Biology subjects

Jimenez-Saiz, R.

Publications and source records attributed to Jimenez-Saiz, R..

9 recordsLinked to original sources

bioRxiv2026

Mast cell desensitization induces a distinct IgE-dependent transcriptional program associated with immune regulation

Allergen-driven IgE-mast cell (MC) activation is a central feature of allergic diseases, whose prevalence continues to increase worldwide. Allergen immunotherapy (AIT) is currently the only disease-modifying treatment and induces a state of MC hyporesponsiveness termed desensitization; however, its underlying molecular mechanisms remain incompletely understood and whether this state reflects passive signal attenuation or active cellular reprogramming remains unresolved. Here, we define the molecular landscape of MC desensitization using a human polyclonal platform that captures the physiological diversity of allergen-specific IgE. Desensitization reduced degranulation in an allergen-specific manner and induced progressive internalization of allergen-specific IgE. Although early steps were associated with LAT phosphorylation, subsequent allergen challenge failed to propagate activation to distal IgE/Fc{varepsilon}RI effectors, revealing selective signaling uncoupling. Transcriptomic profiling uncovered a distinct transcriptional program comprising 168 upregulated genes enriched in immunoregulatory pathways and largely non-overlapping with classical activation signatures. This reprogramming occurred despite minimal alterations in mitochondrial respiration and selective impairment of allergen-induced glycolysis. Functionally, desensitized MCs enhanced allergen-driven proliferation of memory CD4 T cells. Together, these findings demonstrate that MC desensitization is not merely passive hyporesponsiveness but involves time-dependent allergen-specific IgE internalization, selective signal propagation, and a unique immunoregulatory transcriptional imprint that may contribute to tolerance during AIT.

immunology↗

bioRxiv2025

Microbial metabolism of food allergens determines the severity of IgE-mediated anaphylaxis

Anaphylaxis is an acute, potentially life-threatening reaction, often triggered by foods and largely mediated by IgE. Critically important to anaphylaxis are the factors that modulate its severity. The human microbiota is known to influence oral tolerance, but the microbial mechanisms directly involved in IgE-mediated anaphylaxis remain unknown. Here, we demonstrate that human saliva and jejunum harbor peanut-degrading bacteria that metabolize immunodominant allergens (Ara h 1 and 2) and alter IgE-binding. Additionally, we provide in vivo evidence that oral bacteria metabolize peanut allergens, influencing systemic allergen exposure and anaphylaxis severity. Finally, in clinical studies, we observe that common peanut-degrading bacteria, such as Rothia, from the oral cavity, are more abundant in peanut-allergic patients who exhibit better tolerance to allergen exposure. Altogether, these results demonstrate that human microbiota modulates IgE-mediated reactions through allergen metabolism. We reveal a novel microbial mechanism with potential to prevent, or reduce, the severity of IgE-mediated anaphylaxis.

immunology↗

bioRxiv2025

Diacylglycerol kinase zeta dictates CD40-mediated immune synapse formation, mTORC1 signaling and plasma cell fate in B lymphocytes

To mount a robust T-dependent immune response, antigen-specific B lymphocytes require CD40 stimulation through immune synapse formation with CD4+ T follicular helper cells. CD40 triggers the activation of mammalian target of rapamycin complex-1 (mTORC1) and remodels the mitochondria to meet increased bioenergetic and anabolic demands. We show that diacylglycerol-kinase-{zeta} (DGK{zeta}) has a crucial role in activating the mTORC1 pathway and remodeling mitochondria downstream of CD40 signaling in B cells. DGK{zeta} governs organelle translocation to the CD40-mediated immune synapse and the recruitment of mTORC1 to lysosomes. DGK{zeta}-/- B cells exhibited impaired mitochondria function, protein biosynthesis, metabolite transporter expression and cell cycle progression, accompanied by dysregulation of the transcriptional network governing B cell fate. These defects lead to a blockage in the progression of the germinal center response and plasma cell differentiation in vivo. Our findings establish DGK{zeta} as a key mediator of CD40 functions in the B cell response.

immunology↗

bioRxiv2023

Allosteric modulation of the CXCR4:CXCL12 axis by targeting receptor nanoclustering via the TMV-TMVI domain

