ImmunoHorizons

Immune memory responses are rapid and qualitatively distinct from primary responses. They typically develop in the presence of antigen-experienced memory T and B cells and pre-existing antibodies. Although the contribution of T and B cells to recall responses is well defined, the contribution of antibody "memory" and the mechanisms by which pre-existing antibodies modulate the development of germinal center and plasma cell responses is not precisely understood. Here we report on mechanisms that mediate antibody enhancement of germinal center (GC) and plasmablast (PB) compartments, and the parallel process by which they change the affinity threshold for B cell recruitment into immune responses. The data indicate that antibody-mediated enhancement of GC and PB responses is Fc gamma receptor (Fc{gamma}R) dependent and largely complement receptor 1 and 2 (CR1/2) independent. In contrast, the reduction in the affinity threshold for GC entry is independent of both Fc{gamma}Rs and CR1/2. SummaryCipolla et al. show that antibody can modulate immune responses via both Fc gamma receptor dependent and independent mechanisms. These mechanisms influence both the magnitude and composition of the germinal center response.

Mucosal-associated invariant T (MAIT) cells are donor unrestricted T cells capable of both antigen-specific adaptive responses and cytokine driven innate-like functions. Although human MAIT cells uniformly express ROR{gamma}t and IL23R, they generally produce IFN-{gamma}, and only a small fraction produces IL-17. Recent studies show that combined TCR and cytokine stimulation can elicit functional heterogeneity in blood-derived MAIT cells. Here, we investigate the role of IL-23/IL-23R signaling in mediating the function and transcriptional profiles of lung MAIT cell clones. We demonstrate that BAL-derived lung MAIT cell clones exhibit distinct cytokine profiles and variable IL23R expression. Short-term IL-23 stimulation triggers clone-specific transcriptional programs and IL23R-dependent upregulation of type 17-associated genes. Prolonged conditioning of lung MAIT cell clones with TCR (5-OP-RU) and cytokine (IL-23) stimulation induces stable IL-17A production along with unique transcriptional changes. TCR + IL-23 conditioning alone upregulates clone-specific and shared cytoskeletal/structural gene programs, whereas subsequent PMA/Ionomycin stimulation further induces IL-12 family signaling and metabolic genes. Together, these findings demonstrate that IL23R expression and TCR signaling are required for IL-17A production, highlighting that these conditions may be met in tissue environments where MR1-specific antigens and proinflammatory cytokines coexist.

TH17 cells play a central role in several human autoimmune diseases. We and others reported the nuclear receptor, REV-ERB, as a cell-intrinsic repressor of TH17-mediated pathogenicity. REV-ERB{beta}, REV-ERBs closely related family member, is thought to be functionally redundant to REV-ERB, which we sought to explore in TH17-mediated immunity. Our data indicate that deletion of REV-ERB{beta} enhances TH17-mediated pro-inflammatory cytokine expression and exacerbated disease in mouse models of multiple sclerosis and colitis. RNA-sequencing indicates REV-ERB{beta} and REV-ERB do not have similar transcriptional profiles. REV-ERB{beta} does not appear to regulate gene expression through interaction with the classic co-repressor NCoR1, which is in contrast to REV-ERB in TH17 cells, nor does it utilize heme, its known endogenous ligand for its repressive functions. Our results establish that while REV-ERB{beta} also acts as a negative regulator of TH17-cell function and pathogenicity, it does so in a manner that is non-redundant, independent, and unique to REV-ERB.

