Biology subjects

Seddon, B.

Publications and source records attributed to Seddon, B..

11 recordsLinked to original sources

bioRxiv2026

Quorum sensing underlies the establishment and maintenance of marginal zone B cells

The marginal zone (MZ) of the spleen harbors B cells that play an indispensable role in immune defense, orchestrating rapid responses to bloodborne pathogens. Under steady-state conditions, MZ B cell numbers are maintained through the balance of de novo generation from precursors, proliferative self-renewal, and loss. The mechanisms governing this homeostatic control remain elusive. Further, the developmental pathways underlying the establishment and continued supplementation of the MZ B cell compartment are not fullyelucidated. To address these gaps, we combined multiple fate-mapping tools and mathematical models to study MZ B cell dynamics in mice across the life course. Our analyses find evidence of quorum sensing mechanisms that regulate both the accumulation of mature MZ B cells during early life and their maintenance throughout adulthood. Specifically, we demonstrate that they derive predominantly from transitional B cell precursors with an efficiency that increases with age, reaching stable levels only in adulthood. MZ B cells compensate for this early developmental inefficiency through cell density-dependent proliferation, ensuring the timely establishment of a stable pool. Collectively, these findings unveil critical roles of quorum sensing and immune system maturation in the maintenance of this vital B cell subset.

immunology↗

bioRxiv2025

Contrasting roles for IKK regulated inflammatory signalling pathways for development and maintenance of type 1 and adaptive γδ T cells

The inhibitor of kappa B kinase complex (IKK) is a critical regulator of cell death and inflammatory signaling in multiple cell types. Phosphorylation of I{kappa}B proteins by IKK results in their degradation and consequent activation of NF-{kappa}B transcription factors. RIPK1, a critical cell death regulator, is also a direct target of IKK kinase activity, thereby repressing its cell death activity. In {beta} T cells, the RIPK1 kinase activity of IKK is critical for normal thymic development while mature {beta} T cells require IKK for both activation of NF-{kappa}B dependent survival programmes, and repression of RIPK1. {gamma}{delta} T cells play a unique and versatile role in host immunity with specific effector functions that enables them to act as early responders in immune defence. The role of IKK regulated pathways in their development and survival is not known. Here, we use mouse genetics to dissect the function of IKK and downstream pathways in the normal homeostasis of {gamma}{delta} T cells. We find that IKK expression is critical to establish a replete {gamma}{delta} T cell compartment, but that requires vary between different subsets. Type 1 {gamma}{delta} T cells require IKK dependent NF-{kappa}B activation for their generation, while IKK is redundant for development of adaptive {gamma}{delta} T cells. Instead, IKK dependent NF-{kappa}B activation is required for their longterm survival. We also find evidence that IKK repression of RIPK1 is required for survival of peripheral but not thymic {gamma}{delta} T cells. Ablation of CASPASE8 did not rescue {gamma}{delta} T cells in the absence of IKK but rather revealed a potent sensitivity of all {gamma}{delta} subsets to necroptosis, that was rescued by kinase dead RIPK1. Overall, we reveal critical requirements for IKK regulated inflammatory pathways by {gamma}{delta} T cells that contrast with those of {beta} T cells, and between different subsets, highlighting the complexity of the regulation of these pathways in the adaptive immune system.

