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It is well established that T cell maturation and activation are negatively regulated by a mechanism termed apoptosis. We now present evidence that glucocorticoids, known to possess immunosuppressive properties, cause apoptosis in mature Th cells, similarly to what has been reported for thymocytes. Th cells treated with the synthetic glucocorticoid dexamethasone show genome fragmentation into oligonucleosomal fragments, and proliferation of growth factor stimulated Th cells is inhibited by glucocorticoids. We show that IL-4 specifically rescues Th2 cells from dexamethasone-mediated apoptosis, whereas IL-2 and IL-1 are ineffective in these cells. However, IL-2 is the relevant rescue-factor of glucocorticoid-treated Th1 cells. The rescue induced by IL-4 and IL-2 is thought to be mediated by protein kinases (possibly protein kinase C), as evidenced by the fact that the protein kinase inhibitor H7 blocks the action of IL-4 and IL-2 in glucocorticoid-treated cells. Our in vitro data show that mature T cells can be protected by their own growth factors from the deleterious effects of the synthetic glucocorticoid dexamethasone, and suggest that specific interactions occur between lymphokines and naturally produced glucocorticoids in vivo, which may play a role in the regulation of the immune response.

Lymphokine production is regulated both at the transcriptional and the posttranscriptional level. To date, it has been shown that the protein synthesis inhibitor cycloheximide (CHX) up-regulates IL-2 expression in T cells by stabilizing its mRNA. In this report we have examined the effect of CHX on IL-2 at the transcriptional level. We have found that CHX has a positive regulatory function in IL-2 transcription, which is dependent on prior activation of this gene. This is not due to posttranslational conversion of inactive NFkB into its active form by CHX, because a clustered mutation in the kB-like sequence in the IL-2 enhancer that abrogates NFkB binding does not affect the up-regulation of IL-2 transcription. These results favor the hypothesis that, in addition to positive factors, negative elements regulate IL-2 transcription. Furthermore, we have tested the effect of CHX on IL-4 and granulocyte-macrophage-CSF transcription of both lymphokines. These results suggest that transcriptional up-regulation by CHX may be specific for IL-2 with respect to lymphokine expression.

Autocrine growth of Th type 2 cells has been reported to be mediated by the lymphokine IL-4. In this report we present evidence that in addition to IL-4 Th2 cells also produce IL-1 alpha in its active form in the absence of APC. We have found that this cytokine is an autocrine growth factor, because proliferation of Th2 cells in response to several stimuli is inhibited by anti-IL-1 alpha or anti-IL-1R mAb, or by an IL-1 alpha antisense oligodeoxynucleotide. However, Th1 cells do not produce this cytokine. We have investigated the role of endogenous IL-1 alpha on the induction of c-myc and c-myb, two protooncogenes involved in T cell activation. Here we show that endogenous IL-1 alpha is involved in the activation of both protooncogenes. Our results suggest that a possible function of IL-1 alpha, and perhaps other growth factors, might be to sustain or amplify the initial second messengers derived through the TCR. The possible implications of this finding with respect to interactions between T cell subsets and B cells or macrophages are discussed.

We have recently characterized a subline of the Th2 cell line D10.G4.1, D10A, which responds to exogenous IL-1 in the absence of cofactors. In this cell line IL-1 activates two distinct transmission signal pathways, one leading to increased levels of intracellular cAMP, and the other to the phosphorylation of an 80-kDa substrate of protein kinase C (PKC). To determine whether both pathways are activated upon occupancy of a single IL-1R, we used a mAb, M15, which blocks binding of IL-1 to the 80-kDa IL-1R, known to be expressed in Th2 cells. Whereas M15 was able to inhibit the accumulation of cAMP induced by IL-1, it had no effect on the IL-1-induced phosphorylation of the 80-kDa substrate of PKC or the c-fos mRNA expression. In addition, we show that IL-1 induces the expression of the two proto-oncogenes c-myb and c-myc through the 80-kDa IL-1R, and that this induction is PKC independent. The proliferation of D10A cells in response to IL-1 is blocked by M15, but is unaffected by H-7, a potent inhibitor of PKC. These results indicate that the IL-1-induced proliferation of D10A cells is independent of PKC. In addition, IL-1 induces c-fos mRNA expression in thymocytes but not in EL-4 cells.