Th2 Cytokines Down-Regulate TLR Expression and Function in Human Intestinal Epithelial Cells

Abstract

TLRs serve important immune and nonimmune functions in human intestinal epithelial cells (IECs). Proinflammatory Th1 cytokines have been shown to promote TLR expression and function in IECs, but the effect of key Th2 cytokines (IL-4, IL-5, IL-13) on TLR signaling in IECs has not been elucidated so far. We stimulated human model IECs with Th2 cytokines and examined TLR mRNA and protein expression by Northern blotting, RT-PCR, real-time RT-PCR, Western blotting, and flow cytometry. TLR function was determined by I-κBα phosphorylation assays, ELISA for IL-8 secretion after stimulation with TLR ligands and flow cytometry for LPS uptake. IL-4 and IL-13 significantly decreased TLR3 and TLR4 mRNA and protein expression including the requisite TLR4 coreceptor MD-2. TLR4/MD-2-mediated LPS uptake and TLR ligand-induced I-κBα phosphorylation and IL-8 secretion were significantly diminished in Th2 cytokine-primed IECs. The down-regulatory effect of Th2 cytokines on TLR expression and function in IECs also counteracted enhanced TLR signaling induced by stimulation with the hallmark Th1 cytokine IFN-γ. In summary, Th2 cytokines appear to dampen TLR expression and function in resting and Th1 cytokine-primed human IECs. Diminished TLR function in IECs under the influence of Th2 cytokines may protect the host from excessive TLR signaling, but likely also impairs the host intestinal innate immune defense and increases IEC susceptibility to chronic inflammation in response to the intestinal microenvironment. Taken together, our data underscore the important role of Th2 cytokines in balancing TLR signaling in human IECs.

Treatment of experimental autoimmune encephalomyelitis in SJL/J mice with a replicative HSV-1 vector expressing interleukin-5

“…IL-5 also downregulated the TLR3 expression during polyinosinic:polycytidylic acid stimulation (data not shown). Mueller et al 61 have also shown that the Th2 cytokines IL-4 and IL-13 downregulated TLR3 and TLR4, while IFN-g enhanced their expression in human intestinal epithelial cells. The group also studied the effect of IL-5, but did not see the same effect as with IL-4 and IL-13, probably due to the lack of IL-5 receptor in the used cell line.…”

NF-κB and the immune response

“…Therefore, whereas a variety of TLRs are differentially expressed in epidermis, gut, pulmonary, urinary and reproductive epithelium, in many cases it is thought that both TLR expression and responsiveness is tightly controlled in these cells. For example, keratinocytes upregulate TLRs expression and responsiveness following transforming growth factor-alpha (TGFa) exposure (Miller et al, 2005); renal epithelial cells increase expression of TLR2 and TLR4 in response to IFNg or TNFa (Wolfs et al, 2002) and intestinal epithelial cells have been shown to alter TLR expression under inflammatory conditions (Mueller et al, 2006). However, sentinel cells of the innate immune system, particularly tissue resident DCs and macrophages, express a more complete complement of PRRs, and thus are likely to bear the largest portion of the burden in the earliest events of pathogen recognition.…”

Reevaluation of quantitative flow cytometric analysis for TLR2 on monocytes using F(ab′)2 fragments of monoclonal antibodies

“…Cytokines play critical roles in the course of infectious diseases (23)(24)(25)(26), and some cytokines induce up or down-regulation of TLR2 level (17,18,(20)(21)(22). PE-labeled D29 wIgG, whose subclass is IgG1, showed no or less nonantigen-specific bindings to monocytes from normal volunteers, as well as F(ab 0 ) 2 fragments of D45 and D29 ( Figs.…”

“…Furthermore, several cytokines were reported to induce modulation of surface TLR2 and CD64 in vitro (17,18,(20)(21)(22). To examine whether the nonantigen specific binding can be eliminated by the addition of blocking reagents even the cytokine stimulated condition, we compared the binding levels between wIgG and F(ab 0 ) 2 mAbs with cytokine-stimulated monocytes.…”