REGULATION OF MEGAKARYOCYTE GENERATION BY MONOCYTES/MACROPHAGES.

D´ATRI, LINA P; NEGROTTO, SOLEDAD; POZNER, ROBERTO G.; LANDONI, VERÓNICA I.; GOMEZ, RICARDO M.; LAZZARI, MARIA A.; ISTURIZ, MARIN; SCHATTNER, MIRTA

Sydney, Australia.

Congreso; XXth Congress of the International Society on Thrombosis and Haemostasis.; 2005

International Society on Thrombosis and Haemostasis.

It has been recently demonstrated, in a mouse model, that macrophage depletion, increase megakaryocytopoiesis (Alves-Rosa 2003). We evaluated this regulation in human cells. Umbilical cord CD34+ cells were cultured on transwells over monocytes (MO) from peripheral blood in the presence of thrombopoietin (TPO). After 14 days, cell number and megakaryocytes (Mks, CD61+), MO (CD14+), CD34+ cells or lymphocytes frequencies were established by flow cytometry. Although cell expansion was greater in the presence of MO, Mks generation was reduced since differentiation to CD61+ cells was lower (11 ± 3 vs. 63 ± 2%*). On the contrary, MO percentage was increased (31 ± 5% vs. 6 ± 0.7*) and no changes were found in other populations. Similar results were obtained when CD34+ were cultured in conditioned medium (Cm) or by the addition of GM-CSF to TPO-stimulated CD34+ cells. When MO were allowed to mature into macrophages (Mø) by 5 days adhesion, its conditioned medium did not modify cell expansion nor Mks generation but increase the percentage of CD14+ cells. Mø-TPO stimulation, markedly increased cell expansion, CD14+ and CD61+ cells. Our results show that MO down-regulate Mk production in favor of MO generation through soluble factors, including GM-CSF. Opposite Mk regulation was observed by Mø. Total cells Megakaryocytes Monocytes Transwells 140 ± 5 vs. 325 ± 38* 88 ± 7 vs. 32 ± 5* 9 ± 2 vs. 96 ± 3* CmMO 85 ± 14 vs. 240 ± 49* 63 ± 13 vs. 32 ± 7* 3 ± 1 vs. 70 ± 16* TPO + GM-CSF 110 ± 25 vs. 165 ± 26* 70 ± 22 vs. 53 ± 19* 11 ± 3 vs. 63 ± 11* Cm Mø– TPO 58 ± 7 vs. 76 ± 9** 44 ± 8 vs. 53 ± 6** 3 ± 0.5 vs. 11 ± 3* Cm Mø+ TPO 58 ± 7 vs. 157 ± 22* 44 ± 8 vs. 114 ± 21* 3 ± 0.5 vs. 18 ± 4* (Absolute number of cells X ± SEM × 103n= 3–6, *P < 0.05 vs. control, **P < 0.05 vs. TPO).