Lymphocyte Development Research Articles

Hypoxia-adenosinergic regulation of B cell responses

Hypoxic microenvironments induce widespread metabolic changes that have been shown to be critical in regulating innate and adaptive immune responses. Hypoxia-induced changes include the generation of extracellular adenosine followed by subsequent signaling through adenosine receptors on immune cells. This evolutionarily conserved “hypoxia-adenosinergic” pathway of hypoxia → extracellular adenosine → adenosine receptor signaling has been shown to be critical in limiting and redirecting T cell responses including in tumor microenvironments and the gut mucosa. However, the question of whether hypoxic microenvironments are involved in the development of B cell responses has remained unexplored until recently. The discovery that germinal centers (GC), the anatomic site in which B cells undergo secondary diversification and affinity maturation, develop a hypoxic microenvironment has sparked new interest in how this evolutionarily conserved pathway affects antibody responses. In this review we will summarize what is known about hypoxia-adenosinergic microenvironments in lymphocyte development and ongoing immune responses. Specific focus will be placed on new developments regarding the role of the hypoxia-adenosinergic pathway in regulating GC development and humoral immunity.

A mutant BCL11B-N440K protein interferes with BCL11A function during T lymphocyte and neuronal development.

Genetic studies in mice have shown that the zinc finger transcription factor BCL11B has an essential role in regulating early T cell development and neurogenesis. A de novo heterozygous missense BCL11B variant, BCL11BN441K, was isolated from a patient with T cell deficiency and neurological disorders. Here, we show that mice harboring the corresponding Bcl11bN440K mutation show the emergence of natural killer (NK)/group 1 innate lymphoid cell (ILC1)-like NKp46+ cells in the thymus and reduction in TBR1+ neurons in the neocortex, which are observed with loss of Bcl11a but not Bcl11b. Thus, the mutant BCL11B-N440K protein interferes with BCL11A function upon heterodimerization. Mechanistically, the Bcl11bN440K mutation dampens the interaction of BCL11B with T cell factor 1 (TCF1) in thymocytes, resulting in weakened antagonism against TCF1 activity that supports the differentiation of NK/ILC1-like cells. Collectively, our results shed new light on the function of BCL11A in suppressing non-T lymphoid developmental potential and uncover the pathogenic mechanism by which BCL11B-N440K interferes with partner BCL11 family proteins.

Comprehensive Postnatal Anatomical, Histological and Geometric Morphometric Analysis of Thymus Development in Dromedary Camels (Camelus dromedarius).

The thymus, a primary lymphoid organ, plays a critical role in T lymphocyte development and adaptive immunity. This study focuses on the anatomical, histological and geometric morphometric characteristics of the thymus in dromedary camels (Camelus dromedarius) during postnatal development. Thymus samples were collected from camels aged approximately 4, 8, 12 and 16 months. Using photogrammetry and 3D modelling, the samples were analysed to generate landmarks and conduct geometric morphometry with the 3D Slicer and ALPACA algorithm. Principal component analysis (PCA) was then performed to evaluate shape variations. Histologically, the samples underwent Haematoxylin and Eosin and Masson's trichrome staining. Image analysis using QuPath software quantified trabeculae, adipose tissue and Hassall's corpuscles. The results revealed significant anatomical and histological changes in the thymus across the different age groups. Notable variations in tissue composition and structural integrity were observed, with the PCA highlighting distinct morphometric patterns associated with age-related development. These findings provide a deeper understanding of thymus maturation in dromedaries and offer valuable data for comparative anatomy and veterinary medicine. This comprehensive analysis enhances our knowledge of species-specific immune development, with important implications for the health and resilience of these animals in arid environments.