LynA-knockout and LynB-knockout mice, each expressing only one of two isoforms of the Src-family kinase (SFK) Lyn, have differential progression to autoimmunity. It is unclear, however, whether isoform-specificity or Lyn dose underlies differential signaling in the single-isoform knockouts. To address this question, we generated a series of Lyn-knockout mice with a varying LynA and LynB expression and tested macrophage signaling in response to pharmacological pan-SFK activation. We found that the magnitude of initiating signaling is a function of the combined basal expression of LynA and LynB, with the two isoforms equally capable of phosphorylating positive-regulatory Syk and negative-regulatory SHIP1. While expression of either isoform restored basal and SFK-initiated downstream signaling, WT-like levels of Erk and Akt signaling were enabled by expression of any amount of Lyn and insensitive to further upregulation of either isoform. Thus, either LynA or LynB expression at steady state leads to balanced activation of positive- and negative-regulatory signaling, setting a maximal response in the absence of a true microbial encounter. Summary SentenceTotal expression of LynA and LynB determines the steady-state phosphorylation of the activating kinase Syk and the inhibitory phosphatase SHIP1, capping signaling in the absence of a microbial encounter.

Activated T cells increase transferrin-bound iron uptake via the transferrin receptor, also called CD71. We previously demonstrated that targeting CD71 with an antibody to reduce iron update can modify CD4 T cell function, with different effects on TH1, TH17, and regulatory T (Treg) cells. CD71 blocking antibody-treated Tregs had no loss of viability or differentiation, and Foxp3 expression was increased. However, a genetic deletion of Tfrc (the gene for CD71) driven by Foxp3-Cre was reported to cause a lethal autoimmunity. Whether altered immune homeostasis or insufficient early developmental tolerance drive the phenotype of CD71 knockout (KO) Treg mice were unclear. Here, we examined the Foxp3-YFP-Cre KO mouse model and a tamoxifen-inducible KO model in adults to determine the role of CD71 expression in Treg cells. We hypothesized that due to a lack of iron for mitochondrial metabolism, KO Treg adapt to rely heavily on glycolysis and become unstable, promoting pro-inflammatory exTreg cells. This effect was not universal, however, and necropsy analyses revealed tissue-specific inflammation. While the colons of mice with KO Treg cells appeared healthy, skin and lung tissue were severely inflamed. Metabolically, KO Treg cells had a significant decrease in their glycolytic capacity and instead increased oxidation of amino acids and fatty acids. In inflamed skin, which that promotes increased oxidative stress, CD71 expression in Treg cells suppressed tissue inflammation in a model of atopic dermatitis-like disease. These results indicate the CD71-iron axis as a new immunometabolic regulator of Treg cell functions in immune and non-immune organs. Capsule SummaryA loss of the transferrin receptor in Tregs causes severe autoimmunity and here we clarify how Tregs rely on this receptor for iron in specific tissues and disease settings including atopic dermatitis.

Macrophages are now recognised as key players in a range of tissues and biological processes, responding to injury and infection, and facilitating development and regeneration. As the importance of macrophage crosstalk within these processes has been revealed, so too has the significance of studying the spatial positioning of macrophages within the tissue of interest. As such, immunofluorescent microscopy-based analysis is becoming an increasingly attractive technique for immunology research. While tissue fixation preserves the tissue architecture and immobilises target antigens, prolonged fixation can negatively impact protein recognition. We report that prolonged exposure to a paraformaldehyde-based fixative profoundly impacts detection of cell surface markers that define macrophage subsets in the mouse submandibular gland, in contrast to epithelial cell markers which appear more robust. We find that this that this is not exclusive to the salivary gland, and similar effects are seen in the pancreas and kidney. Importantly, a short duration of fixation allowed the detection of macrophage subsets in both mouse and human tissue without compromising the detection of other markers. Adoption of a short fixation approach enables accurate detection of a wide range of cell types in tissues, and facilitates exploration of spatial positioning and cell proximity by immunofluorescent microscopy analysis.

