A cytophotometric and flow cytofluorometric approach to the differentiation of T lymphocytes in the thymus.

By cytophotometric and flow cytofluorometric DNA and protein determinations two main proliferating subpopulations of thymus lymphocytes with a different percentage of cells in the S phase could be distinguished. One subpopulation had a very low protein content, was cortisone sensitive and located in the cortex. Cells with comparable low protein contents were not found amongst lymphocytes of the peripheral blood. The other lymphocyte subpopulation had a higher protein content, was cortisone resistant and situated in the cortex around a group of epithelial cells and in the medulla. The protein content of these thymus lymphocytes appeared to be comparable to that of the peripheral blood lymphocytes. On the basis of the protein content per cell, it is possible to identify and isolate the more often described major subpopulation of cortisone sensitive thymus lymphocytes remaining and dying in the thymus, and the minor cortisone resistant subpopulation of thymus lymphocytes which is the source of the peripheral T lymphocyte.