Intravascular staining for discrimination of vascular and tissue leukocytes

Activation and maturation of antigen-specific B cells in nonectopic lung infiltrates are independent of germinal center reactions in the draining lymph node

Pulmonary T and B cells are important for protection of this mucosal barrier site. While viral infections lead to the development of ectopic lymphoid structures highly similar to those in germinal centers in secondary lymphoid organs, little is known about how T/B cooperation occurs in the unstructured, diffuse tissue infiltrates characteristic of autoimmune diseases and nonviral infections. Using a mouse model of interstitial lung inflammation, we found that naive B cells are directly activated in lung tissue. Despite the absence of any germinal center-like structures, the interaction of B cells with peripheral T helper cells results in efficient somatic hypermutation and class switching. As antigen-presenting cells, macrophages are critical for this process. Unique B-cell repertoires indicated that the lung response was autonomous from the lung-draining lymph node. Only lung GC-like B cells were switched to IgA and had a broader repertoire, making them ideal candidates for producing broadly neutralizing immunoglobulins against respiratory pathogens.

NLRP3 activation induces BBB disruption and neutrophil infiltration via CXCR2 signaling in the mouse brain

NLRP3 is an intracellular sensor molecule that affects neutrophil functionality and infiltration in brain disorders such as experimental autoimmune encephalomyelitis (EAE). However, the detailed molecular mechanisms underlying the role of NLRP3 in these processes remain unknown. We found that NLRP3 is crucial for neutrophil infiltration, whereas dispensable for neutrophil priming. Notably, NLRP3 activation in neutrophils induced blood-brain barrier (BBB) disruption and neutrophil infiltration into the brain via CXCL1/2 secretion and subsequent activation of the CXCL1/2-CXCR2 signaling axis. Moreover, CXCL1 and CXCL2 in the inflamed brain directly reduced Claudin-5 expression, which regulates BBB permeability in brain endothelial cells. Furthermore, neutrophil-specific NLRP3 activation aggravated EAE pathogenesis by promoting CXCR2-mediated infiltration of both neutrophils and CD4+ T cells into the central nervous system at disease onset. Thus, the CXCL1/2-CXCR2 axis plays a role in EAE progression. Therefore, this chemokine axis could be a potential therapeutic target for attenuating neuroinflammatory diseases through modulating of neutrophil and CD4+ T cell infiltration and BBB disruption.

Microvascular immunity is organ-specific and remodeled after kidney injury in mice

Many studies analyze tissue-resident or blood-borne leukocytes to monitor disease progression. We hypothesized that the microvasculature serves as a distinct site for immune cell activity. Here, we investigate microvascular leukocyte phenotypes before, during and after acute kidney injury (AKI) in mice, uncovering unique characteristics in the kidney, liver, and lung. Using single-cell sequencing, we identify several immune cells that were up to 100-fold expanded in the kidney vasculature, including macrophages, dendritic cells (DC), and B cells. Regeneration after AKI is characterized by sustained remodeling of the renal microvascular interface. Homeostatic microvascular C1q+ macrophages withdraw from the vascular barrier which is subsequently repopulated by new subsets, including CD11c+F480+ and CD11c+F480- cells. These newly arrived macrophages exhibit enhanced phagocytic activity toward circulating bacteria and secretion of tumor necrosis factor, pointing to maladaptive repair mechanisms after AKI. These data suggest organ- and disease-specific microvascular immune dynamics which are not detectable through conventional blood and tissue analysis.

Regulation of respiratory CD8+ T-cell immunity by suppressive monocyte-like dendritic cells (MCs)

Active immune suppression can mediate the balance between protective cellular immunity and harmful immunopathology. This suppression can occur locally, at an infection site, or in regional draining lymph nodes (dLNs). Immune regulation is of particular importance in sites such as the lung where aberrant immunopathology can result in loss of tissue function and respiratory failure. We have recently identified a novel population of CD11b+CD103+CCR2+ monocyte-like dendritic cells (MCs) which directly suppress CD8+ T-cell proliferation in vitro. Respiratory infection of mice with RNA viruses recruits these MCs either exclusively to the dLN (after vesicular stomatitis virus infection) or both the dLN and site of viral replication (after influenza infection). Here we show that depletion of MCs from the dLN of mice using CCR2-DTR bone marrow chimeras results in enhanced respiratory CD8+ T-cell responses and lung tissue-resident memory cell (TRM) formation which correlated with enhanced antiviral responses upon heterologous VSV challenge. Conversely, depletion of MCs from both the dLN and respiratory tract following influenza infection results in enhanced respiratory CD8+ T-cell responses coupled with fatal immunopathology. Together, these data suggest that suppressive MCs govern key aspects of respiratory CD8+ T-cell immunity, thereby balancing immunity and adverse pathology in the context of viral infection.

Type I interferon regulation of group I ILC subsets during both homeostasis and cytomegalovirus infection

Type 1 innate lymphoid cells (ILC1s) and conventional natural killer cells belong to the group 1 ILCs (gILC1), characterized largely by T-bet expression and interferon γ secretion. While much has been done to define factors that regulate the development, differentiation, and effector functions of both cell types, little is known about what controls gILC1 homeostasis. Here, mixed bone marrow chimeras were used to define the role of type I interferon receptor (IFNAR) signaling in regulating gILC1 in the spleen and liver at homeostasis and during murine cytomegalovirus infection. We show that basal IFNAR signaling induces cell and tissue-specific phenotypic changes in gILC1, inhibiting bona-fide ILC1 markers (CD49a, CD200R, CXCR6) and regulating expression of perforin and granzymes B and C. Finally, while IFNAR signaling enhances cytokine responsiveness in vitro in both gILC1 subsets, it has a dichotomous effect on interferon γ production during murine cytomegalovirus infection, stimulating it in conventional natural killer cells and inhibiting it in ILC1.

A vasculature-resident innate lymphoid cell population in mouse lungs

Tissue-resident immune cells such as innate lymphoid cells (ILC) are known to reside in the parenchymal compartments of tissues and modulate local immune protection. Here we use intravascular cell labeling, parabiosis and multiplex 3D imaging to identify a population of group 3 ILCs in mice that are present within the intravascular space of lung blood vessels (vILC3). vILC3s are distributed broadly in alveolar capillary beds from which inhaled pathogens enter the lung parenchyma. By contrast, conventional ILC3s in tissue parenchyma are enriched in lymphoid clusters in proximity to large veins. In a mouse model of pneumonia, Pseudomonas aeruginosa infection results in rapid vILC3 expansion and production of chemokines including CCL4. Blocking CCL4 in vivo attenuates neutrophil recruitment to the lung at the early stage of infection, resulting in prolonged inflammation and delayed bacterial clearance. Our findings thus define the intravascular space as a site of ILC residence in mice, and reveal a unique immune cell population that interfaces with tissue alarmins and the circulating immune system for timely host defense.

Inflammatory conditions shape phenotypic and functional characteristics of lung-resident memory T cells in mice

Lung tissue-resident memory T cells (TRM) are critical for the local control of respiratory tract infections caused by influenza A viruses (IAV). Here we compare TRM populations induced by intranasal adenoviral vector vaccines encoding hemagglutinin and nucleoprotein (NP) with those induced by an H1N1 infection in BALB/c mice. While vaccine-induced TRM express high levels of CD103 and persist longer in the lung parenchyma, short-lived, H1N1-induced TRM have a transcriptome associated with higher cytotoxic potential and distinct transcriptional profile as shown by single-cell RNA sequencing. In both the vaccine and H1N1 groups, NP-specific CD8+ T cells expand during heterologous influenza virus infection and protect the mice from disease. Meanwhile, lung inflammation in response to an infection with unrelated respiratory syncytial virus do not influence the fate of pre-existing TRM. Our preclinical work thus confirms that inflammatory conditions in the tissue shape the phenotypic and functional characteristics of TRM to serve relevant informations for optimizing mucosal vaccines.

