Biology subjects

Johnson, A. J.

Publications and source records attributed to Johnson, A. J..

At least 19 recordsLinked to original sources

bioRxiv2026

Invasion history reconstruction and potential distribution of the ambrosia beetles Euwallacea fornicatus and E. perbrevis (Coleoptera: Scolytinae), two global emerging pests

The global spread of invasive insects poses serious ecological and economic threats to forest ecosystems. Euwallacea fornicatus and E. perbrevis are cryptic ambrosia beetles native to Southeast Asia that have invaded multiple regions worldwide, damaging diverse woody hosts through gallery formation and fungal symbiont inoculation. We compiled confirmed and novel occurrence records to describe their global distributions, reconstruct invasion histories and likely origins using mitochondrial COI phylogenies, and compare their potential distributions through models based on bioclimatic variables. Euwallacea fornicatus has expanded rapidly over the past decades, establishing in North America (2003), Israel (2009), South Africa (2016), South America (2020), Australia (2021), Europe (2022) and Turkey (2024). In contrast, E. perbrevis has an earlier but slower invasion history, with establishments in Hawaii (1918), Central America (1979), Oceania (1982), and North America (2004). Phylogenetic analyses revealed at least six independent introductions for each species. Euwallacea fornicatus primarily originated from native populations in China, Taiwan and Vietnam, whereas E. perbrevis from Indonesia and Thailand, with additional introductions from unknown sources. Secondary spread from invaded regions is also likely. Distribution models indicated distinct climatic niches. Euwallacea fornicatus tolerates broader thermal ranges and drier conditions, enabling establishment from subtropical to temperate regions, whereas E. perbrevis appears restricted to tropical climates. Only 32% of predicted suitable habitat overlapped, indicating low coexistence potential. The broader climatic tolerance and faster recent spread of E. fornicatus highlights a higher invasion risk and greater management challenges. These findings provide key insights to strengthen biosecurity strategies aimed at preventing further spread. Key messageO_LIWe updated the global distribution and likely invasion routes of two cryptic ambrosia beetles. C_LIO_LIWe identified multiple independent and secondary introductions worldwide. C_LIO_LIWe revealed distinct climatic niches and limited habitat overlap. C_LIO_LIWe showed higher invasion risk for E. fornicatus due to broader climatic tolerance. C_LIO_LIWe identified high-risk regions for surveillance based on climate suitability. C_LI

ecology↗

bioRxiv2026

TMEM119+ microglia MHC class I restricted antigen presentation impacts CD8 T cell memory, effector status, and blood-brain barrier disruption during neurotropic virus infection

The impact of microglia antigen presentation on CNS infiltrating CD8 T cells responses during neurotropic virus infection has been difficult to define. Using Theilers murine encephalomyelitis virus (TMEV) infection of neurons as a model system, our laboratory has previously determined that H-2Db restricted, but not H-2Kb restricted CD8 T cells are required for viral clearance, demonstrating the role of discrete MHC class I alleles. To determine the extent microglia antigen presentation impacts brain-infiltrating CD8 T cells, our laboratory generated novel single MHC class I conditional knockout mice in which H-2Kb or H-2Db can be specifically deactivated in TMEM119+ microglia with tamoxifen administration. During TMEV infection, conditional knockout of H-2Kb in microglia reduced antigen-specific CD8 T cell proliferation in the brain. Meanwhile, mice with deletion of Db in microglia had reduced levels of perforin in antigen-specific CD8 T cells. Furthermore, microglia specific deletion of H-2Db reduced CD8 T cell numbers in the brain and preserved blood-brain barrier (BBB) integrity. Microglial Db restricted antigen presentation was also essential for the reactivation of CD8 tissue resident memory (TRM) cells and BBB integrity during memory recall responses. These findings further our understanding of how brain infiltrating antiviral CD8 T cell responses are impacted by microglia, as well as define how this cellular interaction contributes to BBB disruption during neuroinflammation. These findings also have high significance to our understanding of how microglia impact CD8 TRM cell populations that reside in the brain long after virus infection is cleared. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=111 SRC="FIGDIR/small/722741v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@1f53d89org.highwire.dtl.DTLVardef@19af9a8org.highwire.dtl.DTLVardef@17cb8b5org.highwire.dtl.DTLVardef@1428440_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2026

Coincident epithelial signals restrain commensal-specific CD8αβ+ T cells in the intestine

