca²⁺ ]_o higher than 625 μm. We tested this hypothesis in CTLs and indeed found that partial down-regulation of Orai1 by siRNA increases the efficiency of cancer cell killing. We found two mechanisms that may account for the Ca²⁺ optimum of cancer cell killing: (1) migration velocity and persistence have a moderate optimum between 500 and 1000 μm [Ca²⁺ ]_o in CTLs, and (2) lytic granule release at the immune synapse between CTLs and cancer cells is increased at 146 μm compared to 3 or 800 μm, compatible with the Ca²⁺ optimum for cancer cell killing. It has been demonstrated in many cancer cell types that Orai1-dependent Ca²⁺ signals enhance proliferation. We propose that a decrease of [Ca²⁺ ]_o or partial inhibition of Orai1 activity by selective blockers in the tumour microenvironment could efficiently reduce cancer growth by simultaneously increasing CTL and NK cell cytotoxicity and decreasing cancer cell proliferation.

Human profilin 1 is a negative regulator of CTL mediated cell-killing and migration

The actin-binding protein profilin1 (PFN1) plays a central role in actin dynamics, which is essential for cytotoxic T lymphocyte (CTL) functions. The functional role of PFN1 in CTLs, however still remains elusive. Here, we identify PFN1 as the only member of the profilin family expressed in primary human CD8⁺ T cells. Using in vitro assays, we find that PFN1 is a negative regulator of CTL-mediated elimination of target cells. Furthermore, PFN1 is involved in activation-induced lytic granule (LG) release, CTL migration and modulation of actin structures at the immunological synapse (IS). During CTL migration, PFN1 modulates the velocity, protrusion formation patterns and protrusion sustainability. In contrast, PFN1 does not significantly affect migration persistence and the rates of protrusion emergence and retraction. Under in vitro conditions mimicking a tumor microenvironment, we show that PFN1 downregulation promotes CTL invasion into a 3D matrix, without affecting the viability of CTLs in a hydrogen peroxide-enriched microenvironment. Highlighting its potential relevance in cancer, we find that in pancreatic cancer patients, PFN1 expression is substantially decreased in peripheral CD8⁺ T cells. Taken together, we conclude that PFN1 is a negative regulator for CTL-mediated cytotoxicity and may have an impact on CTL functionality in a tumor-related context.

Bystander cells enhance NK cytotoxic efficiency by reducing search time

Natural killer (NK) cells play a central role during innate immune responses by eliminating pathogen-infected or tumorigenic cells. In the microenvironment, NK cells encounter not only target cells but also other cell types including non-target bystander cells. The impact of bystander cells on NK killing efficiency is, however, still elusive. In this study we show that the presence of bystander cells, such as P815, monocytes or HUVEC, enhances NK killing efficiency. With bystander cells present, the velocity and persistence of NK cells were increased, whereas the degranulation of lytic granules remained unchanged. Bystander cell-derived H₂O₂ was found to mediate the acceleration of NK cell migration. Using mathematical diffusion models, we confirm that local acceleration of NK cells in the vicinity of bystander cells reduces their search time to locate target cells. In addition, we found that integrin β chains (β1, β2 and β7) on NK cells are required for bystander-enhanced NK migration persistence. In conclusion, we show that acceleration of NK cell migration in the vicinity of H₂O₂-producing bystander cells reduces target cell search time and enhances NK killing efficiency.

Tumor antigen-specific T cells for immune monitoring of dendritic cell-treated glioblastoma patients

BACKGROUND AIMS

CD8(+) T cells are part of the adaptive immune system and, as such, are responsible for the elimination of tumor cells. Dendritic cells (DC) are professional antigen-presenting cells (APC) that activate CD8(+) T cells. Effector CD8(+) T cells in turn mediate the active immunotherapeutic response of DC vaccination against the aggressive glioblastoma (GBM). The lack of tumor response assays complicates the assessment of treatment success in GBM patients.

