Adding NAD to murine T lymphocytes inhibits their functions and induces annexin V binding. This report shows that NAD induces cell death in a subset of T cells within seconds whereas others do not die until many hours later. Low NAD concentrations (<10 μM) suffice to trigger rapid cell death, which is associated with annexin V binding and membrane pore formation, is not blocked by the caspase inhibitor Z-VADfmk, and requires functional P2X7 receptors. The slower induction of death requires higher NAD concentrations (>100 μM), is blocked by caspase inhibitor Z-VADfmk, is associated with DNA fragmentation, and does not require P2X7 receptors. T cells degrade NAD to ADP-ribose (ADPR), and adding ADPR to T cells leads to slow but not rapid cell death. NAD but not ADPR provides the substrate for ADP-ribosyltransferase (ART-2)-mediated attachment of ADP-ribosyl groups to cell surface proteins; expression of ART-2 is required for NAD to trigger rapid but not slow cell death. These results support the hypothesis that cell surface ART-2 uses NAD but not ADPR to attach ADP-ribosyl groups to the cell surface, and that these groups act as ligands for P2X7 receptors that then induce rapid cell death. Adding either NAD or ADPR also triggers a different set of mechanisms, not requiring ART-2 or P2X7 receptors that more slowly induce cell death.

Routine techniques for the isolation of human peripheral blood mononuclear cells (PBMCs) include density centrifugation with Ficoll-Paque and isolation by cell preparation tubes (CPTs) and SepMate tubes with Lymphoprep. In a series of experiments, these three PBMC isolation techniques were compared for cell recovery and viability, PBMC population composition, and cell functionality, aiming to provide a starting basis for the selection of the most appropriate method of PBMC isolation for a specific downstream application. PBMCs were freshly isolated from venous blood of healthy male donors, applying the different techniques in parallel. Cell recovery and viability were assessed using a hemacytometer and trypan blue. Immunophenotyping was performed by flow cytometry. Cell functionality was assessed in stimulated (100 ng/mL staphylococcal enterotoxin B [SEB]) and unstimulated 24 hours PBMC cultures, with cytokine production and lactate dehydrogenase (LDH) release as readout measures. PBMC isolation by SepMate and CPT resulted in a 70% higher recovery than Ficoll isolation. CPT-isolated populations contained more erythrocyte contamination. Cell viability, assessed by trypan blue exclusion, was 100% for all three isolation techniques. SepMate and CPT isolation gave higher SEB-induced cytokine responses in cell cultures, for IFNγ and for secondary cytokines. IL-6 and IL-8 release in unstimulated cultures was higher for CPT-isolated PBMCs compared to Ficoll- and SepMate-isolated PBMCs. LDH release did not differ between cell isolation techniques. In addition to criteria such as cost and application practicalities, these data may support selection of a specific PBMC isolation technique for downstream analysis.

Glia exhibit differential susceptibility to CD8 T cell mediated effector mechanisms during neurotropic coronavirus infection. In contrast to microglia, oligodendroglia are resistant to CD8 T cell perforin-mediated viral control in the absence of IFN gamma. Kinetic induction of MHC Class I expression by microglia and oligodendroglia in vivo was thus analyzed to assess responses to distinct inflammatory signals. Flow cytometry demonstrated delayed Class I surface expression by oligodendroglia compared with microglia. Distinct kinetics of Class I protein upregulation correlated with cell type specific transcription patterns of genes encoding Class I heavy chains and antigen processing components. Microglia isolated from naïve mice expressed high levels of these mRNAs, whereas they were near detection limits in oligodendroglia; nevertheless, Class I protein was undetectable on both cell types. Infection induced modest mRNA increases in microglia, but dramatic transcriptional upregulation in oligodendroglia coincident with IFN alpha or IFN gamma mRNA increases in infected tissue. Ultimately mRNAs reached similar levels in both cell types at their respective time points of maximal Class I expression. Expression of Class I on microglia, but not oligodendroglia, in infected IFN gamma deficient mice supported distinct IFN requirements for Class I presentation. These data suggest an innate immune preparedness of microglia to present antigen and engage CD8 T cells early following infection. The delayed, yet robust, IFN gamma dependent capacity of oligodendroglia to express Class I suggests strict control of immune interactions to avoid CD8 T cell recognition and potential presentation of autoantigen to preserve myelin maintenance.