The effectiveness of CD20-targeting therapies in multiple sclerosis (MS) underscores the role of B cells in the disease, yet the limited success of other B cell-specific treatments suggests additional mechanisms at play. Intriguingly, CD20 is also expressed on a subset of highly active memory T cells, particularly cytotoxic CD8+ T lymphocytes (CTLs). This study investigated the functional characteristics of CD8+CD20+ CTLs in MS. We observed a significant increase in CD8+CD20+ CTL prevalence in MS patients, with enhanced infiltration into the cerebrospinal fluid. Consistent with prior reports, these cells exhibited heightened proliferation and production of IFN-{gamma}, TNF-, and GM-CSF. Notably, we demonstrate for the first time that CD8+CD20+ CTLs display escalated degranulation and produce significantly higher levels of Granzyme B, Perforin, and Granzyme K compared to their CD20-counterparts, with further augmentation in pwMS compared to healthy controls. These findings suggest that in MS, CD8+CD20+ CTLs are actively recruited to the CNS, exhibiting enhanced cytotoxicity and a potent pro-inflammatory profile, particularly through elevated Granzyme K production, contributing significantly to the chronic inflammatory milieu and immunopathogenesis of MS.

Terminally differentiated CD56negCD16pos NK cells have been described after chronic viral and malaria infections, and in children diagnosed with Burkitt lymphoma (BL). Despite CD56neg NK cells appearing to be poor at direct cytotoxicity, they express high levels of cytotoxic granules (i.e. granzymes, perforin), activation markers, and Fc-{gamma} receptors (CD32 and CD16) that are typically engaged in antibody-dependent cell cytotoxicity (ADCC). In addition, the abundance of CD56neg NK cells strongly correlates with IgG1 and IgG3 plasma levels, which are essential subclasses for ADCC. To determine whether CD56neg NK cells have superior ADCC capacity relative to CD56dim NK cells, we performed ADCC assays using effector cells from pediatric cancer patients and healthy children from malaria endemic regions of Kenya, targeting in vitro rituximab-treated commercial and newly established BL cell lines. We found that CD56neg NK cells were indeed capable of in vitro ADCC, showing a significant increase of CD107a-mediated degranulation in the presence of rituximab; however, they were not as efficient as CD56dim NK cells. Moreover, we found that the ADCC magnitude was significantly lower against EBV-Type 2 (EBV-T2) BL lines compared to EBV-Type 1 (EBV-T1). EBV-T2 tumor cell lines expressed significantly more lytic viral proteins than EBV-T1, making them more sensitive to direct cytotoxicity. Results from this study highlight the importance of assessing inter-patient variation in NK cell profiles in conjunction with ADCC sensitivity and EBV type within tumor cells when evaluating clinical outcomes for NK-mediated immunotherapies. SignificanceEBV type dictates NK cytotoxicity: EBV-T1 BL cells require rituximab for NK killing, while EBV-T2 BL cells are eliminated without antibody assistance, highlighting target-specific immune response to EBV-associated cancers.

Mitochondrial dynamics are critical for T cell activation, differentiation, and survival. The inner mitochondrial membrane ATP-dependent metalloprotease YME1L1 regulates proteostasis and the processing of optic atrophy protein 1 (OPA1), thereby shaping mitochondrial cristae architecture and respiratory function in many cell types. Whether YME1L1 fulfils similar roles in lymphocytes remains unknown. Here, we examined YME1L1 function in T cells using conditional knockout mice lacking YME1L1 in lymphocytes (YME1L1{Delta}TB). YME1L1 expression increased upon T cell activation, yet its absence did not alter thymic development, peripheral T cell homeostasis, or the proportions of naive, memory, and regulatory subsets. T cell activation and proliferation in response to anti-CD3{varepsilon} stimulation were also unaffected. Mitochondrial parameters such as mass, membrane potential, and reactive oxygen species production, were largely preserved, with only modest, transient increases in oxidative stress detected in CD4 T cells lacking YME1L1. Electron microscopy revealed no major changes in mitochondrial size or roundness but showed increased cristae branching and reduced tortuosity, indicating subtle alterations in ultrastructure. Additionally, {gamma}{delta} T cells in YME1L1{Delta}TB mice exhibited a mild shift toward interferon-{gamma}-producing phenotypes at the expense of interleukin-17-producing subsets. Collectively, our data indicate that YME1L1, despite its requirement for OPA1 cleavage, is dispensable for T cell development and acute activation but may contribute to fine-tune mitochondrial architecture and {gamma}{delta} T cell effector programming. These findings highlight cell-type-specific redundancies in mitochondrial quality control and underscore the value of negative data in refining the understanding of mitochondrial regulation in immune cells.

