HOST RANGE VARIATION OF EMERGING AND REEMERGING INFLUENZA VIRUSES IN ASIA

在中国南方，禽流感病毒目前正在持续向人群传播。在1999-2000年两年的研究中，我们发现了亚洲流感病毒宿主介导变异的几个重要机制：1）H3型人流感病毒血凝素（HA）不支持病毒在鸭肠中复制，尽管其来源于禽类。人A/Udorn/307/72（H3 N2）HA的226位Leu → Gln突变和228位Ser → Gly突变允许重组病毒在鸭体内复制。2）用Neu 5Gc 2 - 3Gal特异性抗血清进行的免疫荧光检测主要在鸭结肠的隐窝上皮细胞上检测到该部分。3）猪气管上皮细胞具有与禽流感病毒和人流感病毒A结合的受体唾液糖链（Neu 5Ac 2 - 6 Gal，用于抑制禽流感病毒A的生长），而猪气管上皮细胞具有与禽流感病毒A结合的受体唾液糖链（Neu 5Ac 2 - 6 Gal，用于抑制禽流感病毒A的生长）。 ...更多信息 对人和对鸟来说是Neu 5Ac 2 -3Gal）。这些结果表明，猪在自然界中可能充当人禽流感病毒的混合容器。A病毒血凝素受体结合特异性的宿主范围选择发生在病毒在表达不同受体唾液酸糖链的不同宿主细胞中维持期间。4）A流感病毒神经氨酸酶的底物特异性（受体破坏酶）显示所有病毒对Neu 5Ac 2 -3Gal具有相似的特异性，而对Neu 5Gc 2 - 6 Gal的活性范围很小，如禽类和早期N2人病毒所代表的，到高（尽管只有Neu 5Ac 2 -3Gal活性的三分之一），如猪和更近的N2人病毒所代表的。使用位点特异性诱变，我们在Neu 5Ac 2 - 6 Gal特异性可检测到增加的最早的人病毒中鉴定了275位的改变（Leu至瓦尔），其增强了对该底物的特异性。5）具有识别Neu 5Ac 2 - 6 Gal但不识别Neu 5Ac 2 -3Gal或Neu 5Gc 2 -3Gal的HA的流感病毒不能在马中复制。生化和免疫组织化学分析以及凝集素结合试验证明马气管上皮细胞中富含Neu 5 Gc 2 - 3 Gal部分，表明该部分的识别对于病毒在马体内的复制至关重要。上述新结果表明该项目的目标是令人满意的进展，以及阐明亚洲流感病毒血凝素和神经氨酸酶新亚型的宿主范围变异和出现的机制，确立了控制流感病毒变异的基本思路。少

In south China, the continuous transmission of avian influenza viruses into human population is currently occurring. In our two year's investigation (1999-2000), we found several important mechanisms on the host mediated variation of influenza viruses in Asia.1) The Hemagglutinin (HA) of H3 human influenza viruses does not support viral replication in duck intestine despite its avian origin. A Leu-to-Gln mutation at position 226 and a Ser-to-Gly mutation at 228 in the HA of human A/Udorn/307/72 (H3N2) permit a reassortant virus to replicate in ducks.2) Immunofluorescense assays with Neu5Gc2-3Gal-specific antiserum detected this moiety primarily on the crypt epitherial cells of duck colon. Such recognition with biological results suggests that recognition of the Neu5Gc2-3Gal moiety plays an important role in the enterotropism of avian influenza viruses.3) Epitherial cells in pig trachea has receptor sialosugar chains that binds both of bird and human influenza A viruses (Neu5Ac2-6Gal fo … More r humans aud Neu5Ac2-3Gal for birds). These results indicate that pig may play as a mixing vessel of human and bird influenza viruses in nature. The host range selection of the receptor binding specificity of the A virus hemagglutinin occurrs during the maintenance of the virus in different host cells which express different receptor sialo-sugar chains.4) Substrate specificity of influenza A virus neuraminidase (receptor destroying enzyme) showed that all viruses had similar specificities for Neu5Ac2-3Gal, while the activities for Neu5Gc2-6Gal ranged marginal, as represented by avian and early N2 human viruses, to high (although only one-third the activity for Neu5Ac2-3Gal), as represented by swine and more recent N2 human viruses. Using site specific mutagenesis, we identified in the earliest human virus with a detectable increase in Neu5Ac2-6Gal specificity a change at position 275 (Leu to Val) that enhanced the specificity for this substrate.5) An Influenza virus with an HA recognizing Neu5Ac2-6Gal but not Neu5Ac2-3Gal or Neu5Gc2-3Gal failed to replicate in horses. Biochemical and immunohistochemical analyses and a lectin-binding assay demonstrated the abundance of the Neu5Gc2-3Gal moiety in epithelial cells of horse trachea, indicating that recognition of this moiety is critical for viral replication in horses.The above new results show that the aim of this project is satisfactory progressed, and the fundamental experimantal results to elucidate the mechanism of host range variation and emerging of the new subtype of the hemagglutinin and neuraminidase of influenza viruses in Asia and to establish the fundamental idea for the control of the influenza virus variation. Less