Data suggest a two-receptor model for colicin E1 (ColE1) translocation across the outer membrane of Escherichia coli. ColE1 initially binds to the vitamin B 12 receptor BtuB and then translocates through the TolC channel-tunnel, presumably in a mostly unfolded state. Here, we studied the early events in the import of ColE1. Using in vivo approaches, we show that ColE1 is cleaved when added to whole cells. This cleavage requires the presence of the receptor BtuB and the protease OmpT, but not that of TolC. Strains expressing OmpT cleaved ColE1 at K84 and K95 in the N-terminal translocation domain, leading to the removal of the TolQA box, which is essential for ColE1's cytotoxicity. Supported by additional in vivo data, this suggests that a function of OmpT is to degrade colicin at the cell surface and thus protect sensitive E. coli cells from infection by E colicins. A genetic strategy for isolating tolC mutations that confer resistance to ColE1, without affecting other TolC functions, is also described. We provide further in vivo evidence of the multistep interaction between TolC and ColE1 by using cross-linking followed by copurification via histidine-tagged TolC. First, secondary binding of ColE1 to TolC is dependent on primary binding to BtuB. Second, alterations to a residue in the TolC channel interfere with the translocation of ColE1 across the TolC pore rather than with the binding of ColE1 to TolC. In contrast, a substitution at a residue exposed on the cell surface abolishes both binding and translocation of ColE1.

Human in vivo models of systemic inflammation are used to study the physiological mechanisms of inflammation and the effect of drugs and nutrition on the immune response. Although in vivo lipopolysaccharide (LPS) challenges have been applied as methodological tool in clinical pharmacology studies, detailed information is desired on dose-response relationships, especially regarding LPS hyporesponsiveness observed after low-dose in vivo LPS administration. A study was performed to assess the in vivo inflammatory effects of low intravenous LPS doses, and to explore the duration of the induced LPS hyporesponsiveness assessed by subsequent ex vivo LPS challenges. This was a randomized, double-blind, placebo-controlled study with single ascending low doses of LPS (0.5, 1 and 2 ng/kg body weight) administered to healthy male volunteers (3 cohorts of 8 subjects, LPS:placebo 6:2). The in vivo inflammatory response was assessed by measurement of cytokines and CRP. Ex vivo LPS challenges were performed (at −2, 6, 12, 24, 48 and 72 hours relative to in vivo LPS administration) to estimate the duration and magnitude of LPS hyporesponsiveness by assessment of cytokine release (TNF-α, IL-1β, IL-6, IL-8). LPS administration dose-dependently increased body temperature (+1.5°C for 2 ng/kg LPS), heart rate (+28 bpm for 2 ng/kg LPS), CRP and circulating cytokines which showed clearly distinctive increases from placebo already at the lowest LPS dose level tested (0.5 ng/kg, contrast for timeframe 0-6 hours: TNF-α +413%, IL-6 +288%, IL-8 +254%; all p ≤ 0.0001). In vivo LPS administration dose-dependently induced a period of hyporesponsiveness in the ex vivo LPS-induced cytokine release (IL-1β, IL-6 and TNF-α), with maximal hyporesponsiveness observed at 6 hours, lasting no longer than 12 hours. For IL-6 and IL-8, indications for immune cell priming were observed. We demonstrated that an in vivo LPS challenge, with LPS doses as low as 0.5 ng/kg, elicits a cytokine response that is clearly distinctive from baseline cytokine levels. This study expanded the knowledge about the dose-effect relationship of LPS-induced hyporesponsiveness. As such, the low-dose LPS challenge has been demonstrated to be a feasible methodological tool for future clinical studies exploring pharmacological or nutritional immune-modulating effects.