Strong influenza-induced T _FH generation requires CD4 effectors to recognize antigen locally and receive signals from continuing infection

Abstract

While influenza infection induces robust, long-lasting, antibody responses and protection, including the T follicular helper cells (TFH) required to drive B cell germinal center (GC) responses, most influenza vaccines do not. We investigated the mechanisms that drive strong TFH responses during infection. Infection induces viral replication and antigen (Ag) presentation lasting through the CD4 effector phase, but Ag and pathogen recognition receptor signals are short-lived after vaccination. We analyzed the need for both infection and Ag presentation at the effector phase, using an in vivo sequential transfer model to time their availability. Differentiation of CD4 effectors into TFH and GC-TFH required that they recognize Ag locally in the site of TFH development, at the effector phase, but did not depend on specific Ag-presenting cells (APCs). In addition, concurrent signals from infection were necessary even when sufficient Ag was presented. Providing these signals with a second dose of live attenuated influenza vaccine at the effector phase drove TFH and GC-TFH development equivalent to live infection. The results suggest that vaccine approaches can induce strong TFH development that supports GC responses akin to infection, if they supply these effector phase signals at the right time and site. We suggest that these requirements create a checkpoint that ensures TFH only develop fully when infection is still ongoing, thereby avoiding unnecessary, potentially autoimmune, responses.

Mucosal immune responses to infection and vaccination in the respiratory tract

“…It has long been appreciated that while infection by influenza virus induces robust and long-lived humoral responses, seasonal influenza vaccination strategies have largely failed in this regard. Devarajan and colleagues speculated that this could be due to differences in antigen availability and duration of Tfh responses in the LNs between influenza infection and vaccination with inactivated vaccines ( Devarajan et al., 2022 ). Their 2022 study found that strong influenza-induced Tfh responses require CD4 effectors to continually recognize local antigens and receive signals from ongoing infection ( Devarajan et al., 2022 ).…”

“…Devarajan and colleagues speculated that this could be due to differences in antigen availability and duration of Tfh responses in the LNs between influenza infection and vaccination with inactivated vaccines ( Devarajan et al., 2022 ). Their 2022 study found that strong influenza-induced Tfh responses require CD4 effectors to continually recognize local antigens and receive signals from ongoing infection ( Devarajan et al., 2022 ). GC reactions stalled with inactivated vaccination but could be prolonged with the administration of LAIV.…”

Peptide Avidity for TCR on CD4 Effectors Determines the Extent of Memory Generation

“…To evaluate the subsets of CD4 effectors generated, we compared donor and host CD4 effectors at 8 dpi by examining cytokine production and phenotype markers: Th1 (T-bet, IFNγ, TNFα, IL-2), Triple cytokine producers (IFNγ, TNFα, IL-2), Th17 (IL-17), and T REG (FoxP3). We used NKG2A/C/E expression to detect cytotoxic CD4 (ThCTL), found only in the lung (31), and CXCR5 and Bcl-6 co-expression markers for T FH in the spleen (32) (Fig. 1B, Supp.…”

Cytotoxic CD4 Development Requires CD4 Effectors to Concurrently Recognize Local Antigen and Encounter Infection-Induced IL-15

“…Transfer of Ag/APC i.n. successfully restricted Ag presentation to the lung, while transfer of Ag/APC i.s restricted Ag presentation to the spleen (Devarajan et al, 2022) (summarized in Figure S4A ).…”

“…Our previous data show that after intravenous (i.v.) OVA II /APC transfer they are found predominantly in the spleen and not in the lung, though donor effectors in the lung express Nur77 GFP , suggesting that they recognized Ag in the periphery before migrating to the lung (Devarajan et al, 2022) ( Figure S4A ). To test if peripheral Ag presentation was sufficient to drive 6d effectors to ThCTL, we transferred OVA II /APC i.v.…”