The intestinal epithelium harbors a large population of microbiota-dependent CD8{beta}+ T cells whose antigen specificity and regulation are ill-defined. By identifying MHCIa-restricted TCRs and generating tetramers against the gut commensal Segmented Filamentous Bacteria, we demonstrate that a single commensal species drives a clonally expanded, antigen-specific CD8{beta}+ T cell within the intraepithelial lymphocyte compartment. Mechanistically, the intestinal epithelium coordinates coincident signals governing this population: peptide:MHC-dependent TCR engagement drives pIEL accumulation, while v{beta}6-mediated TGF{beta} activation restraints effector cell differentiation. Perturbation of epithelial cell-mediated TGF{beta} activation diverts commensal-specific CD8+ T cells toward inflammatory differentiation states transcriptionally convergent with those observed in ulcerative colitis. The intestinal epithelium thus functions as a dual-signal organizer of commensal-specific CD8+ T cell responses, coupling differentiation to restraint through spatially coincident molecular cues.

immunology↗

bioRxiv2025

Antigen-specific CD8 T cells are generated and reactivated in the bone marrow following viral brain infections and impact the bone marrow niche

Bone marrow is the primary immune organ responsible for stem cell maintenance and hematopoiesis. However, the contribution of the bone marrow niche for the generation of adaptive immune responses is less well-understood. We therefore assessed the capacity of virus antigen-specific CD8 T cells to be generated and expanded in bone marrow following acute neurotropic virus infection. Intracranial infection with the neurotropic Theilers Murine Encephalomyelitis Virus (TMEV) results in an acute infection in the C57BL/6 mouse which is cleared within 4 weeks post infection due to the generation of an antigen-specific CD8 T cell response against the immunodominant epitope VP2121-130. We determined that 1-10% of CD8 T cells present in the femoral, and sternal bone marrow were virus antigen-specific 5-7 days after intracranial TMEV infection. We determined that antigen-specific CD8 T cells were generated in the bone marrow with similar kinetics to that of conventional responses in the secondary lymphoid organs. Importantly, continuous treatment with FTY720, which sequesters T cells outside of the blood, did not eliminate antigen-specific CD8 T cells in the bone marrow compartment indicating generation within the bone marrow niche. Similarly, injection of Poly I:C admixed with fluorescently labeled ovalbumin into the brain generated a similar antigen-specific CD8 T cell response in the bone marrow indicating these responses occur following various brain insults. This model also identified the likely antigen presenting cell (APC) responsible for scavenging antigens from the brain and trafficking into the bone marrow as a migratory myeloid-derived APC. Moreover, following clearance of TMEV infection, CD8 T cells in the bone marrow established durable memory. Antigen-specific memory CD8 T cells in the bone marrow reactivated and expanded upon cognate antigen reencounter. Antigen-specific reactivation of memory CD8 T cells within the bone marrow caused a concurrent increase in Lineage-, Sca-1+, c-Kit+ (LSK) and CD11b+ MHCII+ myeloid cells. This increase in the LSKs and myeloid cells in the bone marrow niche was abrogated with CD8 T cell depletion. We conclude that brain viral infections induce in situ effector and memory T cell responses within the bone marrow compartment. Memory recall CD8 T cell responses induce niche dysregulation by expanding LSK cells and lead to an influx of MHCII+ myeloid cells. Our data pave the way for crucial studies of bone marrow resident antigen-specific CD8 T cells in health and diseases.

immunology↗

bioRxiv2025

Fate of a fallen ant: Time-resolved micro-CT analysis of ant digestion in Nepenthes pitchers

Carnivorous pitcher plants of the genus Nepenthes have evolved highly specialized leaf-derived traps that capture and enzymatically digest insect prey to supplement nutrient acquisition in nutrient-deficient habitats. This study aimed to elucidate the structural dynamics underlying prey digestion in Nepenthes khasiana using high-resolution micro-computed tomography (micro-CT) integrated with biochemical characterization of the pitcher fluid. Three-dimensional morphometric analysis of the invasive yellow crazy ant, Anoplolepis gracilipes, experimentally incubated in N. khasiana pitcher fluid, was conducted to assess time-dependent structural degradation. Quantitative micro-CT parameters, including volume, surface area, and surface-to-volume ratio, were analyzed to visualize and quantify time-dependent structural degradation and three-dimensional morphological changes in the prey during digestion. A triphasic digestion sequence was identified - comprising rapid soft-tissue hydrolysis, progressive exoskeletal fragmentation, and stabilization of chitinous remnants. The acidic, enzymatic fluid (pH 2.5-4.0) promoted uniform degradation through synergistic enzymatic, oxidative, and acidification processes, while dissolved CO2 enhanced acid stability and catalytic efficiency. The integration of micro-CT morphometrics and biochemical insights reveals a coordinated digestion mechanism in N. khasiana, optimized for efficient prey breakdown and nutrient assimilation. ONE-SENTENCE SUMMARYMicro-CT analysis revealed a triphasic digestion process in Nepenthes khasiana, elucidating the structural and enzymatic dynamics of efficient prey degradation.

