OBJECTIVETo construct a recombinant plasmid containing Lgeionella pneumophila pilE gene, detect its expression in NIH3T3 cells and evaluate its immunogenicity.

METHODSPilE gene (LP) was amplified from Legionella pneumophila DNA by PCR and inserted into pcDNA3.1(+) vector to construct the recombinant plasmid pcDNA3.1-pilE, which as verified by restriction endonuclease digestion, PCR and DNA sequencing analysis. NIH3T3 cells were transfected with the recombinant plasmid with Lipofection strategy. Transient and stable pilE gene products were detected by immunofluorescence and Western blotting, respectively. To evaluate the immunogenicity of pcDNA3.1-pilE, the recombinant plasmid was used as a DNA vaccine to immunize female BALB/c mice intramuscularly and the specific antibodies, lymphocyte proliferation response, interferon (IFN)-gamma production and cytotoxic T-lymphocyte response of the immunized mice were detected and evaluated.

RESULTSThe pilE gene of 429 bp in length was amplified. After transfection of NIH3T3 cells with the recombinant plasmid, strong green fluorescence was observed on the cell membrane and inside the cell. A protein with relative molecular mass of 15.7 kD was detected in the transfected cells with Western blotting, suggesting successful protein expression of pilE gene. pcDNA3.1-pilE resulted in much stronger immune response in the immunized mice than pcDNA3.1(+) (P<0.01).

CONCLUSIONThe recombinant plasmid containing Lgeionella pneumophila pilE gene constructed in this study is capable of expression in NIH3T3 cells, and can induce specific humoral and cellular immune responses in mice.

Animals ; Blotting, Western ; Cell Proliferation ; Fimbriae Proteins ; genetics ; immunology ; metabolism ; Fimbriae, Bacterial ; Fluorescent Antibody Technique ; Humans ; Immunization ; methods ; Injections, Intramuscular ; Interferon-gamma ; metabolism ; Legionella pneumophila ; genetics ; immunology ; metabolism ; Lymphocytes ; cytology ; immunology ; metabolism ; Mice ; Mice, Inbred BALB C ; NIH 3T3 Cells ; Plasmids ; genetics ; Recombinant Fusion Proteins ; genetics ; immunology ; metabolism ; T-Lymphocytes, Cytotoxic ; cytology ; immunology ; Transfection ; Vaccines, DNA ; administration & dosage ; genetics ; immunology

Legionella bacterium, an intracellular pathogen of mononuclear phagocytes, causes acute fatal pneumonia, especially in patients with impaired cellular immune responses. Until recently, however, the toll-like receptor (TLR) engagement of bacterial proteins derived from Legionella is uncertain. We previously showed that a 19-kDa highly conserved peptidoglycan-associated lipoprotein (PAL) of Legionella pneumophila induced the PAL-specific B cell and T cell responses in mice. In this study, we observed that the rPAL antigen of L. pneumophila, as an effector molecule, activated murine macrophages via TLR2 and produced proinflammatory cytokines such as IL-6 and TNF-alpha. In both BALB/c and TLR4-deficient C3H/HeJ mice, pretreatment of macrophages with anti-TLR2 mAb showed severely impaired cytokine production in response to the rPAL. In addition, in vitro the rPAL treatment increased the cell surface expression of CD40, CD80, CD86 and MHC I/II molecules. We further showed that the synthetic CpG-oligodeoxynucleotides (CpG ODN) coadministered with the rPAL enhanced IL-12 and IL-6 production and expression of CD40, CD80 and MHC II compared to the rPAL treatment alone. In conclusions, these results indicate that Legionella PAL might activate macrophages via a TLR2-dependent mechanism which thus induce cytokine production and expression of costimulatory and MHC molecules.
Animals ; Antigens, CD/immunology/metabolism ; Bacterial Outer Membrane Proteins/*pharmacology ; Cells, Cultured ; Female ; Histocompatibility Antigens Class II/immunology/metabolism ; Host-Pathogen Interactions ; Interleukin-12/biosynthesis ; Interleukin-6/biosynthesis ; Legionella pneumophila/*immunology/metabolism ; Legionnaires' Disease/immunology/metabolism ; Lipoproteins/*pharmacology ; Macrophage Activation/drug effects/immunology ; Macrophages, Peritoneal/drug effects/immunology/*metabolism ; Mice ; Mice, Inbred BALB C ; Mice, Inbred C3H ; Mice, Inbred C57BL ; Toll-Like Receptor 2/*metabolism ; Tumor Necrosis Factor-alpha/biosynthesis