1,25-Dihydroxyvitamin D3 enhancement of concanavalin-A induced bovine lymphocyte proliferation: requirement of monocytes.

The effect of 1,25-(OH)2D3 on Concanavalin-A (ConA) mediated bovine lymphocyte proliferation was dependent on the magnitude of the proliferative response. Lymphocytes from cows with high inherent proliferative responses (134,904 +/- 15,488 cpm/well) were unaffected by 1,25-(OH)2D3; whereas, lymphocytes from cows with low inherent proliferative responses (46,317 +/- 6000 cpm/well) were stimulated 75% (P less than 0.01) by 10(-10)M 1,25-(OH)2D3. At low initial proliferation rates, seen with low density cultures enriched for lymphocytes, the effect of 1,25-(OH)2D3 on proliferation changed from inhibition in the absence of added monocytes to stimulation at 18-23% monocyte addition. These results suggest that 1,25-(OH)2D3 possesses both stimulatory and inhibitory effects on ConA-induced proliferation that are monocyte dependent.