Exploring the role of the multiple sclerosis susceptibility gene CLEC16A in T cells

C-type lectin-like domain family 16 member A (CLEC16A) is associated with autoimmune disorders, including multiple sclerosis (MS), but its functional relevance is not completely understood. CLEC16A is expressed in several immune cells, where it affects autophagic processes and receptor expression. Recently, we reported that the risk genotype of an MS-associated single nucleotide polymorphism in CLEC16A intron 19 is associated with higher expression of CLEC16A in CD4⁺ T cells. Here, we show that CLEC16A expression is induced in CD4⁺ T cells upon T cell activation. By the use of imaging flow cytometry and confocal microscopy, we demonstrate that CLEC16A is located in Rab4a-positive recycling endosomes in Jurkat TAg T cells. CLEC16A knock-down in Jurkat cells resulted in lower cell surface expression of the T cell receptor, however, this did not have a major impact on T cell activation response in vitro in Jurkat nor in human, primary CD4⁺ T cells.

Tyr192 Regulates Lymphocyte-Specific Tyrosine Kinase Activity in T Cells

TCR signaling critically depends on the tyrosine kinase Lck (lymphocyte-specific protein tyrosine kinase). Two phosphotyrosines, the activating pTyr³⁹⁴ and the inhibitory pTyr⁵⁰⁵, control Lck activity. Recently, pTyr¹⁹² in the Lck SH2 domain emerged as a third regulator. How pTyr¹⁹² may affect Lck function remains unclear. In this study, we explored the role of Lck Tyr¹⁹² using CRISPR/Cas9-targeted knock-in mutations in the human Jurkat T cell line. Our data reveal that both Lck pTyr³⁹⁴ and pTyr⁵⁰⁵ are controlled by Lck Tyr¹⁹² Lck with a nonphosphorylated SH2 domain (Lck Phe¹⁹²) displayed hyperactivity, possibly by promoting Lck Tyr³⁹⁴ transphosphorylation. Lck Glu¹⁹² mimicking stable Lck pTyr¹⁹² was inhibited by Tyr⁵⁰⁵ hyperphosphorylation. To overcome this effect, we further mutated Tyr⁵⁰⁵ The resulting Lck Glu¹⁹²/Phe⁵⁰⁵ displayed strongly increased amounts of pTyr³⁹⁴ both in resting and activated T cells. Our results suggest that a fundamental role of Lck pTyr¹⁹² may be to protect Lck pTyr³⁹⁴ and/or pTyr⁵⁰⁵ to maintain a pool of already active Lck in resting T cells. This provides an additional mechanism for fine-tuning of Lck as well as T cell activity.

High-throughput analysis of T cell-monocyte interaction in human tuberculosis

The lack of efficient tools for identifying immunological correlates of tuberculosis (TB) protection or risk of disease progression impedes the development of improved control strategies. To more clearly understand the host response in TB, we recently established an imaging flow cytometer‐based in‐vitro assay, which assesses multiple aspects of T cell–monocyte interaction. Here, we extended our previous work and characterized communication between T cells and monocytes using clinical samples from individuals with different TB infection status and healthy controls from a TB endemic setting. To identify T cell–monocyte conjugates, peripheral blood mononuclear cells (PBMC) were stimulated with ds‐Red‐expressing Mycobacterium bovis bacille Calmette–Guérin or 6‐kDa early secreted antigenic target (ESAT 6) peptides for 6 h, and analyzed by imaging flow cytometer (IFC). We then enumerated T cell–monocyte conjugates using polarization of T cell receptor (TCR) and F‐actin as markers for synapse formation, and nuclear factor kappa B (NF‐κB) nuclear translocation in the T cells. We observed a reduced frequency of T cell–monocyte conjugates in cells from patients with active pulmonary tuberculosis (pTB) compared to latent TB‐infected (LTBI) and healthy controls. When we monitored NF‐κB nuclear translocation in T cells interacting with monocytes, the proportion of responding cells was significantly higher in active pTB compared with LTBI and controls. Overall, these data underscore the need to consider multiple immunological parameters against TB, where IFC could be a valuable tool.

