IN SITU HYBRIDIZATION FOR INTERLEUKIN 2 AND INTERLEUKIN 2 RECEPTOR rnRNA IN T CELLS ACTIVATED IN THE PRESENCE OR ABSENCE OF CYCLOSPORIN A By ANGELA GRANELLI-PIPERNO

An essential component in the response of T lymphocytes to mitogens and antigens is the expression of genes encoding lymphokines and IL-2-R . This induction can be monitored by hybridizing complementary DNA or RNA probes to the corresponding mRNA by the northern blotting technique (1) . The latter requires large numbers of cells, and it does not provide direct information on the frequency of lymphocytes capable ofexpressing these genes or the level of mRNA per active cell . Such information is ofconcern in primary populations that consist of different lymphocyte subsets with distinct functional potentials . In situ hybridization potentially would allow one to use smaller numbers of cells and to detect induced genes at the level of individual lymphocytes . In this paper, the mRNAs for IL-2 and the low-affinity IL-2-R have been detected by in situ hybridization ofhuman T cells that have been stimulated with three different mitogens, PHA, anti-CD3, and anti-CD28, in conjunction with the tumour promoter PMA. For each of the mitogens, IL-2 mRNA is only found in a minority of the cells (20% or less) and for a short time, between 8 and 16 h after stimulation . In contrast, IL-2-R mRNA is present for a much longer time and in most cells . Using this approach I have analyzed the levels of IL-2 and IL-2-R mRNA in the CD4+ and CD8 + T cell subsets, and have examined the effects of adherent cells and cyclosporin A (CSA)' on lymphokine gene expression .