ecology↗

bioRxiv2025

How rat flooding occurs during mast seeding of Melocanna baccifera?

Gregarious flowering and mast seeding of bamboos have been linked to rat population outbreaks across multiple geographic regions. This study explores the reproductive mechanism driving the surge in rat population triggered by the fruiting of the bamboo species, Melocanna baccifera. We examined four key reproductive parameters, viz., mounting frequency, serum nitric oxide (NO), follicle stimulating hormone (FSH), luteinizing hormone (LH), in mice and rats under M. baccifera fruit- or its amino acid (AA)-fed conditions. The mounting frequency of M. baccifera fruit liquid administered male mice was 5.50 {+/-} 1.73, compared to 2.00 {+/-} 0.82 of control animals. NO level in M. baccifera fruit liquid-fed mice displayed an increase of 131.83%. The pregnancy and pups number in Muli fruit-fed female animals enhanced by 66.66% and 131.25%, respectively. The average pups production in Muli fruit-, dAA (d-Thr-Ser-Glu-Phe-His-Ala)-fed and control female rats were 7.40 {+/-} 0.83, 8.80 {+/-} 0.75, and 5.34 {+/-} 0.52 (pups/animal), respectively. M. baccifera fruit and dAA combination (dSer-dThr-dGlu) showed increments in FSH and LH levels upto (65%, 58.59%), and (286.41%, 99.24%), respectively. Synthesis. The increased mounting frequency, along with elevated levels of serum NO, FSH, and LH, in animals consuming M. baccifera fruits or the AA mix, strongly indicates enhanced reproductive activity. This is the first study providing a mechanistic insight into the rapid rat population boom associated with the cyclical flowering and fruiting of M. baccifera. Our findings suggest that the amino acids present in M. baccifera fruits may have potential applications in the treatment of infertility.

ecology↗

bioRxiv2024

Sugar-rich foods exacerbate antibiotic-induced microbiome injury

Intestinal microbiota composition is implicated in several diseases; understanding the factors that influence it are key to elucidating host-commensal interactions and to designing microbiome-targeted therapies. We quantified how diet influences microbiome dynamics in hospitalized patients. We recorded 9,419 meals consumed by 173 patients undergoing hematopoietic cell transplantation and profiled the microbiome in 1,009 longitudinally collected stool samples from 158 of them. Caloric intake was correlated with fecal microbiota diversity. Bayesian inference revealed associations between intake of sweets or sugars during antibiotic exposure with microbiome disruption, as assessed by low diversity or expansion of the pathobiont Enterococcus. We validated this observation experimentally, finding that sucrose exacerbated antibiotic-induced Enterococcus expansion in mice. Taken together, our results suggest that avoiding sugar-rich foods during antibiotic treatment may reduce microbiome injury. One Sentence SummaryAnalyses of hematopoietic cell transplant patients and of mice uncover links between foods and microbiome disruption.

microbiology↗

bioRxiv2024

Progress in Developing a Bark Beetle Identification Tool

This study presents an initial model for bark beetle identification, serving as a foundational step toward developing a fully functional and practical identification tool. Bark beetles are known for extensive damage to forests globally, as well as for uniform and homoplastic morphology which poses identification challenges. Utilizing a MaxViT-based deep learning backbone which utilizes blocked local and dilated global attention to classify bark beetles down to the genus level from images containing multiple beetles. The methodology involves a comprehensive process of image collection, preparation, and model training, leveraging pre-classified beetle species to ensure accuracy and reliability. The models F1 score estimates of 0.99 and 1.0 indicates a strong ability to accurately classify genera in the collected data, including those previously unknown to the model. This makes it a valuable first step towards building a tool for applications in forest management and ecological research. While the current model distinguishes among 12 genera, further refinement and additional data will be necessary to achieve reliable species-level identification, which is particularly important for detecting new invasive species. Despite the controlled conditions of image collection and potential challenges in real-world application, this study provides the first model capable of identifying the bark beetle genera, and by far the largest training set of images for any comparable insect group. We also designed a function that reports if a species appears to be unknown. Further research is suggested to enhance the models generalization capabilities and scalability, emphasizing the integration of advanced machine learning techniques for improved species classification and the detection of invasive or undescribed species.

