2c). Unlike U937 cells, in MDMs early expression of CCL26 was sustained for as long as 72 hr following stimulation (Fig. 2d).
To investigate whether U937 cells secrete CCL26, the cells were incubated with a range of concentrations of IL-4 for 24 and 48 hr. The supernatants were harvested and then assayed for CCL26 using an ELISA. No CCL26 was detected in the supernatants from U937 cells treated Fulvestrant in vitro with medium alone, suggesting that U937 cells do not constitutively release CCL26 protein (Fig. 3a,b). IL-4 induced robust CCL26 release from U937 cells, with maximal levels detected using 10 ng/ml of IL-4 for 48 hr (692·83 ± 57·44 pg/ml, n = 6, P < 0·01 compared with the control). Similarly to U937 cells, no detectable levels of CCL26 were measured in supernatants from MDMs treated with medium
alone (Fig. 3c). Stimulation with 10 ng/ml of IL-4 induced the release of CCL26 protein at 24 and 48 hr (control: 0·12 ± 0·12 pg/ml, n = 8; 24 hr: 28·00 ± 7·2 pg/ml n = 8, not significant; 48 hr: 90·25 ± 22·91 pg/mL n = 8, P < 0·001) (Fig. 3c). Consistent with mRNA data, this website no CCL26 protein was detected following stimulation of either U937 or MDMs with TNF-α, IL-1β or IFN-γ (data not shown). Notably, we found a high degree of donor-to-donor variation in the levels of CCL26 released from MDMs when the cells from eight different individuals were used. Owing to the variability in the levels of CCL26 released from MDMs, U937 cells were used in subsequent experiments. TNF-α or IL-1β synergize with IL-4 in A549 airway epithelial cells to enhance CCL26 expression and release.8 To investigate whether pro-inflammatory cytokines could synergize with IL-4 to enhance CCL26 mRNA and protein release
in U937 cells, cells were treated with IL-4, either alone or with TNF-α, IL-1β or IFN-γ, for 48 hr. U937 cells treated with IL-4, together with TNF-α or IL-1β, demonstrated a slight, but significant, increase in CCL26 mRNA expression when compared with the Resminostat CCL26 mRNA levels obtained from U937 cells treated with IL-4 alone (Fig. 4a). CCL26 protein release was substantially enhanced in supernatants harvested from U937 cells stimulated with a combination of IL-4/TNF-α and IL-4/IL-1β when compared to U937 cells stimulated with IL-4 alone (IL-4 alone: 474 ± 89 pg/ml, n = 5; IL-4 + TNF-α: 2004 ± 99·27 pg/ml, n = 5, P < 0·001 compared to stimulation with IL-4 alone; IL-4 + IL-1β: 1069 ± 172 pg/ml, n = 5, P < 0·01 compared to stimulation with IL-4 alone) (Fig. 4b). The levels of CCL26 protein detected were greater than the sum of the release induced by the cytokines on their own, clearly demonstrating synergy between IL-4 and either TNF-α or IL-1β. Costimulation with IFN-γ led to a significant increase in CCL26 mRNA, but had no effect on IL-4-mediated CCL26 protein release (Fig. 4).