Significance: Many millions of people take probiotics over the counter, but very little is known about what they do and whether they really work. Here we show that in mice, introducing Bifidobacterium , one of the most commonly used probiotics, not only colonizes the gut, but also alters the entire microbiotic landscape. We previously found that this treatment rescues mice from an otherwise fatal inflammatory syndrome brought on by anti–CTLA-4 antibody, a checkpoint inhibitor that often causes autoimmunity in humans undergoing cancer treatment. Here we show that this is effect is due, at least in part, to the effect of this probiotic treatment on regulatory CD4 ⁺ cells, whose metabolic and immune suppressive functions are altered. These CD4 ⁺ regulatory T cells are known to be a key mechanism in the control of autoreactivity in the immune system in both mice and humans. Thus, we found a direct connection between probiotic treatment and one of the known principal mechanisms for controlling excess immune responses.

A comprehensive understanding of the evolution of the immune landscape in humans across the entire lifespan at single-cell transcriptional and protein levels, during development, maturation and senescence is currently lacking. We recruited a total of 220 healthy volunteers from the Shanghai Pudong Cohort (NCT05206643), spanning 13 age groups from 0 to over 90 years, and profiled their peripheral immune cells through single-cell RNA-sequencing coupled with single T cell and B cell receptor sequencing, high-throughput mass cytometry, bulk RNA-sequencing and flow cytometry validation experiments. We revealed that T cells were the most strongly affected by age and experienced the most intensive rewiring in cell–cell interactions during specific age. Different T cell subsets displayed different aging patterns in both transcriptomes and immune repertoires; examples included GNLY⁺CD8⁺ effector memory T cells, which exhibited the highest clonal expansion among all T cell subsets and displayed distinct functional signatures in children and the elderly; and CD8⁺ MAIT cells, which reached their peaks of relative abundance, clonal diversity and antibacterial capability in adolescents and then gradually tapered off. Interestingly, we identified and experimentally verified a previously unrecognized ‘cytotoxic’ B cell subset that was enriched in children. Finally, an immune age prediction model was developed based on lifecycle-wide single-cell data that can evaluate the immune status of healthy individuals and identify those with disturbed immune functions. Our work provides both valuable insights and resources for further understanding the aging of the immune system across the whole human lifespan.

Various inhibitors targeting T-cell immunoglobulin and mucin-containing molecule 3 (TIM3) aimed at reversing T-cell exhaustion for better immunotherapy outcomes have demonstrated limited clinical efficacy as monotherapy, with the underlying mechanisms remaining ambiguous. TIM3 is markedly expressed in dendritic cells (DCs), and the inconsistent research findings on its role in myeloid cells underscore its vital function within DCs. Through the establishment of an in vitro differentiation model generating mature dendritic cells (mDCs) under TIM3-targeted interventions, combined with an RNA sequencing analysis, this investigation systematically examined TIM3-mediated regulation and ligand interactions in human primary DCs. The findings indicate that TIM3 inhibition hinders DC maturation, which subsequently diminishes the antigen-presenting capacity of DCs, ultimately leading to immune suppression in T cells. These findings collectively establish TIM3 as a regulator of DC differentiation that promotes DC maturation while optimizing the antigen-processing and presentation capacity. This study elucidates the rationale behind the suboptimal efficacy of TIM3 inhibitors and advocates for retaining TIM3 signaling pathways in DCs.

The zinc finger protein 36 (ZFP36) family, including ZFP36/tristetraprolin (TTP), ZFP36 CCCH-type-like 1 (ZFP36L1), and ZFP36 CCCH-type-like 2 (ZFP36L2), consists of conserved CCCH-type tandem zinc-finger RNA-binding proteins. These proteins recognize AU-rich elements (AREs) in target mRNAs and promote deadenylation, decay, and translational repression. In this review, we use the term post-transcriptional immune checkpoint in a restricted conceptual sense: ZFP36 family proteins are intracellular, RNA-level negative regulators that tune the magnitude, duration, and resolution of immune effector programs, rather than classical receptor-ligand immune checkpoints such as programmed cell death protein 1 (PD-1)/ programmed death-ligand 1 (PD-L1) or cytotoxic T-lymphocyte-associated protein 4 (CTLA-4). We summarize structural features, ARE-recognition mechanisms, mRNA decay pathways, translational repression mechanisms, and post-translational regulation of the ZFP36 family, while explicitly distinguishing mechanisms established for ZFP36 from those inferred for ZFP36L1 and ZFP36L2. We then review cell-type-specific roles in innate and adaptive immunity, including myeloid inflammatory responses, barrier tissue inflammation, innate lymphoid cell function, T cell activation and effector differentiation, regulatory T cell stability, B cell development, and antiviral immunity. In cancer, ZFP36 family members show context-dependent functions that should be separated into tumor-cell-intrinsic effects and immune-microenvironment-dependent effects. They suppress tumor progression by destabilizing pro-inflammatory, angiogenic, metabolic, and epithelial–mesenchymal transition (EMT)-associated transcripts, yet may also restrict antitumor immune responses or promote immune evasion in selected tumor contexts. Finally, we discuss autoimmune and inflammatory diseases, allergic disorders, transplant immunity, neuroimmune relevance, and therapeutic strategies, emphasizing the current evidentiary limits, preclinical status, and safety concerns of ZFP36 family modulation.

Background: Systemic inflammatory diseases including rheumatoid arthritis (RA), ankylosing spondylitis (AS), IBD and long covid share convergent multi-organ phenotypes. Long covid provides a tractable model for dissecting gut-driven mechanisms of systemic inflammation, given its defined temporal onset and treatment-naïve postinfectious context. Objective: To characterise a gut-driven mechanism of systemic inflammation in long covid and assess its cross-disease correlates in RA, AS and IBD. Design: Comparative metagenomic analyses across RA, AS, IBD and long covid cohorts. Long covid was established as a paradigm for postdysbiotic inflammatory diseases, single-cell RNA sequencing and functional studies in longitudinal human cohorts and co-infection mouse models (SARS-CoV-2 and Pseudomonas aeruginosa ) were employed to dissect cellular and molecular mechanisms. Genetic and pharmacological interventions targeting the interleukin (IL)-15-arachidonic acid (ARA) axis were validated for therapeutic efficacy. Results: Flagellated bacterial expansion defined a shared intestinal signature across all four diseases. Mechanistic studies in long covid demonstrated that flagellated bacteria activated toll-like receptor 5 (TLR5) on neutrophils, triggering the formation of neutrophil extracellular trap (NET) and IL-15 release. IL-15 subsequently stimulated macrophage ARA production. The co-infection murine model recapitulated multi-organ pathophysiology of long Covid, including pulmonary fibrosis and intestinal lymphoid aggregates. Genetic ablation of macrophage ARA synthesis or neutrophil IL-15 attenuated lung pathology, whereas gut microbiome clearance with gentamicin uniquely suppressed systemic inflammation. Conclusions: We delineate a flagellin-TLR5-IL-15-ARA axis as a candidate mechanism driving systemic inflammation in long covid. These findings position intestinal flagellin as a candidate therapeutic target and ARA as a potential biomarker for long covid, warranting prospective validation across inflammatory disease boundaries.