IMMUNOLOGY
SOSTDC1-producing follicular helper T cells promote
regulatory follicular T cell differentiation
Xin Wu^1 , Yun Wang^1 , Rui Huang^1 , Qujing Gai^1 , Haofei Liu^1 , Meimei Shi^1 , Xiang Zhang^1 , Yonglin Zuo^1 ,
Longjuan Chen^1 , Qiwen Zhao^1 , Yu Shi^1 , Fengchao Wang^2 , Xiaowei Yan^3 , Huiping Lu^4 , Senlin Xu^1 ,
Xiaohong Yao^1 , Lin Chen^2 , Xia Zhang^1 , Qiang Tian^3 *, Ziyan Yang^5 , Bo Zhong^6 , Chen Dong^4 ,
Yan Wang^1 †, Xiu-Wu Bian^1 †, Xindong Liu^1 †
Germinal center (GC) responses potentiate the generation of follicular regulatory T (TFR) cells.
However, the molecular cues driving TFRcell formation remain unknown. Here, we show that sclerostin
domain-containing protein 1 (SOSTDC1), secreted by a subpopulation of follicular helper T (TFH) cells
and T–B cell border–enriched fibroblastic reticular cells, is developmentally required for TFRcell
generation. Fate tracking and transcriptome assessment in reporter mice establishes SOSTDC1-
expressing TFHcells as a distinct T cell population that develops after SOSTDC1–TFHcells and loses
the ability to help B cells for antibody production. Notably,Sostdc1ablation in TFHcells results in
substantially reduced TFRcell numbers and consequently elevated GC responses. Mechanistically,
SOSTDC1 blocks the WNT–b-catenin axis and facilitates TFRcell differentiation.
U
nlike follicular helper T (TFH)cells,which
initiate germinal center (GC) reactions
( 1 – 4 ), follicular regulatory T (TFR) cells,
a recently identified subset of Foxp3-
expressing regulatory T (Treg) cells, con-
strain GC reactions ( 5 – 10 ). Thymus-derived Treg
cells give rise to TFRcells through the up-
regulation of TFHcell–related signature mole-
cules ( 5 , 11 , 12 ). TFRcells thus share chimeric
features with both TFHand Tregcells simulta-
neously ( 11 , 13 – 15 ). However, the environmental
cues attributed to TFRcell commitment re-
main unclear.
We recently observed that sclerostin domain-
containing protein 1 (SOSTDC1), a secreted
protein containing a C-terminal cysteine knot–
like domain, was selectively expressed in TFH
cells ( 16 ). TheSostdc1locus in TFHcells wasmarked with the active marker trimethylated
histone H3 lysine 4 (H3K4me3) and lacked the
repressive marker H3K27me3, as compared
with other CD4+T cell subsets (fig. S1A).Sostdc1
mRNA was expressed in TFHcells but not in
other T cell populations (Fig. 1A). SOSTDC1
protein was highly expressed in cells that
localized in B cell follicles, especially at the T–
B cell border (fig. S1B). InSostdc1EGFPreporter
mice challenged with either influenza viruses
or antigen immunization, SOSTDC1 expression
in CD4+TcellswasconfinedtoCXCR5+PD-1+
TFHcells (fig. S2, A to E). Anatomically,
enhanced green fluorescent protein (EGFP)+
cells were enriched at T–Bcellborderand
B cell follicle regions (fig. S3, A and B). At T–
B cell border regions, Sostdc1+cells com-
prised both EGFP+CD4+T and podoplanin+
fibroblastic reticular cells (FRCs) (fig. S3B).
Notably, the number of Sostdc1+CD4+T cells
located at the T–Bcellborderwassecondonly
to that in the B cell follicle (fig. S3C). Thus,
Sostdc1 is preferentially expressed in TFH
cells and T–B cell border–resident FRCs in
peripheral lymphoid organs.
SOSTDC1expressioninTFHcells was ini-
tiated at day 3, gradually increased from day 3
to 7, and maintained until at least day 15 at
~12% (Fig. 1B). On day 8, SOSTDC1-EGFP+TFH
cells were located in B cell follicles and at T–B
cell borders (Fig. 1C). Additionally, phenotypingRESEARCH
Wuet al.,Science 369 , 984–988 (2020) 21 August 2020 1of5
A
18.8 ± 0.7
60.5 ± 2.4CD4Foxp3-GFP16.6 ± 1.382.7 ± 1.8PD-1CXCR526 ± 2.0
62.5 ± 3.9CD44hi CD4+T cells
105
104
1030
000102102102
103103103104 10
4104105105105(^0) 6.62 13.9 12.2
0
0
102
102
103
103
104
104
105
105
D0 D1 D3 D5 D7 D15
10
WT Bcl6RFP
Bcl6RFP/
Sostdc1EGFP
0
102
103
104
105
0102 103 104 105
Naive T Non-TFH TFH Non-TFR TFR
Cxcr5 Sostdc1
B
T Zone
GC
Follicle
GC^0
20
40
60
80
SOSTDC1-EGFP cell
- C D
E
dLN Sp
IgD / SOSTDC1-EGFP
TFR
non-TFR
TFH
non-TFH
dLNs
Spleens
0
102
11.4
CXCR5
SOSTDC1-EGFP
Follicle
GC
T-B BorderInterfollicle
0102 103 104 105
0
102
103
104
(^5) 0.09240.0924 25.2 0.0297 10.2 5.06
SOSTDC1-EGFP
14.7 7.13^82
5.19 5.65
4.26 78.7
6.38 10.6
BCL6-RFP
SOSTDC1-EGFP
SOSTDC1-EGFP
BCL6-RFP
- (%)
BCL6-RFP
0
10
20
30
Relative mRNA level
0
20
40
60
80
100
Fig. 1. SOSTDC1 is selectively expressed in a subpopulation of TFHcells.
(A)Cxcr5andSostdc1mRNA levels in naïve CD4+T, as well as TFR, non-TFRTregs,
TFH, and non-TFHcells that were sorted from KLH- and complete Freund’s
adjuvant (CFA)–immunizedFoxp3EGFPmice. (B) Flow cytometric analysis of
donor cells from CD45.1+mice that received naïveSostdc1EGFP/OT-II cells,
followed by immunization with ovalbumin (OVA) and CFA. (C) Immuno-
fluorescent staining of dLNs from mice that receivedSostdc1EGFP/OT-II cells,
followed by immunization with OVA in CFA subcutaneously for 8 days. Green:
SOSTDC1-GFP; Red: IgD; scale bars: 200mm. The dashed lines demarcate the
distribution of donor cells in the follicles, GCs, and interfollicular region. (D) Flow
cytometric analysis of CD4+T cells with red fluorescent protein (RFP) and EGFP
gating from WT,Bcl6RFP, andBcl6RFP/Sostdc1EGFPmice immunized sub-
cutaneously with KLH in CFA for 7 days. (E) Flow cytometric analysis of donor
TFHcells in congenic mice that received SOSTDC1-EGFP+Bcl6-RFP+TFHOT-II
cells, followed by immunization with OVA in incomplete Freund’s adjuvant
subcutaneously for 7 days. Sp, spleens. Error bars indicate SEM. Statistical tests:
Student’sttest. P< 0.01. Data represent at least two independent
experiments with three to five mice per group.