The Effects of TLR Activation on T-Cell Development and Differentiation

Table 1

TLR expression and direct effects on T cells [268, 277, 278, 329, 333].

TLR	Location	Typical ligand	Expression in T-cell subsets			Direct effect on T cells
			Naive	Activated/Memory	iTreg
TLR1	Cell surface	Triacryl lipopeptide	±	++	+	Increased effector T-cell proliferation and survival; abrogate the suppressive function of Treg cells
TLR2	Cell surface	Peptidoglycan	±	++	+	Increased cell proliferation and survival; promote cytotoxic activity of CTL; generate efficient memory T cells; augment Treg cell proliferation with temporal loss of suppression
TLR3	Endosome	dsRNA	+	++	−	Promote activated CD4^+ T-cell survival
TLR4	Cell surface	Lipopolysaccharide	±	++	+	Induce Treg cell activation; enhance the suppressive function of Treg cells
TLR5	Cell surface	Flagellin	+	+	+	Augment the suppressive capacity of Treg cells
TLR6	Cell surface	Diacryl lipopeptide	+	+	+	Block the suppressive function of Treg cells
TLR7	Endosome	ssRNA	+	+	−	Augment activation/function of T cells; block the suppressive function of Treg cells
TLR8	Endosome	ssRNA	+	+	+	Augment activation/function of T cells; block the suppressive function of Treg cells
TLR9	Endosome	CpG DNA	+	++	−	Promote activated CD4^+ T-cell survival; inhibit Treg cell suppression

++: enhanced expression; +: normal expression; ±: weak or low expression; −: expression not detectable.