Persistence of viral DNA in the epithelial basal layer suggests a model for papillomavirus latency following immune regression.
Bottom Line: This was not associated with completion of the virus life-cycle or new virion production, indicating that ROPV persists in a latent state.Using novel laser capture microdissection techniques, we could show that the site of latency is a subset of basal epithelial cells at sites of previous experimental infection.We hypothesize that these cells are epithelial stem cells and that reactivation of latency may be a source of recurrent disease.
Affiliation: Division of Virology, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, UK.Show MeSH
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Mentions: Our primary goal was to establish the fate of viral genomes following the immune regression of ROPV papillomas. We therefore sought a means of permanently and accurately identifying areas of the tongue tissue that had previously undergone experimental infection with ROPV, and differentiating them from adjacent regions that had not been infected. A previous study demonstrated that by pin-pricking the undersurface of the tongue with a hypodermic needle and then applying ROPV virions, discrete papillomas measuring 1 mm in size formed at more than 75% of sites (Embers et al., 2002). We modified this technique by pinpricking the tongue with a mixture of ROPV virions and black tattoo ink. Using this modified technique, we also found that visible papillomas formed at 75% of tattoo-marked infected sites but did not appear at uninfected sites. Typically, papillomas were first evident by visual inspection at 2 weeks post-infection. At this time, the tongue was completely healed following the infection procedure and papillomas appeared as small raised and translucent lesions that were associated with no noticeable inflammation. They continued to grow until between 4 and 6 weeks post-infection reaching a maximum size of approximately 2 mm (Fig. 1A). At this time, they had a prominent exophytic appearance with the tattoo mark clearly visible in the underlying tissues. Detrimental effects on general rabbit health, appetite and body condition were not apparent. Around 6 weeks post-infection, immune-mediated regression was apparent, and was associated with a reduction in papilloma size and number, and with complete resolution of papillomas by 8 weeks post-infection. At this time point, the epithelium resumed a normal appearance (other than for the presence of tattoo marks) as determined by gross visual and microscopic examination of tissue sections. We did not observe the formation of visible papillomas at any regions of the lingual mucosa that had not been experimentally infected. Furthermore, papillomas did not form elsewhere within the oral cavity. The location of papillomas was found to correlate very closely with the location of tattoo marks as determined by visual inspection, and tattoo marks were still readily visible as late as a year following experimental infection. Microscopic examination confirmed that tattoo marks were easily visible in the dermis immediately underlying papillomas and that they continued to localize sites of experimental infection beyond the regression of papillomas (Fig. 1B). Addition of tattoo ink did not appear to influence the progression of infection, with identical papillomas forming and regressing concurrently at tattoo-marked and unmarked sites in the same rabbit (data not shown). The tattoo marking technique appears useful therefore, for accurately identifying sites of experimental infection following the regression of papillomas, both by gross inspection and by microscopy.
Affiliation: Division of Virology, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, UK.