Toll-like receptor 4 activation on human amniotic epithelial cells is a risk factor for pregnancy loss

Maternal-fetal tolerance plays a fundamental role in the maintenance of pregnancy. However, this immunological tolerance can be influenced by intrauterine infections. Human amniotic epithelial cells (hAECs) have immunomodulatory effects and respond to invading pathogens through expressing various toll-like receptors (TLRs). We hypothesize that bacteria or bacterial products affect the immunosuppressive effects of hAECs through TLR stimulation. Here, we investigated how a successful pregnancy can be threatened by TLR4 activation on hAECs on lipopolysaccharide (LPS) engagement.

hAECs were isolated from the amniotic membrane received from six healthy pregnant women. The immunophenotyping of hAECs was studied by flow cytometry. The isolated hAECs (4 × 10⁵ cells/ml) were cultured in 24-well plates in the presence or absence of LPS (5 μg/ml). After 24, 48, and 72 h of incubation, the culture supernatants of hAECs were collected, and the levels of interleukin-5 (IL-5), IL-6, IL-1β, tumor necrosis factor-alpha (TNF-α), transforming growth factor-beta 1 (TGF-β1), and prostaglandin E2 (PGE2) were measured by enzyme-linked immunosorbent assay.

TLR4 activation showed a stimulatory effect on TGF-β1 production of hAECs (P < 0.001-0.05). PGE2 production of LPS-stimulated hAECs was significantly increased (P < 0.01-0.05). Moreover, TLR4 could induce TNF-α and IL-1β production of hAECs (P < 0.0001-0.01), while this effect was not observed on IL-6 production of hAECs. The IL-5 was produced at a very low level in two culture supernatants of hAECs, in which its production was independent of LPS effect.

TLR4 activation by bacterial components on hAECs may be a potential risk factor for pregnancy complications.