METHODS

A novel assay to identify specific cytotoxicity of activated T cells by APC was evaluated. Tumor antigen-pulsed DCs from HLA-A*02-positive GBM patients were cultivated to stimulate autologous cytotoxic T lymphocytes (CTL) over a 12-day culture period. To directly correlate antigen specificity and cytotoxic capacity, intracellular interferon (IFN)-γ fluorescence flow cytometry-based measurements were combined with anti-GBM tumor peptide dextramer staining. IFN-γ response was quantified by real-time polymerase chain reaction (PCR), and selected GBM genes were compared with healthy human brain cDNA by single specific primer PCR characterization.

RESULTS

Using CTL of GBM patients stimulated with GBM lysate-pulsed DCs increased IFN-γ messenger RNA levels, and intracellular IFN-γ protein expression was positively correlated with specificity against GBM antigens. Moreover, the GBM peptide-specific CD8(+) T-cell response correlated with specific GBM gene expression. Following DC vaccination, GBM patients showed 10-fold higher tumor-specific signals compared with unvaccinated GBM patients.

DISCUSSION

These data indicate that GBM tumor peptide-dextramer staining of CTL in combination with intracellular IFN-γ staining may be a useful tool to acquire information on whether a specific tumor antigen has the potential to induce an immune response in vivo.

Syntaxin 8 is required for efficient lytic granule trafficking in cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTL) eliminate pathogen-infected and cancerous cells mainly by polarized secretion of lytic granules (LG, containing cytotoxic molecules like perforin and granzymes) at the immunological synapse (IS). Members of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) family are involved in trafficking (generation, transport and fusion) of vesicles at the IS. Syntaxin 8 (Stx8) is expressed in LG and colocalizes with the T cell receptor (TCR) upon IS formation. Here, we report the significance of Stx8 for human CTL cytotoxicity. We found that Stx8 mostly localized in late, recycling endosomal and lysosomal compartments with little expression in early endosomal compartments. Down-regulation of Stx8 by siRNA resulted in reduced cytotoxicity. We found that following perforin release of the pre-existing pool upon target cell contact, Stx8 down-regulated CTL regenerate perforin pools less efficiently and thus release less perforin compared to control CTL. CD107a degranulation, real-time and end-point population cytotoxicity assays, and high resolution microscopy support our conclusion that Stx8 is required for proper and timely sorting and trafficking of cytotoxic molecules to functional LG through the endosomal pathway in human CTL.

A calcium-redox feedback loop controls human monocyte immune responses: The role of ORAI Ca2+ channels

In phagocytes, pathogen recognition is followed by Ca(2+) mobilization and NADPH oxidase 2 (NOX2)-mediated "oxidative burst," which involves the rapid production of large amounts of reactive oxygen species (ROS). We showed that ORAI Ca(2+) channels control store-operated Ca(2+) entry, ROS production, and bacterial killing in primary human monocytes. ROS inactivate ORAI channels that lack an ORAI3 subunit. Staphylococcal infection of mice reduced the expression of the gene encoding the redox-sensitive Orai1 and increased the expression of the gene encoding the redox-insensitive Orai3 in the lungs or in bronchoalveolar lavages. A similar switch from ORAI1 to ORAI3 occurred in primary human monocytes exposed to bacterial peptides in culture. These alterations in ORAI1 and ORAI3 abundance shifted the channel assembly toward a more redox-insensitive configuration. Accordingly, silencing ORAI3 increased the redox sensitivity of the channel and enhanced oxidation-induced inhibition of NOX2. We generated a mathematical model that predicted additional features of the Ca(2+)-redox interplay. Our results identified the ORAI-NOX2 feedback loop as a determinant of monocyte immune responses.

Deep characterization of blood cell miRNomes by NGS

A systematic understanding of different factors influencing cell type specific microRNA profiles is essential for state-of-the art biomarker research. We carried out a comprehensive analysis of the biological variability and changes in cell type pattern over time for different cell types and different isolation approaches in technical replicates. All combinations of the parameters mentioned above have been measured, resulting in 108 miRNA profiles that were evaluated by next-generation-sequencing. The largest miRNA variability was due to inter-individual differences (34 %), followed by the cell types (23.4 %) and the isolation technique (17.2 %). The change over time in cell miRNA composition was moderate (<3 %) being close to the technical variations (<1 %). Largest variability (including technical and biological variance) was observed for CD8 cells while CD3 and CD4 cells showed significantly lower variations. ANOVA highlighted that 51.5 % of all miRNAs were significantly influenced by the purification technique. While CD4 cells were least affected, especially miRNA profiles of CD8 cells were fluctuating depending on the cell purification approach. To provide researchers access to the profiles and to allow further analyses of the tested conditions we implemented a dynamic web resource.

