Transcription at early stages of herpes simplex virus 1 infection and during reactivation

The kinetics of immediate early (IE) and early (E) herpes simplex virus 1 (HSV-1) mRNA transcription was followed in explanted trigeminal ganglia from rabbits with established latency.

The expression of IE and E mRNAs was first assessed in infected Vero cells by RT-PCR and then in explanted trigeminal ganglia by nested RT-PCR.

In infected Vero cells, IE mRNAs [for infected cell protein (ICP) 0, ICP4 and ICP27] were first detected 1-2 h post-inoculation (p.i.), peaking at 3 h p.i. The transcription of E mRNAs [for thymidine kinase (TK), RR1 and UL9], which were first detected from 3 h p.i., peaked between 5 and 10 h p.i. In explanted ganglia, the ICP0, ICP4 and ICP27 mRNAs were first detected after 4 h in culture. This was followed by the appearance of TK mRNA at 8 h and then by the UL9 mRNA, detected from 12 h post-explantation. A further E mRNA (RR1), as well as the late gC mRNA, were first observed after 24 h in culture. Moreover, ICP4 mRNA could be found in non-cultured ganglia.

During reactivation of latent HSV-1 in explanted ganglia, the onset of ICP0 and ICP27 transcription at 4 h in culture was followed by TK transcription (at 8 h). Thus, in the rabbit reactivation model, ICP0 gene transcription rather than ICP4 transcription represents the relevant indicator of latency reactivation.