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Published in final edited form as: J Immunol. 2013 Feb 27;190(7):3049–3053. doi: 10.4049/jimmunol.1203032

STAT1 is required for IL-6 mediated Bcl6 induction for early Tfh differentiation

Youn Soo Choi 1, Danelle Eto 1, Jessica A Yang 1, Christopher Lao 1, Shane Crotty 1,2,3,†
PMCID: PMC3626564  NIHMSID: NIHMS441794  PMID: 23447690

Abstract

Bcl6 is required for CD4 T cell differentiation into follicular helper cells (Tfh). Here, we examined the role of IL-6 in early processes of in vivo Tfh differentiation, as the timing and mechanism of action of IL-6 in Tfh cell differentiation has been controversial in vivo. We found that early Bcl6+CXCR5+ Tfh cell differentiation was severely impaired in the absence of IL-6; however, STAT3 deficiency failed to recapitulate that defect. IL-6 receptor signaling activates the transcription factor STAT1 specifically in CD4 T cells. Strikingly, we found that STAT1 activity was required for Bcl6 induction and early Tfh differentiation in vivo. IL-6 mediated STAT3 activation is important for downregulation of IL-2Rα to limit Th1 differentiation in an acute viral infection. Thus, IL-6 signaling is a major early inducer of the Tfh differentiation program unexpectedly mediated by both STAT3 and STAT1 transcription factors.

Keywords: Tfh cells, acute viral infection, Bcl6 induction, cooperative role of STATs

Introduction

Follicular helper (Tfh) CD4 T cells are a subset of differentiated CD4 T cells with specialized B cell help functions (1). Tfh differentiation of murine and human CD4 T cells is programmed by the transcription factor Bcl6 (1, 2). Effector CD4 T cell differentiation is controlled by induction of key transcription factors by antigen receptor signals, costimulatory receptors, and cytokine receptor mediated activation signals (3). IL-6 has been proposed to induce Tfh differentiation. CXCR5+ CD4 T cell frequencies were impaired in vivo in the absence of IL-6 in one study (4). Perplexingly, following protein immunization and acute viral infections, Tfh differentiation was found to be near normal in the absence of IL-6 at the peak of the CD4 T cell response (5, 6). CD4 T cells have been shown to acquire expression of some Tfh genes in vitro in the presence of IL-6 (7–9). However, other studies have found that Tfh differentiation is not readily recapitulated with in vitro culture of pure CD4 T cells plus IL-6 (10). STAT3 is the best recognized transcription factor downstream of the IL-6 receptor (11). Similar to IL-6, there have been variable outcomes regarding whether STAT3 is required for Tfh differentiation in vivo (4, 12). Tfh differentiation is certainly a multifactorial process (10); nevertheless, recent studies have highlighted that IL-6 signaling is important to Tfh cell biology, as there is a dramatic IL-6 requirement for sustaining Tfh cells in a chronic viral infection of mice (13), and IL-6 strongly correlated with Tfh cell frequency and function in SIV infected macaques (14), the best available animal model of HIV infection.

Recently, we have shown that early signaling events are sufficient for fate committed differentiation of CD4 T cells into Tfh versus Th1 cells during the primary immune response to an acute viral infection (15). Here, we examined the roles of IL-6 in this process. Through cell transfers as well as genetic and molecular approaches, we demonstrate that IL-6 provides critical signals for CD4 T cells to induce Bcl6 and CXCR5 in vivo. We identify that both STAT1 and STAT3 activation is required for IL-6 mediated Bcl6 induction and early Tfh differentiation.

Materials and Methods

Mice and viral infections

C57BL/6J (B6) and IL-6 deficient (Jackson) and CD4-Cre+ (Taconic) mice were purchased. CD45.1+ SMARTA (‘SM’. LCMV gp66–77-IAb specific) (16) and STAT3fl/fl (17) SM mice were obtained from in-house breeders at LIAI. IL-21−/− mice were obtained from the Zajac lab (18). LCMV Armstrong (LCMVArm) strain and recombinant VACV virus that express LCMV gp protein (VACV-gpc) (19) were used. 1 and 0.5 × 106 PFU of LCMVARM, or 50 and 20 × 106 PFU of VACV-gpc, were I.P. injected for analysis at day 2 and 3 after infection, respectively. All animal experiments were performed in compliance with approved animal protocols at LIAI. Naïve or RV+ SM cells were transferred into recipient mice via the retro-orbital sinus. For the analysis of SM cells after LCMV infection, 1 × 106 and 4–5 × 105 SM CD4+ T cells for day 2 and 3 experiments; in VACV-gpc infection system, 3 × 105 and 1.5 × 105 SM cells for day 2 and 3 experiments. Statistical analyses for all experiments were conducted with Prism 5.0 (GraphPad) and P-values were obtained by using two-tailed unpaired t tests with a 95% confidence interval. Data is depicted as mean ± SEM.

