Prior infection with unrelated neurotropic virus exacerbates influenza disease and impairs lung T cell responses

Immunity to infectious diseases is predominantly studied by measuring immune responses towards a single pathogen, although co-infections are common. In-depth mechanisms on how co-infections impact anti-viral immunity are lacking, but are highly relevant to treatment and prevention. We established a mouse model of co-infection with unrelated viruses, influenza A (IAV) and Semliki Forest virus (SFV), causing disease in different organ systems. SFV infection eight days before IAV infection results in prolonged IAV replication, elevated cytokine/chemokine levels and exacerbated lung pathology. This is associated with impaired lung IAV-specific CD8+ T cell responses, stemming from suboptimal CD8+ T cell activation and proliferation in draining lymph nodes, and dendritic cell paralysis. Prior SFV infection leads to increased blood brain barrier permeability and presence of IAV RNA in brain, associated with increased trafficking of IAV-specific CD8+ T cells and establishment of long-term tissue-resident memory. Relative to lung IAV-specific CD8+ T cells, brain memory IAV-specific CD8+ T cells have increased TCR repertoire diversity within immunodominant DbNP366+CD8+ and DbPA224+CD8+ responses, featuring suboptimal TCR clonotypes. Overall, our study demonstrates that infection with an unrelated neurotropic virus perturbs IAV-specific immune responses and exacerbates IAV disease. Our work provides key insights into therapy and vaccine regimens directed against unrelated pathogens.

Divergent molecular networks program functionally distinct CD8+ skin-resident memory T cells

Skin-resident CD8+ T cells include distinct interferon-γ-producing [tissue-resident memory T type 1 (TRM1)] and interleukin-17 (IL-17)-producing (TRM17) subsets that differentially contribute to immune responses. However, whether these populations use common mechanisms to establish tissue residence is unknown. In this work, we show that TRM1 and TRM17 cells navigate divergent trajectories to acquire tissue residency in the skin. TRM1 cells depend on a T-bet-Hobit-IL-15 axis, whereas TRM17 cells develop independently of these factors. Instead, c-Maf commands a tissue-resident program in TRM17 cells parallel to that induced by Hobit in TRM1 cells, with an ICOS-c-Maf-IL-7 axis pivotal to TRM17 cell commitment. Accordingly, by targeting this pathway, skin TRM17 cells can be ablated without compromising their TRM1 counterparts. Thus, skin-resident T cells rely on distinct molecular circuitries, which can be exploited to strategically modulate local immunity.

Single-cell protein expression profiling resolves circulating and resident memory T cell diversity across tissues and infection contexts

Memory CD8⁺ T cells can be broadly divided into circulating (T_CIRCM) and tissue-resident memory T (T_RM) populations. Despite well-defined migratory and transcriptional differences, the phenotypic and functional delineation of T_CIRCM and T_RM cells, particularly across tissues, remains elusive. Here, we utilized an antibody screening platform and machine learning prediction pipeline (InfinityFlow) to profile >200 proteins in T_CIRCM and T_RM cells in solid organs and barrier locations. High-dimensional analyses revealed unappreciated heterogeneity within T_CIRCM and T_RM cell lineages across nine different organs after either local or systemic murine infection models. Additionally, we demonstrated the relative effectiveness of strategies allowing for the selective ablation of T_CIRCM or T_RM populations across organs and identified CD55, KLRG1, CXCR6, and CD38 as stable markers for characterizing memory T cell function during inflammation. Together, these data and analytical framework provide an in-depth resource for memory T cell classification in both steady-state and inflammatory conditions.

Unlocking autofluorescence in the era of full spectrum analysis: Implications for immunophenotype discovery projects

Understanding the complex elements affecting signal resolution in cytometry is key for quality experimental design and data. In this study, we incorporate autofluorescence as a contributing factor to our understanding of resolution in cytometry and corroborate its impact in fluorescence signal detection through mathematical predictions supported by empirical evidence. Our findings illustrate the critical importance of autofluorescence extraction via full spectrum unmixing in unmasking dim signals and delineating the expression and subset distribution of low abundance markers in discovery projects. We apply our findings to the precise definition of the tissue and cellular distribution of a weakly expressed fluorescent protein that reports on a low-abundance immunological gene. Exploiting the full spectrum coverage enabled by Aurora 5L, we describe a novel approach to the isolation of pure cell subset-specific autofluorescence profiles based on high dimensionality reduction algorithms. This method can also be used to unveil differences in the autofluorescent fingerprints of tissues in homeostasis and after immunological challenges.