CXCR4 is a ubiquitously expressed chemokine receptor that regulates leukocyte trafficking and arrest in both homeostatic and pathological states. It also participates in organogenesis, HIV-1 infection and tumor development. Despite the potential therapeutic benefit of CXCR4 antagonists, only one, plerixafor (AMD3100), which blocks the ligand-binding site, has reached the clinic. Recent advances in imaging and biophysical techniques have provided a richer understanding of the membrane organization and dynamics of this receptor. Activation of CXCR4 by CXCL12 reduces the number of CXCR4 monomers/dimers at the cell membrane and increases the formation of large nanoclusters, which are largely immobile and are required for correct cell orientation to chemoattractant gradients. Mechanistically, CXCR4 activation involves a structural motif defined by residues in TMV and TMVI. Using this structural motif as a template, we performed in silico molecular modeling followed by in vitro screening of a small compound library to identify negative allosteric modulators of CXCR4 that do not affect CXCL12 binding. We identified AGR1.137, a small molecule that abolishes CXCL12-mediated receptor nanoclustering and dynamics and blocks the ability of cells to sense CXCL12 gradients both in vitro and in vivo while preserving ligand binding and receptor internalization. Significance StatementThe chemokine receptor CXCR4 and its ligand CXCL12 are key for development, hematopoiesis, neutrophil homeostasis and lymphocyte trafficking. The only commercially available CXCR4 antagonist currently approved for clinical use is plerixafor (AMD3100), a small compound that blocks the ligand-binding site. Unfortunately, its clinical use is limited by poor pharmacokinetics and adverse effects associated with long-term administration. Here, we performed in silico analyses of a small aromatic compound library and in vitro screening to identify allosteric CXCR4 modulators. These compounds abolish the ability of cells to sense chemoattractant gradients without affecting other ligand-mediated functions such as cAMP production or receptor internalization. The selected compounds were also effective in vivo, as demonstrated by reduced tumorigenesis and metastasis in a zebrafish tumor model. Our study describes a new approach to selectively alter some GPCR functions while maintaining other functions.

cell biology↗

bioRxiv2023

Allergic inflammation triggers dyslipidemia via IgG signalling

BackgroundAllergic diseases begin early in life and are often chronic, thus creating an inflammatory environment that may precede or exacerbate other pathologies. In this regard, allergy has been associated to metabolic disorders and with a higher risk of cardiovascular disease, but the underlying mechanisms remain incompletely understood. MethodsWe used a murine model of allergy and atherosclerosis, different diets and sensitization methods, and cell-depleting strategies to ascertain the contribution of acute and late phase inflammation to dyslipidemia. Untargeted lipidomic analyses were applied to define the lipid fingerprint of allergic inflammation at different phases of allergic pathology. Expression of genes related to lipid metabolism was assessed in liver and adipose tissue at different times post-allergen challenge. Also, changes in serum triglycerides (TG) were evaluated in a group of 59 patients [≥]14 days after the onset of an allergic reaction. ResultsWe found that allergic inflammation induces a unique lipid signature that is characterized by increased serum TG and changes in the expression of genes related to lipid metabolism in liver and adipose tissue. Alterations in blood TGs following an allergic reaction are independent of T-cell-driven late phase inflammation. On the contrary, the IgG-mediated alternative pathway of anaphylaxis is sufficient to induce a TG increase and a unique lipid profile. Lastly, we demonstrated an increase in serum TG in 59 patients after undergoing an allergic reaction. ConclusionOverall, this study reveals that IgG-mediated allergic inflammation regulates lipid metabolism.

immunology↗

bioRxiv2023

Sequential Switching Through IgG1 is Redundant for Allergic Reactivity and Memory to Allergens

