In June 2013,the fi rst human H6N1 infl uenza virus infec-tion was confirmed in Taiwan.However,the origin and molecular characterization of this virus,A/Taiwan/2/2013(H6N1),have not been well studied thus far.In the present report,we performed phylogenetic and coalescent analy-ses of this virus and compared its molecular profi le/char-acteristics with other closely related strains.Molecular characterization of H6N1 revealed that it is a typical avian infl uenza virus of low pathogenicity,which might not rep-licate and propagate well in the upper airway in mammals.Phylogenetic analysis revealed that the virus clusters with A/chicken/Taiwan/A2837/2013(H6N1)in seven genes,except PB1.For the PB1 gene,A/Taiwan/2/2013 was clus-tered with a different H6N1 lineage from A/chicken/Taiwan/A2837/2013.Although a previous study demonstrated that the PB2,PA,and M genes of A/Taiwan/2/2013 might be derived from the H5N2 viruses,coalescent analyses revealed that these H5N2 viruses were derived from more recent strains than that of the ancestor of A/Taiwan/2/2013.Therefore,we propose that A/Taiwan/2/2013 is a reassor-tant from different H6N1 lineages circulating in chickens in Taiwan.Furthermore,compared to avian isolates,a sin-gle P186L(H3 numbering)substitution in the hemaggluti-nin H6 of the human isolate might increase the mammali-an receptor binding and,hence,this strain’s pathogenicity in humans.Overall,human infection with this virus seems an accidental event and is unlikely to cause an infl uenza pandemic.However,its co-circulation and potential reas-sortment with other infl uenza subtypes are still worthy of attention.
The demonstration that for infectious diseases vaccine-induced immunity is in principle only effective before rather than after infection occurs,provides valuable insights in understanding the nature of immune system and the challenges in cancer treatment.Besides the already known underlying counter-back mechanisms,the astronomical numbers of tumor cells in established tumors could overwhelm the limited amount of specific T cells induced by vaccination,which may account for the modest efficiency of immunotherapy against cancer.We speculate that the long window period for cancer development will allow immune-intervening strategies(e.g.,the proper prophylactic vaccination)to promote adaptive mechanisms toward an enhanced immunosurveillance,which could effectively eradicate or at least control the few precancerous cells undergoing neoplastic transformation during early premalignant stages in cancer development,and protect the host from lethal tumor formation.It should be emphasized that the pre-cancer-associated antigens but not the tumorassociated antigens seem to be the suitable antigens for designing prophylactic cancer vaccines.In addition,an ideal prophylactic cancer vaccine may contain multiple pre-cancer-associated antigens,which will provide broad and effective immune protection in a heterogeneous human population.Finally,we demonstrated that placenta-derived gp96,which can be readily obtained in high amount for vaccination,has the ability to initiate antitumor T-cell immunity via association with multiple embryo-cancer antigens.Further understanding placental gp96 associated with carcinoembryonic antigen repertoires that orchestrate immune defense networks against cancer formation will allow to provide an effective prophylactic approach in cancer prevention.
Avian infl uenza A virus continues to pose a global threat with occasional H5N1 human infections,which is em-phasized by a recent severe human infection caused by avian-origin H7N9 in China.Luckily these viruses do not transmit effi ciently in human populations.With a few ami-no acid substitutions of the hemagglutinin H5 protein in the laboratory,two H5 mutants have been shown to obtain an air-borne transmission in a mammalian ferret model.Here in this study one of the mutant H5 proteins devel-oped by Kawaoka’s group(VN1203mut)was expressed in a baculovirus system and its receptor-binding properties were assessed.We herein show that the VN1203mut had a dramatically reduced binding affi nity for the avianα2,3-linkage receptor compared to wild type but showed no detectable increase in affi nity for the humanα2,6-linkage receptor,using Surface Plasmon Resonance techonology.Further,the crystal structures of the VN1203mut and its complexes with either human or avian receptors demon-strate that the VN1203mut binds the human receptor in the same binding manner(cis conformation)as seen for the HAs of previously reported 1957 and 1968 pandemic influenza viruses.Our receptor binding and crystallo-graphic data shown here further confi rm that the ability to bind the avian receptor has to decrease for a higher hu-man receptor binding affi nity.As the Q226L substitution is shown important for obtaining human receptor binding,we suspect that the newly emerged H7N9 binds human receptor as H7 has a Q226L substitution.
