The genomic and epidemiological dynamics of human influenza A virus

The evolutionary interaction between influenza A virus and the human immune system, manifest as 'antigenic drift' of the viral haemagglutinin, is one of the best described patterns in molecular evolution. However, little is known about the genome-scale evolutionary dynamics of this pathogen. Similarly, how genomic processes relate to global influenza epidemiology, in which the A/H3N2 and A/H1N1 subtypes co-circulate, is poorly understood. Here through an analysis of 1,302 complete viral genomes sampled from temperate populations in both hemispheres, we show that the genomic evolution of influenza A virus is characterized by a complex interplay between frequent reassortment and periodic selective sweeps. The A/H3N2 and A/H1N1 subtypes exhibit different evolutionary dynamics, with diverse lineages circulating in A/H1N1, indicative of weaker antigenic drift. These results suggest a sink-source model of viral ecology in which new lineages are seeded from a persistent influenza reservoir, which we hypothesize to be located in the tropics, to sink populations in temperate regions.     

Ecological and immunological determinants of influenza evolution

In pandemic and epidemic forms, influenza causes substantial, sometimes catastrophic, morbidity and mortality. Intense selection from the host immune system drives antigenic change in influenza A and B, resulting in continuous replacement of circulating strains with new variants able to re-infect hosts immune to earlier types. This 'antigenic drift' often requires a new vaccine to be formulated before each annual epidemic. However, given the high transmissibility and mutation rate of influenza, the constancy of genetic diversity within lineages over time is paradoxical. Another enigma is the replacement of existing strains during a global pandemic caused by 'antigenic shift'--the introduction of a new avian influenza A subtype into the human population. Here we explore ecological and immunological factors underlying these patterns using a mathematical model capturing both realistic epidemiological dynamics and viral evolution at the sequence level. By matching model output to phylogenetic patterns seen in sequence data collected through global surveillance, we find that short-lived strain-transcending immunity is essential to restrict viral diversity in the host population and thus to explain key aspects of drift and shift dynamics.     

Architecture of ribonucleoprotein complexes in influenza A virus particles

In viruses, as in eukaryotes, elaborate mechanisms have evolved to protect the genome and to ensure its timely replication and reliable transmission to progeny. Influenza A viruses are enveloped, spherical or filamentous structures, ranging from 80 to 120 nm in diameter. Inside each envelope is a viral genome consisting of eight single-stranded negative-sense RNA segments of 890 to 2,341 nucleotides each. These segments are associated with nucleoprotein and three polymerase subunits, designated PA, PB1 and PB2; the resultant ribonucleoprotein complexes (RNPs) resemble a twisted rod (10-15 nm in width and 30-120 nm in length) that is folded back and coiled on itself. Late in viral infection, newly synthesized RNPs are transported from the nucleus to the plasma membrane, where they are incorporated into progeny virions capable of infecting other cells. Here we show, by transmission electron microscopy of serially sectioned virions, that the RNPs of influenza A virus are organized in a distinct pattern (seven segments of different lengths surrounding a central segment). The individual RNPs are suspended from the interior of the viral envelope at the distal end of the budding virion and are oriented perpendicular to the budding tip. This finding argues against random incorporation of RNPs into virions, supporting instead a model in which each segment contains specific incorporation signals that enable the RNPs to be recruited and packaged as a complete set. A selective mechanism of RNP incorporation into virions and the unique organization of the eight RNP segments may be crucial to maintaining the integrity of the viral genome during repeated cycles of replication.     

H1N1猪流感病毒感染猪血管内皮细胞后内参基因的筛选

旨在评价H1N1猪流感病毒感染猪血管内皮细胞(PUVEC)后,肽基脯氨酰异构酶A(Ppia)、β-肌动蛋白(Actb)、核糖体蛋白L4(Rpl4)、酪氨酸3/色氨酸5-单加氧酶激活蛋白(Ywhaz)和甘油醛-3-磷酸脱氢酶(Gapdh)等5个内参基因的稳定性.采用Real-time RT-PCR方法测定H1N1 SIV感染PUVEC后3、6、9、12、15、18、24和30h时5个内参基因mRNA的表达水平,未感染PUVEC为对照,采用2-△Ct值对内参基因进行相对定量,应用Genorm软件对其稳定性进行评价.结果表明,5个内参基因的稳定性由高到低分别为Ppia和Rpl4、Ywhaz、Actb、Gapdh,其中Ppia和Rp14稳定性相同.据此可知,Ppia和Rpl4在所选的5个内参基因中是研究H1N1 SIV与机体互作理想的2个内参基因.     