ICRAC controls the rapid androgen response in human primary prostate epithelial cells and is altered in prostate cancer

Labelled 5α-dihydrotestosterone (DHT) binding experiments have shown that expression levels of (yet unidentified) membrane androgen receptors (mAR) are elevated in prostate cancer and correlate with a negative prognosis. However, activation of these receptors which mediate a rapid androgen response can counteract several cancer hallmark functions such as unlimited proliferation, enhanced migration, adhesion and invasion and the inability to induce apoptosis. Here, we investigate the downstream signaling pathways of mAR and identify rapid DHT induced activation of store-operated Ca²⁺ entry (SOCE) in primary cultures of human prostate epithelial cells (hPEC) from non-tumorous tissue. Consequently, down-regulation of Orai1, the main molecular component of Ca²⁺ release-activated Ca²⁺ (CRAC) channels results in an almost complete loss of DHT induced SOCE. We demonstrate that this DHT induced Ca²⁺ influx via Orai1 is important for rapid androgen triggered prostate specific antigen (PSA) release. We furthermore identified alterations of the molecular components of CRAC channels in prostate cancer. Three lines of evidence indicate that prostate cancer cells down-regulate expression of the Orai1 homolog Orai3: First, Orai3 mRNA expression levels are significantly reduced in tumorous tissue when compared to non-tumorous tissue from prostate cancer patients. Second, mRNA expression levels of Orai3 are decreased in prostate cancer cell lines LNCaP and DU145 when compared to hPEC from healthy tissue. Third, the pharmacological profile of CRAC channels in prostate cancer cell lines and hPEC differ and siRNA based knock-down experiments indicate changed Orai3 levels are underlying the altered pharmacological profile. The cancer-specific composition and pharmacology of CRAC channels identifies CRAC channels as putative targets in prostate cancer therapy.

How ORAI and TRP channels interfere with each other: interaction models and examples from the immune system and the skin

Four types of Ca(2+) selective ion channels are known, ten voltage gated Ca(2+) (CaV) channels, four CatSper channels, three store operated CRAC channels (ORAI channels) and at least two members of the TRPV subfamily (TRPV5, TRPV6). Some of the other TRP channels also show some Ca(2+) selectivity like certain splice variants of TRPM3. In addition to Ca(2+) selective channels, various cation channels play an important role for Ca(2+) entry and furthermore, they may also regulate Ca(2+) entry through other channels by modulating the membrane potential or other means as outlined in this review. Of the different types of cation channels, TRP channels form one of the most prominent families of non-selective cation channels with functional relevance in electrically non-excitable and electrically excitable cell types. Among these, the seven channels of the TRPC subfamily are rather non-selective with very modest Ca(2+) selectivity, whereas in the other subfamilies, cation selectivity ranges from monovalent selectivity (i.e. TRPM4, TRPM5) to divalent selectivity (i.e. TRPM6, TRPM7) or Ca(2+) selectivity (i.e. TRPV5, TRPV6). Rather than discussing the heavily reviewed individual functions of ORAI or TRP channels, we summarize data and present models how TRP and ORAI may functionally interact to guide cellular functions. We focus on T lymphocytes representing a more ORAI-dominated tissue and skin as model system in which both ORAI and TRP channel have been reported to control relevant functions. We present several interaction models how ORAI and TRP may interfere with each other's function.

Calcium, cancer and killing: the role of calcium in killing cancer cells by cytotoxic T lymphocytes and natural killer cells

Killing cancer cells by cytotoxic T lymphocytes (CTL) and by natural killer (NK) cells is of vital importance. Cancer cell proliferation and apoptosis depend on the intracellular Ca(2+) concentration, and the expression of numerous ion channels with the ability to control intracellular Ca(2+) concentrations has been correlated with cancer. A rise of intracellular Ca(2+) concentrations is also required for efficient CTL and NK cell function and thus for killing their targets, in this case cancer cells. Here, we review the data on Ca(2+)-dependent killing of cancer cells by CTL and NK cells. In addition, we discuss emerging ideas and present a model how Ca(2+) may be used by CTL and NK cells to optimize their cancer cell killing efficiency. This article is part of a Special Issue entitled: 12th European Symposium on Calcium.

