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It has previously been shown that the Flavivirus West Nile Virus (WNV) enters the macrophagelike cell line P 388D 1 rapidly on warming to 37°C. Initially particles are internalized in coated vesicles and subsequently appear in endosomes and then lysosomes. WNV particles have been shown to fuse with artificial liposomes optimally at mild acidic pH. In the present study, interaction between WNV and P 388D 1 cells was assayed by following the association of Pronase-resistant ³⁵S-labelled virus with cells. Transmission and Scanning electron microscopy were also used for this purpose. Virus particles were shown to have an increased affinity for the cell structure at pH below 7.0. This was shown to be because virus particles were fusing in a pH-dependent manner with maximum fusion occuring at pH6.4 or below. We have previously showed that lysosomotropic amines can inhibit WNV infection by raising the pH in the endosomal compartments. It is thus probable that acid pH-dependent fusion is important in release of the WNV nuclear capsid from endosome to the cytosol. Radiobinding study and electron microscopy showed that a balance exists between endocytosis and fusion of Flaviviruses with the P 388D 1 cell plasma membrane, with pH of extracellular medium deciding which one predominates.

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Analysis was made of hepatitis B virus surfaceantigen (yHBsAg) expressed in a systen using yeastas host by recombinant genetic techniques. They HBsAg was found to have been produced as a par-tide mainly composed of disulfied-bonded dimers of polypeptides each having a molecular weight of about 23, 000, in which the polypeptide corresponds to the polypeptide of human carrier's plasma-derived hepatitis B surface antigen (hHBsAg) without having glycosylated side-chain thereto. There were strong indications that such dimers are primarily responsible for antigenicity and immunogenicity, and that the steric structures of the yHBsAg due to disulfide bonds are related to the antigenicity and the immunogenicity. The N-terminml amino acid sequence and the amino acid composition of the yHBsAg were found to be in good agreement with those predicted from the DNA sequence. Other properties of the yHBsAg, such as CD spectrum, UV absorption spectrum and tryptic digestion pattern were quite similar to those of hHBsAg. Further, immunization experiments using mice and guinea pigs showed that the immunogenicity of the yHBsAg is equivalent to that of hHBsAg.

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The binding activity of purified and ¹²⁵I-labeled recombinant human interferon alpha-2a (rIFN alfa-2a) to FL cells was studied. The number of receptors per cell and the binding constant were estimated as 1.7×10³ and 9.1×10¹⁰ M^-1, respectively. These values are similar to those reported for natural human interferon alpha (nIFN alfa) and for recombinant human interferon alpha-2b. Unlabeled rIFN alfa-2a and unlabeled nIFN alfa produced in human leukocytes inhibited the binding of ¹²⁵I-labeled rIFN alfa-2a to a similar degree.
These results suggest that rIFN alfa-2a binds to the same cell-receptors as those for nIFN alfa, and that the binding activities of the two are similar.

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