Levels of bystander death occurring in herpes simplex virus type 1 (HSV-1)-infected mouse brain stems were studied, as well as the extent to which bystander death is influenced by
guanosine nucleoside analogue treatment. Consecutive sections from brain stems of HSV-1-infected mice were stained alternately for (i)
viral infection and (ii) cell death (TUNEL assay). Virus
antigen was detectable in brain stems on day 3 of
infection, while TUNEL staining was comparatively lower. An increase in the extent of TUNEL staining was observed on day 4 of
infection. Despite this increase, however, the ratio of TUNEL-stained to
infection marker-stained tissue still indicated that the amount of TUNEL staining remained lower than
infection staining at this time point. On days 5 and 6 of
infection, TUNEL staining continued to increase and the TUNEL/
infection marker ratio switched on day 6 in favour of excess TUNEL staining, which was observed in and around the foci of
infection, suggesting bystander death. The excess TUNEL staining on day 6 of
infection was further increased on treatment with
antivirals. The significance and implications of these results are discussed with respect to the nature and mechanism of action of the TUNEL assay, dynamics of primary HSV-1
infection, immunological influences and potential effects of
antiviral treatment. The potential problems of the TUNEL assay are considered in the context of
viral infection and the TUNEL assay, in combination with
infection marker staining, may potentially provide a model system for quantitative analysis of true bystander death during HSV
infection in vivo.