Hemagglutinin From Avian Influenza Virus Activates The Immune Function Of Murine Dendritic Cells

Avian influenza,caused by influenza A virus,have been identified as the most important pathogens in poultry,which can cause acute and contagious respiratory infection and serous economic problems.Recently,frequent outbreaks of reassortant H7N9 avian influenza virus(AIV)caused great threat to the poultry industry and the public health.Avian influenza virus(AIV)has high mutation rates and recombination rates,which lead to low protective efficacy of existing vaccines.Hemagglutinin(HA)was the most important fragment of avian influenza virus,which was primary account for the inducing of neutralizing antibodies.It is difficult to inhibit AIV mainly due to the highly frequency of mutation in HA fragment,especially in the site of antibody producing.The H5N1 subtype,belonged to high pathogenic avian influenza,has triggered wide concern since it took place in Hong Kong in 1997.Whilst the H9N2 avian influenza virus has caused multiple disease pandemics in recent years may largely due to its high genetic variability and high rates of recombination with other influenza virus subtypes.Sequencing analyses revealed that six internal genes of H7N9 and H10N8 subtype shared the highest similarity with H9N2 subtype viruses that have circulated in poultry.There is a constant struggle between viruses and the host immune system,and the pathogenicity of a virus is determined not only by its characteristics but also by the host immune response.Dendritic cells(DCs),the most important antigen presenting cells in host immune response,monitored the invasion of pathogenic microorganisms constantly and configured the first line of defense in mucosal immunity.Additionally,DCs have a dual role in regulating the immune response.On one hand,it can secrete large amounts of cytokines to regulate the innate immune response.On the other hand,it can extend their dendrites to identify and capture pathogenic microorganisms.After that,DCs would present the microorganisms to lymphocytes after processing,thus to induce the activiation of adaptive immune response.HA fragment,one of the major envelope glycoprotein of the avian influenza viras,has been proved to be the primary target of neutralizing antibodies.Therefore,researches on the regulation of HA activating the characteristics of antigen-presenting of dendritic cells have important theory and practice.In this study,we focus on hemagglutinin fragment from both low pathogenic avian influenza virus(H9N2)and high pathogenic avian influenza virus(H5N1).Firstly,eukaryotic expression vector of truncated hemagglutinin fragments of H5N1 and H9N2 are constructed and then transfected into dendritic cells.Results showed that the removal of HA signal peptide fragment,the expression of CD86,CD80,MHCII,CD40 could be increased significantly.The truncated HA fragments of H9N2 can enhance dendritic cells maturation.Secondly,we will research the function mechanism of HA including cytokine expression secreted by dendritic cells and signaling pathways activated by HA.The truncated HA of H5N1 can stimulate dendritic cells expressing high level of IL-10 and TNF-a,but H9N2 did not change significantly.This indicates that the presence or absence of a signal peptide of HA have a greater impact on stimulating murine dendritic cells to secrete inflammatory cytokines.Then,HA can significantly affect expression level of ERK,JNK,P38 protein and their phosphorylated proteins in MAPK pathway in dendritic cells.P-P38,JNK,ERK,P-ERK proteins are highly expressed in H5N1 HA treated group.This provides the basis for the study reveals signal peptide of hemagglutinin regulating immune function of murine dendritic cells,as well as for the study of the use of the hemagglutinin protein.