FIG. 4.

Timing of late events is highly conserved among lesions caused by the same papillomavirus type. Similarities in the patterns of E4 expression and genome amplification confirmed that E4 was an effective marker of the late stages of the papillomavirus life cycle. Tissue biopsies infected by different papillomaviruses were sectioned and stained using E4-specific antibodies (green) before being counterstained with DAPI (blue). The staining patterns illustrated were typical of those seen following the examination of five or more independent biopsy specimens infected by each virus type (except for HPV63, for which three lesions were examined [see Materials and Methods]). The timing of late-stage onset was a characteristic feature of each infecting virus type. All images were taken using a 4× objective except for the HPV16 and CRPV images, which were taken using a 10× objective lens. The basal layers are indicated by the broken lines.