Effect of retinoid excess and VAD on granulopoiesis in vivo.

BM granulocyte populations were analyzed by flow cytometry with the Mac-1 and GR-1 markers. Granulocyte differentiation proceeds along a curve-shaped path in which increasing levels of Mac-1 and GR-1 are acquired as the cells mature. Thus, Mac-1^low/+GR-1^low cells correspond mainly to promyelocytes, myelocytes, and metamyelocytes, whereas Mac-1⁺GR-1^high cells correspond mainly to band and segmented neutrophils30 (data not shown). (A) WT mice were treated for 3 days with 10 mg/kg BMS493 or vehicle. In the right panels the GR-1 profile of the granulocyte population (Mac-1⁺ cells, gated in the left panels) is shown, and the percentage of GR-1^low immature granulocytes within that population is indicated. (B) Granulocyte populations in VAD mice. Note the overall increase of the granulocyte population (gated in the top panels) and the increase, within that population, of the immature granulocyte population (GR-1^low cells, bottom panels) that occurs specifically in the VAD mice (ie, CRBPI^−/− mice fed a VAD diet). (C) Effect of ATRA administration. Mice were treated with 100 mg/kg ATRA or vehicle for 72 hours. Note the shift to the right of GR-1 expression within the immature granulocyte population (gated) in ATRA-treated WT mice, producing a comet-like profile, which is not seen in the ATRA-treated RARα^−/− mice. Note that a reduction in the number of the mature (GR-1^high) BM granulocytes was also observed in ATRA-treated WT mice, which probably reflects an enhanced efflux of neutrophils from the BM, as peripheral blood neutrophil numbers were increased 1.5- to 3-fold (data not shown).