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Serine at position 624 of the PA subunit of the influenza A virus RNA polymerase is the active site of a serine protease. To examine the role of this protease activity in the viral infection cycle, we compared the growth and pathogenesis of influenza virus A/WSN/33 and the virus encoding a PA with an S624A mutation (S624A virus). The growth and pathogenesis of the S624A virus was less than that of WSN in cells, indicating that the protease activity of PA is not essential for viral growth and pathogenesis, but is required for maximal viral growth.

Zanamivir has been evaluated for treatment and prophylaxis of influenza A and B viruses. However, it is not recommended for children younger than 6 years old because the use of the Diskhaler is required. We developed a new method of administering zanamivir with a straw in order to expand the application of zanamivir to those who are not yet able to use the Diskhaler. Of 142 patients aged 2 months to 5 years old who received zanamivir in this study, 126 were relieved from fever (

Gene expression patterns between encephalitis/encephalopathy patients and respiratory infection patients by the influenza viral infection were compared by DNA microarray analysis. Expression of six genes (interferon (α, β, ω) receptor, ephrin-B2, RNA binding motif protein 5 (RBM5), transcription factor EC (TFEC), Calsenilin/DREAM/KChIP3, and MEGF6 protein) was elevated and that of three genes (non-metastatic protein 23 (Nm23/Awd), neuropeptide Y/peptide YY receptor, and hippocalcin-like protein 4 (HPCAL4)) was decreased in encephalitis/encephalopathy patients.

Background: Influenza virus RNA polymerase consists of three subunits, PB1, PB2 and PA, and catalyzes both transcription and replication of the RNA genome. PB1 is a catalytic subunit of RNA polymerization and a core of subunit assembly. Previously, we mapped the PB1–PB2 binding sites (1–259 of PB2 and 501–757 of PB1), and the PB1–PA binding sites (1–140 of PB1 and 201–716 of PA). In order to determine the fine map of the subunit binding sites, we continued the same line of experiments. Methods: Serial deletion mutants of each subunit were expressed with N-terminal HA-tag, and co-immunoprecipitated with the non-tagged wild-type subunits by anti-HA or subunit-specific antibodies. Results: PB1N599 and PB1C10 were co-immunoprecipitated with PB2wt, but PB1N625 and PB1N700 were weakly co-immunoprecipitated with PB2wt. PB1C25 or PB1C40 were not co-immunoprecipitated with PB2wt. PB2N50 and PB2N75 were co-immunoprecipitated with PB1wt. However, PB2N104 or PB2N150 were not co-immunoprecipitated with PB1wt. PB1C535 and PB1C617 were co-immunoprecipitated with PAwt, but PB1N25 was not. PAN300, PAN400, PAN500 and PA501–692 were co-immunoprecipitated with PB1wt, but PAC49 was not. Conclusions: PB1–PB2 binding sites are mapped in PB1(600–747) and PB2(76–104), and PB1–PA binding sites are in PB1(1–25) and PA(668–692).

Influenza virus RNA polymerase is a multifunctional enzyme that catalyzes both transcription and replication of the RNA genome. The function of the influenza virus RNA polymerase PA subunit in viral replication is poorly understood although the enzyme is known to be required for cRNA→vRNA synthesis. Protease related activity of PA has been discussed ever since protease-inducing activity was demonstrated in transfection experiments. PA protein was highly purified from baculovirus-infected insect cells and a novel chymotrypsin-type serine protease activity with serine624 as an active site was identified in the protein. These results constitute the first demonstration of protease activity in RNA polymerase complexes.

Rapid progressive encephalopathy showing a high fever, consciousness loss and recurrent convulsions has been occasionally reported in childhood during influenza epidemics in Japan since 1995. A clinicopathological study of a 2-year-old female diagnosed with hemorrhagic shock and encephalopathy syndrome associated with influenza A virus (A/Nagasaki/76/98; H3N2) infection showed that the virus antigens are present in CD8-positive T lymphocytes from the lung and spleen, suggesting the possible route of the virus spread. The virus antigens are confined to a very limited part of the brain, especially Purkinje cells in the cerebellum and many neurons in the pons, without inducing an overt immunological reaction of the host. RT-PCR for detecting the hemagglutinin gene demonstrated definite positive bands in all frozen tissues and cerebrospinal fluids taken at autopsy but not in samples on admission. The pathological change induced by the direct viral invasion cannot be sufficient for the rapid and severe clinical course of the disease within 24–48 h after the initial respiratory symptoms. The rapid production of several inflammatory cytokines together with the breakdown of the blood–brain barrier, which will induce severe brain edema, may be the major pathological processes. Any therapeutic strategy to control this multi-step progression could be effective.