Tyrosine phosphorylation of both STAT5A and STAT5B is necessary for maximal IL-2 signaling and T cell proliferation

Cytokine-mediated STAT5 protein activation is vital for lymphocyte development and function. In vitro tyrosine phosphorylation of a C-terminal tyrosine is critical for activation of STAT5A and STAT5B; however, the importance of STAT5 tyrosine phosphorylation in vivo has not been assessed. Here we generate Stat5a and Stat5b tyrosine-to-phenylalanine mutant knockin mice and find they have greatly reduced CD8+ T-cell numbers and profoundly diminished IL-2-induced proliferation of these cells, and this correlates with reduced induction of Myc, pRB, a range of cyclins and CDKs, and a partial G1→S phase-transition block. These mutant CD8+ T cells also exhibit decreased IL-2-mediated activation of pERK and pAKT, which we attribute in part to diminished expression of IL-2Rβ and IL-2Rγ. Our findings thus demonstrate that tyrosine phosphorylation of both STAT5A and STAT5B is essential for maximal IL-2 signaling. Moreover, our transcriptomic and proteomic analyses elucidate the molecular basis of the IL-2-induced proliferation of CD8+ T cells.

Retraction: Arid3b Is Critical for B Lymphocyte Development.

Retraction: Arid3b Is Critical for B Lymphocyte Development.

MicroRNA: A Signature for the Clinical Progression of Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is the most common human leukemia. The disease is caused by abnormal proliferation and development of lymphocytes and their precursors in the blood and bone marrow (BM). Recent studies have shown that the CLL’s clinical course and outcome depend not only on genetic but also epigenetic factors. MicroRNAs (miRNAs) are involved in the development of hematological tumors, including CLL. The aim of this study is to identify the miRNA expression profile in CLL and determine the role of miRNAs in biological pathways associated with leukemogenesis in CLL. The following samples were used in this study: (1) samples obtained by sternal puncture and aspiration biopsy of BM (n = 115). They included samples from 21 CLL patients with anemia and indications for therapy and 45 CLL patients without anemia and with indications for therapy. The control group for the CLL BM samples consisted of patients with non-cancerous blood diseases (n = 35). (2) Lymph node (LN) samples (n = 20) were collected from CLL patients. The control group for the CLL LN samples consisted of patients with lymphadenopathy (n = 37). All cases were patients before treatment. We demonstrated a significant upregulation of miRNA-34a and miRNA-150 in CLL BM samples (p < 0.05) and downregulation of miRNA-451a in CLL LN samples (p < 0.05). We noted a dynamic increase in the levels of miRNA-150 and miRNA-34a in BM at various stages of tumor progression of CLL. We concluded that a dynamic picture of clinical manifestations of CLL closely correlates with changes in epigenetic characteristics of the tumor. Progression of the lymphoproliferative process and indications for cytoreductive therapy are associated with changes in the miRNA profile generated by cancer cells in different sites of clonal expansion.

IKZF3 amplification predicts worse prognosis especially in intestinal-type gastric cancer

PurposeIKAROS family zinc finger 3 (IKZF3) is an oncogene involved in different malignancies, particularly in the development and malignant progression of lymphocytes. However, IKZF3 amplification and clinical significance in gastric cancers (GCs) remain unexplored.MethodsWe examined IKZF3 amplification status in 404 GCs with HER2 amplification status using tissue microarray (TMA) and fluorescence in situ hybridization (FISH) assays.ResultsIKZF3 amplification was detected in 6.9% (28/404) of all GC patients, with higher rates in intestinal-type gastric cancer (IGC) (11.22%, 22/196) compared to other types (2.88%, 6/208). HER2 amplification was identified in 16.09% (65/404) of all GC patients, with higher rates in IGC (20.92%, 41/196) compared to other types (11.54%, 24/208). Co-amplification of IKZF3 and HER2 was detected in 8.16% (16/196) of IGC patients and in 2.40% (5/208) of other types. IKZF3 amplification showed significant correlation with IGC (P = 0.001) and HER2 amplification (P = 0.0001). IKZF3 amplification exhibited significantly worse disease-free survival (DFS) (P = 0.014) and overall survival (OS) (P = 0.018) in GC patients, particularly in IGC (DFS: P < 0.001; OS: P < 0.001), rather than other types. Cox regression analysis demonstrate IKZF3 amplification as an independent poor prognostic factor in all GCs (P = 0.006, P = 0.004 respectively) and in IGC patients, regardless of stages I-II or III-IV (P = 0.007, P = 0.004 respectively). On the other hand, HER2 amplification was significantly associated with worse DFS (P = 0.008) and OS (P = 0.01) in IGC patients, but not in all GCs and in multivariate analysis. Within the subset of patients with HER2 amplification, those also exhibiting IKZF3 amplification displayed potential poorer prognosis (P = 0.08, P = 0.11 respectively).ConclusionIKZF3 amplification was detected in minority of GC patients, especially in IGC, and was an independent indicator of poor prognosis. Our study, for the first time, found the prognostic value of IKZF3 was superior to HER2 for GC patients.