ORAI1 Ca(2+) channels control endothelin-1-induced mitogenesis and melanogenesis in primary human melanocytes

UV radiation of the skin triggers keratinocytes to secrete endothelin-1 (ET-1) that binds to endothelin receptors on neighboring melanocytes. Melanocytes respond with a prolonged increase in intracellular Ca(2+) concentration ([Ca(2+)](i)), which is necessary for proliferation and melanogenesis. A major fraction of the Ca(2+) signal is caused by entry through Ca(2+)-permeable channels of unknown identity in the plasma membrane. ORAI Ca(2+) channels are molecular determinants of Ca(2+) release-activated Ca(2+) (CRAC) channels and are expressed in many tissues. Here, we show that ORAI1-3 and their activating partners stromal interaction molecules 1 and 2 (STIM1 and STIM2) are expressed in human melanocytes. Although ORAI1 is the predominant ORAI isoform, STIM2 mRNA expression exceeds STIM1. Inhibition of ORAI1 by 2-aminoethoxydiphenyl borate (2-APB) or downregulation of ORAI1 by small interfering RNA (siRNA) reduced Ca(2+) entry and CRAC current amplitudes in activated melanocytes. In addition, suppression of ORAI1 caused reduction in the ET-1-induced cellular viability, melanin synthesis, and tyrosinase activity. Our results imply a role for ORAI1 channels in skin pigmentation and their potential involvement in UV-induced stress responses of the human skin.

SNARE protein expression and localization in human cytotoxic T lymphocytes

The major function of cytotoxic T lymphocytes (CTLs) is to eliminate pathogen-infected and tumorigenic cells. This is mediated mainly through the exocytosis of lytic granules (LGs) containing cytotoxic components, such as perforin and granzymes at the immunological synapse (IS). The soluble NSF attachment receptor (SNARE) protein isoforms are well known to be required for vesicle exocytosis in neuronal synapses, but their potential function in CTLs is only partly understood. Here, we examined the expression of SNARE proteins before and after the activation of primary human CD8(+) T cells and determined their co-localization with LGs and CD3 after IS formation with target cells. We found that several key SNARE proteins in neuronal cells were not expressed in CTLs, such as syntaxin1B2 and SNAP-25. Vti1b, Stx8 and Stx16 had the highest degrees of co-localization with LGs while Stx3, Stx4, Stx6, Stx7, Stx8, Stx13, Vti1b, VAMP3 and VAMP4 co-localized with CD3. Our data provide the first complete expression profile and localization of SNAREs in primary human CD8(+) T cells, laying the groundwork for further understanding their potential role in T-cell function.

Docking of lytic granules at the immunological synapse in human CTL requires Vti1b-dependent pairing with CD3 endosomes

Lytic granule (LG)-mediated apoptosis is the main mechanism by which CTL kill virus-infected and tumorigenic target cells. CTL form a tight junction with the target cells, which is called the immunological synapse (IS). To avoid unwanted killing of neighboring cells, exocytosis of lytic granules (LG) is tightly controlled and restricted to the IS. In this study, we show that in activated human primary CD8(+) T cells, docking of LG at the IS requires tethering LG with CD3-containing endosomes (CD3-endo). Combining total internal reflection fluorescence microscopy and fast deconvolution microscopy (both in living cells) with confocal microscopy (in fixed cells), we found that LG and CD3-endo tether and are cotransported to the IS. Paired but not single LG are accumulated at the IS. The dwell time of LG at the IS is substantially enhanced by tethering with CD3-endo, resulting in a preferential release of paired LG over single LG. The SNARE protein Vti1b is required for tethering of LG and CD3-endo. Downregulation of Vti1b reduces tethering of LG with CD3-endo. This leads to an impaired accumulation and docking of LG at the IS and a reduction of target cell killing. Therefore, Vti1b-dependent tethering of LG and CD3-endo determines accumulation, docking, and efficient lytic granule secretion at the IS.

