Résumé
Objective To construct a prokaryotic expression system for tlyA gene of Leptospira in-terrogans ( L.interrogans) strain and to investigate the effects of the expressed rTlyA protein on the hemolysis of sheep erythrocytes and the secretion of pro-inflammatory cytokines by human THP-1 cells and murine J774A.1 macrophages.Methods The fragment of tlyA gene of L.inetrrogans serogroup Icterohaemorrhagiae serovar Lai strain Lai was amplified by PCR.The PCR product was sequenced after T-A cloning.A prokary-otic expression system for the tlyA gene was constructed by using pET-42a as the expression vector and E.coli BL21DE3 strain as the host strain.The expression of rTlyA protein was detected by SDS-PAGE.Ni-NTA af-finity chromatography was performed for purification.The lytic activity of the rTlyA protein on sheep erythro-cytes was determined by plate hemolytic test and spectrophotometry.Real-time fluorescence quantitative PCR and Western blot assay were performed to respectively detect the expression of tlyA gene in THP-1 and J774A.1 cells at mRNA and protein levels after infection with L.interrogans strain Lai.ELISA was per-formed to evaluate the effects of the rTlyA protein on the secretion of several pro-inflammatory cytokines ( IL-β, IL-6 and TNF-α) by THP-1 and J774A.1 cells.Results The nucleotide and amino acid sequences of the cloned tlyA gene were 99.2% and 99.8% identical to those corresponding sequences in GenBank, re-spectively.The constructed prokaryotic expression system for tlyA gene successfully expressed the rTlyA pro-tein.The rTlyA protein at the concentration of 10μg/ml showed stronger lytic activity on sheep erythrocytes. The transcription levels of tlyA gene (P<0.05) and the secretion of TlyA protein in THP-1 and J774A.1 cells were significantly increased after infecting with L.interrogans strain Lai for 1 to 8 hours.The rTlyA pro-tein at concentrations of 0.1, 1 and 10 μg/ml significantly enhanced the secretion of IL-1β, IL-6 and TNF-αby THP-1 and J774A.1 cells (P<0.05).Conclusion The TlyA protein, encoded by the tlyA gene of L.interrogans strain, was confirmed to be a hemolysin with the ability to induce macrophages to secret IL-1β, IL-6 and TNF-α.This study suggested that the TlyA protein played an important role in inflammatory responses during leptospirosis.
Résumé
The pathogenic traits of TlyA proteins of Mycobacterium tuberculosis are not known. Expressions of TlyA in bacteria that do not express endogenous TlyA adhere better to RAW264.7 macrophages and get phagocytosed efficiently. The internalized bacteria avoid acidification to the extent of >65% in the case of both TlyA-expressing E. coli and M. smegmatis. Consistent with this observation, we have observed decreased co-localizaton of Lysosomal Membrane Associated Protein-1 (~35%), Early Endosomal Antigen-1 (~34%), Rab5 (~30%) and Rab7 (~35%) and enhanced colocalizaton of Rab14 (~80%) on both TlyA-expressing bacteria as well as on TlyA-coated latex beads. These results suggest that the mycobacterial TlyA, in general, can modulate phagolysosome maturation pathway immediately after entry into macrophages, while other important molecules may aid the bacterium for long-term, intracellular survival at later point of time.