Retroviral vector production and CD4 T cell transduction

STAT1 (Thermo Scientific; Antisense sequence: TCACCAACAGTCTCAGCTT) or a non-functional shRNA-miR-expressing retroviral vectors (pLMA-mAmetrine (20)) were used to produce virions from the Plat-E cell line. SM cells were in vitro stimulated with 8 µg/ml of αCD3 and αCD28 (BioXcell) and then transduced with retroviral virions 24 and 36 hours post stimulation.

Flow Cytometry

Splenocytes were prepared for staining as previously described (20). Naïve or RV+ SM cells were cultured in 96-well plate with IL-6 or IL-12 (20 ng/ml) at 37°C for 15–30 mins for staining with anti -pSTAT1 (14/P-STAT1), -pSTAT3 (4/P-STAT3), and -pSTAT4 Abs (38/P-STAT4) (BD Biosciences).

Results

IL-6 is required for early Tfh differentiation

Bcl6+CXCR5+ Tfh cells are present at day 3 after LCMV infection (20, 21) and are fate committed (15). We carefully examined the role of IL-6 during early Tfh differentiation by analyzing SM in B6 or IL-6 deficient (IL-6−/− hereafter) recipient mice at early time points after LCMV infection. At day 2 after LCMV infection, Tfh cells can be phenotypically identified as IL-2RαintCXCR5hiBcl6hi(Supplemental Fig. 1A–B). Bcl6 induction was severely impaired in IL-6−/− mice (Fig. 1A). IL-2RαintCXCR5hi Tfh cells were barely present at 48 hours after LCMV infection in the absence of IL-6 (Fig. 1B. p = 0.0001). Bcl6+CXCR5+ Tfh cells were not observed in IL-6−/− mice at day 3 after LCMV infection (Fig. 1C. p = 5.2 × 10−5). Defective early Tfh differentiation was not due to a CD4 T cell activation defect (Supplemental Fig. 1C).

Fig. 1. IL-6 signals are required for development of early Bcl6+CXCR5+ Tfh cells.

Fig. 1

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Naïve SM (CD45.1+) CD4 T cells were transferred into B6 and IL-6−/− mice and analyzed at day 2 and 3 after LCMV infection. (A) Overlaid Bcl6 histograms of SM cells in infected mice (colors). Naïve CD4 T cells of uninfected mice (gray). (B) IL-2RαintCXCR5hi cells gated and calculated as % of total SM cells. (C) Bcl6+CXCR5+ Tfh cells at day 3 after infection. Percent of Tfh cells calculated. (D) Overlaid IL-2Rα histograms of SM cells in infected mice (colors). Naïve CD4 T cells of an uninfected mouse (gray). IL-2Rα geoMFIs calculated. (E) IL-2Rα geoMFIs of day 3 CXCR5− SM cells. Data are representative of three independent experiments (n = 4–5 mice per group). ** P < 0.01, *** P < 0.001.

IL-2 signaling inhibits Tfh differentiation (21, 22). Bcl6+CXCR5+ Tfh cells strongly downregulate IL-2Rα by day 3 after LCMV infection, the high affinity subunit of the IL-2R (20, 21). Interestingly, IL-6 was required for downregulation of IL-2Rα on CD4 T cells. At day 2 and 3 after LCMV infection, SM cells retained much higher level of IL-2Rα in IL-6−/− mice (Fig. 1D). Excessive IL-2Rα expression was also observed on a CXCR5− Th1 SM cells in IL-6−/− mice (Fig. 1E). These findings show a direct antagonism between IL-6 and IL-2 signaling pathways in differentiating CD4 T cells during an antiviral immune response. This is consistent with binding competition between STAT3 and STAT5 to the IL-2Rα gene of CD4 T cells during Th17 differentiation (23).

