Inhibition by Methylprednisolone of Regression of the Shope Rabbit Papilloma2

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Abstract
The effects of methylprednisolone on the Shope rabbit papilloma were investigated. Papillomas were followed on 38 domestic rabbits treated with high doses of methylprednisolone for up to 26 weeks after virus inoculation. These papillomas were compared with papillomas on 41 control rabbits. Only 1 steroid-treated rabbit showed papilloma regression (papilloma loss), whereas papillomas regressed on 18 control rabbits. The rabbits treated with methylprednisolone showed both an increased incidence of papillomas at sites not deliberately inoculated with virus and decreased immunity to reinfection by Shope papilloma virus. Steroid treatment caused a decrease in mononuclear-cell inflammatory reaction about the base of the papillomas. Neither the interval between virus inoculation and papilloma appearance nor the growth rate of the papillomas was influenced by steroid treatment. No increase in virus extractable from papillomas of the steroid-treated rabbits was noted, nor was any change noted in frequency of carcinoma development in papillomas of the steroid-treated rabbits. With steroid treatment, it was possible to establish papillomas on rabbits that had previously regressed papillomas, but these papillomas were not indefinitely maintained. The inhibition by steroid of papilloma regression adds further support to the growing evidence indicating that papilloma regression is mediated by an immune mechanism and is consistent with the view that the mechanism is similar to that responsible for homograft rejection.