Proliferation makes a substantive contribution to the maintenance of airway resident memory T-cell subsets in young pigs

Tissue-resident memory (TRM) T cells play an important role in protection against respiratory infection but whether this memory is maintained by long-lived or dividing cells remains controversial. To address the rate of division of lung TRM T cells, deuterium-enriched water was administered orally to young pigs to label dividing lymphocytes. T-cell subsets were separated from blood, lymph nodes, and airways [bronchoalveolar lavage (BAL)], the latter comprising almost exclusively TRM. We show that, as in other species, circulating memory T-cell subsets divide more rapidly than naïve T cells. Rates of labelling of memory subsets were similar in blood and lymph nodes, consistent with the rapid and free exchange. Strikingly, the fraction of label in BAL was similar to those in blood/lymph nodes after 5-21 days of labelling, suggesting replacement with recently divided cells, but this was preceded at Day 2 by a phase when labelling was lower in BAL than blood/lymph node in some memory subsets. Our data exclude long-lived TRM as the source of BAL memory cells leaving three possible hypotheses: blood/airway exchange, in situ proliferation, or proliferation in the lung interstitium followed by migration to BAL. When considered in the context of other information, we favour the latter interpretation. These results indicate the dynamic nature of memory in the lung and have implications for harnessing immune responses against respiratory pathogens.

The hypervirulent Type-1/Type-17 phenotype of Cryptococcus neoformans clinical isolates is specific to A/J mice

Cryptococcus neoformans is a fungal pathogen that causes cryptococcal meningitis in immunocompromised individuals. Both host- and pathogen-specific factors are known to affect patient outcome, and recent studies showed that strain-specific differences in C. neoformans clinical isolates can influence virulence in A/J mice. However, it is unclear how the immunologic and genetic background of inbred mouse strains affects disease outcome during C. neoformans infection. In this study, we show that a hypervirulent phenotype is dependent on the host immune response and mouse genetic background. A/J mice intranasally infected with the hypervirulent isolates, UgCl247, UgCl422, and UgCl236, have increased neutrophil and T-cell recruitment when compared with infection with the reference strain KN99α. In addition, the cytokine profile of the hypervirulent isolates in A/J mice had a profound IFNγ and IL-17 response, and lung resident CD4 T-cells isolated from A/J mice expressed significantly increased Th1 (CXCR3, Tbet) and Th17 (RORγT) markers compared with KN99α infection. Intriguingly, when C57BL/6J mice were infected with these isolates, the hypervirulent phenotype was not evident, and all isolates had virulence comparable to the KN99α control. The immune response in C57BL/6J mice was also nearly identical in response to infections with the hypervirulent isolates and the KN99α control strain. Finally, we determined that the hypervirulent phenotype in A/J mice is not caused by known genetic mutations in the A/J inbred mouse background. Overall, this study demonstrates that an inbred mouse inhalation model can be used to identify host- and pathogen-specific factors that affect C. neoformans disease progression.

In vivo antibody labeling route and fluorophore dictate labeling efficiency, sensitivity, and longevity

Leukocytes migrate through the blood and extravasate into organs to surveil the host for infection or cancer. Recently, we demonstrated that intravenous (IV) anti-CD45.2 antibody labeling allowed for precise tracking of leukocyte migration. However, the narrow labeling window can make this approach challenging for tracking rare migration events. Here, we show that altering antibody administration route and fluorophore can significantly extend the antibody active labeling time. We found that while both IV and intraperitoneal (IP) anti-CD45.2 antibody labeled circulating leukocytes after injection, they had different kinetic properties that impacted labeling time and intensity. Quantification of circulating antibody revealed that while unbound IV anti-CD45.2 antibody rapidly decreased, unbound IP anti-CD45.2 antibody increased over 1 h. Using in vitro and in vivo serial dilution assays, we found that Alexa Fluor 647 and Brilliant Blue 700 (BB700) dyes had the greatest labeling sensitivity compared with other fluorophores. However, IP antibody injection with anti-CD45.2 BB700, but not Alexa Fluor 647, resulted in continuous blood leukocyte labeling for over 6 h. Finally, we leveraged IP anti-CD45.2 BB700 antibody to track slower migrating leukocytes into tumors. We found that IP anti-CD45.2 antibody injection allowed for the identification of ∼7 times as many tumor-specific CD8+ T cells that had recently migrated from blood into tumors. Our results demonstrate how different injection routes and fluorophores affect anti-CD45.2 antibody leukocyte labeling and highlight the utility of this approach for defining leukocyte migration in the context of homeostasis and cancer.

An early precursor CD8+ T cell that adapts to acute or chronic viral infection

This study examines the origin and differentiation of stem-like CD8+ T cells that are essential for sustained T cell immunity in chronic viral infections and cancer and also have a key role in PD-1 directed immunotherapy1-10. These PD-1+TCF-1+TOX+ stem-like CD8+ T cells (also known as precursors of exhausted T cells8,9) have a distinct program that enables them to adapt to chronic antigen stimulation. Here, using the mouse model of chronic lymphocytic choriomeningitis virus (LCMV) infection, we find that virus-specific stem-like CD8+ T cells are generated early (day 5) during chronic infection, suggesting that this crucial fate commitment occurs irrespective of the infection outcome. Indeed, we find that nearly identical populations of stem-like CD8+ T cells were generated early during acute or chronic LCMV infection, and that antigen was essential for maintaining the stem-like phenotype. We performed reciprocal adoptive transfer experiments to determine the fate of these early stem-like CD8+ T cells after viral clearance versus persistence. After transfer of day 5 stem-like CD8+ T cells from chronically infected mice into acutely infected mice, these cells downregulated canonical markers of the chronic stem-like CD8+ T cells and expressed markers (CD127 and CD62L) associated with central memory CD8+ T cells. Reciprocally, when day 5 stem-like cells from acutely infected mice were transferred into chronically infected mice, these CD8+ T cells functioned like chronic resource cells and responded effectively to PD-1 therapy. These findings highlight the ability of these early PD-1+TCF-1+TOX+ stem-like CD8+ T cells to adapt their differentiation trajectory to either an acute or a chronic viral infection. Importantly, our study shows that the host is prepared a priori to deal with a potential chronic infection.

ATP-Gated P2X7-Ion Channel on Kidney-Resident Natural Killer T Cells and Memory T Cells in Intrarenal Inflammation

Key Points

Parenchymal T cells in the kidney expressed much higher levels of P2X7 than vascular T cells. P2X7-blocking nanobodies uncover a large fraction of kidney-resident natural killer T and tissue-resident memory T cells. These cells were lost during cell preparation because of activation of P2X7 by NAD+ released from damaged cells, unless blocked by nanobodies.

Background

The P2X7 ion channel, a key sensor of sterile inflammation, has been implicated as a therapeutic target in GN, and P2X7-antagonistic nanobodies can attenuate experimental GN. However, little is known about the expression of P2X7 on renal immune cells.

Methods

We used conventional immunofluorescence of kidney sections and intraperitoneal injection of nanobodies in mice followed by flow cytometry analysis of parenchymal T cells and RNA sequencing to elucidate the expression and function of P2X7 on parenchymal and vascular immune cells in the mouse kidney.

Results

Our study showed that parenchymal T cells, including a large subset of natural killer T cells and CD69+ tissue-resident memory T cells, display much higher cell surface levels of P2X7 than vascular T cells. After a single intraperitoneal injection of P2X7-blocking nanobodies, P2X7 on parenchymal T cells was fully occupied by the injected nanobodies within 30 minutes. This resulted in an effective protection of these cells from nicotinamide adenine dinucleotide–induced cell death during cell preparation. Conversely, systemic injection of nicotinamide adenine dinucleotide that mimics sterile inflammation results in the selective depletion of P2X7hiCD69hi T cells from the kidney parenchyma.

Conclusions

Our study uncovered a novel purinergic regulatory mechanism affecting kidney-resident T-cell populations.

Decidualization-associated recruitment of cytotoxic memory CD8+T cells to the maternal-fetal interface for immune defense

Decidual CD8+T (dCD8+T) cells are pivotal in the maintenance of the delicate balance between immune tolerance towards the fetus and immune resistance against pathogens. The endometrium and decidua represent the uterine environments before and during pregnancy, respectively, yet the composition and phenotypic alterations of uterine CD8+T cells in these tissues remain unclear. Using flow cytometry and analysis of transcriptome profiles, we demonstrated that human dCD8+T and endometrial CD8+T (eCD8+T) cells exhibited similar T cell differentiation statuses and phenotypes of tissue infiltrating or residency, compared to peripheral CD8+T (pCD8+T) cells. However, dCD8+T cells showed decreased expression of coinhibitory marker (PD-1), chemotaxis marker (CXCR3), and tissue-resident markers (CD69 and CD103), along with increased expression of granzyme B and granulysin, compared to eCD8+T cells. In vitro cytotoxicity assays further demonstrated that dCD8+T cells had greater effector functions than eCD8+T cells. Additionally, both in vitro and in vivo chemotaxis assays confirmed the recruitment of non-resident effector memory T cell subsets to the pregnant decidua, contributing to the dCD8+T cell-mediated anti-infection mechanism at the maternal-fetal interface. This work demonstrates dCD8+T cells replenished from the circulation retain their cytotoxic capacity, which may serve as an enhanced defense mechanism against infection during pregnancy.