In vitro analysis of antigen induced T cell-monocyte conjugates by imaging flow cytometry

There is a lack of suitable correlates of immune protection against Mycobacterium tuberculosis (Mtb) infection. T cells and monocytes play key roles in host immunity against Mtb. Thus, a method that allows assessing their interaction would contribute to the understanding of immune regulation in tuberculosis (TB). We have established imaging flow cytometer (IFC) based in vitro assay for the analysis of early events in T cell-monocyte interaction, upstream of cytokine production and T cell proliferation. This was achieved through short term stimulation of peripheral blood mononuclear cells (PBMC) from healthy Norwegian blood donors with Mycobacterium bovis Bacille Calmette-Guérin (BCG). In our assay, we examined the kinetics of BCG uptake by monocytes using fluorescently labeled BCG and T cell-monocyte interaction based on synapse formation (CD3/TCR polarization). Our results showed that BCG stimulation induced a gradual increase in the proportion of conjugated T cells displaying NF-κB translocation to the nucleus in a time dependent manner, with the highest frequency observed at 6 h. We subsequently tested PBMC from a small cohort of active TB patients (n = 7) and observed a similar BCG induced NF-κB translocation in T cells conjugated with monocytes. The method allowed for simultaneous evaluation of T cell-monocyte conjugates and T cell activation as measured by NF-κB translocation, following short-term challenge of human PBMC with BCG. Whether this novel approach could serve as a diagnostic or prognostic marker needs to be investigated using a wide array of Mtb specific antigens in a larger cohort of patients with different TB infection status.

Retinoic acid-induced IgG production in TLR-activated human primary B cells involves ULK1-mediated autophagy

In the present study we have established a vital role of autophagy in retinoic acid (RA)-induced differentiation of toll-like receptor (TLR)-stimulated human B cells into Ig-secreting cells. Thus, RA enhanced autophagy in TLR9- and CD180-stimulated peripheral blood B cells, as revealed by increased levels of the autophagosomal marker LC3B-II, enhanced colocalization between LC3B and the lysosomal marker Lyso-ID, by a larger percentage of cells with more than 5 characteristic LC3B puncta, and by the concomitant reduction in the level of SQSTM1/p62. Furthermore, RA induced expression of the autophagy-inducing protein ULK1 at the transcriptional level, in a process that required the retinoic acid receptor RAR. By inhibiting autophagy with specific inhibitors or by knocking down ULK1 by siRNA, the RA-stimulated IgG production in TLR9- and CD180-mediated cells was markedly reduced. We propose that the identified prominent role of autophagy in RA-mediated IgG-production in normal human B cells provides a novel mechanism whereby vitamin A exerts its important functions in the immune system.

T cell specific adaptor protein (TSAd) promotes interaction of Nck with Lck and SLP-76 in T cells

Background

The Lck and Src binding adaptor protein TSAd (T cell specific adaptor) regulates actin polymerization in T cells and endothelial cells. The molecular details as to how TSAd regulates this process remain to be elucidated.

Results

To identify novel interaction partners for TSAd, we used a scoring matrix-assisted ligand algorithm (SMALI), and found that the Src homology 2 (SH2) domain of the actin regulator Non-catalytic region of tyrosine kinase adaptor protein (Nck) potentially binds to TSAd phosphorylated on Tyr²⁸⁰ (pTyr²⁸⁰) and pTyr³⁰⁵. These predictions were confirmed by peptide array analysis, showing direct binding of recombinant Nck SH2 to both pTyr²⁸⁰ and pTyr³⁰⁵ on TSAd. In addition, the SH3 domains of Nck interacted with the proline rich region (PRR) of TSAd. Pull-down and immunoprecipitation experiments further confirmed the Nck-TSAd interactions through Nck SH2 and SH3 domains. In line with this Nck and TSAd co-localized in Jurkat cells as assessed by confocal microscopy and imaging flow cytometry. Co-immunoprecipitation experiments in Jurkat TAg cells lacking TSAd revealed that TSAd promotes interaction of Nck with Lck and SLP-76, but not Vav1. TSAd expressing Jurkat cells contained more polymerized actin, an effect dependent on TSAd exon 7, which includes interactions sites for both Nck and Lck.

Conclusions

TSAd binds to and co-localizes with Nck. Expression of TSAd increases both Nck-Lck and Nck-SLP-76 interaction in T cells. Recruitment of Lck and SLP-76 to Nck by TSAd could be one mechanism by which TSAd promotes actin polymerization in activated T cells.

