T-cell motility in the early stages of the immune response modeled as a random walk amongst targets

The transport process by which a T cell makes high-frequency encounters with antigen-presenting cells following infection is an important element of adaptive immunity. Recent experimental work has allowed in vivo cell motility to be characterized in detail. On the basis of experimental data we develop a quantitative model for encounters between T cells and antigen-presenting cells. We model this as a transport-limited chemical reaction with the dynamics dependent on physical contact between randomly moving reactants. We use asymptotic methods to calculate a time distribution which characterizes the delay before a T cell is activated and use Monte Carlo simulations to verify the analysis. We find that the density of antigen-primed dendritic cells within the lymph node paracortex must be greater than 35 cells/mm3 for a T cell to have a more than 50% chance of encountering a dendritic cell within 24 h. This density is much larger than existing estimates based on calculations which neglect the transport process. We also use simulations to compare a T cell which re-orients isotropically with a T cell which turns according to an experimentally observed distribution and find that the effects of anisotropy on the solution are small.

Insulin-like growth factor-I (IGF-I) and its association with lymphocyte homeostasis in the ageing cat

Ageing affects feline lymphocyte homeostasis in a similar pattern to that observed in other long-lived mammalian species, contributing to increased levels of morbidity and mortality in the ageing cat. Insulin-like growth factor-I (IGF-I) is now recognised as an important endocrine regulator of immunity and has been shown to decline with age in humans and rodent species. Analysis of plasma IGF-I in adult and senior cats confirmed that the older cats had significantly lower circulating levels of IGF-I. In order to determine whether an association existed between lymphocyte subpopulations and IGF-I levels in the cat, each parameter was measured and subjected to regression analysis. A highly significant association was found in vivo between plasma IGF-I and CD4(+) T-cell values in the senior group, but no such association was observed in the adult group. In order that this relationship could be examined further, in vitro studies were undertaken to investigate the effects of physiologically relevant concentrations of recombinant human IGF-I (rhIGF-l) on peripheral blood lymphocyte (PBL) cultures from adult and senior cats. While rhlGF-I induced low-level thymidine incorporation in the lymphocytes isolated from the senior group, it did not enhance the proliferative response to T-cell mitogens, Con A and PHA in either group, nor did it rescue cells from oxidatively induced apoptosis. Furthermore, the proliferative response of PBL from seniors did not attain the magnitude of that from the adults at any concentration of rhIGF-l. We propose that the observed association is not a direct effect of IGF-I on PBL, but may be mediated through an effect of IGF-I on the thymus.

First isolation of a rabies-related virus from a Daubenton's bat in the United Kingdom

On May 30, 1996, a sick Daubenton's bat (Myotis daubentonii) was recovered from the cellar of a public house in Newhaven, East Sussex. Its condition deteriorated rapidly, and it was euthanased and examined. Positive results, establishing the presence of a rabies or rabies-related virus in its brain, were obtained from the fluorescent antibody test, the rabies tissue culture isolation test, and a hemi-nested reverse-transcription PCR. The complete sequence of the nucleoprotein gene was determined and a phylogenetic analysis, based on the 470 nucleotide bases of the amino terminus of the nucleoprotein, established the genotype of the virus as European bat lyssavirus 2. Bat rabies had not previously been recorded in the UK but does occur in mainland Europe. A study of the back-trajectories of the wind on May 29 and 30, established that the infected bat possibly came from near the Franco-Swiss border.

Molecular methods to distinguish between classical rabies and the rabies-related European bat lyssaviruses

A rapid and sensitive reverse transcriptase-polymerase chain reaction (RT-PCR) assay for the detection of classical rabies virus (genotype 1) and the rabies related European bat lyssaviruses (EBLs) (genotypes 5 and 6) was developed. When combined with specific oligonucleotide probes and a PCR-enzyme linked immunosorbent assay (PCR-ELISA), genotype 5 and 6 viruses can be distinguished from each other and from genotype 1 viruses. Ninety-two isolates from the six established genotypes of rabies and rabies-related viruses were screened by RT-PCR and PCR-ELISA to determine the specificity of the assays. All genotype 1, 5 and 6 viruses were detected by RT-PCR while none of the genotype 2, 3 and 4 viruses were detected. All the genotype 5 and 6 viruses were detected by the two PCR-ELISA probes when used in combination while none of the genotype 1-4 viruses were detected. When used individually, the PCR-ELISA probes also distinguished between the genotype 5 and 6 viruses. This new discriminatory test should allow the rapid genotyping of all lyssaviruses likely to be encountered in Europe and as such could provide useful epidemiological information in the event of an outbreak.