Runx3 drives a CD8+ T cell tissue residency program that is absent in CD4+ T cells

Tissue-resident memory T cells (TRM cells) provide rapid and superior control of localized infections. While the transcription factor Runx3 is a critical regulator of CD8+ T cell tissue residency, its expression is repressed in CD4+ T cells. Here, we show that, as a direct consequence of this Runx3-deficiency, CD4+ TRM cells lacked the transforming growth factor (TGF)-β-responsive transcriptional network that underpins the tissue residency of epithelial CD8+ TRM cells. While CD4+ TRM cell formation required Runx1, this, along with the modest expression of Runx3 in CD4+ TRM cells, was insufficient to engage the TGF-β-driven residency program. Ectopic expression of Runx3 in CD4+ T cells incited this TGF-β-transcriptional network to promote prolonged survival, decreased tissue egress, a microanatomical redistribution towards epithelial layers and enhanced effector functionality. Thus, our results reveal distinct programming of tissue residency in CD8+ and CD4+ TRM cell subsets that is attributable to divergent Runx3 activity.

Transitional premonocytes emerge in the periphery for host defense against bacterial infections

Circulating Ly6C^hi monocytes often undergo cellular death upon exhaustion of their antibacterial effector functions, which limits their capacity for subsequent macrophage differentiation. This shrouds the understanding on how the host replaces the tissue-resident macrophage niche effectively during bacterial invasion to avert infection morbidity. Here, we show that proliferating transitional premonocytes (TpMos), an immediate precursor of mature Ly6C^hi monocytes (MatMos), were mobilized into the periphery in response to acute bacterial infection and sepsis. TpMos were less susceptible to apoptosis and served as the main source of macrophage replenishment when MatMos were vulnerable toward bacteria-induced cellular death. Furthermore, TpMo and its derived macrophages contributed to host defense by balancing the proinflammatory cytokine response of MatMos. Consequently, adoptive transfer of TpMos improved the survival outcome of lethal sepsis. Our findings hence highlight a protective role for TpMos during bacterial infections and their contribution toward monocyte-derived macrophage heterogeneity in distinct disease outcomes.

Sphingosine 1-phosphate receptor 5 (S1PR5) regulates the peripheral retention of tissue-resident lymphocytes

Tissue-resident memory T (TRM) cells provide long-lasting immune protection. One of the key events controlling TRM cell development is the local retention of TRM cell precursors coupled to downregulation of molecules necessary for tissue exit. Sphingosine-1-phosphate receptor 5 (S1PR5) is a migratory receptor with an uncharted function in T cells. Here, we show that S1PR5 plays a critical role in T cell infiltration and emigration from peripheral organs, as well as being specifically downregulated in TRM cells. Consequentially, TRM cell development was selectively impaired upon ectopic expression of S1pr5, whereas loss of S1pr5 enhanced skin TRM cell formation by promoting peripheral T cell sequestration. Importantly, we found that T-bet and ZEB2 were required for S1pr5 induction and that local TGF-β signaling was necessary to promote coordinated Tbx21, Zeb2, and S1pr5 downregulation. Moreover, S1PR5-mediated control of tissue residency was conserved across innate and adaptive immune compartments. Together, these results identify the T-bet-ZEB2-S1PR5 axis as a previously unappreciated mechanism modulating the generation of tissue-resident lymphocytes.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (third edition)

The third edition of Flow Cytometry Guidelines provides the key aspects to consider when performing flow cytometry experiments and includes comprehensive sections describing phenotypes and functional assays of all major human and murine immune cell subsets. Notably, the Guidelines contain helpful tables highlighting phenotypes and key differences between human and murine cells. Another useful feature of this edition is the flow cytometry analysis of clinical samples with examples of flow cytometry applications in the context of autoimmune diseases, cancers as well as acute and chronic infectious diseases. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid. All sections are written and peer-reviewed by leading flow cytometry experts and immunologists, making this edition an essential and state-of-the-art handbook for basic and clinical researchers.

Combinatorial Single-Cell Analyses of Granulocyte-Monocyte Progenitor Heterogeneity Reveals an Early Uni-potent Neutrophil Progenitor

Granulocyte-monocyte progenitors (GMPs) have been previously defined for their potential to generate various myeloid progenies such as neutrophils and monocytes. Although studies have proposed lineage heterogeneity within GMPs, it is unclear if committed progenitors already exist among these progenitors and how they may behave differently during inflammation. By combining single-cell transcriptomic and proteomic analyses, we identified the early committed progenitor within the GMPs responsible for the strict production of neutrophils, which we designate as proNeu1. Our dissection of the GMP hierarchy led us to further identify a previously unknown intermediate proNeu2 population. Similar populations could be detected in human samples. proNeu1s, but not proNeu2s, selectively expanded during the early phase of sepsis at the expense of monocytes. Collectively, our findings help shape the neutrophil maturation trajectory roadmap and challenge the current definition of GMPs.