IL-21, in addition to IL-6, is associated with Tfh differentiation (4, 24), and can signal via partially overlapping pathways. IL-21 per se, however, is not required for development of Tfh cells at the peak of the CD4 T cell response in multiple acute viral infections and protein immunizations (5, 6, 24). IL-21 is also not required for Tfh cell priming (Supplemental Fig. 1D–E). IL-21 plays an important role in the absence of IL-6 later in acute viral infections and protein immunizations (5, 24). Collectively, our data show that IL-6, but not IL-21, is required for early Tfh differentiation in vivo.

STAT3 contributes to IL-6 mediated Bcl6 induction and Tfh differentiation

STAT3 binds to the IL-6 receptor and is activated by JAK-mediated phosphorylation (pSTAT3) upon IL-6 stimulation (17). Therefore, we investigated whether the IL-6 receptor mediated Tfh differentiation signal is delivered by STAT3. Wild type (WT) and STAT3fl/fl CD4-Cre+ (referred to as STAT3−/− hereafter) SM cells were transferred into B6 mice, and analyzed for Tfh differentiation at day 2 and 3 after LCMV infection. STAT3 deficiency resulted in severely impaired Tfh differentiation during the first 48 hours after infection. Bcl6 induction was defective (Fig. 2A) and Bcl6hiCXCR5hi CD4 T cells were severely reduced in STAT3−/− SM cells (Fig. 2B. p = 0.0007). Quite surprisingly however, STAT3−/− SM cells differentiated into Bcl6+CXCR5+ Tfh cells comparably to WT SM cells within an additional 24 hours (Fig. 2C). Interestingly, STAT3 activation controlled IL-2Rα downregulation downstream of IL-6R. In comparison to WT SM cells, STAT3−/− SM cells were severely impaired in downregulation of IL-2Rα at both day 2 (Supplemental Fig. 2A. p = 0.01) and 3 (Fig. 2D. p = 2.6 × 10−5) after LCMV infection. Nonetheless, the relatively normal Tfh differentiation of STAT3−/− SM cells at day 3 after infection was a sharp contrast to the severely defective Tfh differentiation in IL-6−/− mice at the same time point (Fig. 1C), strongly implicating the presence of a second pathway downstream of IL-6R signaling for Bcl6 induction. Collectively, our data show that STAT3 participates in Bcl6 induction and IL-2Rα downregulation downstream of IL-6R signaling.

Fig. 2. STAT3 contributes to early Bcl6 induction and Tfh differentiation.

Fig. 2

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Naïve WT or STAT3−/− SM (CD45.1+) cells were transferred into B6 mice that were infected with LCMV. SM cells were analyzed for Tfh differentiation at day 2 (A–B) and 3 (C–D) after infection. (A) Bcl6 histograms of WT (red) and STAT3/− (blue) SM cells. Naïve CD4 T cells of an uninfected mouse (gray). (B) Bcl6hiCXCR5hi cells gated and calculated as % of total SM cells. (C) Gates indicate Bcl6+CXCR5+ SM cells at day 3 after LCMV infection. Percent of total SM cells. (D) Overlaid IL-2Rα histogram of WT (red) and STAT3−/− (blue) SM Tfh cells, gated in Fig. 2C. IL-2Rα geoMFIs. Data are representative of three independent experiments (n = 4–5 mice per group). ** P < 0.01, *** P < 0.001. NS, not statistically different.

STAT1 is required for early Tfh differentiation

The disparate requirements for IL-6 and STAT3 led us to investigate whether another transcription factor is required for IL-6 mediated early Tfh differentiation. Interestingly, while IL-6 stimulation of IL-6R activates STAT3 in multiple hematopoietic cell types, STAT1 is strongly activated by IL-6 selectively in CD4 T cells (Fig. 3A) (25). Therefore, we investigated the role of the transcription factor STAT1 in early Tfh differentiation. STAT1 expression was inhibited by a STAT1-specific shRNAmir (STAT1KD hereafter) (Fig. 3A. pSTAT1 MFI was reduced by about 80%). STAT1KD activity was specific for STAT1, as activation of both STAT3 (Fig. 3A.) and STAT4 (Supplemental Fig. 2B) in vitro was normal upon IL-6 and IL-12 stimulation, respectively. We then examined the role of STAT1 in Tfh differentiation in vivo. While IL-6 stimulation led to pSTAT1 in day 3 WT SM cells, STAT1 activity was further elevated in STAT3−/− SM cells (Supplemental Fig. 2C). 48 hours after LCMV infection STAT1KD SM cells failed to differentiate into Bcl6hiCXCR5hi and IL-2RαintCXCR5hi cells (Fig. 3B. p = 0.0004; Supplemental Fig. 2D p = 0.001).

