Der p2 Internalization by Epithelium Synergistically Augments Toll-like Receptor-Mediated Proinflammatory Signaling (1)
Myeloid differentiation-2 (MD2), is an LPS-binding member of the Toll-like receptor 4 (TLR4) signaling complex. Because of the structures of MD2 and Der p2 exhibit homology, Der p2 can facilitate TLR4 signaling through direct interactions with the TLR4 complex, reconstituting LPS- promoted TLR4 signaling in the absence of MD2 and facilitating such signaling in the presence of MD2.
Although rDer p2-EGFP alone induced trivial secretion of IL-6/IL-8 by BEAS-2B cells, it was concentration-dependently augmented by LPS from 2.0- to19.1/78.8-fold for IL-6 and from 3.3- to 31.7/104.9-fold for IL-8, respectively. IL-6/IL-8 secretion was reduced in the presence of anti-MD2 antibody from 25.7- to 11.5-fold for IL-6 and from 44.6- to 28.5-fold for IL-8, respectively.
Compared to non-transfected cells, cells overexpressing MD2 were more sensitive to rDer p2 stimulation for IL-6 secretion.
Der p2 concentration-dependently increased the expression of mRNA encoding IL-6 and IL-8 in these cells over the 16-hours time period, and this effect was further augmented in the presence of LPS.
The most effective inhibitors on IL-6 mRNA expression were dexamethasone, SP600125 (JNK inhibitor), SB203580 (p38 inhibitor), calcitriol, and BAY 11-7082 (IκB inhibitor), which caused 77.0%, 65.5%, 33.8%, 33.8%, and 25.0% reductions, respectively. The most effective inhibitors on IL-8 mRNA expression were dexamethasone, SP600125, calcitriol, and BAY 11-7082, which caused 42.4%, 30.0%, 27.3%, and 24.2% reductions, respectively.
The most effective inhibitors on IL-6/IL-8 protein secretion were dexamethasone, SP600125 (JNK inhibitor), SB203580 (p38 inhibitor), anti-TLR2 neutralizing antibody, and calcitriol.
The spectrum of responsiveness to TLR2 is wider than that to TLR4 because both receptors respond to LPS, but TLR2 additionally responds to lipoproteins, lipopeptides, and peptidoglycans. Native, but not recombinant, Der p2 which lacks glycosylated lectin ligands can stimulate monocyte-derived dendritic cells through its interaction with DC-SIGN, a lectin receptor. Der p2 could be internalized by human airway epithelium, and the activation of epithelium to secrete IL-6/IL-8 might up-regulate MD2 and TLR2. Secretion of IL-6/IL-8 was inhibited by MAPK and IκB inhibitors.
