Toll-like receptors (TLRs) are pivotal components of the innate immune response, which is responsible for eradicating invading microorganisms through the induction of inflammatory molecules. These receptors are also involved in responding to harmful endogenous molecules and have crucial roles in the activation of the innate immune system and shaping the adaptive immune response. However, TLR signaling pathways must be tightly regulated because undue TLR stimulation may disrupt the fine balance between pro- and anti-inflammatory responses. Such disruptions may harm the host through the development of autoimmune and inflammatory diseases, such as rheumatoid arthritis and systemic lupus erythematosus. Several studies have investigated the regulatory pathways of TLRs that are essential for modulating proinflammatory responses. These studies reported several pathways and molecules that act individually or in combination to regulate immune responses. In this review, we have summarized recent advancements in the elucidation of the negative regulation of TLR signaling. Moreover, this review covers the modulation of TLR signaling at multiple levels, including adaptor complex destabilization, phosphorylation and ubiquitin-mediated degradation of signal proteins, manipulation of other receptors, and transcriptional regulation. Lastly, synthetic inhibitors have also been briefly discussed to highlight negative regulatory approaches in the treatment of inflammatory diseases.
Animals ; Cytokines/biosynthesis ; Humans ; Ligands ; Models, Immunological ; Signal Transduction/*immunology ; Toll-Like Receptors/antagonists & inhibitors/*metabolism

OBJECTIVE: To observe the expression of progesterone receptor (PR), interleukin-1β (IL-1β), and cyclooxygenase-2 (COX-2) induced by lipopolysaccharide (LPS) or Toll-like receptor 4 antagonist (TLR4 mAb) in decidual cells in vitro, and then to explore the effect of LPS and its antagonist on PR of decidual cells and the relation between PR and inflammatory cytokines. METHODS: We isolated and cultured human decidua of early abortion in the sterile state. When the cells passaged to the 4th generation, the cells were randomly divided into 6 pore plates: A control group was added the culture medium alone; experimental group I was added 100 ng/mL of LPS; experimental group II was add 1 μg/mL of TLR4 mAb; experimental group III was added 3 μg/ mL of TLR4 mAb; experimental group IV was added 1 μg/mL of TLR4 mAb pretreatment for 24 h, and then 100 ng/mL LPS; and experimental group V was added 3 μg/mL of TLR4 mAb pretreatment for 24 h, and then 100 ng/mL LPS for 24 h culture. Subsequently, HE staining and immunofluorescence were used to observe the morphology and identify the purity of decidual cells in the 6 groups. The levels of mRNA expression of PR, IL-1β, and COX-2 were detected by reverse transcription PCR (RT-PCR). RESULTS: LPS reduced the mRNA expression of PR (P<0.05), increased the mRNA expression of IL-1β and COX-2 (P<0.05). TLR4 mAb increased the mRNA expression of PR (P<0.05) and reduced the mRNA expression of IL-1β (P<0.05) after LPS-stimulated decidual cells. High concentrations of TLR4 mAb reduced the mRNA expression of COX-2 (P<0.05) after LPS stimulated decidual cells. CONCLUSION The mRNA expression of PR is reduced, and the mRNA expressions of IL-1β and COX-2 are increased after LPS-stimulated decidual cells in vitro. TLR4 mAb antagonize the role of LPS on PR, IL-1β, and COX-2.
Adult ; Cells, Cultured ; Cyclooxygenase 2 ; genetics ; metabolism ; Decidua ; cytology ; metabolism ; Female ; Humans ; Interleukin-1beta ; genetics ; metabolism ; Lipopolysaccharides ; pharmacology ; RNA, Messenger ; genetics ; metabolism ; Receptors, Progesterone ; genetics ; metabolism ; Toll-Like Receptor 4 ; antagonists & inhibitors ; Young Adult