Predicting susceptibility and incubation time of human-to-human transmission of vCJD.

BACKGROUND: Identification of possible transmission of variant Creutzfeldt-Jakob disease (vCJD) via blood transfusion has caused concern over spread of the disease within the human population. We aimed to model iatrogenic spread to enable a comparison of transmission efficiencies of vCJD and bovine spongiform encephalopathy (BSE) and an assessment of the effect of the codon-129 polymorphism on human susceptibility. METHODS: Mice were produced to express human or bovine prion protein (PrP) by direct replacement of the mouse PrP gene. Since the human PrP gene has variation at codon 129, with MM, VV, and MV genotypes, three inbred lines with an identical genetic background were produced to express human PrP with the codon-129 MM, MV, and VV genotypes. Mice were inoculated with BSE or vCJD and assessed for clinical and pathological signs of disease. FINDINGS: BSE was transmitted to the bovine line but did not transmit to the human lines. By contrast, vCJD was transmitted to all three human lines with different pathological characteristics for each genotype and a gradation of transmission efficiency from MM to MV to VV. INTERPRETATION: Transmission of BSE to human beings is probably restricted by the presence of a significant species barrier. However, there seems to be a substantially reduced barrier for human-to-human transmission of vCJD. Moreover, all individuals, irrespective of codon-129 genotype, could be susceptible to secondary transmission of vCJD through routes such as blood transfusion. A lengthy preclinical disease is predicted by these models, which may represent a risk for further disease transmission and thus a significant public-health issue.

Inhibition of macrophage differentiation and function by cortisol.

Neuroendocrine mechanisms are involved in modulation of the immune system, but the mode of action of the complex interplay between hormones and the immune system is only partially understood. This study examines the role of cortisol in monocyte differentiation and function, with regard to interleukin-1 beta (IL-1 beta) expression. The differentiation of the human histiocytic lymphoma cell line U 937 into macrophage-like cells by phorbol ester [phorbol myristate acetate (PMA)] is inhibited by cortisol. Some cells remain in suspension and continue to divide; others stop proliferation, but do not undergo full morphological differentiation. When cells are washed after 3 days to remove PMA and cortisol, all cells stop dividing and become fully differentiated. The PMA, therefore, commits the cells to differentiate even after its removal, while cortisol is only suppressive when present. Differentiated cells are shown to produce IL-1 beta mRNA when stimulated with lipopolysaccharide. This effect is inhibited by cortisol in a dose-dependent manner. After removal of cortisol, the least differentiated cells that remained in suspension were found to be overproducers of IL-1 beta mRNA after stimulation with lipopolysaccharide. This suggests that PMA induces a buildup of transcription-activating factors that were suppressed in the presence of cortisol. We conclude that the adrenal glucocorticoids that are elevated in acute stress conditions or major depression attenuate the differentiation and function of monocytes.

Molecular cloning and sequencing of the F and 22K membrane protein genes of the RSS-2 strain of respiratory syncytial virus.

The nucleotide sequences of the adjacent genes coding for the F protein and 22K protein of the RSS-2 strain of human respiratory syncytial (RS) virus were determined from cDNA clones of genomic RNA. Comparison of these sequences and the inferred amino acid sequences of the F and 22K proteins with the corresponding published sequences of another subgroup A virus, the A2 strain of RS virus, reveals extensive overall homology (greater than 95%) at both the nucleotide and amino acid levels, even though these two viruses were isolated 15 years apart in different continents. The intergenic region and the hydrophobic amino-terminal signal sequence of the F proteins of the two viruses, however, are much less conserved.

The molecular biology of rotaviruses. VII. Detailed structural analysis of gene 10 of bovine rotavirus.

cDNA cloning and nucleotide sequence analysis have allowed detailed structural studies on RNA segment 10 of the U.K. bovine rotavirus to be undertaken. The complete sequence of 751 nucleotides was determined and found to contain only a single long open reading frame capable of coding for a protein of 175 amino acids. The gene has an unusually long 3' untranslated region of 184 nucleotides or some 24.5% of the total sequence, whose start was confirmed by analysing the carboxyterminal amino acid of the gene 10 product, the glycoprotein VP10c. Analysis of purified virions radio-labelled with [3H]glucosamine and [3H]mannose showed that VP10c is not a detectable component of the virus particle. The two potential glycosylation sites were found to be very close to the amino terminus of the putative translation product, strongly suggesting that the glycoprotein VP10c does not contain a cleavable signal sequence.

Adaptation of coronavirus JHM to persistent infection of murine sac(-) cells.

Coronaviruses can establish persistent infections in the central nervous system of rodents, and these are associated with demyelinating encephalomyelitis. The effects of persistence on the virus are difficult to study in vivo but may have a crucial influence on the course of infection. We therefore produced a persistent infection in vitro using the neurotropic coronavirus JHM, in order to investigate the events underlying the establishment of such an infection and the adaptation of the virus to persistence. The persistent infection was maintained for over 115 passages and continued to release high levels of infectious virus. During the 18 months of culture the number of cells expressing virus antigen detected by indirect immune fluorescence decreased to 40%. Analysis showed that the carried virus contained a significant proportion of heterogeneous temperature-sensitive mutants. All virus clones isolated possessed the capacity to induce a more productive growth cycle, a less pronounced cytopathic effect and showed a much reduced neurovirulence when inoculated into newborn and weanling rats. Evidence for structural changes involving the surface peplomer protein (E2) was obtained using hybridoma antibodies, which neutralized the parental JHM virus but not the JHM-Pi virus. Defective interfering particles and interferon activities have been excluded as possible agents instrumental in the establishment and maintenance of the chronic infection, and we suggest that the emergence of virus variants of lowered virulence is central to these processes.

The effect of polyamines on herpes simplex virus type 1 DNA polymerase purified from infected baby hamster kidney cells (BHK-21/C13).

The DNA polymerase whose synthesis is directed by the herpes simplex virus type 1 (HSV-1) DNA was purified 545-fold from BHK-21/C13 cells 16 h after infection with the virus. Spermidine and spermine stimulated the activity of the polymerase over the concentration range 0.5 mM to 2.5 mM. This effect was enhanced with increased concentrations of polyamine, maximum stimulation being threefold and fourfold for spermidine and spermine respectively. The diamine, putrescine, had little effect on the enzyme at the concentrations used (0.25 to 1.25 mM).