Disruption of the ZFP574–THAP12 complex suppresses B cell malignancies in mice

Despite the availability of life-extending treatments for B cell leukemias and lymphomas, many of these cancers remain incurable. Thus, the development of new molecular targets and therapeutics is needed to expand treatment options. To identify new molecular targets, we used a forward genetic screen in mice to identify genes required for development or survival of lymphocytes. Here, we describe Zfp574, an essential gene encoding a zinc finger protein necessary for normal and malignant lymphocyte survival. We show that ZFP574 interacts with zinc finger protein THAP12 and promotes the G1-to-S-phase transition during cell cycle progression. Mutation of ZFP574 impairs nuclear localization of the ZFP574-THAP12 complex. ZFP574 or THAP12 deficiency results in cell cycle arrest and impaired lymphoproliferation. Germline mutation, acute gene deletion, or targeted degradation of ZFP574 suppressed Myc-driven B cell leukemia in mice, but normal B cells were largely spared, permitting long-term survival, whereas complete lethality was observed in control animals. Our findings support the identification of drugs targeting ZFP574-THAP12 as a unique strategy to treat B cell malignancies.

Methods of Prevention and Mitigation of Autoimmune Diseases - A Review of The Literature

Introduction and purpose: Autoimmune diseases are conditions where the body’s immune system is unable to distinguish between auto- and foreign antigens and mistakenly attacks its cells, tissues, and organs. In recent years it became major public health concern because of the increasing diagnosis rate. Currently, about 5% of the population in Western countries is affected by such diseases, more often in women population. The exact cause of autoimmune diseases is unknown, although most probably it results from a combination of genetic predisposition, environmental risk factors and immune dysregulation. Development of autoantigen-specific lymphocytes and autoantibodies might be decisive in starting the process of autoimmunity. Most common medication used in autoimmune diseases treatment are nonsteroidal anti-inflammatory drugs (NSADs), glucocorticoids, disease-modifying antirheumatic drugs (DMARDs). Additionally, there is biological medication available for many of them. It is known that non-pharmacological interventions, such as specific diets, supplementation or physical exercise is useful to mitigate the disease or even to prevent the body from its onset. Materials and methods: The data for the article was found using the PubMed and Google Scholar websites. The key words used for the search included: ‘diet and autoimmunity’, ‘autoimmunity and estrogens’, ‘microbiota and autoimmunity’. Articles not written in English, conference abstracts only and duplicated papers were excluded. Conclusions: There is still no cure for autoimmune diseases, although various prevention and mitigation strategies can help manage these conditions and improve quality of life for affected individuals. However, for the use of some of them, evidence-based recommendations are not available. This review highlights current non-pharmacological therapeutic options.

ATM-dependent Phosphorylation of Nemo SQ Motifs Is Dispensable for Nemo-mediated Gene Expression Changes in Response to DNA Double-Strand Breaks.