Th17 cells (CD4+ T cells producing IL-17) are important for clearance of fungal infections and play a critical role in the development and exacerbation of numerous autoimmune diseases. Their differentiation, signalling pathways, cytokine production and metabolism are now well-characterised. As well as CD4+ T cells, CD8+ cells also produce IL-17 family members, and these have been named Tc17 cells. However, much less is known about their development, signalling or metabolism compared to their CD4+ counterparts. Here, we performed a series of in vitro and in vivo analyses of Tc17 cells as well as computational analysis of the published Tabula muris dataset, comparing Tc17 to IL-17- CD8+ T cells and to Th17 cells. We show that murine Tc17 cells are generated in the presence of TGF-{beta} and IL-6, and that cells produced by these culture conditions substantially reflect Tc17 cells seen in vivo; that is, with high expression of PD1, CD6, ICOS and CD161. Tc17 cells show phenotypic and functional differences to their Th17 counterparts, with increased production of IL-2 and IL-22 as well as an increased tendency to produce IL-17F as well as IL-17A. They show a more glycolytic profile than Th17 cells, with lowered mitochondrial membrane potential. This divergent phenotype and cytokine production suggests differential roles in vivo for these two cells.

BackgroundNK cells are major innate and adaptive responders to malaria, with multiple roles in protection. Function of NK cells is heterogeneous, underpinned by expression of a diversity of receptors. One driver of NK cell heterogeneity is latent CMV infection, which drives the expansion of memory-like NK cells. We have recently reported that latent CMV infection can negatively impact the adaptive immune response to malaria, but whether CMV-mediated changes to the NK cell compartment also impact innate responses to malaria is unknown. MethodsWe investigated the impact of latent CMV infection on NK cell response to the malaria parasite Plasmodium falciparum in vitro, and in CMV seronegative and seropositive individuals during controlled human malaria infection. We analysed NK cell activation, cytotoxicity and NK cell receptor expression. Additionally, we investigated the impact of CMV serostatus on cytokine production in response to TLR stimulation in the myeloid cell compartment. The impact of CMV and NK cell responses on parasite control and malaria symptoms was investigated. ResultsNK cells from CMV seropositive individuals had reduced responsiveness to P. falciparum parasites in vitro and had reduced activation during controlled human infection. Reduced activation was not restricted to NK subsets modulated by CMV but occurred across the entire NK cell compartment. Consistent with global NK cell attenuation, IL-12 production from myeloid cells, a response that supports NK cell activation on exposure to P. falciparum parasites, was lower in CMV infected individuals. Linking NK cell activation to clinical outcomes, NK cells expressing perforin were associated with parasite control in CMV seronegative individuals. ConclusionCMV infection modulates NK cell responses during malaria by disruption of IL-12, leading to reduced parasite control.

It has been well established that females have a more active immune system. Females respond better to vaccines, are more resistant to somatic cell cancers, display better pathogen responses, present antigens better, and, conversely, are more prone to autoimmune diseases compared to male counterparts. Though these trends have been observed across normal and pathogenic states, the mechanisms underlying these sex differences have not been fully explained. Some hormonal effects on immune cell populations have been reported, but much less is known about effects contributed by genes on the sex chromosomes, for example those that are more highly expressed in females due to X inactivation escape, or Y-linked genes those unique to males. Here we use the Four Core Genotypes (FCG) mouse model and wildtype XY male mice to disentangle the effects of sex hormones, sex chromosome complement, and their interactions on baseline B and T cell populations in the periphery and T cells in the thymus. We test the effects of a previously described X-Y chromosomal translocation and those of the Sry transgene insertion on chromosome 3. We observe that mice harboring the Sry transgene show significant depletion of peripheral CD8+ T cell subpopulations. In the thymus, the XY XY,but not the XX males, show significant decrease to both CD8+ and CD4+ single positive T cells and an increase to CD4/CD8 double positive T cells. We also show that Y chromosome-bearing mice exhibit depletion in splenic marginal zone B cells. Our data suggests that the gonadal sex is the strongest contributor to this phenotype. Our studies define a critical framework for the use of this model and provide valuable data to assess the use of the FCGs model, especially for diseases involving the immune response.