ecology↗

bioRxiv2023

Rationally designed modular STAT-activating scaffolds enforce cell-intrinsic transcriptional programs augmenting the anti-tumor potency of CAR T cells

Chimeric antigen receptor (CAR)-expressing T cells can mediate anti-tumor responses in a variety of preclinical models and clinical settings, however, strategies to enhance anti-tumor potency is the subject of intense investigation. Signals emanating from gamma-c cytokine receptors modulate the transcriptional state of activated T cells impacting proliferation, survival, differentiation, and effector functioning through the STAT family of transcription factors. Design of ligand-independent cell-intrinsic cytokine STAT activation scaffolds is a conceptually attractive strategy to provide CAR T cells with a surrogate for exogenous cytokine support. Here, we designed a series of ligand-autonomous STAT inducer (LASI) scaffolds comprised of an extracellular identification tag, a homodimerizing transmembrane domain, and a membrane proximal IL7R Box1 domain followed by STAT5 and/or STAT3 docking sequences derived from IL7R and IL21R, respectively. We constructed LASI scaffolds having STAT5 (LASI-5), STAT3 (LASI-3), and combined STAT5 and STAT3 (LASI-5+3) docking domains and then interrogated their impact in primary human CD8+ anti-CD19 (4-1BB:zeta) CAR T cells. While LASI-5 expression had limited effects on CAR T cells, LASI-3 transcriptional programming was found to be indispensable to achieving anti-tumor functional enhancement associated with limited terminal differentiation, heightened T cell proliferation in response to antigen, and dampened expression of exhaustion-associated genes. Moreover, CAR T cells supplemented with LASI-3 or 5+3 displayed superior potency against human leukemia tumors in NSG mice. LASI-5+3 mediated the highest magnitude of CAR T cell engraftment in vivo that evolved into a fatal lymphoproliferative syndrome. However, the same efficacy enhancement was achieved with LASI-3 without the lymphoproliferative complication. Our findings provide a rationale for utilization of constitutively expressed LASI-3 to enhance the anti-tumor potency of CAR T cells, the need to regulate the activity of LASI-5+3, and a generalizable scaffold design for studying additional combinations of STAT family transcription factors.

bioengineering↗

bioRxiv2023

Bait, not reward: CO2-enriched Nepenthes pitchers secrete toxic nectar

Nepenthes pitchers are leaf-evolved biological traps holding high levels of CO2 within them. Extrafloral nectar (EFN) secreted by these pitchers has long been regarded as the major reward to visiting arthropods, but its chemical constituents and their role in prey capture are least explored. Here we demonstrate Nepenthes EFN as a sugar (glucose-fructose-sucrose) mix with high C:N ratio, minimal amino acids, proteins, and vitamin C. Nepenthes khasiana peristome and lid EFNs displayed strong acetylcholinesterase (AChE) inhibition; the naphthoquinone derivative, (+)-isoshinanolone, has been identified as the AChE inhibitor. Plumbagin, the major volatile naphthoquinone in Nepenthes, also showed strong AChE inhibition. Direct EFN- and (+)-isoshinanolone-feeding bioassays demonstrated symptoms of cholinergic toxicity in ants. We testify that Nepenthes EFN is a toxic bait which hinders neuronal activity in visiting arthropods. These unique traps adopt various deceptive strategies for prey capture, and our discovery abolishes the notion that Nepenthes EFN is a reward to visiting ants and other arthropods. Moreover, our findings infer elevated CO2 within their pitchers as the key factor influencing the growth, metabolism, herbivory, and carnivory in Nepenthes. HighlightNepenthes extrafloral nectar has high content of carbohydrates and minimal nitrogenous metabolites. It is laced with (+)-isoshinanolone, an acetylcholinesterase inhibitor, and acts as a toxic bait, aiding prey capture.