Fig. 3. Both STAT1 and STAT3 are required for early Tfh differentiation of CD4 T cells.

Fig. 3

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(A) Ctrl- or STAT1KD SM (CD45.1+) cells were stimulated with IL-6 for pSTAT stainings. Overlaid histograms of pSTAT1 and pSTAT3. (B) Ctrl- or STAT1KD SM cells were transferred into B6 mice that were infected with LCMV. Gates indicate Bcl6hiCXCR5hi at day 2 after infection. % of Bcl6+CXCR5+ Tfh cells among total SM cells. (C–E) Ctrl-, STAT1KD, STAT3−/−, or STAT3−/−STAT1KD SM cells were transferred into B6 mice. SM analyzed at day 3 after infection. (C) Gates indicate Bcl6+CXCR5+ Tfh cells. (D) % of Tfh cells calculated. (E) CXCR5 MFIs were normalized with cell size of donor cells (CXCR5MFI/FSCMFI). Data are representative of two (C–E) and three (A–B) independent experiments (n = 4–5 mice per group). ** P < 0.05, *** P < 0.01.

While a major defect in Bcl6 and CXCR5 expression was seen in the absence of STAT1 expression at day 2 after LCMV infection, like STAT3 the STAT1 defect could be compensated for, as STAT1KD SM cells regained comparable Bcl6 and CXCR5 expression to control SM cells by day 3 in vivo (Supplemental Fig. 2E). This again was in contrast to the requirement for IL-6 signaling through day 3 of CD4 T cell priming in vivo (Fig. 1C). Therefore, we investigated whether STAT1 and STAT3 cooperate to induce Tfh differentiation. To test this, STAT1 activity was repressed in STAT3−/− SM cells (STAT1KDSTAT3−/−). In vitro stimulation with IL-6 of STAT3−/−, STAT1KD, or STAT1KDSTAT3−/− SM cells confirmed the expected STAT1 and STAT3 phosphorylation defect(s) (data not shown). Quite strikingly, we found that STAT1KDSTAT3−/− SM cells failed to develop into Bcl6+CXCR5+ Tfh cells at 72 hours post LCMV infection (Fig. 3C–E. p = 0.005). T-bet was upregulated by CXCR5− Th1 STAT1KDSTAT3−/− SM cells (Supplemental Fig. 2F). These findings indicate strong cooperation between STAT1 and STAT3 downstream of IL-6 in Tfh cell priming.

Type I IFN signal is critical for CD4 T cell survival in LCMV infected mice (26) and STAT1 activation is critical for type I IFN signaling. As a consequence, SM cells were 5 to 10-fold less abundant when STAT1 activity was curtailed in STAT1KD cells (data not shown). However, CD4 T cell type I IFN signaling is not required in other infections (26). Therefore, acute vaccinia virus (VACV) was used as an independent model (Supplemental Fig. 2G–H). STAT1KD SM cells failed to differentiate into Tfh cells two days after VACV-gpc infection (Fig. 4A. p = 0.0001). Notably, STAT1KD CD4 T cells had continued Tfh differentiation defects at day 3 after VACV-gpc infection, even in the presence of STAT3 (Fig. 4B. p = 0.047). Residual STAT1 in STAT1KD cells may have low level activity. Taken together, our data demonstrate that STAT1 is an important transcription factor directing IL-6 dependent Bcl6 induction and Tfh differentiation during the DC priming stage of acute viral infections.

Fig. 4. STAT1 is necessary for early Tfh differentiation after VACV infection.

Fig. 4

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Ctrl- or STAT1KD SM (CD45.1+) cells were transferred into B6 mice that were infected with VACV-gpc. Bcl6+CXCR5+ Tfh cells gated and calculated as % of total SM cells at day 2 (A) and 3 (B) after infection. Data are representative of two independent experiments (n = 4–5 mice per group). ** P < 0.05, *** P < 0.001.