Xishan LuYi ShiWei ZhangYanfang ZhangJianxun QiGeorge F Gao
Leukocyte immunoglobulin-like receptors(LILRs),also called CD85s,ILTs,or LIRs,are important mediators of immune activation and tolerance that contain tandem immunoglobulin(Ig)-like folds.There are 11(in addition to two pseudogenes)LILRs in total,two with two Ig-like domains(D1D2)and the remaining nine with four Ig-like domains(D1D2D3D4).Thus far,the structural features of the D1D2 domains of LILR proteins are well defi ned,but no structures for the D3D4 domains have been reported.This is a very important fi eld to be studied as it relates to the unknown functions of the D3D4 domains,as well as their relative orientation to the D1D2 domains on the cell surface.Here,we report the crystal structures of the D3D4 domains of both LILRB1 and LILRB2.The two Ig-like domains of both LILRB1-D3D4 and LILRB2-D3D4 are arranged at an acute angle(~60°)to form a bent struc-ture,resembling the structures of natural killer inhibitory receptors.Based on these two D3D4 domain structures and previously reported D1D2/HLA I complex structures,two alternative models of full-length(four Ig-like domains)LILR molecules bound to HLA I are proposed.
Gol NamYi ShiMyongchol RyuQihui WangHao SongJun LiuJinghua YanJianxun QiGeorge F Gao
Influenza virus contains three integral membrane proteins:haemagglutinin,neuraminidase,and matrix protein(M1 and M2).Among them,M2 protein functions as an ion channel,important for virus uncoating in endosomes of virus-infected cells and essential for virus replication.In an effort to explore potential new functions of M2 in the virus life cycle,we used yeast two-hybrid system to search for M2-associated cellular proteins.One of the positive clones was identified as human Hsp40/Hdj1,a DnaJ/Hsp40 family protein.Here,we report that both BM2(M2 of influenza B virus)and A/M2(M2 of influenza A virus)interacted with Hsp40 in vitro and in vivo.The region of M2-Hsp40 interaction has been mapped to the CTD1 domain of Hsp40.Hsp40 has been reported to be a regulator of PKR signaling pathway by interacting with p58^(IPK) that is a cellular inhibitor of PKR.PKR is a crucial component of the host defense response against virus infection.We therefore attempted to understand the relationship among M2,Hsp40 and p58^(IPK) by further experimentation.The results demonstrated that both A/M2 and BM2 are able to bind to p58^(IPK)in vitro and in vivo and enhance PKR autophosphorylation probably via forming a stable complex with Hsp40 and P58^(IPK),and consequently induce cell death.These results suggest that influenza virus M2 protein is involved in p58^(IPK)mediated PKR regulation during influenza virus infection,therefore affecting infected-cell life cycle and virus replication.
Zhenhong GuanDi LiuShuofu MiJie ZhangQinong YeMing WangGeorge F.GaoJinghua Yan
Enolase is a conserved cytoplasmic metalloenzyme existing universally in both eukaryotic and prokaryotic cells.The enzyme can also locate on the cell surface and bind to plasminogen,via which contributing to the mucosal surface localization of the bacterial pathogens and assisting the invasion into the host cells.The functions of the eukaryotic enzymes on the cell surface expression(including T cells,B cells,neutrophils,monocytoes,neuronal cells and epithelial cells)are not known.Streptococcus suis serotype 2(S.suis 2,SS2)is an important zoonotic pathogen which has recently caused two large-scale outbreaks in southern China with severe streptococcal toxic shock syndrome(STSS)never seen before in human sufferers.We recently identified the SS2 enolase as an important protective antigen which could protect mice from fatal S.suis 2 infection.In this study,a 2.4-angstrom structure of the SS2 enolase is solved,revealing an octameric arrangement in the crystal.We further demonstrated that the enzyme exists exclusively as an octamer in solution via a sedimentation assay.These results indicate that the octamer is the biological unit of SS2 enolase at least in vitro and most likely in vivo as well.This is,to our knowledge,the first comprehensive characterization of the SS2 enolase octamer both structurally and biophysically,and the second octamer enolase structure in addition to that of Streptococcus pneumoniae.We also investigated the plasminogen binding property of the SS2 enzyme.
