Immunofluorescent Study on Early Virus-Cell Interaction in Shope Papilloma in Vitro System ∗

Discussion and Conclusion

Embryonic skin culture of domestic rabbit was infected with Shope papilloma virus in vitro and the early phase of virus-cell interaction was studied sequentially up to 30-hours post infection by the immunofluorescence technique. The cells of infected cultures showed a specific fluorescent reaction in the nucleus when stained with antipapilloma antisera conjugated with FITC. The ratio of positively stained cells was about 20% of the whole cell population in cultures 5-6 hours after infection with the virus and it reached a maximum of approximately 90% at around 11 hours. The morphological pattern of the intranuclear fluorescent staining was reminiscent of the reaction of T antigen reported in the SV40-infected hamster cells (6).

Kreider et al. (7) have recently reported their findings on the persistence of Shope papilloma virus absorbed onto the cell surface of cells of in vitro cultured embryonic skin of rabbits. The viral antigen was detectable in cultured cells even after 6-days postinfection by immunofluorescence. The fluorescent granules were seen randomly distributed all over the cell in most of the cases.

The specific immunofluorescence in the SPV-infected embryonic cells as shown in the present study was clearly associated with the nucleus and the positive staining reaction was only induced by the antipapilloma antiserum. Experiments with the anti-SPV antiserum yielded only negative results. From these findings, it seems plausible to conclude that the antigen demonstrated in the nucleus of the SPV-infected rabbit cells by immunofluorescence possibly meets at least a part of the criteria of T antigen. Studies are being carried out to assess the problem from different approaches such as complement fixation test between the cellular extract of the infected cell culture and the antipapilloma and anti-SPV antisera.