Conditions Determining Melanosis of a Virus-Induced Rabbit Papilloma (Shope)

Abstract

The Shope papilloma, a growth caused by a virus 1 and having the immediate characters of a tumor, 2 is frequently colored gray, brown or black with melanin. 1 Bits of the proliferating tissue when implanted in the leg muscles and viscera of the host grow vigorously, and portions of the resulting mass are often melanotic, and occasionally it is darkly pigmented everywhere. 2 This paper is concerned with the conditions determining the pigmentation.

The possibility that certain strains of the causative virus determine the pigmentation was investigated first. Two virus suspensions were prepared from glycerinated fragments of 2 peritoneal autotransplants in a wild rabbit. One of the growths was coal black, the other unpigmented. The suspensions were inoculated by tattooing them into numerous spots in the shaved skin of the sides of 2 cottontail rabbits, 4 brown-gray or agouti rabbits of domestic breed and 2 of the Dutch variety (show type). These last had white hair on the anterior half of the body, black hair on the posterior, and the inoculations were made into both regions. All of the papillomas that arose in the “white” regions were devoid of pigment, whereas all those in the “black” were gray or sooty, irrespective of the derivation of the inoculum. The results in the other animals corroborated these findings.

In the animals just considered, as well as in many others inoculated with other strains of the virus, melanotic papillomas developed only where the hair was pigmented. This distribution of the pigmented growths corresponded absolutely with that of melanoblasts or potential melanoblasts in the skin of the rabbit. That melanotic papillomas arise only where such cells are present was shown even more clearly in frozen sections of early stages of growths induced in the skin of the ear.