Lymphocyte stimulation with skin cells. A function of maturation.

Cell monolayers grown from trypsin dispersions of whole rat embryos were tested for their capacity to stimulate allogeneic rat thymus cells in mixed cell cultures. Cells from whole embryos of only 15-days gestation were virtually ineffective at stimulating allogeneic thymus cells. Cells from 19-day-old whole embryos produced definite stimulation and stronger stimulation was obtained with skin cell monolayers prepared from these embryos. The average amount of allogeneic stimulation obtained with rat skin cells increased with the age of the donor animals. The greatest degree of stimulation occurred when the skin cells were obtained from rats about 1 week postpartum. Thereafter, the stimulating potential of allogeneic skin cells declined and was found to stabilize at the levels observed when adult skin cells were used as the stimulator cells. Neither rat brain cells nor rat kidney cells (taken from embryos, neonates, and adults) were capable of inducing allogeneic rat thymocytes to undergo significant transformation in culture. We conclude that the in vitro lymphocyte response to skin cell stimulation is a function of skin cell maturation, and that the inability of kidney cells or brain cells to provoke the same sort of stimulation is not attributable to antigen loss during or after foetal development, but exists as a feature of these cells at the earliest stages of differentiation.