immunology↗

bioRxiv2025

Evidence for a RIPK1-independent survival mechanism for CASPASE-8 in αβ T cells

CASPASE8 promotes both cell death and survival by acting as a trigger of apoptosis but also a repressor of necroptosis. In T cells, CASPASE8 is required for FAS induced apoptosis, but protects activated T cells from necroptosis. The broader role and mechanisms of CASPASE8 in the wider T cell compartment is less certain. Here, we analysed mice in which Casp8 was conditionally deleted in the lymphoid compartment by huCD2iCre. In the thymus, we found evidence of a modest impairment of early thymic progenitors and a striking absence of NKT cell development. Amongst mature peripheral T cells, there was a substantial and specific reduction in the CD8 T cell compartment, that included naive, central memory and virtual memory subsets. While life spans and turnover of CD8 T cells appeared largely normal, we did identify an acute requirement for continued CASPASE8 expression for survival of a fraction of CD8 T cells, since induced Casp8 deletion by tamoxifen induced CD8CreERT resulted in an acute loss of CD8 T cells. CASPASE8 deficient T cells were resistant to FAS or TNF induced cell death in vitro. Generating Casp8 deficient mice that express a kinase dead RIPK1 confirmed that necroptosis contributed to death of thymic progenitors and some peripheral CD8 T cell subsets in the absence of CASPASE8. However, kinase dead RIPK1 failed to restore NKT cell development and only partially rescued CD8 VM T cells, while analysing mixed bone marrow chimeras suggested that CASPASE8 deficient CD4 and CD8 T cells were less competitively fit than WT T cells, even in the absence of RIPK1 kinase activity. These latter observations suggest the existence of a novel mechanism by which CASPASE8 promotes T cell survival that is independent of its established role in repressing necroptosis.

immunology↗

bioRxiv2024

Tissue resident memory CD4+ T cells are sustained by site-specific levels of self-renewal and replacement from precursors

Tissue-resident memory T cells (TRM) protect from repeat infections within organs and barrier sites. The breadth and duration of such protection is defined at minimum by three quantities; the rate at which new TRM are generated from precursors, their rate of self-renewal, and their rate of loss through death, egress, or differentiation. Quanti-fying these processes individually is challenging. Here we combine genetic fate mapping tools and mathematical models to untangle these basic homeostatic properties of CD4+ TRM in the skin and gut lamina propria (LP) of healthy adult mice. We show that CD69+CD4+ TRM in skin reside for [~]24 days and self-renew more slowly, such that clones halve in size approximately every 5 weeks; and approximately 2% of cells are replaced daily from precursors. CD69+CD4+ TRM in LP have shorter residencies ([~]14 days) and are maintained largely by immigration (4-6% per day). We also find evidence that the continuous replacement of CD69+CD4+ TRM at both sites derives from circulating effector-memory CD4+ T cells, in skin possibly via a local CD69- intermediate. Our approach maps the ontogeny of CD4+ TRM in skin and LP and exposes their dynamic and distinct behaviours, with continuous seeding and erosion potentially impacting the duration of immunity at these sites.

immunology↗

bioRxiv2024

A linear ontogeny accounts for the development of naive, memory and tumour-infiltrating regulatory T cells in mice

Foxp3+ Regulatory T cells (Treg) are a subset of CD4+ T cells that play critical functions in maintaining tolerance to self antigens and suppressing autoimmunity, regulating immune responses to pathogens and have a role in the pathophysiology of anti-tumoural immunity. Treg ontogeny is complex since they are generated following recognition of self antigens in the thymus during normal T cell development (thymic Treg), but are also induced from mature conventional T cells when activated by foreign antigen with appropriate additional cues (inducible Treg). How these distinct ontogenic pathways contribute to the maintenance and function of the mature Treg compartment in health and disease remains unclear. Here, we use a combination of fate mapping approaches in mice to map the ontogeny of Treg subsets throughout life and estimate rates of production, loss and self-renewal. We find that naive and effector/memory (EM) Treg subsets exhibit distinct dynamics but are both continuously replenished by de novo generation throughout life. Using an inducible Foxp3-dependent Cre fate reporter system, we show that naive Treg and not conventional T cells, are the predominant precursors of EM Treg in adults. Tonic development of new EM Treg is not influenced by foreign antigens from commensals, rather suggesting a role for self recognition. To investigate the ontogeny of Treg development in malignant disease, we used the same fate reporter systems to characterise the Treg infiltrate of three different model tumours. In all three cases, we found that Treg derived from pre-existing, EM Treg. Together, these results reveal a predominantly linear pathway of Treg development from thymic origin to EM Treg associated with pathophysiology of malignant disease, that is driven by self antigen recognition throughout.

