The Study About Immune Regulations Of Mouse Scavenger Receptor AⅠ In Leptospira Infection

Leptospires are thin,helical bacteria with distinctive hooked ends,classified into pathogenic and saprophytic species.Human and other domestic animals can suffer from Leptospirosis if infected with pathogenic leptospires and this kind of disease still is a worldwide spread zoonosis.The Innate Immune system of host plays an important role in the defense of Leptospira infection.As a Pattern Recognition Receptor which mainly expressing on macrophages and dendritic cells,Scavenger receptor A-I（SR-AⅠ）acts an important part in helping innate immune system recognize,phagocytize and clear pathogens.However,it is still not clear what the roles of SR-AⅠ in the Leptospira infection.Basing on the experiments of cellular and animal levels,this study carried out a systematic study about the role of SR-AⅠ in the immunity to Leptospira infection from many aspects such as phagocytosis,inflammatory regulation and histopathology.On cellular level（in vitro）,we use the C57BL/6 mouse peritoneal macrophage（PEM-WT）and SR-AⅠ^-/-knocked out mouse peritoneal macrophage(PEM-SR-AⅠ^-/-),as well as RAW264.7 cells that overexpressed SR-AⅠ or GFP vector（RAW-SR-AⅠ/RAW-GFP）to study the role of SR-AⅠ receptor in phagocytosis and inflammatory regulation.We found that PEM-WT cells and RAW-SR-AⅠ cells phagocytized more Leptospira interrogans strain 56606v（56606v）than PEM-SR-AⅠ^-/-cells and RAW-GFP cells respectively,which indicated that SR-AⅠ receptor could enhance macrophages’phagocytizing abilities agaist 56606v.Except the phagocytosis,we also used 56606v stimulating above cells to check whether SR-AⅠ plays an inflammatory regulating role in this process.We found that the cytokines expression such as TNF,IL-6,IL-10 or IL-12bwere more higher in PEM-WT cells compared with PEM-SR-AⅠ^-/-cells and cytokines such as IL-1bor iNOS also were expressed higher in RAW-SR-AⅠ cells rather than RAW-GFP cells.This suggested that SR-AⅠ receptor could participate and improve the macrophages’inflammatory reaction in suffering from Leptospira infection.Furthermore,by using MS spectrum technique,we found that,SR-AⅠ could directly interacted with intracellular component such as MVP,HSC-71,ENO1,HSPA9,et.al,which may attribute a possible inflammatory regulating machnism of SR-AⅠ during Leptospira infection.On animal level（in vivo）,WT C57BL/6 mouse and SR-AⅠ^-/-gene knocked out C57BL/6 mouse were infected with proper dosage of 56606v by peritoneal injection.We found that the infectious SR-AⅠ^-/-mouse suffered from more severe hemorrhages in subcutaneous and more 56606v burden and stronger inflammatory reaction happened in liver compared with WT mouse.This result suggested that SR-AⅠ receptor could protect mouse from Leptospira infection and help host defending the pathology responses.Besides,we also had a study about the intraction between SR-AⅠ receptor and K.pneumonia or P.Aeruginosa with above cell models.We found that SR-AⅠ could promoted macrophages phagocytizing K.pneumonia and suppressed inflammatory cytokines expressions such as IL-1b,IL-6 and IL-12b.In P.Aeruginosa stimulation,we found that macrophages had higher phagocytizing abilities and inflammatory responses against this pathogen after knocking out SR-AⅠ receptor,cytokines such as IL-1b,IL-6 and IL-12bwere expressed more in SR-AⅠ knocked out cells.Both of them showed a different interaction with SR-AⅠ receptor compared with Leptospira.It also indicated the interaction between SR-AⅠ receptor and Leptospira was something special compared with other Gram-negative bacterias.Overall,from all these consequences,it could conclude that SR-AⅠ enhances macrophages’abilities in phagocytizing Leptospira,participates in and improves cells’inflammatory responses against Leptospira stimulation.This inflammatory regulating role of SR-AⅠ receptor in Leptospira infection is different with other Gram-negative bacterias and may be correlated with the interaction between SR-AⅠ and intracellular components such as MVP,HSC-71,ENO1,HSPA9,et.al.In the meantime,in vivo,SR-AⅠ could relieve subcutaneous hemorrhages in Leptospira infection;alleviate liver injury by reducing survival Leptospira amounts.All this suggested that SR-AⅠ can protect and help host defending Leptospira infection.