1,25-Dihydroxyvitamin D attenuates cAMP accumulation in cultured human lymphocytes

1,25-Dihydroxyvitamin D (1,25(OH)2D3) receptors appear in cultured lymphocytes after activation; 1,25(OH)2D3 has been shown to affect both the immune function and proliferation of activated cells. However, the mechanism of these effects is not completely understood. We therefore studied the effect of 1,25(OH)2D3 on forskolin-stimulated lymphocyte cAMP production during concanavalin A (ConA) activation. Purified lymphocytes were cultured with ConA; 1,25(OH)2D3 was added concurrently or 24-48 h later. To measure cAMP production, aliquots of 10(6) cells were preincubated with a phosphodiesterase inhibitor and then stimulated with the diterpene activator, forskolin (15 microM, x 10 min). The cAMP production was 4 +/- 2 pmol/10(6) cells prior to activation, increasing markedly in 48-72 h and then declining. When 1,25(OH)2D3 was added to the culture for 48 h beginning 24 h after activation, forskolin-stimulated cAMP production was consistently reduced by greater than half. This effect on cAMP production was dose dependent with half-maximal attenuation at 5 X 10(-10) M 1,25(OH)2D3. Neither 10(-8) M 24,25(OH)2D3 nor 25(OH)D3 diminished the cAMP response to forskolin. Blastic transformation was not altered by 48 h exposure to 1,25(OH)2D3 at any time during the 120 h the cultures were maintained. We conclude that 1,25(OH)2D3 can modulate cAMP production and suggest that this may contribute to other effects on T lymphocyte function. We have described the ability of 1,25(OH)2D3 to attenuate the hormone-stimulated cAMP production in other cell types and suggest that this may be a generalized mechanism through which 1,25(OH)2D3 works.