BackgroundGroup 2 innate lymphoid cells (ILC2s) are key effector cells of type-2 immunity. A subset of ILC2s expresses KIT (CD117), which display increased phenotypic plasticity and were previously linked to severe asthma and psoriasis. However, the molecular mechanisms promoting a KIT+ ILC2 state remain poorly understood. ObjectiveDefine the molecular basis for the enhanced plasticity of KIT+ ILC2s and identify signals that induce this phenotype, including links with immune disease susceptibility. MethodsWe combine bulk as well as single-cell transcriptome (RNA-seq) and epigenome (ATAC-seq) with in vitro culture assays using primary human KIT+ or KITneg ILC2s and multipotent ILC precursors (ILCPs). Epigenomic data were integrated with genetic risk variants for major human immune diseases. ResultsMulti-omics analyses revealed that KIT+ ILC2s maintain a unique hybrid character marked by expression and open chromatin of genes linked to both ILCP and ILC2 biology. KIT+ ILC2s showed extensive epigenomic priming at gene loci related to naive lymphocyte biology, tissue homing, and ILC3 effector functions, including IL17 and IL23R - explaining why KIT+ ILC2s are poised to adopt an ILC3-like phenotype. Genetic risk variants for asthma and autoimmunity are enriched in the poised epigenome of KIT+ ILC2s. Common {gamma}-chain cytokines IL-2 and IL-7 induced a KIT+ phenotype in KITneg ILC2s through STAT5 activation. ConclusionsOur study defines KIT+ ILC2s as a developmentally immature state carrying a precursor-like epigenome that promotes phenotypic plasticity and is linked to immune disease susceptibility. Importantly, we identify STAT5-mediated cytokine signals as candidates for therapeutic targeting of KIT+ ILC2s.

T follicular cytotoxic (Tfc) cells are a specialized subset of CD8 T lymphocytes that combine helper and cytotoxic functions. While their phenotypic and functional properties have been described in several infectious and inflammatory settings, little is known whether Tfc cells exhibit distinct characteristics across secondary lymphoid organs. Using acute Trypanosoma cruzi infection as a model of systemic immune activation, we performed a comparative phenotypic, transcriptomic, metabolic, and functional characterization of Tfc cells arising in the spleen and inguinal lymph nodes. Tfc cells emerged transiently in both organs with similar kinetics and antigen specificity yet segregated primarily according to tissue of analysis at the transcriptional level. Splenic Tfc cells exhibited enhanced glycolytic and mTORC1-associated signatures, increased mitochondrial mass, and stronger cytotoxic and B cell helper functions, promoting immunoglobulin production and plasmablast death. In contrast, Tfc cells from lymph node preferentially displayed memory-associated features, including higher CD127 and CD122 expression, increased IL-2 production, and preferential persistence during chronic infection. Together, these findings demonstrate that Tfc cells are not a homogeneous population but can adopt organ-associated transcriptional, metabolic, and functional states during T. cruzi infection.