In response to DNA double-strand breaks (DSBs), the ATM kinase activates NF-κB factors to stimulate gene expression changes that promote survival and allow time for cells to repair damage. In cell lines, ATM can activate NF-κB transcription factors via two independent, convergent mechanisms. One is ATM-mediated phosphorylation of nuclear NF-κB essential modulator (Nemo) protein, which leads to monoubiquitylation and export of Nemo to the cytoplasm where it engages the IκB kinase (IKK) complex to activate NF-κB. Another is DSB-triggered migration of ATM into the cytoplasm, where it promotes monoubiquitylation of Nemo and the resulting IKK-mediated activation of NF-κB. ATM has many other functions in the DSB response beyond activation of NF-κB, and Nemo activates NF-κB downstream of diverse stimuli, including developmental or proinflammatory stimuli such as LPSs. To elucidate the invivo role of DSB-induced, ATM-dependent changes in expression of NF-κB-responsive genes, we generated mice expressing phosphomutant Nemo protein lacking consensus SQ sites for phosphorylation by ATM or related kinases. We demonstrate that these mice are viable/healthy and fertile and exhibit overall normal B and T lymphocyte development. Moreover, treatment of their B lineage cells with LPS induces normal NF-κB-regulated gene expression changes. Furthermore, in marked contrast to results from a pre-B cell line, primary B lineage cells expressing phosphomutant Nemo treated with the genotoxic drug etoposide induce normal ATM- and Nemo-dependent changes in expression of NF-κB-regulated genes. Our data demonstrate that ATM-dependent phosphorylation of Nemo SQ motifs invivo is dispensable for DSB-signaled changes in expression of NF-κB-regulated genes.

A distal enhancer of GATA3 regulates Th2 differentiation and allergic inflammation

Asthma is a widespread airway disorder where GATA3-dependent Type-2 helper T (Th2) cells and group 2 innate lymphoid cells (ILC2s) play vital roles. Asthma-associated single nucleotide polymorphisms (SNPs) are enriched in a region located 926-970 kb downstream from GATA3 in the 10p14 (hG900). However, it is unknown how hG900 affects the pathogenesis of allergic airway inflammation. To investigate the roles of the asthma-associated GATA3 enhancer region in experimental allergic airway inflammation, we first examined the correlation between GATA3 expression and the activation of the hG900 region was analyzed by flow cytometry and ChIP-qPCR. We found that The activation of enhancers in the hG900 region was strongly correlated to the levels of GATA3 in human peripheral T cell subsets. We next generated mice lacking the mG900 region (mG900KO mice) were generated by the CRISPR-Cas9 system, and the development and function of helper T cells and ILCs in mG900KO mice were analyzed in steady-state conditions and allergic airway inflammation induced by papain or house dust mite (HDM). The deletion of the mG900 did not affect the development of lymphocytes in steady-state conditions or allergic airway inflammation induced by papain. However, mG900KO mice exhibited reduced allergic inflammation and Th2 differentiation in the HDM-induced allergic airway inflammation. The analysis of the chromatin conformation around Gata3 by circular chromosome conformation capture coupled to high-throughput sequencing (4C-seq) revealed that the mG900 region interacted with the transcription start site of Gata3 with an influencing chromatin conformation in Th2 cells. These findings indicate that the mG900 region plays a pivotal role in Th2 differentiation and thus enhances allergic airway inflammation.

The multifaceted functions of DNA-PKcs: implications for the therapy of human diseases.

The DNA-dependent protein kinase(DNA-PK), catalytic subunit, also known as DNA-PKcs, is complexed with the heterodimer Ku70/Ku80 to form DNA-PK holoenzyme, which is well recognized as initiator in the nonhomologous end joining (NHEJ) repair after double strand break (DSB). During NHEJ, DNA-PKcs is essential for both DNA end processing and end joining. Besides its classical function in DSB repair, DNA-PKcs also shows multifaceted functions in various biological activities such as class switch recombination (CSR) and variable (V) diversity (D) joining (J) recombination in B/T lymphocytes development, innate immunity through cGAS-STING pathway, transcription, alternative splicing, and so on, which are dependent on its function in NHEJ or not. Moreover, DNA-PKcs deficiency has been proven to be related with human diseases such as neurological pathogenesis, cancer, immunological disorder, and so on through different mechanisms. Therefore, it is imperative to summarize the latest findings about DNA-PKcs and diseases for better targeting DNA-PKcs, which have shown efficacy in cancer treatment in preclinical models. Here, we discuss the multifaceted roles of DNA-PKcs in human diseases, meanwhile, we discuss the progresses of DNA-PKcs inhibitors and their potential in clinical trials. The most updated review about DNA-PKcs will hopefully provide insights and ideas to understand DNA-PKcs associated diseases.

