The refractoriness of the skin of hairless mice to chemical carcinogenesis.

ceous apparatus. Billingham et a!. (3), after painting mouse sldn with MCA, transplanted the epidermis onto an un treated area of dermis and grafted untreated epidermis onto the treated area of dermis. Invariably, epitheial carcinomas arose only from the areas in which the dermis had been treated, where the only epithelial structures present were the hair follicles. In 1968, Steinmuller (25), using F1 hybrids in comparable grafting experiments, elegantly demonstrated that the hair follicle is the only possible origin of such tumors. In apparent contradiction to the findings cited above are a number of reports stating that the skin of the hairless mouse is susceptible to chemical ca.rcinogenesis (2, 9†" 12, 15, 17, 21 , 23). We have reinvestigated the induction of skin tumors in hairless mice by chemical carcinogens, using the induction promotion technique. Haired and hairless mice of the same strain, differing only in the presence or absence of the hairless mutation, were exposed to the same carcinogenic stimulus at doses just below those required to produce papillomas in 100% of the haired mice, after we made sure that the hairless mice used were really hairless. The mice used were a homogeneous strain, bb cc hr hr or bb cc Hr hr. Throughout this paper, the former are referred to as hairless mice and the latter are referred to as haired mice. Each group was composed of siblings. This strain originated at the Jackson Laboratory, where it was inbred through at least 23 generations of sister-brother matings (d bb cc hr hr x9bb cc Hr hr). In1963, some animals of this strain were given to the Division of Biological and Medical Research of the Argonne National Laboratory. At the Argonne National Laboratory these animals were bred randomly, crossing haired females with hairless males. The animals for the adult experiments were obtained directly from the Argonne National Laboratory over the period of 1964 to 1968 through the kindness of Dr. Charles Auerbach or were bred in our animal room. We obtained the â€oenewborns†• by crossing haired females with hairless males. All the mice were housed in plastic cages and received water and Rockland pellets ad libitum. distilled acetone was used as an initiator. This solution (0.1 ml containing 100 pg of DMBA) was placed on the backs of the mice with a micropipet. For promotion, a solution of 0.5% croton oil in acetone (kindly donated by Dr. …