Syntaxin7 is required for lytic granule release from cytotoxic T lymphocytes

SNARE proteins are essential fusion mediators for many intracellular trafficking events. Here, we investigate the role of Syntaxin7 (Stx7) in the release of lytic granules from cytotoxic T lymphocytes (CTLs). We show that Stx7 is expressed in CTLs and is preferentially localized to the region of lytic granule release, the immunological synapse (IS). Interference of Stx7 function by expression of a dominant-negative Stx7 construct or by small interfering RNA leads to a dramatic reduction of CTL-mediated killing of target cells. Real-time visualization of individual lytic granules at the IS by evanescent wave microscopy reveals that lytic granules in Stx7-deprived CTLs not only fail to fuse with the plasma membrane but even fail to accumulate at the IS. Surprisingly, the accumulation defect is not caused by an overall reduction in lytic granule number, but by a defect in the trafficking of T cell receptors (TCRs) through endosomes. Subsequent high-resolution nanoscopy shows that Stx7 colocalizes with Rab7 on late endosomes. We conclude from these data that the accumulation of recycling TCRs at the IS is a SNARE-dependent process and that Stx7-mediated processing of recycling TCRs through endosomes is a prerequisite for the cytolytic function of CTLs.

Differential redox regulation of ORAI ion channels: a mechanism to tune cellular calcium signaling

Reactive oxygen species (ROS) are involved in many physiological and pathophysiological cellular processes. We used lymphocytes, which are exposed to highly oxidizing environments during inflammation, to study the influence of ROS on cellular function. Calcium ion (Ca(2+)) influx through Ca(2+) release-activated Ca(2+) (CRAC) channels composed of proteins of the ORAI family is essential for the activation, proliferation, and differentiation of T lymphocytes, but whether and how ROS affect ORAI channel function have been unclear. Here, we combined Ca(2+) imaging, patch-clamp recordings, and measurements of cell proliferation and cytokine secretion to determine the effects of hydrogen peroxide (H(2)O(2)) on ORAI channel activity and human T helper lymphocyte (T(H) cell) function. ORAI1, but not ORAI3, channels were inhibited by oxidation by H(2)O(2). The differential redox sensitivity of ORAI1 and ORAI3 channels depended mainly on an extracellularly located reactive cysteine, which is absent in ORAI3. T(H) cells became progressively less redox-sensitive after differentiation into effector cells, a shift that would allow them to proliferate, differentiate, and secrete cytokines in oxidizing environments. The decreased redox sensitivity of effector T(H) cells correlated with increased expression of Orai3 and increased abundance of several cytosolic antioxidants. Knockdown of ORAI3 with small-interfering RNA rendered effector T(H) cells more redox-sensitive. The differential expression of Orai isoforms between naïve and effector T(H) cells may tune cellular responses under oxidative stress.

A myosin IK-Abp1-PakB circuit acts as a switch to regulate phagocytosis efficiency

Actin dynamics and myosin (Myo) contractile forces are necessary for formation and closure of the phagocytic cup. In Dictyostelium, the actin-binding protein Abp1 and myosin IK are enriched in the closing cup and especially at an actin-dense constriction furrow formed around the neck of engulfed budded yeasts. This phagocytic furrow consists of concentric overlapping rings of MyoK, Abp1, Arp3, coronin, and myosin II, following an order strikingly reminiscent of the overall organization of the lamellipodium of migrating cells. Mutation analyses of MyoK revealed that both a C-terminal farnesylation membrane anchor and a Gly-Pro-Arg domain that interacts with profilin and Abp1 were necessary for proper localization in the furrow and efficient phagocytosis. Consequently, we measured the binding affinities of these interactions and unraveled further interactions with profilins, dynamin A, and PakB. Due to the redundancy of the interaction network, we hypothesize that MyoK and Abp1 are restricted to regulatory roles and might affect the dynamic of cup progression. Indeed, phagocytic uptake was regulated antagonistically by MyoK and Abp1. MyoK is phosphorylated by PakB and positively regulates phagocytosis, whereas binding of Abp1 negatively regulates PakB and MyoK. We conclude that a MyoK-Abp1-PakB circuit acts as a switch regulating phagocytosis efficiency of large particles.

