Year

1991

Degree Name

Doctor of Philosophy

Department

Department of Biology

Abstract

The interaction of human cytomegalovirus ( HCMV ) with stimulated peripheral blood T cells and T-cell clones was studied using the laboratory adapted strain (AD 169) and clinical isolate (p72) of HCMV. PHA stimulated lymphocytes isolated from healthy seronegative donors were found to undergo changes in the expression of several functionally important T-cell markers following HCMV challenge. CD4 and CD8 expression were downregulated within 6 hours of viral challenge. By 24 hours postchallenge, CD4 levels had recovered and CD 8 levels were found to increase. This ability of HCMV to upregulate CD8 expression was shown using a CD4+ T-cell clone in which it was found that HCMV challenge caused an inversion in the CD4 : CD8 cell ratio by 12 days post-challenge. It is proposed that the early changes seen in marker expression due to a direct physical interaction of the virus with T-cells whereas later changes to the virus inducing functional changes. HCMV challenge was found to cause an increase in the number of CD8+UCHL-1 (CD45RO) cells in PHA stimulated T-cells analysed at 48 and 96 hours post-challenge. In addition virus challenge resulted in persistence of CD4+2H4+ (CD45RA) cells in these cultures when compared to mockchallenged controls at 24-48 hours post-challenge. These latter cells have been proposed as being suppressor-inducers. These results suggest that HCMV challenge influences functional populations of T-cells. The clinical isolate of HCMV was found to persist cells stimulated with ConA+IL-2 , a mode of stimulation known to elevate levels of CD4+CD8+ cells. Further HCMV was found to persist and to replicate, albeit at low levels, in a CD4+CD8+UCHL-1+ T-cell clone up to 18 days post-challenge. HCMV DNA was also found to be present in PHA stimulated and cloned T-cells of a memory (UCHL-1+; CD45RO) phenotype at 96 hours and 21 days post-challenge. These results suggest that HCMV may persist in a small subset of T-cells which may provide a possible cell vector for blood transfusion related HCMV transmission. The effect of HCMV challenge on the production of Interleukin-4 (IL-4) and EFN-ywas studied in a CD4+CD8+ T-cell clone and in PHA and ConA+IL-2 stimulated peripheral T-cells. IL-4 production was found to increase in HCMV-challenged cells when compared to levels in mock-challenged cells, thus providing a possible mechanism whereby H C M V alters immune functions. IFN-y production in mixed populations of P H A and ConA stimulated T-cells increased marginally following challenge with A D 169 whilst challenge with the clinical isolate resulted in suppression of _FN-y production when compared to mockchallenged cultures. This effect indicates a possible difference in the immunosuppressive capacities between the two strains of virus.

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