BackgroundNatural killer (NK) cell degranulation is a key immune defense mechanism where exposure to tumor or virus-infected cells triggers the fusion of cytoplasmic granules containing apoptotic proteins, perforin, and granzyme with the cell membrane. This process transiently expresses CD107a on the NK cell surface, and measuring CD107a is a standard method to assess NK cell activity. MethodsWe compared two stimulation protocols differing only in duration (6-hour vs. 18-hour) using K562 target cells to induce NK cell degranulation. Isolated PBMCs without stimulation served as controls to assess spontaneous degranulation. Anti-CD107a-PE antibody was present throughout stimulation in both test and control samples. After stimulation, cells were stained with anti-CD45, anti-CD3, and anti-CD56 and analyzed by flow cytometry. ResultsFor 6 of 7 healthy controls, results from both methods fell within 2 standard deviations. Notably, longer (18-hour) stimulation resulted in lower CD107a expression than the 6-hour assay. Interlaboratory comparisons of two samples showed no significant difference (p>0.05). In a suspected hemophagocytic lymphohistiocytosis (HLH) case, two labs reported similarly reduced CD107a expression (9% and 7%). Inter-day variability was observed in a donor across both time points. The 6-hour assay showed higher sensitivity and specificity than the 18-hour assay. A resting period before ex vivo PBMC assays was found necessary. ConclusionStimulation periods beyond 6 hours are unsuitable for clinical NK degranulation assays. Screening for HLH should include multiple stimulants to improve assay reliability.

GFI1 is a DNA-binding zinc finger transcription factor regulating the commitment of hematopoietic precursors to myeloid and lymphoid lineages. Here we report that GFI1 is expressed in {gamma}{delta} T cells and restricts the cellularity of ROR{gamma}t+V{gamma}6+ {gamma}{delta}T cells that produce high levels of IL-17A, while promoting the expansion of V{gamma}1+ and V{gamma}4+ {gamma}{delta}T cells. Absence of GFI1 results in a pronounced bias toward the production of {gamma}{delta}T17 cells, commencing post-birth. Additionally, we observe an expansion of ROR{gamma}t+/MAF+ cells within the thymic DN1e population of GFI1-deficient mice. The DN1e population, along with other DN subsets in GFI1 knock-out (KO) mice, exhibits a distinctive {gamma}{delta}T17 cell-specific transcriptomic profile. Specifically, DN1, DN3, and {gamma}{delta} T cells lacking GFI1 show upregulation of the B-ZIP transcription factor MAF, which regulates genes critical for {gamma}{delta}T cells, such as Il17a, Il22, and Blk that are all induced in Gfi1 deficient cells. The Maf gene is occupied by GFI1 in DN pre-T cells at cognate binding sites in its promoter region, suggesting that GFI1 acts as a direct repressor of Maf. We conclude that GFI1 functions as a novel regulator of V{gamma}6+ {gamma}{delta}T17 precursor cells restricting their peripheral expansion by acting upstream of a MAF dependent regulatory network. Highlights- GFI1 controls the expansion of {gamma}{delta} T cells in peripheral lymphoid organs and in barrier tissues. - GFI1 specifically restricts expansion of {gamma}{delta} T cells secreting IL-17 by acting upstream of a MAF dependent transcriptional regulatory network. - GFI1 plays a cell intrinsic role in controlling the generation of {gamma}{delta}T cells through the repression of Maf. - GFI1 controls a MAF+/ROR{gamma}t+ {gamma}{delta}T cell precursor cell population within the DN1e cell subset.

