The effects of allergen and anti-allergic drugs on murine hemopoietic cells: moving targets, unusual mechanisms, and changing paradigms.

We used a variety of techniques to evaluate the effects of airway allergen exposure in mice on the responses of hemopoietic cells to cytokines and drugs in vitro and in vivo. Initial studies have shown that allergen exposure of sensitized mice leads to release of circulating mediators, that induce rapid upregulation of bone-marrow responses to IL-5 and GM-CSF. This may be related to glucocorticoids, because exogenous dexamethasone has similar effects on cultured murine bone-marrow, and because stress-induced glucocorticoids, in naïve or sensitized mice, have effects indistinguishable from those of allergen challenge in sensitized animals. Upregulation of eosinophil production is associated with an increased expression of alpha4 integrins, which may contribute to retention of these cells in the bone-marrow. Glucocorticoids regulate the adhesiveness, maturation and survival of eosinophils in murine bone-marrow culture, partly by counteracting the actions of Prostaglandin E2 and possibly other prostanoids. Allergen exposure of sensitized mice leads to accumulation of hemopoietic progenitors in the lungs, which differ from those in bone-marrow in growth properties and sensitivity to glucocorticoids. Lung transplantation has been used to demonstrate that the lung acts as a source of endocrine factors that promote hemopoietic cell accumulation, independently of damage caused by local allergic inflammation.

Murine myeloid progenitor responses to GM-CSF and eosinophil precursor responses to IL-5 represent distinct targets for downmodulation by prostaglandin E(2).

1. Because Prostaglandin E(2) (PGE(2)) and dibutiryl cyclic AMP (dbcAMP) modulate the production and effects of haemopoietic cytokines in allergy, we examined their ability to modulate responses of myeloid progenitors to GM-CSF, and of eosinophil precursors to IL-5. 2. The ability of PGE(2), dbcAMP, rolipram, forskolin, dbcGMP and PGD(2), to modulate the responses to GM-CSF and IL-5 in colony formation (progenitor) and eosinophil differentiation (precursor) assays using bone-marrow from nonsensitized or from intranasally-challenged, ovalbumin-sensitized mice of five strains was studied. 3. PGE(2) (10(-7) M) inhibited GM-CSF-stimulated colony formation in bone-marrow from BP-2 mice. This effect was duplicated by dbcAMP (0.3 - 1x10(-6) M), Rolipram (10(-5) M) and forskolin (3x10(-5) M), but not Prostaglandin D(2) (10(-6) M). Inhibition affected similarly all myeloid colony types. Progenitors from sensitized and challenged BP-2 mice were also inhibited by PGE(2) and cyclic AMP. PGE(2) inhibited progenitors from C57BL/10, CBA/J and A/J, but not BALB/c mice. However, BALB/c progenitors were sensitive to dbcAMP and Forskolin (10(-4) M). In contrast, in precursor assays, PGE(2) (10(-7) - 10(-9) M) blocked responses to IL-5 in bone-marrow from BP-2 and BALB/c mice, either naïve or sensitized and challenged, to a similar extent. PGD(2) (10(-6) M) was ineffective, as was PGE(2) (10(-7) M), if added after 48 h of culture. 4. In conclusion, PGE(2) inhibits the responses of bone-marrow myeloid progenitors to GM-CSF and of eosinophil precursors to IL-5, in naïve or ovalbumin sensitized and challenged mice. These effects are duplicated by cyclic AMP-elevating agents. In the BALB/c strain, the resistance of progenitors, but not precursors, to PGE(2) inhibition, indicates these developmental stages are separate targets for PGE(2) modulation.

Upregulation by glucocorticoids of responses to eosinopoietic cytokines in bone-marrow from normal and allergic mice.

Since the production of eosinopoietic cytokines (GM-CSF, IL-3, IL-5) is inhibited by glucocorticoids, while responsiveness to these cytokines is enhanced in bone-marrow of allergic mice, we studied the ability of glucocorticoids to modulate murine bone-marrow eosinopoiesis. Progenitor (semi-solid) and/or precursor (liquid) cultures were established from bone-marrow of: (a) normal mice; (b) ovalbumin-sensitized and challenged 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, and numbers of eosinophil-peroxidase-positive cells were determined at day 7. In BALB/c mice, dexamethasone (10(-7) M) increased GM-CSF-stimulated myeloid colony formation (P = 0.01), as well as the frequency (P=0.01) and size (P<0.01) of eosinophil colonies. Dexamethasone (10(-7) M) alone had no effect. Dexamethasone (10(-7)-10(-10) M) increased (P<0.002) eosinophil precursor 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. Hydrocortisone 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). These effects were blocked by RU 486 (20 mg kg(-1), orally, 2 h before dexamethasone, or added in vitro at 10 microM, P<0.001). Glucocorticoids, acting in vivo or in vitro, through glucocorticoid receptors, enhance bone-marrow eosinopoiesis in naïve and allergic mice.