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Caffeine alters intracellular calcium signalling patterns in lymphocytes which are important for the specific regulation of activation and effector function in lymphocytes. The effect of caffeine on calcium signalling is probably mediated via a ryanodine receptor type 3 dependent intracellular calcium store which releases calcium after exposure to caffeine. Also, caffeine decreases lymphocyte cytotoxicity against allogenic myocyte.
Which cytotoxic mechanisms are actually altered by caffeine is unknown.
In our experiments we examined the effect of caffeine on expression of IL-2, which is a marker of T-cell-activation, as well as caffeine’s effects on expression of TNF-a and IFN-g, that have been often described as cytokines with cardiotoxic effects. In mouse splenocyte cultures containing about 87% lymphocytes we show that concanavalin A (ConA, 5 µg/ml) stimulated cells increase the expression of TNF-alpha, IL-2 and IFN-gamma (ELISA) significantly. Caffeine (3.75 mM) inhibits cytokine expression of ConA stimulated cells almost completely. Ryanodine (1 µM) specifically blocks ryanodine receptors and thereby prevents caffeine induced calcium release. In our experiments, however, ryanodine (100 pM – 10µM) has no effect on ConA stimulated IL-2 and IFN-gamma expression and only suppresses TNF-alpha expression by 20%. Furthermore, ryanodine does not prevent the inhibitory effect of caffeine on TNF-alpha, IL-2 and IFN-gamma expression in stimulated effector cells.
We postulate that caffeine suppresses cytokine expression and thereby contributes to decreased cytotoxicity of lymphocytes against allogenic myocytes. The ryanodine receptor dependent intracellular calcium store does not seem to play a significant role in this process. Possibly, the blockade of IP3 receptors by caffeine is more important for cytokine suppression.