plant biology↗

bioRxiv2023

Nepenthes pitchers versus thermogenic flowers: thermal patterns and their role in prey capture and pollination

Prey capture in Nepenthes and pollination in angiosperms are two antithetical events; one designed to trap insects and other arthropods (carnivory) and the other to transfer pollen through pollinators (reproduction). In this study infrared thermography is extensively used to obtain thermal profiles of Nepenthes pitchers and thermogenic flowers in field conditions. N. khasiana pitchers displayed below ambient temperatures during evening-night-morning hours (5 pm to 8-9-10 am); pitcher spots recorded lowest and highest temperatures as 14.4 (6-7 am) and 45.6{degrees}C (2 pm), respectively. In the evening-night-morning hours top pitcher spots displayed significant decrease (upto 6.7{degrees}C) from the ambient temperature. The average humidities in the night and day periods were 77.15% and 50.15%, respectively. Thermographic tracking of the pitcher (lid) opening in N. khasiana demonstrated initial wet pitcher in night, which gradually switched to a relatively dry surface in the morning-day times; but the peristome region retained the wetness till 10.30 a.m. The prey capturing zones in Nepenthes pitchers (peristome, lid and their intersection) are colder favoring prey capture, whereas in thermogenic flowers, floral portions are hotter, providing the thermal requirements for the pollinator. In thermogenic plants, floral zones assist pollination by offering a thermal reward through enzymatic processes; but Nepenthes traps achieve lower temperature spots by physical (surface microstructures), chemical (extrafloral nectar) and ecological (rain, humidity) factors.

plant biology↗

bioRxiv2023

Microglial P2Y6 calcium signaling promotes phagocytosis and shapes neuroimmune responses in epileptogenesis

Microglial calcium signaling is rare in a baseline state but shows strong engagement during early epilepsy development. The mechanism and purpose behind microglial calcium signaling is not known. By developing an in vivo UDP fluorescent sensor, GRABUDP1.0, we discovered that UDP release is a conserved response to seizures and excitotoxicity across brain regions. UDP signals to the microglial P2Y6 receptor for broad increases in calcium signaling during epileptogenesis. UDP-P2Y6 signaling is necessary for lysosome upregulation across limbic brain regions and enhances production of pro-inflammatory cytokines--TNF and IL-1{beta}. Failures in lysosome upregulation, observed in P2Y6 KO mice, can also be phenocopied by attenuating microglial calcium signaling in Calcium Extruder ("CalEx") mice. In the hippocampus, only microglia with P2Y6 expression can perform full neuronal engulfment, which substantially reduces CA3 neuron survival and impairs cognition. Our results demonstrate that calcium activity, driven by UDP-P2Y6 signaling, is a signature of phagocytic and pro-inflammatory function in microglia during epileptogenesis.

neuroscience↗

bioRxiv2023

TREM2 mediates MHCII-associated CD4+ T cell response against gliomas

Triggering receptor expressed on myeloid cells 2 (TREM2) was recently highlighted as a novel immune suppressive marker in peripheral tumors. The aim of this study was to characterize TREM2 expression in gliomas and investigate its contribution in glioma progression by using Trem2-/-mouse line. Our results showed that higher TREM2 expression was correlated with poor prognosis in glioma patients. Unexpectedly, TREM2 deficiency did not have a beneficial effect in a pre-clinical model of glioma. The increased TREM2 expression in glioma was likely due to increased myeloid cell infiltration, as evidenced by our single-cell analysis showing that almost all microglia and macrophages in gliomas were TREM2+. Furthermore, we found that deficiency of TREM2 impaired tumor-myeloid phagocytosis and MHCII presentation, and significantly reduced CD4+ T cells in tumor hemispheres. Our results revealed a previously unrecognized protective role of tumor-myeloid TREM2 in promoting MHCII-associated CD4+ T cell response against gliomas. SUMMARYAuthors found that although higher TREM2 expression is correlated with poor prognosis in glioma patients, its absence has no beneficial effect in a pre-clinical model of glioma. Deficiency of TREM2 impairs myeloid cell phagocytosis of tumor debris, leading to a reduction in MHCII-dependent CD4+ anti-glioma immunity.

neuroscience↗

bioRxiv2022

Antigen presentation by discrete class I molecules on brain endothelium dynamically regulates T-cell mediated neuropathology in experimental cerebral malaria