Efficiency of T-cell costimulation by CD80 and CD86 cross-linking correlates with calcium entry

Costimulation is a fundamental principle of T-cell activation. In addition to T-cell receptor engagement, the interaction between CD80 and/or CD86 with CD28 and/or cytotoxic T-lymphocyte antigen 4 (CTLA-4) receptors is required to regulate T-cell activation and tolerance. While the importance of costimulation is clearly established, the exact molecular mechanism is unknown. We demonstrate that T-cell proliferation and the ability of CD8(+) T-effector cells to kill were enhanced slightly by CD80 but dramatically by CD86 costimulation. To further analyse the cellular process of costimulation, we developed a single-cell assay to analyse Ca(2+) signals following costimulation with bi-specific antibodies. We found that this stimulation method worked in every human T-cell that was analysed, making it one of the most efficient T-cell activation methods to date for primary human T cells. The enhanced proliferation and killing by costimulation was paralleled by an increase of Ca(2+) influx following CD86 costimulation and it was dependent on CD28/CTLA-4 expression. The enhanced Ca(2+) influx following CD86 costimulation was abrogated by an antibody that interfered with CD28 function. The differences in Ca(2+) influx between CD80 and CD86 costimulation were not dependent on the depletion of Ca(2+) stores but were eliminated by the application of 10 mum 2-aminoethyldiphenyl borate which has recently been shown to enhance stromal interaction molecule 2 (STIM2)-dependent Ca(2+) entry while reducing STIM1-dependent Ca(2+) entry. Our data indicate that differences in the efficiency of costimulation are linked to differences in Ca(2+) entry.

T cell receptors mediate docking of cytotoxic granules at the immunological synapse (133.7)

TCR enrichment and cytotoxic granules accumulation at the immunological synapse are necessary for cytotoxic T lymphocyte-mediated killing. Using immunocytochemistry, confocal microscopy, 4D fast live cell imaging and total internal reflection fluorescence microscopy, we analyzed the localization and transport of recycling TCR vesicles and cytotoxic granules in parallel. We found that recycling TCR vesicles are very often connected with cytotoxic granules. Both are co-transported in a paired manner to the IS where recycling TCR enhance the docking and release of cytotoxic granules. Quantitative analysis of vesicluar transport revealed that pairing enables CTL to kill within a few minutes after synapse formation. These data not only highlight an important function of recycling TCR, but also show that pairing of different vesicles is an unexpected mechanism to target vesicles to a defined area within CTL.

This project was funded by the Deutsche Forschungsgemeinschaft (Graduate Research School 1326, DFG grant RE 1092/6-1 to J.R and M.H.) and a HOMFOR grant from the Medical Faculty (to J.R. and M.H).

Calcium dependence of T cell proliferation following focal stimulation

Clonal T cell expansion through proliferation is a central process of the adaptive immune response. Apoptosis of activated T cells is required to avoid chronic inflammation. T cell proliferation and apoptosis are often analyzed with stimuli that do not induce formation of a functional immunological synapse. Here we analyze the Ca(2+) dependence of proliferation and apoptosis in primary human CD4(+) T cells following stimulation with anti-CD3/anti-CD28-coated beads, which induce a tight interaction similar to the immunological synapse. We found this focal stimulation to be much more efficient for stimulating IL-2 production and proliferation than non-focal TCR stimuli. Surprising little Ca(2+) entry through Ca(2+) channels was required for T cell proliferation. Transient free intracellular calcium concentration ([Ca(2+)](i)) elevations of up to 220 nM from a baseline level of around 40 nM were sufficient for maximal proliferation in primary human CD4(+) T cells. We also show that proliferation was very Ca(2+) sensitive in the range 90-120 nM, whereas apoptosis was basically constant for [Ca(2+)](i) levels of 90-120 nM. We conclude that very small changes in [Ca(2+)](i) can dramatically change the ratio between proliferation and apoptosis, thus keeping the balance between overshooting and inefficient immune responses.

