Table 1.

TLRs’ temporal patterns of expression in human trophoblasts.

	Main Ligands	TLR Expression			References
		1st Trimester	2nd Trimester	3rd Trimester
TLR1	Triacylated lipopeptides and lipoproteins from Gram-positive bacteria. When forming a heterodimer with TLR2, it recognizes peptidoglycan and triacylated lipoproteins	++	++	-	[149,150,154]
TLR2	Lipoteichoic acid and lipoproteins from Gram-positive bacteria, lipoarabinomannans from mycobacteria and zymosan from yeast. Diacylated or triacylated lipopeptides depending on heterodimerization patterns	++	++	+++	[150,152]
TLR3	Double strand RNA	++	++	+++	[153,154]
TLR4	Lipopolysaccharides from Gram-negative bacteria, paclitaxel, heat shock proteins, heparan sulphate, reactive oxygen species (ROS), fibrinogen and fibronectin	++	+++	+++	[150,151,152]
TLR5	Flagellin from both Gram-positive and Gram-negative bacteria	++	++	++	[154,155]
TLR6	Diacylated lipopeptides from mycoplasmas (also heterodimerizes with TLR2)	-/+	+	++	[149,150,154]
TLR7	Single strand RNA and small synthetic compounds such as guanosine analogs or imidazoquinoline	+	++	+	[153,154]
TLR8	Single strand RNA and small synthetic compounds such as guanosine analogs or imidazoquinoline	+	++	+++	[153,154]
TLR9	Viral single-strand unmethylated CpG DNA and also fetal DNA	-	+	+	[153,154,155]
TLR10	Double strand RNA	+	+	+	[154]

Expression is presented in arbitrary units: - undetectable, + low expression, ++ moderate expression, +++ high expression.