Discussion

Cytokine dependent STAT activation has roles in many T cell differentiation and survival processes (3). Defective IL-6 signaling resulted in a significant loss of Tfh cell maintenance during a chronic LCMV clone 13 infection (13). The ability of SIV infected macaques to make germinal centers and high affinity anti-Env IgG responses correlated with Tfh cell abundance, which correlated with IL-6 availability (14). Those observations have highlighted the likely importance of Tfh cells in HIV infection and other viral infections that are major pubic health burdens (27). In this study, we examined the roles of IL-6 during the early stage of in vivo Tfh differentiation. Our study demonstrates that Bcl6 induction and CXCR5 expression is specifically impaired in the absence of IL-6 during the DC priming phase of the CD4 T cell response, and surprisingly this depends on both STAT1 and STAT3. Through STAT3 activation, IL-6 also can compete with IL-2 signaling by restricting surface expression of IL-2Rα. Hence, these findings may explain mechanisms by which IL-6 affects Tfh cells in numerous contexts.

The early Tfh differentiation defect is not permanent in the response to an acute LCMV infection in IL-6−/− mice (5, 6, 13). We infer that compensatory signals become available at later time points of LCMV infection, which can largely compensate for the lack of IL-6. Having multiple redundant pathways to signal Tfh differentiation is almost certainly a highly evolutionary evolved system to prevent pathogen evasion, since antibody responses are valuable for control and clearance of most pathogens, whether viral, bacterial, fungal, or parasitic (10). Acute LCMV infection is a very robust immunogen, and it is likely that some other immunogens do not engage compensatory pathways effectively. Recent studies indicate that there are nonredundant roles for IL-6 in Tfh cell biology in important physiological conditions (13, 14). In summary, the data presented here shows quite strikingly that IL-6 is a dominant factor during the Tfh priming stage.

The findings reported here have intriguing implications for understanding human Tfh cells and multiple human genetic diseases. Humans with Job’s syndrome have heterozygous dominant negative STAT3 gene mutations (28). In those patients, Th17 cell differentiation is completely lost, demonstrating the central importance of STAT3 for Th17 cells (28). In contrast, in those STAT3mut patients Tfh cell frequencies are only moderately reduced (CD45RA−CXCR5+) (29). Our data confirm that STAT3 contributes to IL-6 dependent Bcl6 induction, but that contribution overlaps with critical roles of STAT1 delivering IL-6 signals to instruct Tfh differentiation in vivo. Notably, a trend of reduced Tfh frequencies was observed in patients with dominant negative STAT1 mutations (29). Interestingly, three patients with gain-of-function mutations in STAT1 exhibited unexpectedly increases in blood Tfh cell frequencies (29). We infer that excessive activation of STAT1 downstream of IL-6R may explain the phenotype of increased Tfh frequencies in those patients. Hence, phenotypes of both STAT1mut and STAT3mut patients may be explained by the demonstration here that both STAT1 and STAT3 contribute to IL-6 mediated Bcl6 induction and Tfh differentiation. Further understanding of the sources of IL-6 production and the pathways downstream of the STAT1 and STAT3 transcription factors are likely to provide mechanistic insights that can contribute to the design of more efficacious vaccines against infectious diseases.

Supplementary Material

1

Acknowledgements

We thank Drs. Mitch Kronenberg for STAT3fl/fl CD4-Cre+ mice and Robert Johnston for preliminary experiments. We also thank Dr. Allan Zajac for IL-21−/− mice.

This work was supported by NIH NIAID grants (R01 072543 and R01 063107), Scripps CHAVI-ID Award (UM1AI100663), and LIAI institutional funds to SC.

