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ts5, a temperature-sensitive mutant of influenza B virus, belongs to one of seven recombination groups. When the mutant infected MDCK cells at the nonpermissive temperature (37.5°C), infectious virus was produced at very low levels compared with the yield at the permissive temperature (32°C) and hemagglutinating and enzymatic activities were undetectable. However, viral protein synthesis and transport of hemagglutinin (HA) and neuraminidase (NA) to the cell surface were not affected. The NA was found as a monomer within cells even at 32°C, in contrast to wild-type virus NA, existing mostly as an oligomer, but the mutant had oligomeric NA, like the wild-type virus. Its enzymatic activity was more thermolabile than that of wild-type virus. Despite the low yield, large aggregates of progeny virus particles were found to accumulate on the cell surface at the nonpermissive temperature, and these aggregates were broken by treatment with bacterial neuraminidase, with the concomitant appearance of hemagglutinating activity, suggesting that NA prevents the aggregation of progeny virus by removal of neuraminic acid from HA and cell receptor, allowing its release from the cells. Further treatment with trypsin resulted in the recovery of infectivity. When bacterial NA was added to the culture early in infection, many hemagglutinable infectious virus was produced. We also suggest that the removal of neuraminic acid from HA by NA is essential for the subsequent cleavage of HA by cellular protease. Nucleotide sequence analysis of RNA segment 6 revealed that ts5 encoded five amino acid changes in the NA molecule but not in NB.

Three kinds of dextran-magnetite (DM) complexes were prepared using alkali-treated dextrans with molecular weights of 1900, 4200 and 9600, respectively. The number of dextrans binding to a magnetite core was determined. The number was proportional to the area of core surface and the area occupied by a dextran was 2.5 nm2 for molecular weight of 1900, 2.8 for 4200 and 3.8 for 9600. The binding of dextrans to core may be conditioned by the conformation of dextran chains in water (possibly by the steric hindrance between dextrans covering core). Stability of the DM solution was examined at 80 degrees C. Aggregation and/or precipitation of DM particles were observed within two weeks. The stability of DM solution was found to increase with increasing molecular weight of dextran. The dissociation of dextran from the core may cause the aggregation and subsequent precipitation of DM particles (the dissociation constant at 20 degrees C, 3.7 x 10(-6) for a molecular weight of 1900 and 5.4 x 10(-7) for 9600).

Dextran-magnetic iron oxide complex (CMDM) consisting of carboxymethyl dextran and a magnetite core has been synthesized. The physical and biological properties were compared with those of the conventional dextran-magnetite complex (ATDM). The CMDM exhibits a super-paramagnetic property, has high stability and low toxicity. The uptake and metabolic behavior of CMDM in live rats after intravenous (iv) administration were studied using pulsed nuclear magnetic resonance, optical microscopy and transmission electron microscopy. The ultrafine particles of CMDM were clearly observed in the lysosomes of Kupffer cells in the liver and of macrophages in the spleen. The CMDM accumulated in the lysosomes was found to disappear within two weeks after the iv-injection. The results obtained in this work suggest that CMDM is appropriate for use as a contrast agent for magnetic resonance imaging (MRI).