B-cell tolerance to the B-cell receptor variable regions

An enormous number of B cells with different B-cell receptors (BCRs) are continuously produced in the bone marrow. BCRs are further diversified during the germinal center reaction. Due to extensive recirculation, B cells with mutually binding BCR are likely to meet in lymphoid organs. We have addressed possible outcomes of such an encounter in vitro. B lymphoma cells were transfected with complementary BCR, one transfectant expressing an Idiotype⁺ (Id⁺) BCR and the other an anti-Id BCR. To exclude confounding effects of secreted Ig, the transfected B lymphoma cells only expressed membrane IgD. Coincubation of paired Id⁺/anti-Id lymphoma cells results in conjugate formation, signaling, activation of Caspase 3/7, and apoptosis of at least one of the two cells in the pair. Our data provide suggestive evidence for a mechanism whereby the B-cell compartment is partly purged of B cells with complementary BCRs.

A patient-derived stem cell model of hereditary spastic paraplegia with SPAST mutations

Hereditary spastic paraplegia (HSP) leads to progressive gait disturbances with lower limb muscle weakness and spasticity. Mutations in SPAST are a major cause of adult-onset, autosomal-dominant HSP. Spastin, the protein encoded by SPAST, is a microtubule-severing protein that is enriched in the distal axon of corticospinal motor neurons, which degenerate in HSP patients. Animal and cell models have identified functions of spastin and mutated spastin but these models lack the gene dosage, mutation variability and genetic background that characterize patients with the disease. In this study, this genetic variability is encompassed by comparing neural progenitor cells derived from biopsies of the olfactory mucosa from healthy controls with similar cells from HSP patients with SPAST mutations, in order to identify cell functions altered in HSP. Patient-derived cells were similar to control-derived cells in proliferation and multiple metabolic functions but had major dysregulation of gene expression, with 57% of all mRNA transcripts affected, including many associated with microtubule dynamics. Compared to control cells, patient-derived cells had 50% spastin, 50% acetylated α-tubulin and 150% stathmin, a microtubule-destabilizing enzyme. Patient-derived cells were smaller than control cells. They had altered intracellular distributions of peroxisomes and mitochondria and they had slower moving peroxisomes. These results suggest that patient-derived cells might compensate for reduced spastin, but their increased stathmin expression reduced stabilized microtubules and altered organelle trafficking. Sub-nanomolar concentrations of the microtubule-binding drugs, paclitaxel and vinblastine, increased acetylated α-tubulin levels in patient cells to control levels, indicating the utility of this cell model for screening other candidate compounds for drug therapies.

SH2D2A modulates T cell mediated protection to a B cell derived tumor in transgenic mice

Background

T cell specific adapter protein (TSAd), encoded by the SH2D2A gene, modulates signaling downstream of the T cell receptor (TCR). Young, unchallenged SH2D2A-deficient C57BL/6 mice exhibit a relatively normal immune phenotype. To address whether SH2D2A regulates physiologic immune responses, SH2D2A-deficient TCR-transgenic BALB/c mice were generated. The transgenic TCR recognizes a myeloma-derived idiotypic (Id) peptide in the context of the major histocompatibility complex (MHC) class II molecule I-E^d, and confers T cell mediated resistance to transplanted multiple myeloma development in vivo.

Principal Findings

The immune phenotype of SH2D2A-deficient C57BL/6 and BALB/c mice did not reveal major differences compared to the corresponding wild type mice. When challenged with myeloma cells, Id-specific TCR-transgenic BALB/c mice lacking SH2D2A displayed increased resistance towards tumor development. Tumor free TCR-transgenic SH2D2A-deficient mice had higher numbers of Id-specific single positive CD4+ thymocytes compared to TCR-transgenic wild-type mice.

Conclusion

Our results suggest a modulatory role for SH2D2A in T cell mediated immune surveillance of cancer. However, it remains to be established whether its effect is T-cell intrinsic. Further studies are required to determine whether targeting SH2D2A function in T cells may be a potential adjuvant in cancer immunotherapy.