MHC class I-related protein 1 (MR1) is a highly conserved antigen presenting molecule that presents small molecule metabolites derived from diverse microbial pathogens to mucosal-associated invariant T (MAIT) cells. We have shown previously that MR1 traffics through endosomal compartments via soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, including Syntaxin 4 and vesicle-associated membrane protein (VAMP) 4. Here, we investigate the role of synaptosome-associated proteins (SNAPs), which pair with Syntaxins and VAMPs to form functional SNARE complexes, in MR1-mediated antigen presentation. Among SNAP homologs, we identify that SNAP23 contributes to the presentation of Mycobacterium tuberculosis (Mtb)-derived antigens and loss of SNAP23 reduces the number of MR1-containing vesicles during infection. In contrast, SNAP25 suppresses MR1 presentation for both intracellular pathogens Mtb and Mycobacterium avium, as well as extracellular pathogen Candida albicans. This study demonstrates opposing roles for SNAP23 and SNAP25 in MR1 antigen presentation to MAIT cells, and extends our understanding of how SNAP family proteins regulate MR1 trafficking.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and long COVID are complex chronic conditions that often follow infectious triggers with overlapping clinical features but poorly defined pathophysiological relationships. This study aimed to identify disease-specific immune signatures through multiparameter immunophenotyping of monocytes, dendritic cells, and T-cell subsets. A total of 207 participants were included (ME/CFS: n = 103; long COVID: n = 63; healthy controls: n = 41). Peripheral blood mononuclear cells were analyzed using multiparameter flow cytometry. Statistical analyses included non-parametric testing, age-adjusted ANCOVA, correlation network analysis, and principal component analysis (PCA). Long COVID was characterized by increased M2-like monocyte polarization, elevated CD80 expression across monocyte subsets, expansion of dendritic cells, and reduced expression of activation markers, indicating persistent immune activation with features of immune exhaustion. In contrast, ME/CFS exhibited reduced costimulatory molecule expression, impaired CCR7-mediated immune cell trafficking, and less coordinated activation patterns, consistent with a state of immune suppression. Correlation network analysis revealed more extensive and integrated immune interactions in long COVID, while PCA identified distinct immunophenotypic components and enabled moderate discrimination between the two conditions. These findings demonstrate that ME/CFS and long COVID are characterized by distinct immune profiles, supporting the concept of divergent immunopathological mechanisms. The identified signatures may contribute to biomarker development and guide targeted therapeutic approaches.

The TP53 mutation associated with Li-Fraumeni syndrome in humans is known to exhibit p53 gain-of-function properties leading to early cancer onset. To explore whether these patients also have compromised immune responses due to p53 mutations, we investigated the humoral immune response using a Li-Fraumeni mouse model harboring a structural mutation, Trp53R172H (equivalent to codon 175 in humans). Trp53R172H mice were immunized with sheep red blood cells, and the Germinal center response was monitored. Our results revealed that SRBC-immunized Trp53R172H mice exhibit reduced B cell activation during the GC reaction. These suggest a selective role for p53 in promoting B cell activation early in the GC reaction prior to BCL6 upregulation. We propose that impaired B cell activation in Li-Fraumeni patients could contribute to immune deficiencies and heightened susceptibility to autoimmune disorders, potentially influencing the development of secondary cancers and impairing therapeutic responses to chemotherapies and immunotherapies. Key PointsO_LITrp52R172H mice exhibit reduced B cell activation during the Germinal center reaction C_LIO_LIRatio of activated B cells in DZ to LZ remain unchanged in Trp52R172H mice. C_LI

miR-378a-3p has been reported to be upregulated in the lesional skin of patients with atopic dermatitis (AD); however, its function in AD remains unclear. Here, we demonstrate that miR-378a-3p expression is induced by IL-4 and live Staphylococcus aureus (S. aureus) in normal human epidermal keratinocytes (NHEKs) cultured in proliferative conditions or in a 3D epidermal culture model. Transcriptomic profiling and gene set enrichment analysis of miR-378a-3p-transfected NHEKs revealed positive enrichment of inflammatory response pathways alongside downregulation of genes associated with epidermal development. More specifically, miR-378a-3p enhanced expression of multiple NF-{kappa}B-dependent inflammatory mediators, accompanied by increased phosphorylation of p65, indicating activation of canonical NF-{kappa}B pathway. Notably, miR-378a-3p concomitantly reduced the expression of several NF-{kappa}B family members and upstream adaptor molecules, supporting a model in which miR-378a-3p promotes canonical NF-{kappa}B activity through coordinated modulation of multiple components within the NF-{kappa}B regulatory network. In NHEKs exposed to live S. aureus, miR-378a-3p significantly increased the secretion of IL-1{beta}, IL-1Ra, and IL-8, indicating that miR-378a-3p may amplify innate immune responses triggered by S. aureus colonization in AD. Collectively, these findings identify miR-378a-3p as a positive regulator of keratinocyte inflammatory responses that may contribute to AD exacerbation, particularly in the context of S. aureus colonization.