Table 1.

Different expression of markers in different types of Tfr and Tfh compared to Tregs and T naive.

	T Naive	bTfh (blood)	cTfh (central GC)	Treg	eTfr	bTfr	iTfr	mTfr	Ref
CD4	++	++	++	++	++	++	++	++	(8, 11–15, 24, 31, 35)
CXCR5	-	+++	+++	-	++	++	++	+++	(8, 11–15, 24, 31, 35, 36)
CD25	-	-	-	+++	+++	+++	+	–	(8, 11–15, 24, 31, 35)
FOXP3	-	-	-	++	++	++	++	++	(8, 11–15, 24, 31, 35)
ICOS	+	-	++	+	?	-	++	+++	(8, 11, 12, 15, 24, 31, 35, 36)
PD-1	-	-	++	±	–	-	+	++	(8, 11–15, 24, 31, 35)
Bcl6	-	-	++	-	+	-	+	++	(8, 11–13, 15, 24, 35)
Blimp1	-	-	-	+	+	?	+	+	(8, 11, 12, 15, 24, 31)
CTLA-4	-	+	?	+++	?	+++	+++	+++	(12, 15, 37)

Expression of different surface markers (CD4, CXCR5, CD25, ICOS,PD-1) and intracellular markers (FOXP3, Bcl-6, Blimp-1, CTLA-4) in different subtypes of T cells: Naïve T cell, blood T follicular helper cells (bTfh), central Tfh (cTfh), regulatory T cells (Tregs), early T follicular regulatory cell (eTfr), blood Tfr (bTfr), intermediate Tfr (iTfr), and mature Tfr (mTfr). The markers described have been identified in both mouse and human (dark gray), in mouse only (light gray), or hypothesized in the publication from Fonseca et al., in Immunol rev 2019 (white). Of note, “bTfr” refers to blood Tfr, and “cTfr” to circulating Tfr as indicated in some publications (7, 15). mTfr refers to mature Tfr and these subtype of Tfr has been described within the germinal centre.

“-” refers to no expression, “+” refers to low expression, “++” refers to intermediate expression, and “+++” refers to high expression.