We applied the Mann–Whitney U-test to assess the sensitivity or robustness of the results, and the results were consistent. We set the criterion for statistical significance a priori at α = 0·05. All P-values were reported to two decimal places. We have previously shown that CB CD34+ progenitor cells express functional TLR4 and respond to LPS stimulation through Eo/B CFU find more formation.[12] To confirm and extend those findings,

freshly isolated CD34+ cells were stimulated with LPS and haematopoietic cytokines for 14 days in methylcellulose cultures. Although LPS alone could not induce Eo/B CFU formation, the combination of GM-CSF (P = 0·02) and LPS resulted in a significant increase in the number of enumerable Eo/B colonies (Fig. 1a). Although the mean value was increased, IL-5-responsive Eo/B CFU formation in the presence of LPS did not reach significance (Fig 1b). We next assessed whether CD34+ cells stimulated with LPS secrete the Eo/B differentiation-inducing

cytokines, GM-CSF and IL-5, using a bioplex cytokine assay. Although none of these cytokines was found in the culture medium, CD34+ cells alone do secrete ambiently low levels of cytokines. As shown in Fig. 2(a), LPS induces significant levels of GM-CSF (P = 0·02) from CB progenitors. The mean level of IL-5 was increased in LPS-stimulated supernatant but this did not reach significance (Fig 2b). Phospho-flow cytometry is an especially valuable tool for investigating signalling HA-1077 price pathways buy AG-014699 in rare cell populations,[20] like CD34+ progenitor cells.

As it has been previously used to detect MAPK and STAT5 signalling pathways,[16] which may be involved in cytokine secretion from TLR-stimulated CB progenitor cells,[21] we investigated whether these pathways were activated by LPS stimulation of CB CD34+ cells. As shown in Fig 3, detectable levels of phosphorylated p38 MAPK were seen 5 min after LPS stimulation (P = 0·046) followed by a steady decline thereafter. Additionally, there was a trend to increased ERK 1/2 between 5 and 30 min (P = 0·06) with LPS stimulation. No significant differences in STAT5 expression, as evaluated over time, were detected in LPS-stimulated CB progenitor cells. As we show that LPS induces a significant increase in GM-CSF secretion from CB CD34+ cells (Fig 2), and that LPS can induce the rapid activation of p38 MAPK (Fig 3), we next assessed whether these pathways were involved in GM-CSF secretion by CB CD34+ cells. To do this, CD34+ cells were pre-incubated with MAPK inhibitors SB203580 (p38 MAPK inhibitor) or PD98059 (ERK 1/2 inhibitor) or a STAT5 inhibitor and GM-CSF secretion was assessed by Luminex.