Helen M. Laird

Determinants of the host range of feline leukaemia viruses.

Summary Feline leukaemia viruses of subgroups B and C multiply in human and canine cells, while subgroup A viruses do not. This host range restriction is determined by the virus envelope and operates at the level of virus entry into the cell. Subgroup A virus genomes are expressed and replicated when they are introduced within B subgroup envelopes into human or dog cells. Therefore, since they are phenotypic mixtures of A and B subgroup viruses, the majority of feline leukaemia virus isolates will infect human and canine cells with the subsequent production of FeLV of each subgroup.

A novel bovine papillomavirus (BPV-6) causing true epithelial papillomas of the mammary gland skin: a member of a proposed new BPV subgroup

A papillomavirus has been isolated from frond epithelial papillomas of the bovine udder. It is clearly distinguishable from all other bovine papillomaviruses (BPVs) based on DNA sequence homology and antigenic properties and is thus characterised as a new entity, designated BPV-6. BPV-6 does not possess the interspecific papillomavirus antigen, its genomic DNA (7.2 kb) is smaller than, and does not show any sequence homology to BPV-1, BPV-2, or BPV-5, whereas it is approximately the same length as BPV-3 or BPV-4, with which it shares some sequence homology. The bovine papillomaviruses have been classified into two subgroups: subgroup A, composed of BPV-1, BPV-2, and BPV-5, all of which induce fibropapillomas, and subgroup B, composed of BPV-3, BPV-4, and BPV-6, all of which cause true epithelial papillomas.

Molecular heterogeneity and lesion site specificity of cutaneous bovine papillomaviruses.

Abstract We have characterized the DNA of papillomaviruses from cutaneous papillomas of British cattle using restriction enzymes and physical mapping. We have found three main types of BPV: one is a newly reported distinct type (BVP-5) specifically associated with a very common tumor of the skin of the teat and udder, descriptively known as “rice grain” papilloma; a second is associated with papillomas of the neck and shoulder (BVP-2); and a third is associated with papillomas of the penis and teat (BVP-1). We have investigated the DNA sequence homology between these viruses by nucleic acid cross-hybridization. We discuss the relationship between the five bovine papillomaviruses which have been characterized so far.

Ultrastructural features of canine distemper virus infection in a dog kidney cell line.

Summary Cultures of dog kidney cells were infected with canine distemper virus at an input multiplicity of 1.9 and the subsequent events followed by electron microscopy, conventional staining methods and virus titration. Maturation and release of virus commenced within 24 hr of infection and was a slow but prolonged process, the infected cell producing small amounts of virus for at least 48 hr. After formation in cytoplasmic foci, often perinuclear, the virus nucleocapsid migrated to the cell membrane, below which it adopted a symmetrical configuration, the cell membrane at the same time acquiring a layer of fine surface projections. Maturation of virus then occurred by a protrusion and pinching off of these areas. Cytoplasmic aggregates of nucleocapsid were not detected by light microscopy. The characteristic phloxinophilic cytoplasmic inclusions, which appeared between 24 and 48 hr after infection, did not stain with acridine orange. Some consisted of a mass of amorphous electron-dense material and others of nucleocapsid-like filaments enmeshed in an electron-dense matrix but all contained a number of pockets in which membrane-bound vacuoles and tubules were prominent.

Two populations of virus-specific particles released from feline calicivirus-infected cells

Abstract In harvests of a feline calicivirus (FCV) grown in feline embryo cells two populations of viral components were observed after centrifugation in sucrose and CsCl gradients. Particles in the first (PI) were mature virions since they had a buoyant density of 1.39 g · cm−3, a sedimentation coefficient of 170 S, were infectious and showed characteristic calicivirus morphology by electron microscopy. The second particle (P2), which in terms of protein was 10 times as abundant as P1, had a buoyant density of 1.31 g · cm−3, a sedimentation coefficient of 15 S, and contained little or no infectivity. Evidence that P2 was virus specific was that P2 as well as P1 contained a polypeptide with a molecular weight of 65,000 which is the weight of the viral capsid protein, and P1 and P2 shared an antigenic determinant which was responsible for inducing neutralizing antibodies. The 15 S component was not generated from the virion by conditions encountered during viral growth and purification. It is considered likely that the 15 S particle is a stable product of FCV infection and may be a subunit in the assembly of the viral capsid.

Unique Morphological Alterations of the HTLV-I Transformed C8166 Cells by Infection with HIV- 1

C8166 cells express T lymphocyte markers, a monocyte-specific esterase,tax polypeptide of HTLV-I. In spite of this transactivator, their HIV-1 yield is low. Their culture conditions were modified, and infected cells were immobilized on a poly-L lysine sheet under semisolid overlays to study their phenotypic alterations and HIV-1 production by microscopy and electron microscopy. Another lymphoid cultures (MT-4, CEM, CEM-ss, AdCEM) similarly treated were infected with either HIV-l/RF or IIIB. Specificity of HIV-1 was compared to the effects of vesicular stomatitis virus (VSV). Unlike other cultures, HIV-l/RF infected C8166 cells in Eagle’s MEM exhibited surface projections resembling hairy leukemia cells, which was followed by balloon degeneration and apoptosis. Immobilized HIV-1 infected cultures formed flat syncytia with several interdigitating dendritic projections. Syncytia shrunk with condensed nuclear material and axon-like filaments characteristic for infected macrophages. VSV induced enlargement and necrotic lysis of all cell types. Early postinfection with HIV-1, electron microscopy revealed irreversible membrane fusion above cell nuclei, and transient fusion between filaments. Transient presence of coated vesicles containing intact HIV-1 particles, Birbeck granule-like structures of Langerhans cells, fibrillar-lamellar structures resembling hairy leukemia or Sézary cells were detected. Late postinfection, high proportion of HIV-1 bud from polarized cytoplasm was empty particle, while that bud and entrapped in cytoplasmic vacuoles contained two or multiple cores in a fused envelope. The effect of early gene products of HIV-1 on HTLV-I and C8166 cells might elicit their latent potentials for monocyte or interdigitating dendritic cells, while in the later phase HTLV-I products might alter HIV-1 virion assembly.