Autoantigen Exposure in Murine Fetuses Elicited Nonpathogenic Autoimmunity

Autoimmunity refers to the presence of autoantibodies and autoreactive lymphocytes against the structural molecules of an individual's cells or tissues, known as self-antigens or autoantigens. It might exist in the absence of autoimmune disease. However, how autoimmunity develops remains a mystery, despite the discovery of autoantibodies in human cord blood. Murine fetuses on day 14 of gestation were subjected to intraperitoneal injection of murine thyroid peroxidase (TPO) peptides or collagen type II (CII) at graded doses via transuterine approach. Postnatally, the recipients were examined for autoantibodies by ELISA and autoreactive lymphocytes by in vitro incorporation of tritium and for the development of autoimmune thyroiditis or arthritis. At one month of age, the recipients did not secrete significant levels of anti-TPO or CII IgG2a in sera until a dose of 0.5 µg TPO or 5.0 µg CII was injected in utero. Serum anti-TPO or CII IgG2a persisted for at least two to four months postnatally. In recipients with elevated autoantibodies, their lymphocytes also showed proliferative responses specifically to TPO or CII. However, the development of autoantibodies and autoreactive lymphocytes was not associated with inflammatory cell infiltration of thyroid glands or paw joints even though anti-TPO or CII IgG2a was enhanced by postnatal TPO or CII challenge. Fetal exposure to free autoantigens could be immunogenic, shedding new light on the in utero origin of autoantibodies and autoreactive lymphocytes. The development of autoimmunity requires a threshold intensity of autoantigen exposure in the fetus.

Peripheral apoptosis and limited clonal deletion during physiologic murine B lymphocyte development

Self-reactive and polyreactive B cells generated during B cell development are silenced by either apoptosis, clonal deletion, receptor editing or anergy to avoid autoimmunity. The specific contribution of apoptosis to normal B cell development and self-tolerance is incompletely understood. Here, we quantify self-reactivity, polyreactivity and apoptosis during physiologic B lymphocyte development. Self-reactivity and polyreactivity are most abundant in early immature B cells and diminish significantly during maturation within the bone marrow. Minimal apoptosis still occurs at this site, however B cell receptors cloned from apoptotic B cells show comparable self-reactivity to that of viable cells. Apoptosis increases dramatically only following immature B cells leaving the bone marrow sinusoids, but above 90% of cloned apoptotic transitional B cells are not self-reactive/polyreactive. Our data suggests that an apoptosis-independent mechanism, such as receptor editing, removes most self-reactive B cells in the bone marrow. Mechanistically, lack of survival signaling rather than clonal deletion appears to be the underpinning cause of apoptosis in most transitional B cells in the periphery.

#2240 The complex fluctuation of circulating T follicular cells in patients with lupus nephritis (LN)