Antigen-presenting innate lymphoid cells induced by BCG vaccination promote a respiratory antiviral immune response through the skin‒lung axis

The route of vaccine administration is associated with various immune outcomes, and the relationship between the route of administration and broad protection against heterologous pathogens remains unclear. Here, we found that subcutaneous vaccination with Bacillus Calmette-Guérin (BCG) promotes respiratory influenza clearance and T-cell responses. Group 1 innate lymphoid cells (ILC1s) express MHCII molecules and engage in antigen processing and presentation after BCG vaccination. During influenza virus infection, ILC1s in the lungs of BCG-vaccinated mice can present influenza virus antigens and prime Th1 cells. After subcutaneous vaccination with BCG, MHCII+ ILC1s migrate from the skin to the lungs and play an antigen-presenting role in influenza infection. Both the BCG and the BCG component lipomannan can induce MHCII expression and skin-to-lung migration of ILC1s via TLR2 signaling. Our study revealed an important regulatory mechanism by which subcutaneous vaccination with BCG promotes respiratory antiviral immune responses via the skin‒lung axis.

Kupffer cell and recruited macrophage heterogeneity orchestrate granuloma maturation and hepatic immunity in visceral leishmaniasis

In murine models of visceral leishmaniasis (VL), the parasitization of resident Kupffer cells (resKCs) drives early Leishmania infantum growth in the liver, leading to granuloma formation and subsequent parasite control. Using the chronic VL model, we demonstrate that polyclonal resKCs redistributed to form granulomas outside the sinusoids, creating an open sinusoidal niche that was gradually repopulated by monocyte-derived KCs (moKCs) acquiring a tissue specific, homeostatic profile. Early-stage granulomas predominantly consisted of CLEC4F+KCs. In contrast, late-stage granulomas led to remodeling of the sinusoidal network and contained monocyte-derived macrophages (momacs) along with KCs that downregulated CLEC4F, with both populations expressing iNOS and pro-inflammatory chemokines. During late-stage infection, parasites were largely confined to CLEC4F-KCs. Reduced monocyte recruitment and increased resKCs proliferation in infected Ccr2-/- mice impaired parasite control. These findings show that the ontogenic heterogeneity of granuloma macrophages is closely linked to granuloma maturation and the development of hepatic immunity in VL.

Interleukin-1 receptor antagonist is a conserved early factor for exacerbating tuberculosis susceptibility

Mycobacterium tuberculosis (Mtb) causes 1.25 million deaths a year. However, tuberculosis (TB) pathogenesis remains poorly understood and is not fully recapitulated in standard mouse models. Here we find that gene signatures from three different Mtb-susceptible mouse models predict active TB disease in humans significantly better than a signature from resistant C57BL/6 (B6) mice. Conserved among susceptible mice, non-human primates, and humans, but largely absent from B6 mice, was Mtb-induced differentiation of macrophages into an Spp1 + differentiation state. Spp1 + macrophages expressed high levels of immunosuppressive molecules including IL-1 receptor antagonist (IL-1Ra). IL-1Ra was previously reported to cause Mtb susceptibility in one mouse model, but whether IL-1Ra is broadly important remains uncertain. Here we report that enhancement of IL-1 signaling via deletion of IL-Ra promoted bacterial control across three susceptible mouse models. We found IL-1 signaling amplified production of multiple cytokines by lymphoid and stromal cells, providing a multifactorial mechanism for how IL-1 promotes Mtb control. Our results indicate that myeloid cell expression of immunosuppressive molecules, in particular IL-1 receptor antagonist, is a conserved early mechanism limiting Mtb control in mice, non-human primates, and humans.

Helminth infection favors reprogramming and proliferation of lung neutrophils

Neutrophils are a granulocytic population of myeloid cells that have critical effector functions during infectious disease but are generally thought to be short-lived and nonproliferative with markedly limited activation states. In these studies, we directly compared lung neutrophil activation following infection with different groups of pathogens including bacteria, fungi, and helminths. Our results demonstrate considerable heterogeneity depending on the type of infectious agent. In contrast to bacterial and fungal infection, after helminth infection neutrophils expressed markers associated with characteristic type 2 responses and unexpectedly upregulated genes associated with cell cycling and protein synthesis. Further studies showed reduced neutrophil cell death following helminth infection and increased proliferation, which was dependent on IL-4R signaling. This distinct subset of proliferating neutrophils expanded following helminth infection and was released from the endothelial niche to colocalize with invading parasites in the airways. These studies demonstrate a novel long-lived cycling phenotype for neutrophils following helminth infection.

Lung CD4+ resident memory T cells use airway secretory cells to stimulate and regulate onset of allergic airway neutrophilic disease

Neutrophilic asthma is a vexing disease, but mechanistic and therapeutic advancements will require better models of allergy-induced airway neutrophilia. Here, we find that periodic ovalbumin (OVA) inhalation in sensitized mice elicits rapid allergic airway inflammation and pathophysiology mimicking neutrophilic asthma. OVA-experienced murine lungs harbor diverse clusters of CD4+ resident memory T (TRM) cells, including unconventional RORγtnegative/low T helper 17 (TH17) cells. Acute OVA challenge instigates interleukin (IL)-17A secretion from these TRM cells, driving CXCL5 production from Muc5achigh airway secretory cells, leading to destructive airway neutrophilia. The TRM and epithelial cell signals discovered herein are also observed in adult human asthmatic airways. Epithelial antigen presentation regulates this biology by skewing TRM cells toward TH2 and TH1 fates so that TH1-related interferon (IFN)-γ suppresses IL-17A-driven, CXCL5-mediated airway neutrophilia. Concordantly, in vivo IFN-γ supplementation improves disease outcomes. Thus, using our model of neutrophilic asthma, we identify lung epithelial-CD4+ TRM cell crosstalk as a key rheostat of allergic airway neutrophilia.

PLZF-expressing CD4+ T cells promote tissue-resident memory T cells in breaking immune tolerance in allergic asthma via IL-15/IL-15Rα signaling

BACKGROUND

Allergic asthma is a chronic airway disease characterized by an allergic response and altered immune tolerance. CD4+ tissue-resident memory T (TRM) cells are crucial in the chronic and relapsing pathogenesis of asthma. Furthermore, promyelocytic leukemia zinc finger (PLZF) is an essential transcription factor involved in asthmatic tolerance and has been implicated in the regulation of CD4+CD44+ memory T cells. However, the role of CD4+ TRM cells in asthmatic tolerance, as well as their potential modulation by PLZF, remain unclear. Therefore, in the current study, we explore the role of CD4+ TRM cells in asthmatic immune tolerance and as well as the regulatory role of PLZF in this process.

METHODS

To elucidate the role of CD4+ TRM cells in immune tolerance, asthma memory mouse models were treated with the immunomodulator FTY720. Subsequently, CD4+ T cells were isolated from the lungs and spleens and transferred to oral tolerance mouse models. To explore the regulation of PLZF in CD4+ TRM cells, asthma and oral tolerance were established in Zbtb16flox/flox CD4Cre and wild-type mice. Flow cytometry, histological analysis, and cytokine measurements were performed to characterize the immune response. The regulatory activity of PLZF on CD4+ TRM cells was analyzed through quantitative proteomics and verified in vitro and vivo.

RESULTS

The CD4+ TRM cell proportion positively correlated with the pathological phenotypes and molecular characteristics of asthma. Adoptive transfer of CD4+ TRM cells induced asthmatic phenotypes. This suggested that CD4+ TRM cells contributed to the pathogenesis of asthma. Conditional knockout of PLZF substantially reduced the proportion of CD4+ TRM cells, relieved asthmatic symptoms, and suppressed the interleukin (IL)-15/IL-15Rα signaling pathway. Furthermore, exposure to the IL-15Rα agonist restored asthma-related Th2 inflammation, accompanied by a markedly increased proportion of CD4+ TRM cells. Meanwhile, IL-15 and ovalbumin(OVA)-primed Beas2b supernatant co-stimulation in vitro enhanced the differentiation of pulmonary PLZF-expressing CD4+ T cells into CD4+ TRM cells.  CONCLUSIONS: This study identified CD4+ TRM cells as key mediators of immune tolerance in asthma. This process is regulated by the transcription factor PLZF in CD4+ T cells through IL-15/IL-15Rα signaling. Thus, targeting PLZF or the IL-15/IL-15Rα pathway may represent a promising therapeutic strategy for treating asthma.

