Long-lived T follicular helper cells retain plasticity and help sustain humoral immunity

CD4; +; memory T cells play an important role in protective immunity and are a key target in vaccine development. Many studies have focused on T central memory (T; cm; ) cells, whereas the existence and functional significance of long-lived T follicular helper (T; fh; ) cells are controversial. Here, we show that T; fh; cells are highly susceptible to NAD-induced cell death (NICD) during isolation from tissues, leading to their underrepresentation in prior studies. NICD blockade reveals the persistence of abundant T; fh; cells with high expression of hallmark T; fh; markers to at least 400 days after infection, by which time T; cm; cells are no longer found. Using single-cell RNA-seq, we demonstrate that long-lived T; fh; cells are transcriptionally distinct from T; cm; cells, maintain stemness and self-renewal gene expression, and, in contrast to T; cm; cells, are multipotent after recall. At the protein level, we show that folate receptor 4 (FR4) robustly discriminates long-lived T; fh; cells from T; cm; cells. Unexpectedly, long-lived T; fh; cells concurrently express a distinct glycolytic signature similar to trained immune cells, including elevated expression of mTOR-, HIF-1-, and cAMP-regulated genes. Late disruption of glycolysis/ICOS signaling leads to T; fh; cell depletion concomitant with decreased splenic plasma cells and circulating antibody titers, demonstrating both unique homeostatic regulation of T; fh; and their sustained function during the memory phase of the immune response. These results highlight the metabolic heterogeneity underlying distinct long-lived T cell subsets and establish T; fh; cells as an attractive target for the induction of durable adaptive immunity

Consecutive interactions with HSP90 and eEF1A underlie a functional maturation and storage pathway of AID in the cytoplasm

International audienceActivation-induced deaminase (AID) initiates mutagenic pathways to diversify the antibody genes during immune responses. The access of AID to the nucleus is limited by CRM1-mediated nuclear export and by an uncharacterized mechanism of cytoplasmic retention. Here, we define a conformational motif in AID that dictates its cytoplasmic retention and demonstrate that the translation elongation factor eukaryotic elongation factor 1 α (eEF1A) is necessary for AID cytoplasmic sequestering. The mechanism is independent of protein synthesis but dependent on a tRNA-free form of eEF1A. Inhibiting eEF1A prevents the interaction with AID, which accumulates in the nucleus and increases class switch recombination as well as chromosomal translocation byproducts. Most AID is associated to unspecified cytoplasmic complexes. We find that the interactions of AID with eEF1A and heat-shock protein 90 kD (HSP90) are inversely correlated. Despite both interactions stabilizing AID, the nature of the AID fractions associated with HSP90 or eEF1A are different, defining two complexes that sequentially produce and store functional AID in the cytoplasm. In addition, nuclear export and cytoplasmic retention cooperate to exclude AID from the nucleus but might not be functionally equivalent. Our results elucidate the molecular basis of AID cytoplasmic retention, define its functional relevance and distinguish it from other mechanisms regulating AID