mapping the early development of lcmv-specific follicular helper t-cells in mice

Deciphering Early Follicular Helper T-Cell Commitment in Acute LCMV Infection

Encountering different pathogens or threats, na&#239;ve CD4+ T cells tailor their immune responses by differentiating into various helper T (TH) cell subsets with specialized functions1. In the scenario of acute viral infection, a large portion of na&#239;ve CD4+ T cells differentiate into follicular helper T (TFH) cells that provide help to B cells2,3. Distinct from other CD4+ TH cell subsets (e.g., TH1, TH2, TH9, and TH17 cells), TFH cells express a substantial level of CXCR5, which is the chemokine receptor for the B cell homing chemokine CXCL13, enabling TFH cells to migrate into B cell follicles. In the B cell follicles, TFH cells assist cognate B cells in initiating and maintaining germinal center reactions, thus enabling rapid high-affinity antibody production and long-term humoral memory2,3.
Upon acute viral infection, the early fate commitment of virus-specific TFH cells occurs within 72 h4,5and is controlled by the transcriptional repressor B cell lymphoma-6 (Bcl-6)5,6,7,8, which acts as the &#34;master regulator&#34; governing TFH cell fate decisions. Deficiency of Bcl-6 severely blunts TFH cell differentiation, while ectopic Bcl-6 expression substantially promotes TFH cell fate commitment. In addition to Bcl-6, multiple molecules are involved in instructing early TFH cell fate commitment. Transcription factors TCF-1 and LEF-1 initiate TFH cell differentiation via the induction of Bcl-69,10,11. The inhibition of Blimp1, by both Bcl-6 and TCF-1, is required for early TFH cell fate commitment11,12. STAT1 and STAT3 are also required for early TFH cell differentiation13. Besides, epigenetic modifications by histone methyltransferase EZH214,15and m6A methyltransferase METTL316 help to stabilize TFH cell transcriptional programs (especially Bcl6 and Tcf7) and thus prime early TFH cell fate commitment. While advances, including the aforementioned molecules and others, summarized elsewhere3, have been made in understanding the transcriptional and epigenetic regulations of early TFH&#160;cell fate commitment, previously unknown molecules remain to be learned.
In the mouse model of acute lymphocytic choriomeningitis virus (LCMV) infection, adoptively transferred congenic TCR-transgenic SMARTA (SM) CD4+ T cells, which specifically recognize the LCMV glycoprotein epitope I-AbGP66-77, undergo either TFH or TH1 cell differentiation during viral infection. This TFH/TH1 bifurcation differentiation pattern supports the advancement of the SM/acute LCMV infection model in studying the biology of virus-specific TFH cells. Indeed, the SM/acute LCMV infection model has been widely used in the TFH cell research field and has played a crucial role in milestone discoveries in TFH cell biology. This includes the identification of the aforementioned Bcl-6 as the lineage-defining transcription factor of TFH cells5,6, as well as other important transcriptional factors (e.g., Blimp-16, TCF-1/LEF9,10,11, STAT1/STAT313, STAT517, KLF218, and Itch19) guiding TFH cell differentiation, post-transcriptional regulations (e.g., METTL316 and miR-17~9220) of TFH cell differentiation, TFH cell memory and plasticity21,22, and rational vaccination strategies targeting TFH cells (e.g., selenium23).
The current study describes reproducible methods for accessing the early fate commitment of virus-specific TFH cells, including (1) establishing an acute LCMV-infected SM chimera mouse model suitable for accessing early-differentiated TFH cells, (2) conducting flow cytometry stainings of molecules related to early-differentiated TFH cells, and (3) performing retroviral vector-based gene manipulation in SM CD4+ T cells. These methods will be useful for studies investigating the early fate commitment of virus-specific TFH cells.

Author Spotlight: Elucidating the Pathways of TFH Cell Differentiation in Acute LCMV Challenges

Accessing Early Differentiation of Virus-Specific Follicular Helper CD4+ T Cell in Acute LCMV-Infected Mice

Our research describes reproducible methods for assessing the early fate commitment of virus-specific TFH cells, including establishing acute LCMV-infected monoclonal mouse model, conducting flow cytometry staining, and performing retroviral-vector-based gene manipulation. Compared to in-vitro T-cell stimulation, in-vivo stimulation could activate T cells more quickly, even in 12 hours, and it's fully activated for the next retrovirus transduction. Our findings will help in studies exploring the mechanisms underlying the early commitment of various specific TFH cells.Furthermore, our research will contribute to understanding T-cell-dependent humoral immunity and optimizing vaccine design.

Mapping the Early Development of LCMV-Specific Follicular Helper T-Cells in Mice

To begin, obtain a six to eight week old CD 45.1 positive SMARTA mouse and inject it with 200 micrograms of LCMV GP 61-77 peptide in 100 microliters of RPMI medium intravenously. After acquiring the splenocytes from the mouse, suspend them in 2%RPMI to achieve a cell density of one times 10 to the eighT-cells per milliliter and place the tube with cells on ice. Dispense 50 microliters of cell suspension along with 150 microliters of staining buffer to each well of a round-bottom 96-well plate.Centrifuge the 96-well plate at 800 G for one minute at four degrees Celsius and carefully decant the supernatant. Vortex the plate and add 200 microliters of staining buffer to each well. After pelleting the cells, resuspend and incubate them with surface antibody cocktail on ice for 30 minutes in the dark.After washing two times, resuspend the cells in 200 microliters of staining buffer and transfer them into a flow cytometry tube. Perform flow cytometry analysis to check the activation status of SMARTA CD4 positive T-cells. Then seed one times 10 the six SMARTA CD4 positive T-cells per well into a 24 well plate.Spin down the cells at 800 G for three minutes at four degrees Celsius and carefully remove the supernatant medium. Next, add one milliliter of retrovirus medium and eight micrograms of polybrene to each well. Spin transduce the cells at 800 G for two hours at 37 degrees Celsius.After discarding the retrovirus medium, incubate the cells with one milliliter of prewarmed 10%RPMI supplemented with interleukin 2. Transfer the cell suspension into a 15 milliliter conical tube and centrifuge it. After discarding the supernatant, resuspend the cells with 2%RPMI to achieve a cell density of one times 10 to the eighth cells per milliliter.For assessing the transduction efficiency, aliquot 50 microliters of cell suspension into a round bottom 96-well plate. Incubate them on ice with the surface antibody cocktail including CD4, V alpha two, and vector tag-associated antibody. Wash the cells and perform flow cytometry as demonstrated earlier.Then inject one times 10 of the six CD 45.1 positive SMARTA CD4 positive T-cells to a C57BL/6 recipient mouse intravenously followed by one times 10 to the six plaque forming units of LCMV Armstrong the next day. After acquiring the splenocytes from the mouse, stain them to check the desired markers. To detect transcriptional factors, incubate the cells with 200 microliters of 2%paraformaldehyde at room temperature for 20 minutes in the dark.Finally, perform flow cytometry to detect factors at the early acute LCMV infection stage. On day three after infection, a balanced bifurcation of follicular helper T-cells and T-helper 1 cells Among MIGR1 SMARTA CD4 positive T-cells was found. A predominant follicular helper T-cell directed differentiation and enhanced BCL6 expression levels were observed in MIGR1 BCL6 SMARTA CD4 positive T-cells.

Research

JoVE Journal

Immunology and Infection

Follicular Helper T (TFH) cells are perceived as an independent CD4+ T cell lineage that assists cognate B cells in producing high-affinity antibodies, ...