immunology↗

bioRxiv2023

Cell age, not chronological age, governs the dynamics and longevity of circulating CD4+ memory T cells

Quantifying the kinetics with which memory T cell populations are generated and maintained is essential for identifying the determinants of the duration of immunity. The quality and persistence of circulating CD4+ effector memory (TEM) and central memory (TCM) T cells in mice appear to shift with age, but it is unclear whether these changes are driven by the aging host environment, by cell age effects, or both. Here we address these issues by combining DNA labelling methods, established fate-mapping systems, a novel reporter mouse strain, and mathematical models. Together, these allow us to quantify the dynamics of both young and established circulating memory CD4+ T cell subsets, within both young and old mice. We show that that these cells and their descendents become more persistent the longer they reside within the TCM and TEM pools. This behaviour may limit memory CD4 T cell diversity by skewing TCR repertoires towards clones generated early in life, but may also compensate for functional defects in new memory cells generated in old age. Author summaryOur long-term protection against infections depends in part on the maintenance of diverse populations of memory CD4 T cells, which are made in response to the initial exposure to the pathogen or a vaccine. These cells are not long-lived, but instead are maintained dynamically at a clonal level through loss and division. Understanding how immune memory persists therefore requires measuring these rates of these processes, and how they might change with age. Here we combine experiments in mice with mathematical models to show that memory CD4 T cells exhibit complex dynamics but increase their capacity to survive as they age. This dynamic implies that as individuals age, their memory CD4 T cell populations become enriched for older clones. This established memory may compensate for functional defects in new T cell responses generated later in life.

immunology↗

bioRxiv2023

NF-κB dependent expression of A20 controls IKK repression of RIPK1 dependent cell death in activated T cells

The Inhibitor of Kappa B Kinase (IKK) complex is a critical regulator of canonical NF-{kappa}B activation. More recently, RIPK1 has also been identified as a phosphorylation target of the IKK complex, resulting in repression of extrinsic cell death pathways. Our previous work shows that normal thymocyte development is exclusively reliant on repression of TNF triggered cell death pathways by IKK, and that NF-{kappa}B signalling is in fact redundant for development. The role of IKK signalling in activated T cells is unclear. To investigate this, we analysed activation of IKK2 deficient TCR transgenic T cells with cognate peptide. While early activation events were normal, proliferation of blasts was impaired. Surprisingly, cell cycle progression in IKK2 KO T cells was unperturbed. Instead, dividing cells were more sensitive to apoptosis triggered by extrinsic cell death pathways, since inhibition of RIPK1 kinase activity almost completely rescued cell survival. Transcriptomic analysis of activated IKK2 deficient T cells revealed defective expression of several NF-{kappa}B targets, including Tnfaip3, that encodes A20, a negative regulator of NF-{kappa}B in T cells. To test whether A20 expression was required to protect IKK2 deficient T cells from cell death, we generated mice with T cells lacking both A20 and IKK2. Conditional deletion of both Ikk2 and Tnfaip3 in T cells resulted in near complete ablation of peripheral naive T cells, in contrast to mice lacking one or other gene. Strikingly, this phenotype was completely reversed by inhibition of RIPK1 kinase activity in vivo. Therefore, our data suggests that IKK signalling in T cells protects against RIPK1 dependent death, both by direct phosphorylation of RIPK1 and through NF-{kappa}B mediated induction of A20, that we identify for the first time as a modulator of RIPK1 function in T cells.

