On cell signalling mechanism of Mycobacterium leprae soluble antigen (MLSA) in Jurkat T cells.

We investigated the role of Mycobaterium leprae soluble antigen (MLSA) in the modulation of calcium signalling, phosphorylation of mitogen-activated protein (MAP) kinases and IL-2 mRNA expression in human Jurkat T cells. We observed that MLSA induced an increase in free intracellular calcium concentrations, [Ca2+]i, via opening CRAC (Ca2+-release activated- Ca2+) channels. Furthermore, MLSA failed to potentiate both thapsigargin- and anti-CD3 antibodies-induced capacitative calcium influx in Jurkat T cells. We observed that MLSA failed to affect the degree of phosphorylation of two MAP kinases, i.e., ERK1/ERK2, stimulated by anti-CD3 antibodies alone or phorbol 12-myristate 13-acetate (PMA) alone. In order to mimic co-stimulation of T cells, we stimulated them by both PMA and anti-CD3 antibodies. MLSA significantly curtailed the phosphorylation of ERK1/ERK2, stimulated by both PMA and anti-CD3 antibodies in Jurkat T cells. Also MLSA was found to reduce the transcription of IL-2 gene in PMA plus anti-CD3 antibodies-activated Jurkat T cells. Our finding demonstrates that Ca2+ influx via CRAC channels, inhibition of ERK1/ERK2 phosphorylation and IL-2 gene transcription may be implicated in immunosuppressive effects of MLSA antigen.

Management of erythema nodosum leprosum by thalidomide: thalidomide analogues inhibit M. leprae-induced TNFalpha production in vitro.

Thalidomide is being successfully used for the treatment of erythema nodosum leprosum (ENL), among other disorders with inflammatory and immunological bases. Although the active molecules responsible for the diverse therapeutic activities of the drug and the sequence of reactions triggered inside the cells remain unclear, it was demonstrated that thalidomide (THAL) inhibits TNFalpha mRNA expression and protein production by stimulated monocytes and activated T lymphocytes. Patients treated with THAL experienced a reduction in serum TNFalpha levels and it diminished cytokine gene expression at the lesion site, with a concomitant abrogation of clinical symptoms. It has been reported that thalidomide as well as some its analogues decrease M. leprae-induced TNFalpha and IL-12 mRNA in vitro. THAL also reduced monocyte apoptosis in the cultures. The present data further support thalidomide's effects on TNFa synthesis and the growing need to search for new specific TNFalpha inhibitors (non-teratogenic compounds) that might be potentially used in clinical disorders such as leprosy.

Inhibition of IL-12 production by thalidomide.

The immunomodulatory properties of thalidomide are currently being exploited therapeutically in conditions as diverse as erythema nodosum leprosum, chronic graft-vs-host disease, rheumatoid arthritis, and sarcoidosis. The relevant mechanism of action of thalidomide in these diseases remains unclear. The important role recently ascribed to IL-12, a cytokine critical to the development of cellular immune responses, in the pathogenesis of several of these conditions led us to examine whether thalidomide affects the production of IL-12. Thalidomide potently suppressed the production of IL-12 from human PBMC and primary human monocytes in a concentration-dependent manner. Thalidomide-induced inhibition of IL-12 production was additive to that induced by suboptimal inhibiting doses of dexamethasone, and occurred by a mechanism independent of known endogenous inhibitors of IL-12 production. These results suggest that thalidomide may have therapeutic utility in a wide range of immunologic disorders that are characterized by inappropriate cellular immune responses.