T cell activation requires mitochondrial translocation to the immunological synapse

T helper (Th) cell activation is required for the adaptive immune response. Formation of the immunological synapse (IS) between Th cells and antigen-presenting cells is essential for Th cell activation. IS formation induces the polarization and redistribution of many signaling molecules; however, very little is known about organelle redistribution during IS formation in Th cells. We show that formation of the IS induced cytoskeleton-dependent mitochondrial redistribution to the immediate vicinity of the IS. Using total internal reflection microscopy, we found that upon stimulation, the distance between the IS and mitochondria was decreased to values<200 nm. Consequently, mitochondria close to the IS took up more Ca2+ than the ones farther away from the IS. The redistribution of mitochondria to the IS was necessary to maintain Ca2+ influx across the plasma membrane and Ca2+-dependent Th cell activation. Our results suggest that mitochondria are part of the signaling complex at the IS and that their localization close to the IS is required for Th cell activation.

T-cell activation requires mitochondrial translocation towards the immunological synapse (87.32)

Activation of the adaptive immune response requires the interaction between antigen-presenting cells and T-cells. This cell-cell interaction, called the immunological synapse (IS), facilitates the activation of several T-cell receptor (TCR)-mediated signalling cascades including a rise in the cytosolic Ca2+ concentration ([Ca2+]i) through the activation of CRAC/ORAI1 channels. These channels are opened after depletion of intracellular Ca2+ stores and inactivated by the inflowing Ca2+ itself. We show by epifluorescence, 2-photon and total internal reflection microscopy, that a large fraction of mitochondria was moved to the immediate vicinity of the IS, a process highly dependent on the actin cytoskeleton. Mitochondrial movement to the IS was required to sustain the CRAC/ORAI1-mediated Ca2+ influx. Disruption of the actin cytoskeleton prevented mitochondrial movement and subsequent [Ca2+]i rises. The increased [Ca2+]i signals following interaction of the IS with mitochondria correlated with an enhanced T-cell proliferation. Our results show that actin cytoskeleton-mediated movement of mitochondria into the vicinity of the IS is required to sustain Ca2+ influx and permit efficient T-cell activation.

This project was funded by the Deutsche Forschungsgemeinschaft (SFB 530 and GRK 845) and a grant from the Saarland University (HOMFOR).

TRP channels in lymphocytes

TRP proteins form ion channels that are activated following receptor stimulation. Several members of the TRP family are likely to be expressed in lymphocytes. However, in many studies, messenger RNA (mRNA) but not protein expression was analyzed and cell lines but not primary human or murine lymphocytes were used. Among the expressed TRP mRNAs are TRPC1, TRPC3, TRPM2, TRPM4, TRPM7, TRPV1, and TRPV2. Regulation of Ca2+ entry is a key process for lymphocyte activation, and TRP channels may both increase Ca2+ influx (such as TRPC3) or decrease Ca2+ influx through membrane depolarization (such as TRPM4). In the future, linking endogenous Ca2+/cation channels in lymphocytes with TRP proteins should lead to a better molecular understanding of lymphocyte activation.

Sustained Activity of Calcium Release-activated Calcium Channels Requires Translocation of Mitochondria to the Plasma Membrane

A rise of the intracellular Ca(2+) concentration has multiple signaling functions. Sustained Ca(2+) influx across plasma membrane through calcium release-activated calcium (CRAC) channels is required for T-cell development in the thymus, gene transcription, and proliferation and differentiation of naïve T-cells into armed effectors cells. Intracellular Ca(2+) signals are shaped by mitochondria, which function as a highly dynamic Ca(2+) buffer. However, the precise role of mitochondria for Ca(2+)-dependent T-cell activation is unknown. Here we have shown that mitochondria are translocated to the plasma membrane as a consequence of Ca(2+) influx and that this directed movement is essential to sustain Ca(2+) influx through CRAC channels. The decreased distance between mitochondria and the plasma membrane enabled mitochondria to take up large amounts of inflowing Ca(2+) at the plasma membrane, thereby preventing Ca(2+)-dependent inactivation of CRAC channels and sustaining Ca(2+) signals. Inhibition of kinesin-dependent mitochondrial movement along microtubules abolished mitochondrial translocation and reduced sustained Ca(2+) signals. Our results show how a directed movement of mitochondria is used to control important cellular functions such as Ca(2+)-dependent T-cell activation.

