[Construction, expression and identification of recombinant plasmid encoding bifunctional protein sflk1-IFN-gamma].

OBJECTIVE: To construct, express and identify the recombinant plasmid pcDNA3.1(+)/sflk1-IFN-gamma encoding bifunctional protein sflk1-IFN-gamma (soluble fetal liver kinase 1 and interferon-gamma). METHODS: sflk1 and IFN-gamma gene fragments were cloned by RT-PCR, and then inserted into pcDNA3.1(+) plasmid between BamHI-EcoRI and XhoI-XbaI restriction sites to form the recombinant plasmid pcDNA3.1(+)/sflk1-IFN-gamma. The recombinant sflk1-IFN-gamma transiently expressed in COS-7 cells was detected by ELISA and Western blotting. Bioactivities of sflk1-IFN-gamma fusion protein were identified by proliferation inhibition assay with H5V cells and NK activity assay. RESULTS: pcDNA3.1(+)/sflk1-IFN-gamma can be effectively expressed in COS-7 cells. Concentrations of sflk1 and IFN-gamma in culture supernatants of pcDNA3.1(+)/sflk1-IFN-gamma transfected COS-7 cells were (20.85+/-2.48) ng/ml and (1.08+/-0.09) ng/ml, respectively. Western blotting showed that the molecular weight of sflk1-IFN-gamma fusion protein was about 130 kDa, while that of sflk1 was 115 kDa. The supernatants of transfected cells significantly inhibited the proliferation of H5V cells stimulated by mouse VEGF 164 and enhanced the NK activity of splenocytes, demonstrating that sflk1-IFN-gamma fusion protein possessed the bioactivities of both sflk1 and IFN-gamma. CONCLUSION: The constructed plasmid pcDNA3.1(+)/sflk1-IFN-gamma can be effectively expressed in eukaryotes. The expressed sflk1-IFN-gamma fusion protein has the biological activities of both sflk1 and IFN-gamma.

Eosinophils from Murine Lamina Propria Induce Differentiation of Naïve T Cells into Regulatory T Cells via TGF-ß1 and Retinoic Acid.

Treg cells play a crucial role in immune tolerance, but mechanisms that induce Treg cells are poorly understood. We here have described eosinophils in lamina propria (LP) that displayed high aldehyde dehydrogenase (ALDH) activity, a rate-limiting step during all-trans retinoic acid (ATRA) synthesis, and expressed TGF-ß1 mRNA and high levels of ATRA. Co-incubation assay confirmed that LP eosinophils induced the differentiation of naïve T cells into Treg cells. Differentiation promoted by LP eosinophils were inhibited by blocked either TGF-ß1 or ATRA. Peripheral blood (PB) eosinophils did not produce ATRA and could not induce Treg differentiation. These data identifies LP eosinophils as effective inducers of Treg cell differentiation through a mechanism dependent on TGF-ß1 and ATRA.

Identification of Leptospira interrogans phospholipase C as a novel virulence factor responsible for intracellular free calcium ion elevation during macrophage death.

BACKGROUND: Leptospira-induced macrophage death has been confirmed to play a crucial role in pathogenesis of leptospirosis, a worldwide zoonotic infectious disease. Intracellular free Ca(2+) concentration ([Ca(2+)]i) elevation induced by infection can cause cell death, but [Ca(2+)]i changes and high [Ca(2+)]i-induced death of macrophages due to infection of Leptospira have not been previously reported. METHODOLOGY/PRINCIPAL FINDINGS: We first used a Ca(2+)-specific fluorescence probe to confirm that the infection of L. interrogans strain Lai triggered a significant increase of [Ca(2+)]i in mouse J774A.1 or human THP-1 macrophages. Laser confocal microscopic examination showed that the [Ca(2+)]i elevation was caused by both extracellular Ca(2+) influx through the purinergic receptor, P2X7, and Ca(2+) release from the endoplasmic reticulum, as seen by suppression of [Ca(2+)]i elevation when receptor-gated calcium channels were blocked or P2X7 was depleted. The LB361 gene product of the spirochete exhibited phosphatidylinositol phospholipase C (L-PI-PLC) activity to hydrolyze phosphatidylinositol-4,5-bisphosphate (PIP2) into inositol-1,4,5-trisphosphate (IP3), which in turn induces intracellular Ca(2+) release from endoplasmic reticulum, with the Km of 199 µM and Kcat of 8.566E-5 S(-1). Secretion of L-PI-PLC from the spirochete into supernatants of leptospire-macrophage co-cultures and cytosol of infected macrophages was also observed by Western Blot assay. Lower [Ca(2+)]i elevation was induced by infection with a LB361-deficient leptospiral mutant, whereas transfection of the LB361 gene caused a mild increase in [Ca(2+)]i. Moreover, PI-PLCs (PI-PLC-ß3 and PI-PLC-γ1) of the two macrophages were activated by phosphorylation during infection. Flow cytometric detection demonstrated that high [Ca(2+)]i increases induced apoptosis and necrosis of macrophages, while mild [Ca(2+)]i elevation only caused apoptosis. CONCLUSIONS/SIGNIFICANCE: This study demonstrated that L. interrogans infection induced [Ca(2+)]i elevation through extracellular Ca(2+) influx and intracellular Ca(2+) release cause macrophage apoptosis and necrosis, and the LB361 gene product was shown to be a novel PI-PLC of L. interrogans responsible for the [Ca(2+)]i elevation.