Selective down-regulation of T cell- and non-T cell-derived tumour necrosis factor alpha by thalidomide: comparisons with dexamethasone

Both thalidomide and dexamethasone have been shown to inhibit the productio n of tumour necrosis factor alpha (TNF-alpha), but little is known of their cellular selectivity. Inhibition of monocyte TNF-alpha expression has been implicated in the clinical efficacy of thalidomide, and it has been sugges ted that the drug modulates only monocyte-derived cytokines. Given the impo rtance of T lymphocyte responses in immunological disorders in which treatm ent with thalidomide has been successful, it is pertinent to study the effe cts of this drug on T cell-derived TNF-alpha. In the present investigations we have examined the influence of both thalidomide and dexamethasone on mi togen-induced elaboration of TNF-alpha by CD3(+) peripheral blood mononucle ar cells (PBMC) and the T cell line MOLT-4. PBMC from healthy human volunte ers were stimulated optimally with phytohaemagglutinin (PHA) in the presenc e of varying concentrations of thalidomide or dexamethasone, and supernatan ts assayed for TNF-alpha and interleukin 2 (IL-2). Concurrently, PHA-stimul ated PBMC were treated with 1 x 10(-1) mM thalidomide or dexamethasone and the cells fixed, permeabilised, stained with anti-CD3 and anti-TNF-alpha fl uorescently labelled antibodies and analysed by flow cytometry. MOLT-4 cell s were cultured in the presence or absence of the drugs following activatio n with phorbol myristate acetate (PMA)/ionophore, and supernatants analysed by enzyme-linked immunosorbent assay (ELISA) for cytokine expression. Thal idomide was found to inhibit PBMC-derived TNF-alpha, but not IL-2. In contr ast, dexamethasone down-regulated both TNF-alpha and IL-2 in a dose-depende nt manner. Thalidomide and dexamethasone both suppressed intracellular leve ls of TNF-alpha in CD3(+) PBMC, reducing percentages of double positive sta ining cells by 28 and 52%, respectively, compared with controls. In additio n, TNF-alpha. production by CD3(-) PBMC was inhibited by 31% by thalidomide and by 47% by dexamethasone. In order to determine whether thalidomide was acting directly on T cells, or indirectly through effects on accessory cel ls, TNF-alpha production in the T cell line MOLT-4 was investigated. TNF-al pha secretion by PMA/ionophore activated MOLT-4 cells was reduced by 80% fo llowing thalidomide treatment and close to background levels following dexa methasone treatment. To verify that thalidomide was acting selectively to d own-regulate TNF-alpha, IL-2 production by MOLT-4 cells was also measured a nd found to be unaffected by the drug. In contrast, dexamethasone reduced M OLT-4-derived IL-2 levels by 20%. These observations suggest that thalidomi de, in addition to its known inhibitory effect on monocyte-derived TNF-alph a, is capable also of down-regulating T cell-derived TNF-alpha in a direct and selective manner. In addition, the inhibition of intracellular levels o f TNF-alpha strengthens the evidence that the inhibitory effect of thalidom ide is at the level of transcription and/or translation and does not reduce cellular TNF-alpha secretion. Such effects could explain the efficacy of t halidomide treatment in various immunological disorders where T cell activa tion plays an important role in the pathogenesis of the disease. (C) 1999 E lsevier Science B.V. All rights reserved.