Toll-like receptor 4: A potential link between "danger signals," the innate immune system, and preeclampsia?

Objective: Toll-like receptors (TLRs) recognize microbial ligands and host products that are released during tissue damage, the so-called "danger signals." This study was conducted to determine whether changes in TLR-4 and TLR-2 expressions can be detected in the trophoblasts at the placental bed of women with and without preeclampsia. Study design: Placental bed biopsy specimens were obtained from women with: (1) normal term pregnancies with and without labor (each n = 20); (2) preeclampsia who delivered preterm (n = 15); and (3) preterm labor and intact membranes with and without chorioamnionitis (each n = 15). The expression pattern of TLR-4 and TLR-2 in the trophoblasts was analyzed by double immunohistochemistry. Results: (1) The median percentage of TLR-4 positive interstitial trophoblasts was significantly higher in patients with preeclampsia than in patients with preterm labor without or with histologic chorioamnionitis (P = .0002 and P = .02, respectively). (2) The median percentage of TLR-2 positive interstitial trophoblasts was not different among the study groups (P > .05). (3) TLR-4 positive trophoblasts were also frequently immunoreactive to activated nuclear factor-κB, tumor necrosis factor-α, and M30 (a specific apoptosis antigen for trophoblast). (4) Lipopolysaccharide treatment inhibited the migration of trophoblast cell lines in vitro. Conclusion: TLR-4 protein expression is increased in interstitial trophoblasts of patients with preeclampsia. We propose that "danger signals" at the feto-maternal interface, which are recognized by trophoblasts through TLR-4, may play a key role in the creation of a local abnormal cytokine milieu. This suggests a novel mechanism that links the activation of the innate immune system through TLR-4 and preeclampsia.