immunology↗

bioRxiv2022

Defining the dynamics of naive CD4 and CD8 T cells across the mouse lifespan

Naive CD4 and CD8 T cells are cornerstones of adaptive immunity, but the dynamics of their establishment early in life and how their kinetics change as they mature following release from the thymus are poorly understood. Further, due to the diverse signals implicated in naive T cell survival, it has been a long-held and conceptually attractive view that they are sustained by active homeostatic control as thymic activity wanes. Here we employ multiple experimental systems to identify a unified model of naive CD4 and CD8 T cell population dynamics across the mouse lifespan. We infer that both subsets divide rarely and progressively increase their survival capacity with cell age. Strikingly, this simple model captures naive CD4 T cell dynamics throughout life. In contrast, we find that newly generated naive CD8 T cells are lost more rapidly during the first 3-4 weeks of life, likely due to increased recruitment into memory. We find no evidence for elevated division rates in neonates, or for feedback regulation of naive T cell numbers at any age. We show how confronting mathematical models with diverse datasets can reveal a quantitative and remarkably simple picture of naive T cell dynamics from birth into old age.

immunology↗

bioRxiv2021

Tonic IKK signalling regulates naive T cell survival in vivo by both repressing RIPK1 dependent extrinsic cell death pathways and independent activation of NF-κB

The Inhibitor of Kappa B Kinase (IKK) complex is a critical regulator of NF-{kappa}B activation. In addition, IKK has recently been shown to repress RIPK1 dependent extrinsic cell death pathways by directly phosphorylating RIPK1. Our previous work shows that normal thymopoiesis relies on IKK exclusively for repression of TNF triggered cell death pathways, and that NF-{kappa}B activation by IKK is redundant for development. The role of these pathways in mature naive T cells has not previously been reported. Here, we show that, like thymocytes, naive peripheral T cells require continued IKK1/2 expression for survival. In contrast, however, cell loss is only partially prevented by blocking extrinsic cell death pathways by either deleting Casp8 or inhibiting RIPK1 kinase activity. Inducible deletion of Rela in mature CD4+ T cells also results in a significant loss of naive CD4+ T cells and loss of IL7R expression, revealing an additional reliance upon NF-{kappa}B for long term survival of mature T cells. Together, these data show that IKK dependent survival of naive T cells depends upon both repression of extrinsic cell death pathways and activation of NF-{kappa}B survival programme. One sentence summaryIKK regulates naive T cell survival

immunology↗

bioRxiv2019

Fate mapping quantifies the dynamics of B cell development and activation throughout life

Follicular mature (FM) and germinal centre (GC) B cells underpin humoral immunity but the dynamics of their generation and maintenance are not clearly defined. Here we exploited a fate-mapping system in mice that tracks B cells as they develop into peripheral subsets, together with a cell division fate reporter mouse and mathematical models. We find that FM cells are kinetically homogeneous, recirculate freely, continually replenished from transitional populations, and self-renew rarely. In contrast, GC B cell lineages persist for weeks with rapid turnover and site-specific dynamics. Those in the spleen derive from transitional cells and are kinetically homogeneous, while those in lymph nodes derive from FM B cells and comprise both transient and persistent clones. These differences likely derive from the nature of antigen exposure at the different sites. Our integrative approach also reveals how the host environment drives cell-extrinsic, age-related changes in B cell homeostasis.

immunology↗

bioRxiv2019

Differential impact of self and environmental antigens on the ontogeny and maintenance of CD4+ T cell memory

Laboratory mice develop populations of circulating memory CD4+ T cells in the absence of overt infection. We have previously shown that these populations are replenished from naive precursors at high levels throughout life (Gossel et al., 2017). However, the nature, relative importance and timing of the forces generating these cells remain unclear. Here, we tracked the generation of memory CD4+ T cell subsets in mice housed in facilities differing in their dirtiness. We found evidence for sequential naive to central memory to effector memory development, and confirmed that both memory subsets are heterogeneous in their rates of turnover. We also inferred that early exposure to self and environmental antigens establishes persistent memory populations at levels determined largely, though not exclusively, by the dirtiness of the environment. After the first few weeks of life, however, these populations are continuously supplemented by new memory cells at rates that are independent of environment.

immunology↗