Investigating pulmonary neutrophil responses to inflammation in mice via flow cytometry

Neutrophils play a crucial role in maintaining lung health by defending against infections and participating in inflammation processes. Here we describe a detailed protocol for evaluating pulmonary neutrophil phenotype using a murine model of sterile inflammation induced by the fungal cell wall particle zymosan. We provide step-by-step instructions for the isolation of single cells from both lung tissues and airspaces, followed by comprehensive staining techniques for both cell surface markers and intracellular components. This protocol facilitates the sorting and detailed characterization of lung neutrophils via flow cytometry, making it suitable for downstream applications such as mRNA extraction, single-cell sequencing, and analysis of neutrophil heterogeneity. We also identify and discuss essential considerations for conducting successful neutrophil flow cytometry experiments. This work is aimed at researchers exploring the intricate functions of neutrophils in the lung under physiological and pathological conditions with the aid of flow cytometry.

Collaboration between interleukin-7 and -15 enables adaptation of tissue-resident and circulating memory CD8+ T cells to cytokine deficiency

Interleukin-7 (IL-7) is considered a critical regulator of memory CD8+ T cell homeostasis. However, this is primarily based on circulating memory populations, and the cell-intrinsic requirement for IL-7 signaling during memory homeostasis has not been directly tested. Here, we addressed the role for IL-7Rα in circulating and resident memory CD8+ T cells (Trm) after their establishment. We found that inducible Il7ra deletion had only a modest effect on persistence of circulating memory and Trm subsets, causing reduced basal proliferation. Loss of IL-15 signaling imposed heightened IL-7Rα dependence on memory CD8+ T cells, including Trm cells described as IL-15 independent. In the absence of IL-15 signaling, IL-7Rα was elevated, and loss of IL-7Rα signaling reduced IL-15-elicited proliferation, suggesting crosstalk between these pathways in memory CD8+ T cells. Thus, across subsets and tissues, IL-7 and IL-15 act in concert to support memory CD8+ T cells, conferring resilience to altered availability of either cytokine.

Severe malaria enforces short-lived effector cell differentiation but does not prevent effective secondary responses by memory CD8 T cells

Parasitic infections are a major worldwide health burden, yet most studies of CD8 T cell differentiation focus on acute viral and bacterial infections. To understand effector and memory CD8 T cell responses during erythrocytic malaria infection in mice, we utilized transgenic OT-I T cells and compared CD8 T cell responses between infection with OVA-expressing strains of Listeria monocytogenes (Lm) and Plasmodium berghei ANKA (PbA). We find that CD8 T cells expand vigorously during both infections. However, in contrast to Lm infection, PbA infection induces T cells that are heavily biased toward an IL-7Ra-deficient and KLRG1+ short-lived effector cell (SLEC) phenotype at the expense of memory precursor effector cell (MPECs) formation. PbA-induced inflammation, including IFNγ, is partially responsible for this outcome. Following treatment with antimalarial drugs and T cell contraction, PbA-primed memory T cells are rarely found in the blood and peripheral tissues but do maintain a low presence in the spleen and bone marrow. Despite these poor numbers, PbA memory T cells robustly expand upon vaccination or viral infection, control pathogen burden, and form secondary memory pools. Thus, despite PbA enforced SLEC formation and limited memory, effective secondary responses can still proceed.

Intranasal recombinant protein subunit vaccine targeting TLR3 induces respiratory tract IgA and CD8 T cell responses and protects against respiratory virus infection

BACKGROUND

Intranasal vaccines against respiratory viruses are desired due to ease of administration and potential to protect against virus infection of the upper respiratory tract.

METHODS

We tested a cationic liposomal adjuvant delivering the TLR3 agonist Poly (I:C) (CAF®09b) for intranasal administration, by formulating this with SARS-CoV-2 spike trimeric protein and assessing airway mucosal immune responses in mice. The vaccine was further evaluated in SARS-CoV-2 virus challenge models, using mice expressing the human ACE2 receptor and Syrian hamsters.

FINDINGS

The intranasal vaccine elicited both serum neutralising antibody responses and IgA responses in the upper respiratory tract. Uniquely, it also elicited high-magnitude CD4 and CD8 T cell responses in the lung parenchyma and nasal-associated lymphoid tissue. In contrast, parenteral administration of the same vaccine, or the mRNA-1273 (Spikevax®) vaccine, led to systemic antibody responses and vaccine-induced CD4 T cells were mainly found in circulation. The intranasal vaccine protected against homologous SARS-CoV-2 (Wuhan-Hu-1) challenge in K18-hACE2 mice, preventing weight loss and virus infection in the upper and lower airways. In Syrian hamsters, the vaccine prevented weight loss and significantly reduced virus load after challenge with the homologous strain and Omicron BA.5.

INTERPRETATION

This study demonstrates that intranasal subunit vaccines containing TLR3-stimulating cationic liposomes effectively induce airway IgA and T cell responses, which could be utilised in future viral pandemics.

FUNDING

This work was primarily supported by the European Union Horizon 2020 research and innovation program under grant agreement no. 101003653.

The meninges host a distinct compartment of regulatory T cells that preserves brain homeostasis

Our understanding of the meningeal immune system has recently burgeoned, particularly regarding how innate and adaptive effector cells are mobilized to meet brain challenges. However, information on how meningeal immunocytes guard brain homeostasis in healthy individuals remains limited. This study highlights the heterogeneous, polyfunctional regulatory T cell (Treg) compartment in the meninges. A Treg subtype specialized in controlling interferon-γ (IFN-γ) responses and another dedicated to regulating follicular B cell responses were substantial components of this compartment. Accordingly, punctual Treg ablation rapidly unleashed IFN-γ production by meningeal lymphocytes, unlocked access to the brain parenchyma, and altered meningeal B cell profiles. Distally, the hippocampus assumed a reactive state, with morphological and transcriptional changes in multiple glial cell types. Within the dentate gyrus, neural stem cells underwent more death and were blocked from further differentiation, which coincided with impairments in short-term spatial-reference memory. Thus, meningeal Tregs are a multifaceted safeguard of brain homeostasis at steady state.

Mucosal immunity elicited by a human-Fcγ receptor-I targeted intranasal vaccine platform enhances resistance against nasopharyngeal colonization of Streptococcus pneumoniae and induces broadly protective immunity against respiratory pathogens

The development of safe and effective mucosal vaccines are hampered by safety concerns associated with adjuvants or live attenuated microbes. We previously demonstrated that targeting antigens to the human-Fc-gamma-receptor-I (hFcγRI) eliminates the need for adjuvants, thereby mitigating safety concerns associated with the mucosal delivery of adjuvant formulated vaccines. Here we evaluated the role of the route of immunization in the mucosal immunity elicited by the hFcγRI-targeted vaccine approach. To enable Ag targeting, PspA from Streptococcus pneumoniae (Sp) was genetically fused with the hFcγRI-targeting antibody (α-hFcγRI) to generate PspA-FP. Intranasal (IN) immunization with the PspA-FP induced significantly higher IgA, IgG, and memory T cell response in the lung mucosa compared to that of the intramuscular (IM) route, while both routes exhibited similar increase in the systemic IgG response. The IN immunization elicited better resistance against nasal colonization (NC) of Sp compared to the IM immunization. Additionally, the resistance to NC with the IN administered PspA-FP was higher than the PspA-Alum formulation administered by the IM route. While the protection form lethal pulmonary Sp infection correlated with the systemic Ab response, the resistance from NC (of Sp) correlated with the mucosal immune response. Similar to the pneumococcal pneumoniae model, the hFcγRI-targeted vaccine (based on HA as Ag) was equally protective against pulmonary Influenza virus infection via both routes. However, the IN route promoted better protection compared to the IM route against a lethal pulmonary infection with Francisella tularensis (Ft). The enhanced protection against Ft correlated with the superior mucosal immune response elicited by the IN route compared to the IM route. These observations showed a differential requirement for mucosal delivery for protection depending on the type of pathogen. Moreover, this study revealed that the hFcγRI-targeted vaccine platform is broadly-effective as an adjuvant-free mucosal vaccine platform against respiratory pathogens.

