Upregulation by glucocorticoids of responses to eosinopoietic cytokines inbone-marrow from normal and allergic mice

1 Since the production of eosinopoietic cytokines (GM-CSF, IL-3, IL-5) is i nhibited by glucocorticoids, while responsiveness to these cytokines is enh anced in bone-marrow of allergic mice, we studied the ability of glucocorti coids to modulate murine bone-marrow eosinopoiesis. 2 Progenitor (semi-solid) and/or precursor (liquid) cultures were establish ed from bone-marrow of: (a) normal mice; (b) ovalbumin-sensitized and chall enged mice or (c) dexamethasone(1-5 mg kg(-1)) injected mice. Cultures were established with GM-CSF (2 ng ml(-1)) or IL-5 (1 ng ml(-1)), respectively. alone or associated with dexamethasone, hydrocortisone or corticosterone. Total myeloid colony numbers, frequency and size of eosinophil colonies, an d numbers of eosinophil-peroxidase-positive cells were determined at day 7. 3 In BALB/c mice, dexamethasone (10(-7) M) increased GM-CSF-stimulated myel oid colony formation (P = 0.01), as well as the frequency (P = 0.01) and si ze (P<0.01) of eosinophil colonies. Dexamethasone (10-7 M) alone had no eff ect. Dexamethasone (10(-7)-10(-10) M) increased (P<0.002) eosinophil precur sor responses to IL-5. Potentiation by dexamethasone was still detectable: (a) on low density, immature, nonadherent BALB/c bone-marrow cells, (b) on bone-marrow from other strains, and (c) on cells from allergic mice. Hydroc ortisone and corticosterone had similar effects. Dexamethasone administered in vivo, 24 h before bone-marrow harvest, increased subsequent progenitor responses to GM-CSF (P=0.001) and precursor responses to IL-5 (P<0.001). Th ese effects were blocked by RU 486 (20 mg kg(-1), orally, 2 h before dexame thasone, or added in vitro at 10 mu M, P<0.001). 4 Glucocorticoids, acting in vivo or in vitro, through glucocorticoid recep tors, enhance bone-marrow eosinopoiesis in naive and allergic mice.