TRPV6 potentiates calcium-dependent cell proliferation

The Ca(2+) homeostasis within cells controls a diversity of cellular processes including gene transcription, proliferation and apoptosis. Perturbance of Ca(2+) signaling may induce deregulation of cell proliferation and suppression of cell death providing the basis for cancer development. In human prostate cancer, a correlation between the mRNA expression of the Ca(2+) channel TRPV6 and the staging of the cancer has been described. We have analyzed the influence of TRPV6 on cell proliferation within HEK-293 cells. We show that TRPV6 increases cell proliferation of HEK-293 cells in a Ca(2+) dependent manner. The increased proliferation correlates with slightly increased intracellular Ca(2+) levels without interfering with the intrinsic Ca(2+) dependence of HEK-293 cell proliferation. Low doses of econazole inhibit both, TRPV6 dependent Ca(2+) signals and cell proliferation while BTP2, a potent inhibitor of Ca(2+) signals and cell proliferation in T-cells, neither influences TRPV6 dependent Ca(2+) signals nor cell proliferation of HEK-293 cells. Our data demonstrate that TRPV6 increases the rate of Ca(2+) dependent cell proliferation which is a prerequisite for its potential role in tumor progression.

Calcium-dependent activation of T-lymphocytes

Activation of T-lymphocytes requires stimulation of T-cell receptors (TCR) and co-stimulatory signals. Among different signalling cascades, TCR engagement induces Ca(2+) entry through plasma membrane Ca(2+) channels, which is an indispensable step for T-cells to expand clonally and to acquire effector functions. The Ca(2+) channels are activated by depletion of Ca(2+) stores and are called Ca(2+) release-activated Ca(2+) (CRAC) channels. Ca(2+) influx through CRAC channels is also controlled, directly or indirectly, by K(+) channels, Ca(2+)-ATPases, mitochondria, endoplasmic reticulum and Ca(2+) buffers. We review the functional implications of these transporters, organelles and buffers and develop a model of Ca(2+) signal generation that depends mainly on their relative mutual localization. This model offers the possibility of controlling amplitude and kinetics of Ca(2+) signals in T-cells. Decoding of various Ca(2+) signals allows differential activation of the transcription factor families nuclear factor of activated T-cells (NFAT), nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1). Variation of amplitude and kinetics of Ca(2+) signals thus is an important mechanism for modulating the specificity of T-cell responses.

Ca2+ Signaling in Identified T-lymphocytes from Human Intestinal Mucosa

Ca2+ entry across the plasma membrane is necessary for the activation and proliferation of T-lymphocytes. Human intestinal lamina propria lymphocytes physiologically exhibit minimal proliferation in response to antigen receptor stimulation when compared with peripheral blood T-lymphocytes. This hyporeactivity is partially abolished in inflammatory bowel disease. We hypothesized that differences in Ca2+ signaling could be related to the disease. To test this possibility, we measured Ca2+ signals in identified lymphocytes from human blood and human intestinal mucosa. Ca2+ signals in lamina propria T-lymphocytes from non-inflamed tissue were drastically reduced when compared with Ca2+ signals of blood T-lymphocytes from the same persons. However, Ca2+ signals in T-lymphocytes from inflamed intestinal mucosa were much higher than the ones from non-inflamed mucosa and almost reached levels of Ca2+ signals in peripheral blood T-cells. Furthermore, Ca2+ influx was closely linked to cell proliferation in both peripheral blood T-lymphocytes and lamina propria lymphocytes cells. We conclude that differences in Ca2+ signaling can explain the differences of T-lymphocyte reactivity in blood versus lamina propria and, importantly, also between T-lymphocytes from inflamed and non-inflamed intestinal mucosa. Ca2+ channels in the plasma membrane of T-lymphocytes might thus prove an excellent target to screen for immunosuppressiva to potentially treat the symptoms of inflammatory bowel disease.