顶板应力长期演化规律

介绍了伯格蠕变粘塑性模型,此模型体应变分量和偏应变分量均包含塑性变形部分,这可以有效地模拟永久变形,由于在屈服后体积应变中包含了塑性部分,因此即考虑了屈服后的球应力分量对偏应变的影响。从而使模拟更趋于实际。并以某浅煤层煤矿为例,模拟了顶板应力的长期演化规律,为顶板的支护从时间上给予了解释。指出支护的最佳时间是在工作面前后出现最大压应力时,同时也指出了回填的安全时间。此模型也可模拟其它地下岩体。     

Structure and mechanism of the M2 proton channel of influenza A virus

The integral membrane protein M2 of influenza virus forms pH-gated proton channels in the viral lipid envelope. The low pH of an endosome activates the M2 channel before haemagglutinin-mediated fusion. Conductance of protons acidifies the viral interior and thereby facilitates dissociation of the matrix protein from the viral nucleoproteins--a required process for unpacking of the viral genome. In addition to its role in release of viral nucleoproteins, M2 in the trans-Golgi network (TGN) membrane prevents premature conformational rearrangement of newly synthesized haemagglutinin during transport to the cell surface by equilibrating the pH of the TGN with that of the host cell cytoplasm. Inhibiting the proton conductance of M2 using the anti-viral drug amantadine or rimantadine inhibits viral replication. Here we present the structure of the tetrameric M2 channel in complex with rimantadine, determined by NMR. In the closed state, four tightly packed transmembrane helices define a narrow channel, in which a 'tryptophan gate' is locked by intermolecular interactions with aspartic acid. A carboxy-terminal, amphipathic helix oriented nearly perpendicular to the transmembrane helix forms an inward-facing base. Lowering the pH destabilizes the transmembrane helical packing and unlocks the gate, admitting water to conduct protons, whereas the C-terminal base remains intact, preventing dissociation of the tetramer. Rimantadine binds at four equivalent sites near the gate on the lipid-facing side of the channel and stabilizes the closed conformation of the pore. Drug-resistance mutations are predicted to counter the effect of drug binding by either increasing the hydrophilicity of the pore or weakening helix-helix packing, thus facilitating channel opening.     

The mechanism by which influenza A virus nucleoprotein forms oligomers and binds RNA

Influenza A viruses pose a serious threat to world public health, particularly the currently circulating avian H5N1 viruses. The influenza viral nucleoprotein forms the protein scaffold of the helical genomic ribonucleoprotein complexes, and has a critical role in viral RNA replication. Here we report a 3.2 A crystal structure of this nucleoprotein, the overall shape of which resembles a crescent with a head and a body domain, with a protein fold different compared with that of the rhabdovirus nucleoprotein. Oligomerization of the influenza virus nucleoprotein is mediated by a flexible tail loop that is inserted inside a neighbouring molecule. This flexibility in the tail loop enables the nucleoprotein to form loose polymers as well as rigid helices, both of which are important for nucleoprotein functions. Single residue mutations in the tail loop result in the complete loss of nucleoprotein oligomerization. An RNA-binding groove, which is found between the head and body domains at the exterior of the nucleoprotein oligomer, is lined with highly conserved basic residues widely distributed in the primary sequence. The nucleoprotein structure shows that only one of two proposed nuclear localization signals are accessible, and suggests that the body domain of nucleoprotein contains the binding site for the viral polymerase. Our results identify the tail loop binding pocket as a potential target for antiviral development.     

甲型流感病毒感染BALB/c鼠动物模型的建立

目的:建立甲型流感病毒感染BALB/c鼠动物模型,为研究病毒变异、致病机制及抗病毒药物筛选提供模型动物.方法:通过滴鼻的方法将甲型流感病毒感染到BALB/c鼠,观察小鼠的症状和组织病理改变.结果:BALB/c鼠的临床症状明显,病理变化典型.结论:甲型流感病毒感染BALB/c鼠的疾病模型建成.     

乙型肝炎母婴垂直传播(综述)

综述乙肝母婴传播的途径及其阻断方法。乙肝母婴传播主要通过胎盘、乳汁、羊水及唾液传播。目前主要阻断方法为应用乙肝免疫球蛋白、乙肝疫苗及拉米夫定等治疗