Research On The Action Mechanism Of Complement In Severe Pneumonic Flu-s.aureus Coinfection

Background: In recent years,studies have shown that the mortality of respiratory infectious diseases was in relationship with virus-bacteria coinfections.Especially in severe or lethal cases of influenza virus,50%-90%of them involved bacterial coinfections.A variety of bacteria species have been reported be of capacity to coinfected with influenza virus.There are three most common species: streptococcus pneumoniae,staphylococcus aureus and haemophilus lungs.It was reported that influenza coinfection with s.aureus yielded highest mortality.Further study of infection in pathogenic mechanism was essential to reduce the mortality.Research shows that severe or lethal coinfection cases were always accompanied by severe lung inflammation.In addition,the complements were proved associated with inflammatory injury in many disease.So we wonder that complements also play a key role in the inflammatory response caused by virus/bacteria coinfection.Now the question was not yet clear,also there was little related research reported.Therefore,we chose influenza virus and s.aureus bacteria to build coinfection mouse model,and proposed to study the activations of complement in the process of coinfection and its role in severe pneumonia.Aim: We investigate of the activation of complements in severe pneumonia caused by influenza virus/S.aureus coinfection and study the relationship among complement and severe pneumonia and impact on mortality,using complement inhibitor and complement deficiency mice.By complement inhibitor treatment of influenza virus/S.aureus coinfection,we explore a new technology that using complement regulation as a treatment strategy for severe pneumonia caused by coinfection.By studying the relationship between pathogen and complement,we investigate how complements were over activated during coinfection.Methods: Coinfected mice model was established by infected mice with the sub lethal doses of influenza viruses(A/Puerto Rico/8/34 strain)and resistant staphylococcus aureus(MRSA,Methicillin-resistant Staphylococcus aureus).Using various different co-infection time points and orders,and other common,high mortality co-infection model was selected.By means of pathological slice and ELISA,pathological inflammation reaction and expression level of inflammatory related cytokines(IFN-a,IFN-g,TNF-a,TNF-b,IL-4,IL-6,IL-8,IL-10)was detected,especially for C3 a and C5 a,which is related to complements.Distribution of pathogens in the lung was detected through measuring accumulation of C3 d protein in lung tissue using immunofluorescence technique.Finally using complement defected mice or treating mice with CVF and C5 aR antibody to observe the change of lung inflammation reaction and mice mortality.Results: High mortality of infected mice model was successfully established through inoculation with sub lethal doses of influenza viruses and s.aureus bacteria.The results showed that mortality was highest when bacteria was infected 1-3 days after infection of influenza viruses.In addition,pathological slice and lung inflammation factor detection showed that severe pneumoniaresponse happened in these high death cases,at the same time there also occurred cytokine storm.Especially that expression of C3 a and C5 a,inflammatory factor related to complement,obviously increased.In a high mortality cases,massive C3 d molecular accumulated in mice lung.Results of immunofluorescence detection for intensity of virus and bacteria showed that pathogens proliferated into large quantity in high mortality group while there was no obvious pathogen proliferation in defected mice groups.Finally after removal of complement using complement inhibitors and complement defected mice,mortality of coinfection groups were significantly reduced.Conclusion: Coinfection mice model with high mortality was established successfully.Excessive activation of complement in high mortality groups was proved,which play an important role in the process of severe pneumonia.It's reduce the mortality rate of co-infected mice significantly that getting rid of complement effect such as complement defects and complement inhibitors(CVF,C5aR)in mice.Prove that co-infection of sublethal flu virus and s.aureus Interactions into a lethal dose,and in the complement activation.