Allergic reactions to foods are driven by allergen-binding immunoglobulin (Ig)E antibodies. IgE- expressing cells can be generated through a sequential class switching pathway where activated B cells first switch to an intermediary isotype, most frequently IgG1, and then to IgE. It has been proposed that sequential class switch recombination is important in generating high affinity IgE, augmenting anaphylactic reactions, and in holding the memory of IgE responses. Here, we observed surprising redundancy of sequential switching through IgG1 for the functional affinity of the IgE repertoire against multiple food allergens as well as for the ability of IgE to elicit anaphylaxis. We further found that sequential switching via IgG1 was irrelevant for allergic memory. These results indicate that allergen-specific IgG1 B cells are redundant in sensitization, anaphylaxis, and food allergy persistence, thereby implicating other switching pathways as important considerations in the development of therapeutics for allergic diseases.

immunology↗

bioRxiv2020

Interrupting reactivation of immunological memory reprograms allergy and averts anaphylaxis

IgE production against innocuous antigens can lead to life-threatening reactions such as anaphylaxis. While IgE levels drastically decline with strict allergen avoidance, the ability to regenerate IgE can persist for a lifetime, as is the case for peanut allergy. The mechanism by which IgE regenerates remains unresolved. A novel culture system and application of single-cell RNA-sequencing, elucidated the transcriptomic signature of human peanut-reactive B and T cells and revealed IL-4/IL-13 as a signaling pathway critical for the IgE recall response. Indeed, interruption of this pathway not only prevented IgE production and anaphylaxis, but also reprogrammed the pathogenic response against peanut. This investigation advances our understanding of the mechanism that regenerates IgE in food allergy and spotlights IL-4/IL-13 blockade as a therapeutic with disease-transforming potential. One Sentence SummarySingle-cell transcriptomics of allergic memory responses reveals how to teach the immune system to forget.

immunology↗

bioRxiv2019

Microbial regulation of enteric eosinophils and its impact on tissue remodeling and Th2 immunity

Eosinophils have emerged as multifaceted cells that contribute to tissue homeostasis. However, the factors that control their frequency and function at mucosal sites remain unclear. Here, we investigated the role of the microbiota in regulating enteric eosinophils. We found that small intestinal (SI) eosinophilia was significantly greater in germ-free (GF) mice compared to specific pathogen free (SPF) controls. This phenomenon was associated with enteric overexpression of signals that mediate attraction, retention and survival of eosinophils, and was reversed by colonization. Additionally, we generated a novel strain of eosinophil-deficient GF mice. These mice displayed intestinal fibrosis and were less prone to allergic sensitization as compared to GF controls. Overall, our study demonstrates that commensal microbes regulate intestinal eosinophil frequency and function, which impacts tissue repair and allergic sensitization to food antigens. These data support a critical interplay between the commensal microbiota and intestinal eosinophils in shaping homeostatic, innate and adaptive immune processes in health and disease.

immunology↗

bioRxiv2019

BCR analysis of single-sorted, putative IgE+ memory B cells in food allergy: an ephemeral existence?

Immunoglobulin (Ig) E is the critical effector molecule in allergic reactions. Consequently, research efforts to understand the biology of IgE-expressing cells is of paramount importance. In particular, the role of IgE+ memory B cells (MBCs) in the perpetuation of allergic reactivity has been the subject of intense research. Studies in mice have convincingly established that IgE+ B cells are rare and transient and, therefore, an unlikely candidate to maintain allergic disease. In contrast, IgE+ MBCs have been detected by flow cytometry in the sputum and peripheral blood of humans and have been proposed as a clinical marker of allergic disease. We established a method to genetically validate, at the single-cell level, the putative IgE+ MBCs identified by flow cytometry from humans. We, then used this information to develop an enhanced flow cytometry protocol that more accurately identifies bona fide IgE+ MBCs. We found that IgE+ MBCs were detected in some patients with atopic dermatitis, but at a frequency that was ~100 times lower than previously reported. We also found that IgE+ MBCs were undetectable in PBMCs from peanut allergic patients. These findings provide tools to identify bona fide IgE+ MBCs, demonstrate their extreme rarity in circulation and are consistent with the lack of a central role for IgE+ MBCs in the maintenance of allergic sensitivity.\n\nOne Sentence SummaryThe frequency of IgE+ MBCs in the peripheral circulation of humans is orders of magnitude lower than previously reported and comparable between allergic and healthy donors, which cautions about the clinical utility of their assessment.

immunology↗