Abstract Background and Aims Follicular T (TF) cells constitute a subgroup of cells recently discovered, located in the germinal center (GC) of lymphoid follicles, where they mediate B lymphocyte development, maturation, and antibody production. Meanwhile, T cells with similar markers have also been detected in the peripheral blood, considered as a circulating memory compartment with unknown origin or function. TF cells seem to be implicated in the pathogenesis of systemic lupus erythematosus (SLE) and lupus nephritis (LN) by assisting the selection of high-affinity B cells in germinal centers; nonetheless, research about their circulating regimen is lacking. Herein, we describe the population of circulating TF cells in patients with LN and their association with disease hallmarks. Method Flow cytometry was performed to identify cTF (CD4+CD45RA-CXCR5+) cells and their subsets, defined as cTF1 (CD4+CD45RA-CXCR5+CXCR3+CCR6-), cTF2 (CD4+CD45RA-CXCR5+CXCR3-CCR6-), cTF17 (CD4+CD45RA-CXCR5+CXCR3-CCR6+), and activated-cTF, cTF-ICOS+ (CD4+CD45RA-CXCR5+ICOS+), as well as cTF-Regulatory (cTFR) (CD4+CD45RA-CXCR5+CD127-CD25+FOXP3+). Peripheral blood was collected from 25 LN patients (LN) and 25 healthy controls (HC) of similar age. Results Here are presented preliminary results analyzed in 15 LN patients (age = 38 ± 8yrs) and compared to 9 HC (age = 31.5 ± 7yrs). Although our findings were not significant in total and the percentage and total number of cTFH cells were similar between LN and HC [7.1 (0.6-22.4)% and 52.57 (3.38-412.7)cells/μL, vs. 6.6 (1.9-12.1)% and 45.65 (13.3-69.6)cells/μL, respectively], the fluctuation of the different subsets is interesting. cTF-ICOS+, cTF1, cTF2, and also surprisingly cTFR cells were upregulated in LN compared to HC [0.9 (0-5.2) vs 0.51 (0-1.45)cells/μL, 9.3 (0.2-31.6) vs. 3.02 (0.4-23.08)cells/μL, 10.89 (0-47.41) vs 3.37 (0.46-39.01)cells/μL, and 0.21 (0-12) vs 0.12 (0-1.53) cells/μL, respectively], while the cTF17 compartment was condensed [5.36 (0.79-213.8) vs 8.37 (0.22-29.2)cells/μL, respectively]. Clinical and laboratory markers of the disease were then assessed, resulting in a strong positive correlation of the SLEDAI score with the percentage of cTF2 and cTFR (r = 0.643 and 0.706, respectively) and of C3 levels with cTF percentage (r = 0.663) and cTF-ICOS (+) number (r = 0.719) while the correlation was negative between C4 levels with the percentage of cTF1 (r = −0.577) and cTF2 (r = −582) and between ANA antibody levels and cTF-ICOS (+) cells (r = −657). The analysis did not show any association between the anti-dsDNA antibody levels and the understudied subpopulations. Conclusion cTF cells tend towards 1 and 2 rather than the 17 phenotype in LN. From the various subsets, cTF2 appear to serve as a possible monitoring marker. Certainly, the complexity of the disease imposes further investigation.

Identification and Functional Analysis of a de novo IKZF3 Mutation in a Pediatric Patient with Combined Immunodeficiency.

AIOLOS, a vital member of the IKAROS protein family, plays a significant role in lymphocyte development and function through DNA binding and protein-protein interactions. Mutations in the IKZF3 gene, which encodes AIOLOS, lead to a rare combined immunodeficiency often linked with infections and malignancy. In this study, we evaluated a 1-year-4-month-old female patient presenting with recurrent infections, diarrhea, and failure to thrive. Laboratory investigations revealed decreased T lymphocyte and immunoglobulin levels. Through whole-exome and Sanger sequencing, we discovered a de novo mutation in IKZF3 (NM_012481; exon 5 c.571G > C, p.Gly191Arg), corresponding to the third DNA-binding zinc finger region of the encoded protein AIOLOS. Notably, the patient with the AIOLOS G191R mutation showed reduced recent thymic emigrants in naïve CD4+T cells compared to healthy counterparts of the same age, while maintaining normal levels of Th1, Th2, Th17, Treg, and Tfh cells. This mutation also resulted in decreased switched memory B cells and lower CD23 and IgM expression. In vitro studies revealed that AIOLOS G191R does not impact the expression of AIOLOS but compromises its stability, DNA binding and pericentromeric targeting. Furthermore, AIOLOS G191R demonstrated a dominant-negative effect over the wild-type protein. This case represents the first reported instance of a mutation in the third DNA-binding zinc finger region of AIOLOS highlighting its pivotal role in immune cell functionality.

Using in silico models to predict lymphocyte activation and development in a data rich era

It has become a routine to get insights into the multi-scale nature of immune response in health and disease through ‘omics datasets. This presents us with a unique opportunity to leverage our access to such data to develop computational models that can generate usable predictions and mechanistic insights capable of seeding new ideas. However, this is a particularly challenging task due to the difficulty in integrating data and processes across multiple scales. In this review we discuss some of the challenges associated with this task and also the recent advances and opportunities that will help to makes these tractable, using the innate lymphocyte, the natural killer cell as an exemplar.

BAP31 Plays an Essential Role in Mouse B Cell Development via Regulation of BCR Signaling.

