Human Cytomegalovirus Interacts with Toll-like Receptor 2 and CD14 on Syncytiotrophoblasts to Stimulate Expression of TNFalpha MRNA and Apoptosis

Placentae from newborns with congenital human cytomegalovirus (HCMV) infection often display shallow implantation, chronic villitis and disruptions of the syncytiotrophoblast. Little is known about how HCMV infection induces inflammation in the placenta and loss of the trophoblast. We propose that the inflammation is initiated with innate defense responses of mature syncytiotrophoblast (ST) to virus. Previously we have shown that ultraviolet irradiation-inactivated (UV-) HCMV interacts with toll-like receptor 2 (TLR2) on primary placental cytotrophoblasts (CT) differentiated into ST-like cells thereby stimulating the release of tumor necrosis factor alpha (TNFalpha) and inducing apoptosis of neighboring cells (Chan et al, J. Pathol. 210: 111, 2006). We now determine whether known co-factors of the interaction of HCMV and TLR2 (TLR1 and CD14) bind to UV-HCMV to stimulate expression of TNFalpha and apoptosis in ST-like cells but not CT. We show that CT both fail to express detectable TLR1 and express much less CD14 than ST and that ST express CD14 but not TLR1 both in vivo and in cultured cells. The interaction of UV-HCMV and HCMV with CD14 on the surface of ST-like cells increases TNFalpha expression and induces apoptosis in the population. Antibody to CD14 also inhibits infectious HCMV induction of HCMV immediate early (HCMV IE) expressing ST-like cells. We conclude that primary villous CT express low levels of CD14 and no TLR1 but that ST strongly expresses CD14 which acts upstream of TLR2 to collect even transcriptionally inactive virus particles to stimulate TNFalpha expression and villous trophoblast damage.