Adoptive cellular therapy with T cells expressing the dendritic cell growth factor Flt3L drives epitope spreading and antitumor immunity

Adoptive cell therapies using genetically engineered T cell receptor or chimeric antigen receptor T cells are emerging forms of immunotherapy that redirect T cells to specifically target cancer. However, tumor antigen heterogeneity remains a key challenge limiting their efficacy against solid cancers. Here, we engineered T cells to secrete the dendritic cell (DC) growth factor Fms-like tyrosine kinase 3 ligand (Flt3L). Flt3L-secreting T cells expanded intratumoral conventional type 1 DCs and substantially increased host DC and T cell activation when combined with immune agonists poly (I:C) and anti-4-1BB. Importantly, combination therapy led to enhanced inhibition of tumor growth and the induction of epitope spreading towards antigens beyond those recognized by adoptively transferred T cells in solid tumor models of T cell receptor and chimeric antigen receptor T cell therapy. Our data suggest that augmenting endogenous DCs is a promising strategy to overcome the clinical problem of antigen-negative tumor escape following adoptive cell therapy.

PD-L1 expression on nonclassical monocytes reveals their origin and immunoregulatory function

The role of nonclassical monocytes (NCMs) in health and disease is emerging, but their location and function within tissues remain poorly explored. Imaging of NCMs has been limited by the lack of an established single NCM marker. Here, we characterize the immune checkpoint molecule PD-L1 (CD274) as an unequivocal marker for tracking NCMs in circulation and pinpoint their compartmentalized distribution in tissues by two-photon microscopy. Visualization of PD-L1⁺ NCMs in relation to bone marrow vasculature reveals that conversion of classical monocytes into NCMs requires contact with endosteal vessels. Furthermore, PD-L1⁺ NCMs are present in tertiary lymphoid organs (TLOs) under inflammatory conditions in both mice and humans, and NCMs exhibit a PD-L1-dependent immunomodulatory function that promotes T cell apoptosis within TLOs. Our findings establish an unambiguous tool for the investigation of NCMs and shed light on their origin and function.

Organ-specific isoform selection of fatty acid binding proteins in tissue-resident lymphocytes

Tissue-resident memory T (TRM) cells exist throughout the body where they are poised to mediate local immune responses. Although studies have defined a common mechanism of residency independent of location, there is likely to be a level of specialization that adapts TRM cells to their given tissue of lodgment. It has been shown that TRM cells in the skin rely on the uptake of exogenous fatty acids for their survival and upregulate fatty acid binding proteins (FABP) 4 and FABP 5 as part of their transcriptional program. However, FABPs exist as a larger family of isoforms with different members selected in a tissue-specific fashion that is optimized for local fatty acid availability. Here we show that although TRM cells in a range of tissue widely express FABPs, they are not restricted to FABP 4 and 5. Instead, TRM cells show varying patterns of isoform usage that are determined by tissue-derived factors. These patterns are malleable since TRM cells relocated to different organs modify their FABP expression in line with their new location. As a consequence, these results argue for tissue-specific overlays to the TRM cell residency program, including FABP expression that is tailored to the particular tissue of TRM cell lodgment.

Organ-specific isoform selection of fatty acid–binding proteins in tissue-resident lymphocytes

Tissue-resident memory T (TRM) cells exist throughout the body, where they are poised to mediate local immune responses. Although studies have defined a common mechanism of residency independent of location, there is likely to be a level of specialization that adapts TRM cells to their given tissue of lodgment. It has been shown that TRM cells in the skin rely on the uptake of exogenous fatty acids for their survival and up-regulate fatty acid–binding protein 4 (FABP4) and FABP5 as part of their transcriptional program. However, FABPs exist as a larger family of isoforms, with different members selected in a tissue-specific fashion that is optimized for local fatty acid availability. Here, we show that although TRM cells in a range of tissue widely express FABPs, they are not restricted to FABP4 and FABP5. Instead, TRM cells show varying patterns of isoform usage that are determined by tissue-derived factors. These patterns are malleable because TRM cells relocated to different organs modify their FABP expression in line with their new location. As a consequence, these results argue for tissue-specific overlays to the TRM cell residency program, including FABP expression that is tailored to the particular tissue of TRM cell lodgment.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.

A Neutrophil Timer Coordinates Immune Defense and Vascular Protection

Neutrophils eliminate pathogens efficiently but can inflict severe damage to the host if they over-activate within blood vessels. It is unclear how immunity solves the dilemma of mounting an efficient anti-microbial defense while preserving vascular health. Here, we identify a neutrophil-intrinsic program that enabled both. The gene Bmal1 regulated expression of the chemokine CXCL2 to induce chemokine receptor CXCR2-dependent diurnal changes in the transcriptional and migratory properties of circulating neutrophils. These diurnal alterations, referred to as neutrophil aging, were antagonized by CXCR4 (C-X-C chemokine receptor type 4) and regulated the outer topology of neutrophils to favor homeostatic egress from blood vessels at night, resulting in boosted anti-microbial activity in tissues. Mice engineered for constitutive neutrophil aging became resistant to infection, but the persistence of intravascular aged neutrophils predisposed them to thrombo-inflammation and death. Thus, diurnal compartmentalization of neutrophils, driven by an internal timer, coordinates immune defense and vascular protection.

