Ouabain effects on activated lymphocytes: augmentation of CD25 expression on TPA-stimulated cells and of CD69 on PHA-and TPA-stimulated cells.

Ouabain (OUA) was capable of inhibiting peripheral blood lymphocyte (PBL) proliferation induced by phyothaemagglutinin (PHA) of phorbol ester (TPA), as measured by thymidine incorporation or cell cycle analysis. In this latter case it was possible to detect a block in the progression from G1 to S phase. This inhibition could not be reversed by interleukin (IL)-2 and was not due to an effect on CD 25 expression, as this molecule was only reduced in PHA cultures treated with OUA. Conversely, cultures activated by TPA and OUA showed an increased expression of CD25. The activation antigen CD69 was increased in both situation, suggesting that despite the absence of proliferative response the cells were being activated. The possibility that these cells were being deviated to the activation pathway leading to apoptosis is now under investigation. This study also suggested that CD25 induction may occur via different pathways, and that the selective effect of OUA for PHA-activated cells may become a useful tool for the understanding of the process.