Kinetic studies on the sialidase of three influenza B and three influenza A virus strains

Sialidase of influenza virus type A has been extensively studied through structural and kinetic approaches. However, sialidase of influenza virus type B has been less investigated. In this work, we have studied the activity and some properties (optimal pH, K_M, V_max, thermal stability) of sialidase in three influenza virus strains of type B (circulating in the period 1983–86) and also the activity and properties of sialidase from three virus strains of type A circulating at the same period of time.The results show that the activity and the V_max was always higher for sialidase of type A viruses relative to those values of type B. Differences were also found for optimal pH and, in some cases, for thermal stability of the sialidase between strains belonging to the influenza viruses type A and B. However, the behaviour for the sialidase in all strains was very similar towards two competitive inhibitors. Thus, it could be suggested that the evolution pattern of the sialidase of both types of influenza viruses determines some modifications which result in a higher efficiency for sialidase of some strains of influenza virus type A, but maintaining in the two types of viruses a similar behaviour towards competitive inhibitors.Dedicated to Professor Maurice Leclerc by one of us (J.A.C.) on the occasion of his retirement.     

Peculiarities of influenza infection caused by highly and poorly immunogenic strains of influenza virus

The authors studied the peculiarities of the course of experimental influenza infection induced by the administration of highly and poorly immunogenic strains of influenza virus to mice. Influenza viruses with varying immunogenic activity were obtained from the vaccine strain A/Victoria/35/72/50 (H3N2) by immunoselection modelling the process of natural selection. The administration of strains with high and poor immunogenicity to mice of the F1 (CBA X C57B1) line led to the development of acute influenza infection accompanied by reproduction of viruses in the tissue of the lungs and other internal organs. The poorly immunogenic strain 5/II-Victoria, unlike the initial virus A/Victoria/35 and its highly immunogenic variant 2/I-Victoria, is able to circulate for a long time in the organism of the infected animal causing development of chronic inflammatory processes and stimulating the formation of neoplasms. Immunogenicity is thus one of the factors determining the character of the course of experimental influenza infection. A conclusion was drawn concerning the epidemiological and aetiological importance of viruses with reduced immunogenicity and their role in the evolution of influenza virus. It is presumed that reduced immunogenicity is one of the adaptation mechanisms of aggression permitting the population of influenza virus to escape control by specific humoral immunity.     

Kinetic profile of influenza virus infection in three rat strains

Influenza is a respiratory tract disease of viral origin that can cause major epidemics in humans. The influenza virus infects and damages epithelial cells of the respiratory tract and causes pneumonia. Lung lesions of mice infected with influenza virus resembles those seen in humans with influenza, and can result in severe and even fatal pneumonia. In contrast, experimental infection of rats with the virus induces a milder form of the disease, with no mortality. The purpose of the study reported here was to determine the time course of influenza infection and lung injury in Brown Norway (BN), Fischer-344 (F344), and Sprague-Dawley (SD) rats to ascertain whether genetic background impacts susceptibility to infection and host responses. Rats of each strain were inoculated intranasally with 10,000 plaque-forming units of rat-adapted influenza virus (RAIV), and lungs were assessed at postinoculation hour (PIH) 2, 24, 48, 72, and 144 for viral titer, inflammatory cells, pro-inflammatory cytokines, and biochemical indicators of lung edema (protein) and injury (lactate dehydrogenase [LD] activity). Virus titer peaked at PIH 24, and was 100-fold higher in the F344 and SD, compared with the BN strain. Alveolar macrophages, LD activity, and total protein concentration were higher in the BN rats, whereas neutrophil numbers and interleukin 6 and tumor necrosis factor-alpha activities were greatest in the bronchoalveolar lavage fluid of F344 and SD rats. The results indicate that F344 and SD rats respond in similar manner to viral infection, whereas viral replication was more limited in BN rats and was associated with a different profile of pulmonary cells.     

细胞适应性流感病毒高产株的制备研究

与鸡胚培养制备的流感疫苗相比,细胞制备的疫苗具有免疫原性好、生产不受鸡胚限制等优点。但目前流感病毒株在细胞上产量较低,成为疫苗生产的主要限制因素。现就用于制备细胞适应性高产株主要的3种方法,即连续传代、随机突变构建病毒突变体和病毒重配的研究进展,以及突变位点对病毒增殖的影响作一概述。