CD8 T cell engagement of brain vasculature is a putative mechanism of neuropathology in human cerebral malaria. To define contributions of brain endothelial cell MHC class I antigen-presentation to CD8 T cells in establishing this pathology, we developed novel H-2Kb LoxP and H-2Db LoxP mice crossed with Cdh5-Cre mice to achieve targeted deletion of discrete class I molecules on brain endothelium. Using the Plasmodium berghei ANKA model of experimental cerebral malaria (ECM), we observe that H-2Kb and H-2Db regulate distinct patterns of disease onset, CD8 T cell infiltration, targeted cell death, and regional blood-brain barrier (BBB) disruption. Strikingly, ablation of H-2Kb or H-2Db from brain endothelial cells resulted in reduced CD8 T cell activation, attenuated T cell interaction with brain vasculature, lessened targeted cell death, preserved BBB integrity, and prevented ECM and the death of the animal. These data demonstrate that interactions of CD8 T cells with discrete MHC class I molecules on brain endothelium regulate development of ECM neuropathology. Therefore, targeting MHC class I interactions therapeutically may hold potential for treatment of cases of severe malaria.

neuroscience↗

bioRxiv2022

Mutant huntingtin exon-1 impaired GTPCH and DHFR expression in plants and mice

Pathophysiology associated with Huntingtons disease (HD) has been studied extensively in various cell and animal models since the 1993 discovery of the mutant huntingtin (mHtt) with abnormally expanded polyglutamine (polyQ) tracts as the causative factor. However, the sequence of early pathophysiological events leading to HD still remains elusive. To gain new insights into the polyQ-induced early pathogenic events, we expressed Htt exon1 (Httex1) with a normal (21), or an extended (42 or 63) number of polyQ in tobacco plants, which lack an Htt ortholog to avoid any associated effects from endogenous Htt. Here, we show that transgenic plants accumulated Httex1 proteins with corresponding polyQ tracts, and that mHttex1 induced protein aggregation and affected plant growth, especially root and root hair development, in a polyQ length-dependent manner. Quantitative proteomic analysis of young roots from severely affected Httex1Q63 and unaffected Httex1Q21 plants showed that the most impaired protein by polyQ63 is a GTP cyclohydrolase I (GTPCH) along with many its related one-carbon (C1) metabolic pathway enzymes. GTPCH is a key enzyme involved in folate biosynthesis in plants and tetrahydrobiopterin (BH4) biosynthesis in mammals. Validating studies in 4-week-old R6/2 HD mice expressing a mHttex1 showed reduced levels of GTPCH and dihydrofolate reductase (DHFR, a key folate utilization/alternate BH4 biosynthesis enzyme), and impaired C1 and BH4 metabolisms. Our findings from mHttex1 plants and mice reveal impaired expressions of GTPCH and DHFR and contribute to a better understanding of mHtt-altered C1 metabolism and C1 interconnected BH4 metabolism leading to the pathogenesis of HD.

molecular biology↗

bioRxiv2022

Brain resident memory T cells rapidly expand and initiate neuroinflammatory responses following CNS injury and viral infection

The contribution of circulating verses tissue resident memory T cells (TRM) to clinical neuropathology is an enduring question due to a lack of mechanistic insights. The prevailing view is TRM cells are protective against pathogens in the brain. However, the extent antigen-specific TRM cells can induce neuropathology upon reactivation has not been determined. Using the described phenotype of TRMs, we found that brains of naive mice harbor populations of CD69+ CD103- T cells. Notably, numbers of CD69+ CD103- TRM cells rapidly increase following neurological insults of physical, cancerous, or viral origins. This TRM expansion precedes infiltration of virus specific CD8 T cells and is due to proliferation of T cells within the brain. In contrast, the CD69+ CD103+ TRMs in the brain are generated after the initial expansion of CD69+ CD103- cells following injury and are antigen-specific. We next evaluated the capacity of antigen-specific TRMs in the brain to induce significant neuroinflammation post virus clearance, including infiltration of inflammatory monocytes, activation of T cells in the brain, and significant blood brain barrier disruption. These neuroinflammatory events were induced by TRMs, as depletion of peripheral T cells or blocking T cell trafficking using FTY720 did not change the neuroinflammatory course. Reactivation of antigen-specific TRMs in the brain also induced profound lymphopenia within the blood compartment. We have therefore determined that antigen-specific TRMs can induce significant neuroinflammation, neuropathology, and peripheral immune suppression. Importantly, understanding functions of brain TRMs is crucial in investigating their role in neurodegenerative disorders, CNS cancers, and long-term complications associated with viral infections including COVID-19. Graphical AbstractHealthy brain harbors populations of resident memory T cells (TRM). These TRM cells rapidly proliferate in response to CNS insults of various origins. Following clearance of the insult, populations of TRM cells in the brain decline, but an antigen-specific TRM subset remains within the brain. Antigen-specific reactivation of brain TRMs mediates neuroinflammatory sequalae involving activation and blasting of resident T cells, infiltration of inflammatory monocytes and blood brain barrier disruption. Severe neuroinflammation within the brain following antigen-specific TRM reactivation is concurrent with profound lymphopenia within the blood compartment. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=132 SRC="FIGDIR/small/487707v1_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@a22867org.highwire.dtl.DTLVardef@a90e0org.highwire.dtl.DTLVardef@1ad904eorg.highwire.dtl.DTLVardef@1dd281c_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2021