References

  • 1.Crotty S. Follicular helper CD4 T cells (TFH) Annu Rev Immunol. 2011;29:621–663. doi: 10.1146/annurev-immunol-031210-101400. [DOI] [PubMed] [Google Scholar]
  • 2.Kroenke MA, Eto D, Locci M, Cho M, Davidson T, Haddad EK, Crotty S. Bcl6 and Maf cooperate to instruct human follicular helper CD4 T cell differentiation. J Immunol. 2012;188:3734–3744. doi: 10.4049/jimmunol.1103246. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3.O'Shea JJ, Plenge R. JAK and STAT signaling molecules in immunoregulation and immune-mediated disease. Immunity. 2012;36:542–550. doi: 10.1016/j.immuni.2012.03.014. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Nurieva RI, Chung Y, Hwang D, Yang XO, Kang HS, Ma L, Wang Y-h, Watowich SS, Jetten AM, Tian Q, Dong C. Generation of T follicular helper cells is mediated by interleukin-21 but independent of T helper 1, 2, or 17 cell lineages. Immunity. 2008;29:138–149. doi: 10.1016/j.immuni.2008.05.009. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 5.Eto D, Lao C, Ditoro D, Barnett B, Escobar TC, Kageyama R, Yusuf I, Crotty S. IL-21 and IL-6 are critical for different aspects of B cell immunity and redundantly induce optimal follicular helper CD4 T cell (Tfh) differentiation. PloS one. 2011;6:e17739. doi: 10.1371/journal.pone.0017739. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Poholek AC, Hansen K, Hernandez SG, Eto D, Chandele A, Weinstein JS, Dong X, Odegard JM, Kaech SM, Dent AL, Crotty S, Craft J. In vivo regulation of Bcl6 and T follicular helper cell development. J Immunol. 2010;185:313–326. doi: 10.4049/jimmunol.0904023. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 7.Nurieva RI, Chung Y, Martinez GJ, Yang XO, Tanaka S, Matskevitch TD, Wang Y-H, Dong C. Bcl6 mediates the development of T follicular helper cells. Science. 2009;325:1001–1005. doi: 10.1126/science.1176676. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8.Nakayamada S, Kanno Y, Takahashi H, Jankovic D, Lu KT, Johnson TA, Sun H-w, Vahedi G, Hakim O, Handon R, Schwartzberg PL, Hager GL, O'Shea JJ. Early Th1 Cell Differentiation Is Marked by a Tfh Cell-like Transition. Immunity. 2011;35:919–931. doi: 10.1016/j.immuni.2011.11.012. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 9.Oestreich KJ, Mohn SE, Weinmann AS. Molecular mechanisms that control the expression and activity of Bcl-6 in T(H)1 cells to regulate flexibility with a T(FH)-like gene profile. Nat Immunol. 2012;13:405–411. doi: 10.1038/ni.2242. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 10.Crotty S. The 1-1-1 fallacy. Immunol Rev. 2012;247:133–142. doi: 10.1111/j.1600-065X.2012.01117.x. [DOI] [PubMed] [Google Scholar]
  • 11.Heinrich PC, Behrmann I, Müller-Newen G, Schaper F, Graeve L. Interleukin-6-type cytokine signalling through the gp130/Jak/STAT pathway. Biochem J. 1998;334:297–314. doi: 10.1042/bj3340297. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 12.Eddahri F, Denanglaire S, Bureau F, Spolski R, Leonard WJ, Leo O, Andris F. Interleukin-6/STAT3 signaling regulates the ability of naive T cells to acquire B-cell help capacities. Blood. 2009;113:2426–2433. doi: 10.1182/blood-2008-04-154682. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 13.Harker JA, Lewis GM, Mack L, Zuniga EI. Late Interleukin-6 Escalates T Follicular Helper Cell Responses and Controls a Chronic Viral Infection. Science. 2011;334:825–829. doi: 10.1126/science.1208421. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 14.Petrovas C, Yamamoto T, Gerner MY, Boswell KL, Wloka K, Smith EC, Ambrozak DR, Sandler NG, Timmer KJ, Sun X, Pan L, Poholek A, Rao SS, Brenchley JM, Alam SM, Tomaras GD, Roederer M, Douek DC, Seder RA, Germain RN, Haddad EK, Koup RA. CD4 T follicular helper cell dynamics during SIV infection. J Clin Invest. 2012;122:3281–3294. doi: 10.1172/JCI63039. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Choi YS, Yang JA, Yusuf I, Johnston RJ, Greenbaum J, Peters B, Crotty S. Bcl6 expressing follicular helper CD4 T cells are fate committed early and have the capacity to form memory. Revised manuscript submitted. 2013 doi: 10.4049/jimmunol.1202963. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 16.Oxenius A, Bachmann MF, Zinkernagel RM, Hengartner H. Virus-specific MHC-class II-restricted TCR-transgenic mice: effects on humoral and cellular immune responses after viral infection. Eur J Immunol. 1998;28:390–400. doi: 10.1002/(SICI)1521-4141(199801)28:01<390::AID-IMMU390>3.0.CO;2-O. [DOI] [PubMed] [Google Scholar]