Repetitive antigen stimulation in the periphery dictates the composition and recall responses of brain-resident memory CD8+ T cells

The human brain harbors virus-specific, tissue-resident memory (TRM) CD8+ T cells. However, the impact of repeated peripheral viral infection on the generation, phenotype, localization, and recall responses of brain TRM remains elusive. Here, utilizing two murine models of peripheral viral infection, we demonstrate that circulating memory CD8+ T cells with previous antigen exposure exhibit a markedly reduced capacity to form brain TRM compared to naive CD8+ T cells. Repetitively stimulated brain TRM also demonstrate differential inhibitory receptor expression, preserved functionality, and divergent localization patterns compared to primary memory counterparts. Despite these differences, repetitively stimulated brain TRM provide similar protection against intracranial infection as primary populations with superior recall-based recruitment of peripheral lymphocytes. As CD8+ T cells may distinctly seed the brain with each repeated infection of the same host, these findings point to heterogeneity in the brain TRM pool that is dictated by prior peripheral antigen stimulation history.

Triggering mouth-resident antiviral CD8+ T cells potentiates experimental periodontitis

Emerging evidence indicates that gingival-resident helper CD4+ T cells are major drivers of periodontal inflammation in response to commensal and pathogenic oral microorganisms. Whether tissue-resident memory CD8+ T cells (TRM), which principally safeguard against viruses and cancer but also drive certain autoimmune and inflammatory conditions, impact periodontitis progression and severity remain unknown. We asked whether local reactivation of oral CD8+ TRM of a defined antigen specificity could exacerbate ligature-induced periodontitis (LIP), a well-established model of periodontal disease in mice. Topical application of virus-mimicking peptides to the oral mucosa concurrent with LIP 1) intensified alveolar bone loss, 2) amplified gingival and cervical lymph node inflammation, and 3) stimulated gingival transcriptional changes in genes related to innate immune sensing and cell-mediated cytotoxicity. Therapeutic depletion of CD103-expressing oral CD8+ TRM in advance of LIP prevented exacerbation of disease. These observations provide evidence that oral CD103+ CD8+ TRM have the potential to participate in gingival inflammation, alveolar bone loss, and periodontitis.

Lung-resident memory Th2 cells regulate pulmonary cryptococcosis by inducing type-II granuloma formation

Lung-resident memory T cells (lung TRMs) settle in the lung and respond rapidly to external antigens, and are therefore considered to have great potential for development of respiratory vaccines. Here, we demonstrate that lung-resident memory Th2 cells (lung TRM2) protect against pulmonary mycosis caused by Cryptococcus gattii. We developed novel whole-cell intranasal vaccines using a heat-inactivated C.gattii capsule-deficient strain cap59Δ, which induced ST-2+ Gata-3+ lung TRM2 specifically responding to C.gattii whole-cell antigen. Lung fungal burden and survival rate were significantly improved in immunized mice after infection challenge. The immunosuppressive agent FTY720 did not impact vaccine effectiveness, and adoptive transfer of lung TRMs into Rag-1-deficient mice decreased the lung fungal burden. In IL-4/IL-13 double-knockout (DKO) mice, immunization did not efficiently induce eosinophil recruitment and granuloma formation, and the fungal burden was not decreased after infection challenge. Co-culture of lung TRM2 with myeloid lineages induced multinucleated giant cells (MGCs) in the presence of antigen, which phagocytosed live C.gattii cells without opsonization, whereas lung TRM2 from DKO mice did not induce MGCs. These findings provide a new model in which lung TRM2 suppress C.gattii infection via granuloma induction.

Durable lymphocyte subset elimination upon a single dose of AAV-delivered depletion antibody dissects immune control of chronic viral infection

To interrogate the role of specific immune cells in infection, cancer, and autoimmunity, immunologists commonly use monoclonal depletion antibodies (depletion-mAbs) or genetically engineered mouse models (GEMMs). To generate a tool that combines specific advantages and avoids select drawbacks of the two methods, we engineered adeno-associated viral vectors expressing depletion mAbs (depletion-AAVs). Single-dose depletion-AAV administration durably eliminated lymphocyte subsets in mice and avoided accessory deficiencies of GEMMs, such as marginal zone defects in B cell-deficient animals. Depletion-AAVs can be used in animals of different genetic backgrounds, and multiple depletion-AAVs can readily be combined. Exploiting depletion-AAV technology, we showed that B cells were required for unimpaired CD4+ and CD8+ T cell responses to chronic lymphocytic choriomeningitis virus (LCMV) infection. Upon B cell depletion, CD8+ T cells failed to suppress viremia, and they only helped resolve chronic infection when antibodies dampened viral loads. Our study positions depletion-AAVs as a versatile tool for immunological research.

In vivo engineering of murine T cells using the evolved adeno-associated virus variant Ark313

Genetic engineering of T cells in mouse models is essential for investigating immune mechanisms. We aimed to develop an approach to manipulate T cells in vivo using an evolved adeno-associated virus (AAV) capsid named Ark313. Delivery of a transient transgene expression cassette was feasible using Ark313, and this serotype outperformed natural serotypes. A single intravenous injection of a Cre recombinase-expressing Ark313 in the Ai9 fluorescent reporter mouse model achieved permanent genetic modifications of T cells. Ark313 facilitated in vivo gene editing in both tissue-resident and splenic T cells and validation of immunotherapy targets in solid tumor models. Ark313 delivered large DNA donor templates to T cells in vivo and integrated transgenes in primary CD4+ and CD8+ T cells, including naive T cells. Ark313-mediated transgene delivery presents an efficient approach to target mouse T cells in vivo and a resource for the interrogation of T cell biology and for immunotherapy applications.

Manipulating the EphB4-ephrinB2 axis to reduce metastasis in HNSCC

The EphB4-ephrinB2 signaling axis has been heavily implicated in metastasis across numerous cancer types. Our emerging understanding of the dichotomous roles that EphB4 and ephrinB2 play in head and neck squamous cell carcinoma (HNSCC) poses a significant challenge to rational drug design. We find that EphB4 knockdown in cancer cells enhances metastasis in preclinical HNSCC models by augmenting immunosuppressive cells like T regulatory cells (Tregs) within the tumor microenvironment. EphB4 inhibition in cancer cells also amplifies their ability to metastasize through increased expression of genes associated with hallmark pathways of metastasis along with classical and non-classical epithelial-mesenchymal transition. In contrast, vascular ephrinB2 knockout coupled with radiation therapy (RT) enhances anti-tumor immunity, reduces Treg accumulation into the tumor, and decreases metastasis. Notably, targeting the EphB4-ephrinB2 signaling axis with the engineered ligands ephrinB2-Fc-His and Fc-TNYL-RAW-GS reduces local tumor growth and distant metastasis in a preclinical model of HNSCC. Our data suggests that targeted inhibition of vascular ephrinB2 while avoiding inhibition of EphB4 in cancer cells could be a promising strategy to mitigate HNSCC metastasis.

Bacterial components-driven intrahepatic CXCR5hi B cells are important population for MASH progression through inducing inflammation

Metabolic dysfunction-associated steatohepatitis (MASH) is characterized by severe liver inflammation and fibrosis due to an imbalanced immune response caused by enhanced bacterial components. The progression of MASH is closely linked to increased permeability of intestinal mucosal barrier facilitating enter of bacterial components into hepatic portal venous system. B cells are important immune cells for adaptive responses and enhance hepatic inflammation through cytokine production and T cell activation. B cells are influenced by gut microbiota, but the specific B cell populations in MASH and their pathologic mechanism remain obscure. Here, we found that the numbers of B cells highly expressing CXCR5, the receptor of CXCL13 chemokine, were increased in the livers of MASH. CXCR5 high B cells are non-proliferating naive B cells with inflammatory features mainly residing in hepatic parenchyma to affect liver pathology. Importantly, we revealed that CXCR5 high B cells were induced by bacterial components stimulating TLRs. These bacterial stimulator-induced CXCR5hi B cells highly express TNFα, CD80, and MHC class II, leading to T cell activation. Consistently, we confirmed that intravenous injection of CXCR5 high B cells enhanced hepatic inflammation in MASH model. Ultimately, this study elucidates the role and mechanisms of CXCR5 high B cells in advancing MASH progression.