B cell receptor-associated protein 31 (BAP31) is a transmembrane protein that is widely expressed and primarily located in the endoplasmic reticulum (ER). B cells play a crucial role in the immune system, and BAP31 significantly contributes to the functions of various immune cells. However, the specific role of BAP31 in B lymphocytes development remains unknown. In this study, we utilized a mouse model with BAP31 deleted from B cells to investigate its effects. Our findings reveal a block in early B cell development in the bone marrow and a significant decrease in the number of B cells in peripheral lymphoid organs taken from BAP31 B cell conditional knockout (BAP31-BCKO) mice. B cell receptor (BCR) signaling is crucial for the normal development and differentiation of B lymphocytes. BAP31, an endoplasmic reticulum membrane protein, directly regulates the BCR signaling pathway and was shown to be significantly positively correlated with B cell activation and proliferation. These findings establish BAP31 as a crucial regulator of early B cell development.

Dynamic Changes in Lymphocyte Populations Establish Zebrafish as a Thymic Involution Model.

The thymus is the site of T lymphocyte development and T cell education to recognize foreign, but not self, Ags. B cells also reside and develop in the thymus, although their functions are less clear. During "thymic involution," a process of lymphoid atrophy and adipose replacement linked to sexual maturation, thymocytes decline. However, thymic B cells decrease far less than T cells, such that B cells comprise ∼1% of human neonatal thymocytes but up to ∼10% in adults. All jawed vertebrates possess a thymus, and we and others have shown zebrafish (Danio rerio) also have thymic B cells. In this article, we investigated the precise identities of zebrafish thymic T and B cells and how they change with involution. We assessed the timing and specific details of zebrafish thymic involution using multiple lymphocyte-specific, fluorophore-labeled transgenic lines, quantifying the changes in thymic T- and B-lymphocytes pre- versus postinvolution. Our results prove that, as in humans, zebrafish thymic B cells increase relative to T cells postinvolution. We also performed RNA sequencing on D. rerio thymic and marrow lymphocytes of four novel double-transgenic lines, identifying distinct populations of immature T and B cells. Collectively, this is, to our knowledge, the first comprehensive analysis of zebrafish thymic involution, demonstrating its similarity to human involution and establishing the highly genetically manipulatable zebrafish model as a template for involution studies.

Simultaneous deletion of ORMDL1 and ORMDL3 proteins disrupts immune cell homeostasis.

ORMDL3 is a prominent member of a family of highly conserved endoplasmic reticulum resident proteins, ORMs (ORM1 and ORM2) in yeast, dORMDL in Drosophila and ORMDLs (ORMDL1, ORMDL2, and ORMDL3) in mammals. ORMDL3 mediates feedback inhibition of de novo sphingolipid synthesis. Expression levels of ORMDL3 are associated with the development of inflammatory and autoimmune diseases including asthma, systemic lupus erythematosus, type 1 diabetes mellitus and others. It has been shown that simultaneous deletions of other ORMDL family members could potentiate ORMDL3-induced phenotypes. To understand the complex function of ORMDL proteins in immunity in vivo, we analyzed mice with single or double deletions of Ormdl genes. In contrast to other single and double knockouts, simultaneous deletion of ORMDL1 and ORMDL3 proteins disrupted blood homeostasis and reduced immune cell content in peripheral blood and spleens of mice. The reduced number of splenocytes was not caused by aberrant immune cell homing. A competitive bone marrow transplantation assay showed that the development of Ormdl1-/-/Ormdl3-/- B cells was dependent on lymphocyte intrinsic factors. Highly increased sphingolipid production was observed in the spleens and bone marrow of Ormdl1-/-/Ormdl3-/- mice. Slight, yet significant, increase in some sphingolipid species was also observed in the spleens of Ormdl3-/- mice and in the bone marrow of both, Ormdl1-/- and Ormdl3-/- single knockout mice. Taken together, our results demonstrate that the physiological expression of ORMDL proteins is critical for the proper development and circulation of lymphocytes. We also show cell-type specific roles of individual ORMDL family members in the production of different sphingolipid species.