METHYLPREDNISOLONE AND 2-CHLOROADENOSINE INDUCE DNA FRAGMENTATION AT DIFFERENT STAGES OF HUMAN T-LYMPHOCYTE DEVELOPMENT

Both methylprednisolone (MPS) and 2-chloroadenosine (2-CA) were shown previously to induce DNA fragmentation and cell death in human thymocy tes at an optimum concentration of 1 and 40 mu M, respectively. Though both compounds affected the CD4(+) CD8(+) population, 2-CA depleted p rimarily thymocytes expressing medium or high levels of CD3-T-cell rec eptor molecule, while the glucocorticoid treatment affected cells expr essing a lower level of CD3-T-cell receptor. Their effect on thymocyte viability and DNA fragmentation was observed already at day 1 of cult ure and involved the bcl-2 negative thymocytes. Incubation of peripher al T-lymphocytes (which express bcl-2) with the same concentration of MPS did nor affect the viability for up to 5 days, while 2-CA induced 100% cell death and DNA fragmentation by day 5. If T-cells were stimul ated with concanavalin A in the presence of MPS or 2-CA the cell proli feration was inhibited and a decrease in cell viability with a concomi ttant increase in DNA fragmentation was observed. Ii MPS was added at 24 h or later after mitogenic stimulation, it was not able to induce a poptosis and the inhibition of proliferation was less pronounced. 2-CA , on the other hand, inhibited proliferation and induced cell death wh enever it was added to the culture. The decreased sensitivity towards the apoptosis induction effects of glucocorticoids at later phases of mitogenic stimulation can not be explained by an increased bcl-2 expre ssion, since its expression level remained constant up to 48 h after m itogenic stimulation. Our data presented in this paper suggest: (1) th at T-cells may show different sensitivity towards the same apoptosis i nducer signals at different stages of the T-cell development; (2) the apoptotic sensitivity towards various signals may be different at the same stage of T-cell differentiation; and (3) their apoptotic sensitiv ity does not always correlate with the bcl-2 expression alone. (C) 199 7 Elsevier Science B.V.