Prolactin decreases LPS-induced inflammatory cytokines by inhibiting TLR-4/NFκB signaling in the human placenta

Prolactin (PRL) plays an important role in trophoblast growth, placental angiogenesis and immunomodulation within the feto-maternal interface, where different cell types secrete PRL and express its receptor. During pregnancy, inflammatory signalling is a deleterious event that has been associated with poor fetal outcomes. The placenta is highly responsive to the inflammatory stimulus; however, the actions of PRL in placental immunity and inflammation remain largely unknown. The aim of this study was to evaluate PRL effects on the TLR4/NFkB signalling cascade and associated inflammatory targets in cultured explants from healthy term human placentas. An in utero inflammatory scenario was mimicked using lipopolysaccharides (LPS) from Escherichia coli. PRL significantly reduced LPS-dependent TNF-α, IL-1β and IL-6 secretion and intracellular levels. Mechanistically, PRL prevented LPS-mediated upregulation of TLR-4 expression and NFκB phosphorylation. In conclusion, PRL limited inflammatory responses to LPS in the human placenta, suggesting that this hormone could be critical in inhibiting exacerbated immune responses to infections that could threaten pregnancy outcome. This is the first evidence of a mechanism for anti-inflammatory activity of PRL in the human placenta, acting as a negative regulator of TLR-4/NFkB signaling.