Muscle macrophage regenerative response after squalene-adjuvanted influenza vaccination drives Th2-skewed response and is reduced with age

Squalene-based adjuvants like MF59, and its research alternative AddaVax, induce transient muscle injury, but their working mechanisms downstream of muscle injury remain unclear. We show that an AddaVax-adjuvanted quadrivalent inactivated influenza virus vaccine (QIV) intramuscular injection triggers muscle regeneration-like immune processes and increases CX3CR1+Ly6C+ macrophages in the muscle and inguinal lymph nodes by day 4 post-injection. This leads to a Th2 skewed vaccine response with higher levels of vaccine specific IgG1 titers, and Th2-associated cytokines in the lungs 5 days after subsequent influenza viral challenge. In aged mice, the macrophage recruitment and polarization is diminished, which is consistent with age-associated muscle mass loss, reflecting the age-related decline in muscle regeneration. Unlike young mice, aged mice exhibit a reduction in magnitude and skewing of AddaVax-mediated Th2 responses to QIV. We found that adoptive transfer of bone marrow-derived macrophages derived from young mice into aged mice at the moment of vaccination leads to their infiltration into the injected muscle, where they collect vaccine antigens, drain to the lymph node, and enhance the Th2 response, recapitulating the young host response but in an older host. However, rescuing the Th2-skewing effects of AddaVax alone was not sufficient to enhance protection against mismatched subsequent influenza viral infection in aged mice, suggesting additional factors at play in the diminished vaccine response in aged hosts. This underscores the importance of the macrophage-driven muscle regenerative response in the mechanism of action for squalene-based adjuvants like AddaVax and emphasizes the need to study how muscle damage and regenerative pathways in intramuscular vaccine responses contribute to vaccine effectiveness.

Interleukin-1 signaling and CD4+ T cells control B cell recruitment to the lungs in chronic beryllium disease

Chronic beryllium disease (CBD) is a debilitating pulmonary disorder that occurs due to persistent exposure to beryllium (Be) particles in the workplace. Be-exposure causes activation of the innate immune system, resulting in the secretion of interleukins and chemokines that drive the accumulation of B and T cells in the lungs. However, the mechanisms by which innate molecules influence the recruitment of B cells and B cell-mediated protection in CBD are poorly understood. In this study, we employed multiple approaches to examine the role of innate immune signaling and CD4+ T cells in B cell recruitment and function in the lungs. We show that the absence or blocking of IL-1R1 signaling prevents the recruitment of B cells to the lungs of BeO-exposed mice. Additionally, we show that B cell recruitment to the lungs depends on the chemokine receptor, CXCR5, and CD4+ T cells. In BeO-exposed mice, lung B cells down-regulate IgM but showed an increased IgD and CD44 surface expression. Further, RNA sequencing of pulmonary tissue-specific B cells in CBD revealed distinct gene signatures compared to splenic B cells, with increased expression of pathways involved in antigen presentation, tight junction interactions, and interferon signaling. Overall, our study shows that B cell recruitment and aggregate formation during CBD depend on sequential activation of innate and adaptive immune responses.

The type I IFN-IL-27 axis promotes mRNA vaccine-induced CD8 + T cell responses

The ability of lipid nanoparticle (LNP)-delivered mRNA vaccines to induce type I IFNs is critical to promote CD8 + T cell responses. The studies presented here indicate that immunization with nucleoside modified mRNA-LNP vaccines drives myeloid cell expression of the cytokine IL-27, which acts on antigen-specific CD8 + T cells to sustain T cell expansion. In vitro and in vivo studies revealed that type I IFN signaling is necessary for mRNA-LNP-induced IL-27 production, that immunization failed in IL-27 KO mice, and that immunization of IFNAR1-deficient mice with mRNA-LNP particles that also encode IL-27 mRNA restored antigen-specific CD8 + T cell responses. In addition, IL-27 mRNA-LNPs served as an adjuvant that improved cytolytic CD8 + T cell responses and the therapeutic efficacy of mRNA-LNPs to drive anti-pathogen and anti-tumor immunity. These studies highlight the central role of IL-27 in mRNA-LNP induced CD8 + T cell responses and the ability of this cytokine to augment the functionality of the CD8 + T cell response for prophylactic or therapeutic immunization.

Selective expression and significance of ACKR2 in lung aerocytes

BACKGROUND

ACKR2 is an atypical chemokine receptor that plays a significant role in regulating inflammation by binding to inflammatory CC chemokines and facilitating their degradation. Previous findings suggest that the genetic absence of ACKR2 leads to heightened tumor growth in inflammation-driven models. Conversely, mice lacking ACKR2 exhibit protection against lung metastasis in melanoma and breast cancer models. This study aims to explore the specific cell types expressing ACKR2 and their relative contributions to the protection against lung metastasis.

METHODS

ACKR2 expression was studied by the generation of an inducible and conditional knockout (KO) mouse expressing two reporter genes, luciferase and TdTomato visible by In Vivo Imaging System, flow cytometry and immunofluorescence. Gene expression in lung endothelial cells (ECs) was investigated by RNA sequencing analysis. In vivo models of lung metastasis and inflammation were performed in wild-type (WT) and conditional KO mice by intravenous injection of melanoma and colon cancer cell lines; the induction of acute lung injury model was done by intranasal injection of lipopolysaccharide (LPS). Leukocytes infiltrating lung metastasis were studied by fluorescence-activated cell sorting (FACS) analysis. The serum chemokine levels were studied with a multiplex ELISA.

RESULTS

The analysis of the reporter mouse revealed that ACKR2 is expressed by lymphatic endothelial cells (LECs) in most murine organs. However, uniquely in the lungs, ACKR2 expression is observed in blood endothelial cells (BECs), specifically in capillaries known as aerocytes specialized for regulating leukocyte trafficking. Selective deletion of Ackr2 from ECs (ACKR2ΔCdh5 mice) but not from LECs (ACKR2ΔProx1 mice) resulted in protection in models of melanoma and colorectal cancer lung metastasis. This protection was associated with an increased presence of activated T lymphocytes infiltrating the lungs compared with WT mice. Additionally, in a model of acute lung injury, mice with selective deletion from the endothelial compartment exhibited heightened extravasation of T lymphocytes compared with both ACKR2 KO and WT mice.

CONCLUSIONS

These results indicate that ACKR2 is selectively expressed by lung vascular capillaries (aerocytes) that are devoted to the regulation of leukocyte extravasation. Selective ACKR2 targeting in this compartment, by modulating chemokine availability, promotes T lymphocyte extravasation resulting in reduced lung metastases.

Tissue-resident immune cells: from defining characteristics to roles in diseases

Tissue-resident immune cells (TRICs) are a highly heterogeneous and plastic subpopulation of immune cells that reside in lymphoid or peripheral tissues without recirculation. These cells are endowed with notably distinct capabilities, setting them apart from their circulating leukocyte counterparts. Many studies demonstrate their complex roles in both health and disease, involving the regulation of homeostasis, protection, and destruction. The advancement of tissue-resolution technologies, such as single-cell sequencing and spatiotemporal omics, provides deeper insights into the cell morphology, characteristic markers, and dynamic transcriptional profiles of TRICs. Currently, the reported TRIC population includes tissue-resident T cells, tissue-resident memory B (BRM) cells, tissue-resident innate lymphocytes, tissue-resident macrophages, tissue-resident neutrophils (TRNs), and tissue-resident mast cells, but unignorably the existence of TRNs is controversial. Previous studies focus on one of them in specific tissues or diseases, however, the origins, developmental trajectories, and intercellular cross-talks of every TRIC type are not fully summarized. In addition, a systemic overview of TRICs in disease progression and the development of parallel therapeutic strategies is lacking. Here, we describe the development and function characteristics of all TRIC types and their major roles in health and diseases. We shed light on how to harness TRICs to offer new therapeutic targets and present burning questions in this field.

Deep profiling deconstructs features associated with memory CD8+ T cell tissue residence

Tissue-resident memory CD8+ T (Trm) cells control infections and cancer and are defined by their lack of recirculation. Because migration is difficult to assess, residence is usually inferred by putative residence-defining phenotypic and gene signature proxies. We assessed the validity and universality of residence proxies by integrating mouse parabiosis, multi-organ sampling, intravascular staining, acute and chronic infection models, dirty mice, and single-cell multi-omics. We report that memory T cells integrate a constellation of inputs-location, stimulation history, antigen persistence, and environment-resulting in myriad differentiation states. Thus, current Trm-defining methodologies have implicit limitations, and a universal residence-specific signature may not exist. However, we define genes and phenotypes that more robustly correlate with tissue residence across the broad range of conditions that we tested. This study reveals broad adaptability of T cells to diverse stimulatory and environmental inputs and provides practical recommendations for evaluating Trm cells.

