The influence of calciotrophic hormones on lymphocyte transformation and interleukin-2 production in human mononuclear cells.

Peripheral blood mononuclear cells (PBMC) display receptors for parathyroid hormone (PTH) and calcitonin (CT) and, when activated, express receptors for 1,25 dihydroxyvitamin D3 (1,25(OH)2D3). The role of these receptors in unclear. It is well established that 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) has a significant effect on lymphocyte transformation and interleukin-2 (IL-2) activity in PBMC's. We have proceeded to compare the effects of the calciotrophic hormones, 1,25(OH)2D3, 24,25 dihydroxyvitamin D3 (24,25(OH)2D3), 25 dihydroxyvitamin D3 (25(OH)D3), bovine (1-35)PTH (b(1-35)PTH) and salmon CT on both lymphocyte transformation and IL-2 activity in PBMC's from normal human volunteers. We have also sought an indication as to which subset of cells is responsible for the 1,25(OH)2D3 effect. Unlike the other calciotrophic hormones 1,25(OH)2D3 inhibited the proliferation of phytohemagglutinin (PHA), concanavalin A (ConA) and pokeweed mitogen (PWM) stimulated cells. 1,25(OH)2D3 had a significantly greater effect on PHA induced cell proliferation and only inhibited cells with the T-helper/inducer (TH, CD4 + ve) phenotype, this suggested that 1,25(OH)2D3 may act selectively on the cells with CD4 + ve phenotype. In addition, of the calciotrophic hormones, 1,25(OH)2D3 had a greater effect on IL-2 activity. These findings indicate that 1,25(OH)2D3 and not the other calciotrophic hormones has a significant immunomodulatory effect.