Microglia and perivascular macrophages act as antigen presenting cells to promote CD8 T cell infiltration of the brain

CD8 T cell infiltration of the central nervous system (CNS) is necessary for host protection but contributes to neuropathology. Antigen presenting cells (APCs) situated at CNS borders are thought to mediate T cell entry into the parenchyma during neuroinflammation. The identity of the CNS-resident APC that presents antigen via major histocompatibility complex (MHC) class I to CD8 T cells is unknown. Herein, we characterize MHC class I expression in the naive and virally infected brain and identify microglia and macrophages (CNS-myeloid cells) as APCs that upregulate H-2Kb and H-2Db upon infection. Conditional ablation of H-2Kb and H-2Db from CNS-myeloid cells allowed us to determine that antigen presentation via H-2Db, but not H-2Kb, was required for CNS immune infiltration during Theilers murine encephalomyelitis virus (TMEV) infection and drives brain atrophy as a consequence of infection. These results demonstrate that CNS-myeloid cells are key APCs mediating CD8 T cell brain infiltration.

immunology↗

bioRxiv2020

Severe and multifaceted systemic immunosuppression caused by experimental cancers of the central nervous system requires release of non-steroid soluble mediators

Immunosuppression of unknown etiology is a hallmark feature of glioblastoma (GBM) and is characterized by decreased CD4 T cell counts and down regulation of MHC class II expression on peripheral blood monocytes in patients. This immunosuppression is a critical barrier to the successful development of immunotherapies for GBM. We recapitulated the immunosuppression observed in GBM patients in the C57BL/6 mouse and investigated the etiology of low CD4 T cell counts. We determined that thymic involution was a hallmark feature of immunosuppression in three distinct models of CNS cancer, including mice harboring GL261 glioma, B16 melanoma, and in a spontaneous model of Diffuse Intrinsic Pontine Glioma (DIPG). In addition to thymic involution, we determined that tumor growth in the brain induced significant splenic involution, reductions in peripheral T cells, reduced MHC class II expression on hematopoietic cells, and a modest increase in bone marrow resident CD4 T cells with a naive phenotype. Using parabiosis we report that thymic involution, declines in peripheral T cell counts, and reduced MHC class II expression levels were mediated through circulating blood-derived factors. Conversely, T cell sequestration in the bone marrow was not governed through circulating factors. Serum isolated from glioma-bearing mice potently inhibited proliferation and functions of T cells both in vitro and in vivo. Interestingly, the factor responsible for immunosuppression in serum is nonsteroidal and of high molecular weight. Through further analysis of neurological disease models, we determined that the aforementioned immunosuppression was not unique to cancer itself, but rather occurs in response to CNS injury. Noncancerous acute neurological insults also induced significant thymic involution and rendered serum immunosuppressive. Both thymic involution and serum-derived immunosuppression were reversible upon clearance of brain insults. These findings demonstrate that CNS cancers cause multifaceted immunosuppression and pinpoint circulating factors as a target of intervention to restore immunity. Short SummaryCNS cancers and other brain-injuries suppress immunity through release of non-steroid soluble factors that disrupt immune homeostasis and dampen responses of the peripheral immune system. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=139 SRC="FIGDIR/small/006825v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@14e90c2org.highwire.dtl.DTLVardef@101de5corg.highwire.dtl.DTLVardef@1ad8534org.highwire.dtl.DTLVardef@1041fef_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract C_FIG

immunology↗