Airway-resident memory CD4 T cell activation accelerates antigen presentation and T cell priming in draining lymph nodes

Specialized memory CD4 T cells that reside long-term within tissues are critical components of immunity at portals of pathogen entry. In the lung, such tissue-resident memory (Trm) cells are activated rapidly after infection and promote local inflammation to control pathogen levels before circulating T cells can respond. However, optimal clearance of Influenza A virus can require Trm and responses by other virus-specific T cells that reach the lung only several days after their activation in secondary lymphoid organs. Whether local CD4 Trm sentinel activity can affect the efficiency of T cell activation in secondary lymphoid organs is not clear. Here, we found that recognition of antigen by influenza-primed Trm in the airways promoted more rapid migration of highly activated antigen-bearing DC to the draining lymph nodes. This in turn accelerated the priming of naive T cells recognizing the same antigen, resulting in newly activated effector T cells reaching the lungs earlier than in mice not harboring Trm. Our findings, thus, reveal a circuit linking local and regional immunity whereby antigen recognition by Trm improves effector T cell recruitment to the site of infection though enhancing the efficiency of antigen presentation in the draining lymph node.

mRNA vaccine-induced IgG mediates nasal SARS-CoV-2 clearance in mice

Coronavirus disease 2019 (COVID-19) mRNA vaccines that have contributed to controlling the SARS-CoV-2 pandemic induce specific serum antibodies, which correlate with protection. However, the neutralizing capacity of antibodies for emerging SARS-CoV-2 variants is altered. Suboptimal antibody responses are observed in patients with humoral immunodeficiency diseases, ongoing B cell depletion therapy, and aging. Common experimental mouse models with altered B cell compartments, such as B cell depletion or deficiency, do not fully recapitulate scenarios of declining or suboptimal antibody levels as observed in humans. We report on SARS-CoV-2 immunity in a transgenic mouse model with restricted virus-specific antibodies. Vaccination of C57BL/6-Tg(IghelMD4)4Ccg/J mice with unmodified or N1mΨ-modified mRNA encoding for ancestral spike (S) protein and subsequent challenge with mouse-adapted SARS-CoV-2 provided insights into antibody-independent immunity and the impact of antibody titers on mucosal immunity. Protection against fatal disease was independent of seroconversion following mRNA vaccination, suggesting that virus-specific T cells can compensate for suboptimal antibody levels. In contrast, mRNA-induced IgG in the nasal conchae limited the local viral load and disease progression. Our results indicate that parenteral mRNA immunization can elicit nasal IgG antibodies that effectively suppress local viral replication, highlighting the potential of vaccines in controlling SARS-CoV-2 transmission and epidemiology.

Early RSV infection aggravates asthma-related Th2 responses by increasing the number of CD4 + TRM cells through upregulation of PLZF

Respiratory syncytial virus (RSV) infection is correlated with the chronic pathogenesis and exacerbation of asthma. However, the mechanism remains unclear. In this study, acute and memory (Mem) asthma models with early RSV infection are established to explore the persistence of the effects of RSV infection on asthma. Intravascular injection of an anti-CD45 antibody is performed to define CD4 + TRM cells accurately. RSV infection has a sustained impact on asthma exacerbation for at least six weeks, with high Th2 cytokine secretion in lung tissue instead of IgE response-related B cells. CD45 -CD4 + TRM cells are positively correlated with RSV-related asthma exacerbation and severe airway inflammation. Mechanistically, overexpression of the transcription factor PLZF in vitro increases the number of CD4 + TRM cells, and conditional knockout of Zbtb16 (encoding PLZF) can decrease the number of CD4 + TRM cells to aggravate allergic inflammation and reduce Th2 responses. This study provides evidence for potential combined strategies that might benefit asthma patients.

Enhanced mucosal SARS-CoV-2 immunity after heterologous intramuscular mRNA prime/intranasal protein boost vaccination with a combination adjuvant

Current COVID-19 mRNA vaccines delivered intramuscularly (IM) induce effective systemic immunity, but with suboptimal immunity at mucosal sites, limiting their ability to impart sterilizing immunity. There is strong interest in rerouting immune responses induced in the periphery by parenteral vaccination to the portal entry site of respiratory viruses, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), by mucosal vaccination. We previously demonstrated the combination adjuvant, NE/IVT, consisting of a nanoemulsion (NE) and an RNA-based RIG-I agonist (IVT) induces potent systemic and mucosal immune responses in protein-based SARS-CoV-2 vaccines administered intranasally (IN). Herein, we demonstrate priming IM with mRNA followed by heterologous IN boosting with NE/IVT adjuvanted recombinant antigen induces strong mucosal and systemic antibody responses and enhances antigen-specific T cell responses in mucosa-draining lymph nodes compared to IM/IM and IN/IN prime/boost regimens. While all regimens induced cross-neutralizing antibodies against divergent variants and sterilizing immunity in the lungs of challenged mice, mucosal vaccination, either as homologous prime/boost or heterologous IN boost after IM mRNA prime, was required to impart sterilizing immunity in the upper respiratory tract. Our data demonstrate the benefit of hybrid regimens whereby strong immune responses primed via IM vaccination are rerouted by IN vaccination to mucosal sites to provide optimal protection against SARS-CoV-2.

Alarm Functions of PD-1+ Brain-Resident Memory T Cells

Resident memory T cells (TRM cells) have been described in barrier tissues as having a "sensing and alarm" function where, upon sensing cognate Ag, they alarm the surrounding tissue and orchestrate local recruitment and activation of immune cells. In the immunologically unique and tightly restricted CNS, it remains unclear whether and how brain TRM cells, which express the inhibitory receptor programmed cell death protein 1 (PD-1), alarm the surrounding tissue during Ag re-encounter. Using mouse models, we reveal that TRM cells are sufficient to drive the rapid remodeling of the brain immune landscape through activation of microglia, dendritic cells, NK cells, and B cells, expansion of regulatory T cells, and recruitment of macrophages and monocytic dendritic cells. Moreover, we report that although PD-1 restrained granzyme B upregulation in brain TRM cells reactivated via viral peptide, we observed no apparent effect on cytotoxicity in vivo, or downstream alarm responses within 48 h of TRM reactivation. We conclude that TRM cells are sufficient to trigger rapid immune activation and recruitment in the CNS and may have an unappreciated role in driving neuroinflammation.

RSV Vaccine with Nanoparticle-Based Poly-Sorbitol Transporter (PST) Adjuvant Improves Respiratory Protection Against RSV Through Inducing Both Systemic and Mucosal Humoral Immunity

Background/Objectives: Respiratory syncytial virus (RSV) causes symptoms similar to a mild cold for adults, but in case of infants, it causes bronchitis and/or pneumonia, and in some cases, mortality. Mucosal immunity within the respiratory tract includes tissue-resident memory T (TRM) cells and tissue-resident memory B (BRM) cells, which provides rapid and efficient protection against RSV re-infection. Therefore, vaccine strategies should aim to generate mucosal immune responses. However, the interactions between RSV vaccines and mucosal immune responses within the respiratory tract are poorly understood. We evaluated a mucosal immune system following immunization by RSV vaccine with poly-sorbitol transporter (RSV-PST), a nanoparticle adjuvant. Methods: We intranasally immunized the RSV-PST and identified the systemic and mucosal immune responses. Furthermore, we challenged with RSV A2 strain after immunization and investigated the protective effects. Results: Consequently, antigen-specific CD8+ TRM cells were markedly elevated in the lung parenchyma, yet exhibited impaired cytokine expression. In contrast, humoral immunity, with systemic antibody production from serum, but not in the respiratory tract, was significantly increased by RSV-PST immunization. Interestingly, the production of respiratory mucosal antigen-specific IgG after RSV A2 challenge dramatically increased in the bronchoalveolar lavage fluid (BALF) of the RSV-PST immunized group in the presence of FTY720, and the lung-infected RSV titer was significantly lower in this group. Furthermore, after RSV A2 challenge, CD69+ IgG+ BRM cells were significantly increased in lung tissues in the RSV-PST group. Conclusions: The RSV-PST vaccine has protective effects against RSV infection by promoting both systemic and local humoral immunity rather than cellular immunity.

