Hormonal regulation of peripheral blood mononuclear cells in sheep

The presence of growth hormone receptors (GHR) on sheep peripheral blood mononuclear (PBMN) cells was studied in two ways. The first was to directly measure specific GH-binding sites on PBMN cells drawn from lambs from birth to 5 months of age. The second was to measure the effect of GH on resting and interleukin-2 (IL-2)-activated PBMN cells in vitro and also the effect of other hormones such as prolactin (PRL), insulin-like growth factor-1 (IGF-1), and glucocorticoid. The specific binding of [125I]human GH (hGH) was low on PBMN cells but increased (P < 0.05) with age up to 5 months. Interestingly, serum concentrations of GH-binding protein also increased (P < 0.01) with age and were highly correlated (r = 0.89; P < 0.05) with the specific binding of GH to PBMN cells. The addition of ovine GH (oGH) to PBMN cells in vitro resulted in increased (P < 0.01) proliferation (at a dose of 100 ng/ml). Higher doses of oGH (2 micrograms/ml) also increased PBMN cell proliferation. When PBMN cells were previously stimulated with IL-2, the dose of 100 ng/ml) oGH was no longer able to stimulate proliferation. IGF-1 inhibited (P < 0.04) resting PBMN cell proliferation at 100 ng/ml but had no effect on IL-2-activated PBMN cells. Other hormones such as PRL caused a stimulation of PBMN cell proliferation (P < 0.01) at 100 ng/ml, whereas dexamethasone (dex) inhibited PBMN cell proliferation at doses as low as 63 ng/ml. These studies show that GH, PRL, IGF-1, and glucocorticoids are effective in modulating the proliferation of PBMN cells from sheep and therefore suggest that a modulation of immune system function in vitro by these hormones is consistent with a purpose in vivo.