Disease-specific, neurosphere-derived cells as models for brain disorders

There is a pressing need for patient-derived cell models of brain diseases that are relevant and robust enough to produce the large quantities of cells required for molecular and functional analyses. We describe here a new cell model based on patient-derived cells from the human olfactory mucosa, the organ of smell, which regenerates throughout life from neural stem cells. Olfactory mucosa biopsies were obtained from healthy controls and patients with either schizophrenia, a neurodevelopmental psychiatric disorder, or Parkinson's disease, a neurodegenerative disease. Biopsies were dissociated and grown as neurospheres in defined medium. Neurosphere-derived cell lines were grown in serum-containing medium as adherent monolayers and stored frozen. By comparing 42 patient and control cell lines we demonstrated significant disease-specific alterations in gene expression, protein expression and cell function, including dysregulated neurodevelopmental pathways in schizophrenia and dysregulated mitochondrial function, oxidative stress and xenobiotic metabolism in Parkinson's disease. The study has identified new candidate genes and cell pathways for future investigation. Fibroblasts from schizophrenia patients did not show these differences. Olfactory neurosphere-derived cells have many advantages over embryonic stem cells and induced pluripotent stem cells as models for brain diseases. They do not require genetic reprogramming and they can be obtained from adults with complex genetic diseases. They will be useful for understanding disease aetiology, for diagnostics and for drug discovery.

EdU, a new thymidine analogue for labelling proliferating cells in the nervous system

Labelling and identifying proliferating cells is central to understanding neurogenesis and neural lineages in vivo and in vitro. We present here a novel thymidine analogue, ethynyl deoxyuridine (EdU) for labelling dividing cells, detected with a fluorescent azide which forms a covalent bond via the "click" chemistry reaction (the Huisgen 1,3-dipolar cycloaddition reaction of an organic azide to a terminal acetylene). Unlike the commonly used BrdU, EdU detection requires no heat or acid treatment. It is quick and easy and compatible with multiple probes for fluorescence immunochemistry, facilitating the characterisation of proliferating cells at high resolution.

Leaching from organic matter-rich soils by rain of different qualities: I. Concentrations

Soil monoliths from an area exposed to acid precipitation and from an unpolluted area were used in a lysimeter experiment to study effects of different rain qualities on the chemical composition of the leachate from shallow soils rich in organic matter. The vegetation was either dominated by moorgrass [Molinia caerulea (L.) Moench] or heather [Calluna vulgaris (L.) Hull]. The lysimeters received either "acid rain" (pH 4.3) or "normal rain" (pH 5.3). High concentrations of dissolved organic carbon (DOC) were characteristic of the leachate. The different "rain" qualities had no significant influence on the DOC concentration. More DOC was, however, leached from lysimeters with heather vegetation. Roughly 50% of the aluminum (Al) was in complex with organic material and the Al charge was calculated to be between +1.4 and +2.0. Sulfate (SO4(2-)) was the only component that was significantly influenced by the treatment, as more was leached from lysimeters receiving "acid rain." Sulfate was poorly correlated with pH, suggesting that reduced SO4(2-) input would not necessarily lead to reduced acidity. Differences in the pH of the leachate due to the treatments were less than 0.15 pH units. Nitrate (NO3-) was only leached in very low concentrations and of little consequence for the leachate acidity. Some observations do, however, suggest that NO3- may contribute to acidification in episodes with high precipitation. High concentrations of Cl- in the leachate and a significant positive correlation between Cl-, H+, and base cations indicate that sea salt episodes may be important for soil acidification and acidity of the leachate.

Sex differences in relation to conditioned fear-induced enhancement of morphine analgesia

A number of studies have reported that both the immediate and proactive effects of exposure to a shock stressor are less pronounced in female than in male rats. A separate area of research has demonstrated that female rats are less sensitive to the analgesic effects of morphine than males. Experiments from our laboratory, as well as others, have found that exposure to a context associated with shock (i.e., conditioned fear context) at the time of morphine administration, enhances the analgesic effects of morphine. Since previous studies have exclusively employed male rats, the purpose of Experiment 1 was to determine if a sex difference exists to this context conditioned fear-induced enhancement of morphine-induced analgesia. The findings of Experiment 1 showed that females do not appear to exhibit conditioned fear-induced enhancement of morphine analgesia as compared to males. Experiment 2 demonstrated that females exhibited higher levels of conditioned fear-induced enhancement of morphine analgesia during diestrus I than estrous. Experiment 3 demonstrated that females exhibited lower levels of conditioned analgesia compared to males, while both groups exhibited similar freezing levels. The findings of the present experiments suggest that the sex difference observed in Experiment 1 may be due to differences in conditioned analgesia.