Mucosal immunization with the lung Lactobacillus-derived amphiphilic exopolysaccharide adjuvanted recombinant vaccine improved protection against P. aeruginosa infection

Respiratory infections caused by Pseudomonas aeruginosa are a major health problem globally. Current treatment for P. aeruginosa infections relies solely on antibiotics, but the rise of antibiotic-resistant strains necessitates an urgent need for a protective vaccine. Traditional parenteral vaccines, despite employing potent adjuvants aimed at serotype-dependent immunity, often fail to elicit the desired mucosal immune response. Thus, developing vaccines that target both localized mucosal and systemic immune responses represents a promising direction for future research on P. aeruginosa vaccination. In this study, we explored EPS301, the exopolysaccharide derived from the lung microbiota strain Lactobacillus plantarum WXD301, which exhibits excellent self-assembly properties, enabling the formation of homogeneous nanoparticles when encapsulating recombinant PcrV of P. aeruginosa, designated as EPS301@rPcrV. Notably, the EPS301 vector effectively enhanced antigen adhesion to the nasal and pulmonary mucosal tissues and prolonged antigen retention. Moreover, EPS301@rPcrV provided effective and sustained protection against P. aeruginosa pneumonia, surpassing the durability achieved with the "gold standard" cholera toxin adjuvant. The EPS301-adjuvanted vaccine formulation elicited robust mucosal IgA and Th17/γδ17 T cell responses, which exceeded those induced by the CTB-adjuvanted vaccination and were sustained for over 112 days. Additionally, Th 17 and γδ 17 resident memory T cells induced by EPS301@rPcrV were crucial for protection against P. aeruginosa challenge. Intriguingly, IL-17A knockout mice exhibited lower survival rates, impaired bacterial clearance ability, and exacerbated lung tissue damage upon EPS301 adjuvanted vaccination against P. aeruginosa-induced pneumonia, indicating an IL-17A-dependent protective mechanism. In conclusion, our findings provided direct evidence that EPS301@rPcrV mucosal vaccine is a promising candidate for future clinical application against P. aeruginosa-induced pulmonary infection.

Chronic inflammation drives epididymal tertiary lymphoid structure formation and autoimmune fertility disorders

The incomplete understanding of epididymal mucosal immunity is a significant contributing factor to the classification of many male infertility cases as idiopathic. Conditions that disrupt the immune balance in the male reproductive tract, such as vasectomy and infections, can expose sperm to the immune system, leading to increased production of anti-sperm antibodies (ASAs) and subsequent reproductive challenges. Regulatory T cells (Tregs) regulate inflammation and maintain sperm tolerance. In a murine model, we demonstrated that disrupting sperm immunotolerance induces chronic autoimmune responses characterized by antibody production targeting sperm and reproductive tissue autoantigens and unique tissue-specific immune cell signatures in the epididymis and testis. Such inflammatory features impair sperm function, contribute to epididymal damage, and drive sustained male subfertility. Tertiary lymphoid structures (TLSs) were formed within the epididymis after Treg depletion, defined by clusters of heterogenous B and T cells, fibroblasts, and endothelial cells. These ectopic structures perpetuate inflammation and lower the activation threshold for future immune threats. Similar isotypes of autoantibodies were detected in the seminal plasma of infertile patients, suggesting shared mechanistic pathways between mice and humans. Overall, we provide an in-depth understanding of the diverse B- and T-cell dynamics and TLS formation during epididymitis to develop precision-targeted therapies for infertility and chronic inflammation. Additionally, this immunological characterization of the epididymal microenvironment has the potential to identify novel targets for the development of male contraceptives.

One Sentence Summary

Understanding the epididymal immune cell landscape dynamics aids in developing targeted therapies for infertility and contraception.

Regulatory T cell-derived enkephalin gates nociception

T cells have emerged as sex-dependent orchestrators of pain chronification but the sexually dimorphic mechanisms by which T cells control pain sensitivity is not resolved. Here, we demonstrate an influence of regulatory T cells (Tregs) on pain processing that is distinct from their canonical functions of immune regulation and tissue repair. Specifically, meningeal Tregs (mTregs) express the endogenous opioid, enkephalin, and mTreg-derived enkephalin exerts an antinociceptive action through a presynaptic opioid receptor signaling mechanism that is dispensable for immunosuppression. We demonstrate that mTregs are both necessary and sufficient to suppress mechanical pain sensitivity in female, but not male, mice, with this modulation reliant on sex hormones. These results uncover a fundamental sex-specific, and immunologically-derived endogenous opioid circuit for nociceptive regulation with critical implications for pain biology.

In vivo antibody labeling route and fluorophore dictate labeling efficiency, sensitivity, and longevity

Leukocytes migrate through the blood and extravasate into organs to surveil the host for infection or cancer. Recently, we demonstrated that intravenous (IV) anti-CD45.2 antibody labeling allowed for precise tracking of leukocyte migration. However, the narrow labeling window can make this approach challenging for tracking rare migration events. Here, we show that altering antibody administration route and fluorophore can significantly extend the antibody active labeling time. We found that while both IV and intraperitoneal (IP) anti-CD45.2 antibody labeled circulating leukocytes after injection, they had different kinetic properties that impacted labeling time and intensity. Quantification of circulating antibody revealed that while unbound IV anti-CD45.2 antibody rapidly decreased, unbound IP anti-CD45.2 antibody increased over one hour. Using in vitro and in vivo serial dilution assays, we found that Alexa Fluor 647 (AF647) and Brilliant Blue 700 (BB700) dyes had the greatest labeling sensitivity compared to other fluorophores. However, IP antibody injection with anti-CD45.2 BB700, but not AF647, resulted in continuous blood leukocyte labeling for over 6 hours. Finally, we leveraged IP anti-CD45.2 BB700 antibody to track slower migrating leukocytes into tumors. We found that IP anti-CD45.2 antibody injection allowed for the identification of ~seven times as many tumor-specific CD8+ T cells that had recently migrated from blood into tumors. Our results demonstrate how different injection routes and fluorophores affect anti-CD45.2 antibody leukocyte labeling and highlight the utility of this approach for defining leukocyte migration in the context of homeostasis and cancer.

Hematopoietic aging promotes cancer by fueling IL-1⍺-driven emergency myelopoiesis

Age is a major risk factor for cancer, but how aging impacts tumor control remains unclear. In this study, we establish that aging of the immune system, regardless of the age of the stroma and tumor, drives lung cancer progression. Hematopoietic aging enhances emergency myelopoiesis, resulting in the local accumulation of myeloid progenitor-like cells in lung tumors. These cells are a major source of interleukin (IL)-1⍺, which drives the enhanced myeloid response. The age-associated decline of DNA methyltransferase 3A enhances IL-1⍺ production, and disrupting IL-1 receptor 1 signaling early during tumor development normalized myelopoiesis and slowed the growth of lung, colonic, and pancreatic tumors. In human tumors, we identified an enrichment for IL-1⍺-expressing monocyte-derived macrophages linked to age, poorer survival, and recurrence, unraveling how aging promotes cancer and offering actionable therapeutic strategies.

Epstein-Barr virus infection induces tissue-resident memory T cells in mucosal lymphoid tissues

EBV contributes to around 2% of all tumors worldwide. Simultaneously, more than 90% of healthy human adults persistently carry EBV without clinical symptoms. In most EBV carriers, it is thought that virus-induced tumorigenesis is prevented by cell-mediated immunity. Specifically, memory CD8+ T cells recognize EBV-infected cells during latent and lytic infection. Using a symptomatic primary infection model, similar to infectious mononucleosis (IM), we found EBV-induced CD8+ tissue resident memory T cells (TRMs) in mice with a humanized immune system. These human TRMs were preferentially established after intranasal EBV infection in nasal-associated lymphoid tissues (NALT), equivalent to tonsils, the primary site of EBV infection in humans. They expressed canonical TRM markers, including CD69, CD103, and BLIMP-1, as well as granzyme B, CD107a, and CCL5. Despite cytotoxic activity and cytokine production ex vivo, these TRMs demonstrated reduced CD27 expression and proliferation and failed to control EBV viral loads in the NALT during infection, although effector memory T cells (TEMs) controlled viral titers in spleen and blood. Overall, TRMs are established in mucosal lymphoid tissues by EBV infection, but primarily, systemic CD8+ T cell expansion seems to control viral loads in the context of IM-like infection.