Assessment of template quality by the incorporation of an internal control into a RT-PCR for the detection of rabies and rabies-related viruses

A method is described to assess RNA template quality by the incorporation of a ribosomal RNA (rRNA) internal (in tube) control into a standard rabies and rabies-related virus specific RT-PCR. Specific virus and rRNA templates were co-amplified in a duplex reaction from RNA extracts derived from 60 isolates representing all six of the established lyssavirus genotypes. To ensure a wide species applicability of this technique we demonstrated that the rRNA assay was capable of functioning using the cells or tissues of 14 different mammals. Parallel studies between the duplex and the unlinked lyssavirus assay demonstrated only a minor reduction in the sensitivity of the former test. The ribosomal and viral targets (unlike beta-actin RNA) were shown to have similar degradation kinetics making rRNA amplification a good control for viral target integrity. As a consequence, the use of this system would reduce the likelihood of obtaining false negative RT-PCR results from lyssavirus infected material.

Detection and identification of rabies and rabies-related viruses using rapid-cycle PCR

The rapid identification of suspect rabies infection is essential in human cases, to ensure appropriate post-exposure treatment of contacts, and in animal cases to allow specific control strategies to be decided and implemented. We describe here the use of high speed air thermo-cycler PCR as a diagnostic tool for the detection of rabies and rabies-related viruses. Using this technique we were able to diagnose rabies in a human within 5 h. Furthermore, the application of automated sequencing of the resultant product enabled a definitive characterisation of classical rabies within 16 h. The utility of this assay was confirmed further by the successful detection of representatives of the six lyssavirus genotypes.

Investigation of the cellular tropism of bovine immunodeficiency-like virus

Bovine immunodeficiency-like virus (BIV) was first isolated from an animal showing transient leucocytosis, lymphadenopathy, lesions in the central nervous system and progressive weakness and emaciation. Similar signs are observed in other immunosuppressive lentiviral infections. BIV, like other lentiviruses, has been isolated from peripheral blood mononuclear cells and lymphoid tissue of infected animals. However, the in vivo cellular tropism of BIV remains unclear although initial studies indicate that BIV may be pantropic, infecting T cells, B cells and monocytes similar to some of the immunodeficiency-causing lentiviruses. PCR, Southern blot hybridisation, cell culture and reverse transcriptase assays were used to demonstrate the presence of BIV proviral DNA and the production of infectious virus in CD2+, WC1+, B cells and monocytes during the acute stages of infection. Western immunoblot assays were used to assess the development of antibody responses towards the virus.

Rapid detection of rabies and rabies-related viruses by RT-PCR and enzyme-linked immunosorbent assay

A rapid detection method for the six established genotypes of rabies and rabies-related viral RNA using RT-PCR-ELISA is described. The detection of digoxigenin-labelled amplified products is performed by solution hybridization to two specific, biotin-labelled, capture probes, which are complementary to the inner region of the amplification products. The capture probe and amplified product hybrid are then immobilised on a streptavidin-coated microtitre plate, bound products are detected by an anti-DIG Fab fragment conjugated to peroxidase, and colorimetric reaction automatically measured. This method was up to 100-fold more sensitive than Southern blot hybridization, detecting 0.00002 TCID50/ml of a genotype 1, classical rabies virus strain. The complete detection methodology from RT-PCR to PCR-ELISA detection could be completed within 10 h. Using this procedure, we were 100% successful in detecting 60 isolates from a representative selection of the six established genotypes from all over the world. This test is a useful additional tool for the detection of the rabies and rabies-related viruses, which is easy to perform, rapid and highly sensitive.

Heminested PCR assay for detection of six genotypes of rabies and rabies-related viruses

A heminested reverse transcriptase PCR (hnRT-PCR) protocol which is rapid and sensitive for the detection of rabies virus and rabies-related viruses is described. Sixty isolates from six of the seven genotypes of rabies and rabies-related viruses were screened successfully by hnRT-PCR and Southern blot hybridization. Of the 60 isolates, 93% (56 of 60) were positive by external PCR, while all isolates were detected by heminested PCR and Southern blot hybridization. We also report on a comparison of the sensitivity of the standard fluorescent-antibody test (FAT) for rabies antigen and that of hnRT-PCR for rabies viral RNA with degraded tissue infected with a genotype 1 virus. Results indicated that FAT failed to detect viral antigen in brain tissue that was incubated at 37 degrees C for greater than 72 h, while hnRT-PCR detected viral RNA in brain tissue that was incubated at 37 degrees C for 360 h.