  • 17.Takeda K, Kaisho T, Yoshida N, Takeda J, Kishimoto T, Akira S. Stat3 activation is responsible for IL-6-dependent T cell proliferation through preventing apoptosis: generation and characterization of T cell-specific Stat3-deficient mice. J Immunol. 1998;161:4652–4660. [PubMed] [Google Scholar]
  • 18.Yi JS, Du M, Zajac AJ. A vital role for interleukin-21 in the control of a chronic viral infection. Science. 2009;324:1572–1576. doi: 10.1126/science.1175194. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 19.Whitton JL, Southern PJ, Oldstone MB. Analyses of the cytotoxic T lymphocyte responses to glycoprotein and nucleoprotein components of lymphocytic choriomeningitis virus. Virology. 1988;162:321–327. doi: 10.1016/0042-6822(88)90471-0. [DOI] [PubMed] [Google Scholar]
  • 20.Choi YS, Kageyama R, Eto D, Escobar TC, Johnston RJ, Monticelli L, Lao C, Crotty S. ICOS receptor instructs T follicular helper cell versus effector cell differentiation via induction of the transcriptional repressor Bcl6. Immunity. 2011;34:932–946. doi: 10.1016/j.immuni.2011.03.023. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 21.Johnston RJ, Choi YS, Diamond JA, Yang JA, Crotty S. STAT5 is a potent negative regulator of TFH cell differentiation. J Exp Med. 2012;209:243–250. doi: 10.1084/jem.20111174. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Ballesteros-Tato A, León B, Graf BA, Moquin A, Adams PS, Lund FE, Randall TD. Interleukin-2 inhibits germinal center formation by limiting T follicular helper cell differentiation. Immunity. 2012;36:847–856. doi: 10.1016/j.immuni.2012.02.012. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23.Liao W, Lin J-X, Wang L, Li P, Leonard WJ. Modulation of cytokine receptors by IL-2 broadly regulates differentiation into helper T cell lineages. Nat Immunol. 2011;12:551–559. doi: 10.1038/ni.2030. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Karnowski A, Chevrier S, Belz GT, Mount A, Emslie D, D'Costa K, Tarlinton DM, Kallies A, Corcoran LM. B and T cells collaborate in antiviral responses via IL-6, IL-21, and transcriptional activator and coactivator, Oct2 and OBF-1. J Exp Med. 2012;209:2049–2064. doi: 10.1084/jem.20111504. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Hotson AN, Hardy JW, Hale MB, Contag CH, Nolan GP. The T cell STAT signaling network is reprogrammed within hours of bacteremia via secondary signals. J Immunol. 2009;182:7558–7568. doi: 10.4049/jimmunol.0803666. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 26.Havenar-Daughton C, Kolumam GA, Murali-Krishna K. Cutting Edge: The direct action of type I IFN on CD4 T cells is critical for sustaining clonal expansion in response to a viral but not a bacterial infection. J Immunol. 2006;176:3315–3319. doi: 10.4049/jimmunol.176.6.3315. [DOI] [PubMed] [Google Scholar]
  • 27.Hendrik S, D'Souza MP, Littman DR, Crotty S. Harnessing CD4 T cell responses in HIV Vaccine Development. Nat Med. 2013 doi: 10.1038/nm.3054. in press. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 28.Milner JD, Brenchley JM, Laurence A, Freeman AF, Hill BJ, Elias KM, Kanno Y, Spalding C, Elloumi HZ, Paulson ML, Davis J, Hsu A, Asher AI, O'Shea J, Holland SM, Paul WE, Douek DC. Impaired T(H)17 cell differentiation in subjects with autosomal dominant hyper-IgE syndrome. Nature. 2008;452:773–776. doi: 10.1038/nature06764. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 29.Ma CS, Avery DT, Chan A, Batten M, Bustamante J, Boisson-Dupuis S, Arkwright PD, Kreins AY, Averbuch D, Engelhard D, Magdorf K, Kilic SS, Minegishi Y, Nonoyama S, French MA, Choo S, Smart JM, Peake J, Wong M, Gray P, Cook MC, Fulcher DA, Casanova J-L, Deenick EK, Tangye SG. Functional STAT3 deficiency compromises the generation of human T follicular helper cells. Blood. 2012;119:3997–4008. doi: 10.1182/blood-2011-11-392985. [DOI] [PMC free article] [PubMed] [Google Scholar]

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