Mechanism Study Of FlaA And FlaA-C In Host Recognition Of Legionella Pneumophila Infection

Legionella,as a pathogenic microorganism,is widely distributed in natural water and artificial water conditions.It can cause Legionaires disease and Pontiac fever with the high fatality rate.It can infect different host cells.When it enters a cell,its Ⅳ secretion system releases effector proteins into the host cell to escape lysosomal digestion.The morphological structure of the strain changes with its living environment,the flagellum is one of the most obvious characteristics of its morphology change.In addition,the host’s innate immune system is able to recognize the L.pneumophila flagellum by pattern recognition receptors,which inhibits intracellular proliferation of the strain by activating inflammation response.In this study,we analyzed the presence,virulence,distribution and drug resistance characteristics of Legionella in public places of Macao;second,we constructed a L.pneumophila mutant strain that stably expressed high levels of GFP and could be used to replace the wild type strain in study of the infection.Then we used this strain evaluate the invasion and proliferation of L.pneumophila in association with several cell lines;third,we analyzed the change of transcriptome of the host cell J774.1 after infection with L.pneumophila;Finally,we constructed two L.pneumophila mutant strains that missing flaA or flaA-C,and study the influence of flaA or flaA-C gene mutation on the bacterial intracellular proliferation and the recognition by host cell receptor.Our results indicated that Legionella species were widely distributed in the public environment of Macau and possessed a certain degree of virulence,and the Legionella isolates are inhibited by low concentrations of fluoroquinolones.We found that the multiplicative processes of L.pneumophila in different cell lines were similar.We also found the transcript levels of many genes related to TNF signal pathway,NOD-like receptor,Toll-like receptor and inflammation were up-regulated after L.pneumophila infection,and the deletion of flaA and flaA-C of L.pneumophila influenced the recognization of pathogenic infection through Toll-like receptors of the host cell.These findings help researchers further understand the existence of Legionella in the environment and learn more about the characteristics of the Legionella isolates,provide the possibility to trace and control for a large area of epidemic and appropriate precaution strategy against Legionella infection.The comparison among different cell lines infected with L.pneumopila help us determine the key surface proteins and mechanisms involved in bacteria uptake,and analyze the biochemical functions of bacterial effector proteins.The transcriptome analysis of host cells before and after infection extends our knowledge of the global response of host after infection with L.pneumophila,provides theoretical basis to clarify the regulating mechanism of inflammatory response,and to put forward some effective ways to prevent the intracellular proliferation of the strain.Finally,the study further verified the flagellum protein FlaA influence on the recognition of host receptor.The involved genes and pathways are helpful to further reveal the role of pathogen flagellum in cell infection and receptor identification,and its related mechanism underline.This study also found that the C-terminal of FlaA play a role in the progress of which Legionella flagellum is recognized by toll-like receptors.This finding will provide a new clue for antibody research.