MBL inhibits monocytes proliferation by TGF-β1.
Monocytes or 50 ng/ml rhM-CSF-induced monocytes were incubated with MBL at 2.5 μg/ml or 20 μg/ml for 24 h (A and B). MBL augmented TGF-β1 secretion. The effects of MBL on TGF-β1 mRNA expression were analyzed by real-time RT-PCR (A). The effects of MBL on the secretion of TGF-β1 were analyzed by ELISA (B). The expression of TGF-β1 induced by MBL was dependent on PI3K, ERK and p38 pathways (C). Monocytes were pretreated with 0.2% DMSO vehicle control or with inhibitors against PI3K (LY294002, 5 μM), ERK (U0126, 5 μM), and p38 (SB203580, 10 μM) at 37°C for 0.5 h, and then treated with MBL at 2.5 μg/ml or 20 μg/ml for 24 h. TGF-β1 expression levels were measured by ELISA. It was the addition of anti-TGF-β1 or the TGF-β1 receptor antagonist SB-431542 rather than control Rb IgG that abolished the inhibitory effect of MBL and restored the growth rate of monocytes to almost control levels (D). rhM-CSF-induced (50 ng/ml) monocytes were incubated with MBL alone at 20 μg/ml or in the presence of affinity-purified, neutralizing rabbit anti-M-CSF (0.2 μg/ml) or with anti-TGF-β1 (0.1 μg/ml) or with the TGF-β1 receptor antagonist SB-431542 (5 μM). Effects of MBL on proliferation of monocytes were assessed by the CCK-8 assay. Each bar represents the mean ± S.D. of three independent experiments. Indicated levels of significance are shown: * p<0.05; ** p<0.01; *** p<0.001.