Streamlining volumetric multi-channel image cytometry using hue-saturation-brightness-based surface creation

Image cytometry is the process of converting image data to flow cytometry-style plots, and it usually requires computer-aided surface creation to extract out statistics for cells or structures. One way of dealing with structures stained with multiple markers in three-dimensional images, is carrying out multiple rounds of channel co-localization and image masking before surface creation, which is cumbersome and laborious. We propose the application of the hue-saturation-brightness color space to streamline this process, which produces complete surfaces, and allows the user to have a global view of the data before flexibly defining cell subsets. Spectral compensation can also be performed after surface creation to accurately resolve different signals. We demonstrate the utility of this workflow in static and dynamic imaging datasets of a needlestick injury on the mouse ear, and we believe this scalable and intuitive approach will improve the ease of performing histocytometry on biological samples.

Yingrou Tan et al. present a method streamlining surface creation in 3D imaging by applying the hue-saturation-brightness transformed channels simultaneously. They show the utility of this approach by imaging ear skin following needlestick injury, observing immune cell infiltration.

Hyaluronan Receptor LYVE-1-Expressing Macrophages Maintain Arterial Tone through Hyaluronan-Mediated Regulation of Smooth Muscle Cell Collagen

The maintenance of appropriate arterial tone is critically important for normal physiological arterial function. However, the cellular and molecular mechanisms remain poorly defined. Here, we have shown that in the mouse aorta, resident macrophages prevented arterial stiffness and collagen deposition in the steady state. Using phenotyping, transcriptional profiling, and targeted deletion of Csf1r, we have demonstrated that these macrophages-which are a feature of blood vessels invested with smooth muscle cells (SMCs) in both mouse and human tissues-expressed the hyaluronan (HA) receptor LYVE-l. Furthermore, we have shown they possessed the unique ability to modulate collagen expression in SMCs by matrix metalloproteinase MMP-9-dependent proteolysis through engagement of LYVE-1 with the HA pericellular matrix of SMCs. Our study has unveiled a hitherto unknown homeostatic contribution of arterial LYVE-1⁺ macrophages through the control of collagen production by SMCs and has identified a function of LYVE-1 in leukocytes.

The impact of ischemia-reperfusion injuries on skin resident murine dendritic cells

Pressure ulcers are a chronic problem for patients or the elderly who require extended periods of bed rest. The formation of ulcers is due to repeated cycles of ischemia-reperfusion (IR), which initiates an inflammatory response. Advanced ulcers disrupt the skin barrier, resulting in further complications. To date, the immunological aspect of skin IR has been understudied, partly due to the complexity of the skin immune cells. Through a combination of mass cytometry, confocal imaging and intravital multiphoton imaging, this study establishes a workflow for multidimensionality single cell analysis of skin myeloid cell responses in the context of IR injury with high spatiotemporal resolution. The data generated has provided us with previously uncharacterized insights into the distinct cellular behavior of resident dendritic cells (DCs) and recruited neutrophils post IR. Of interest, we observed a drop in DDC numbers in the IR region, which was subsequently replenished 48h post IR. More importantly, in these cells, we observe an attenuated response to repeated injuries, which may have implications in the subsequent wound healing process.

Organic nanoparticles with ultrahigh quantum yield and aggregation-induced emission characteristics for cellular imaging and real-time two-photon lung vasculature imaging

Organic nanoparticles with a high quantum yield of 90% and aggregation-induced emission characteristics were prepared for cellular imaging and real-time two-photon vasculature imaging of the lungs.

Illuminating the covert mission of mononuclear phagocytes in their regional niches

Monocytes, dendritic cells (DCs) and macrophages have been classically categorized into the mononuclear phagocyte system (MPS) based on their similar functional and phenotypic characteristics. While an increasing amount of research has revealed substantial ontogenic and functional differences among these cells, the reasons behind their heterogeneity and strategic positioning in specific niches throughout the body are yet to be fully elucidated. In this review, we outline how recent advances in intravital imaging studies have dissected this phenomenon and have allowed us to appreciate how MPS cells exploit their regional niches to specialize and maximize their functional properties. Understanding their cellular behavior in each of their specialized microenvironment will eventually allow us to target specific cells and their behavioral patterns for improved vaccine and therapeutic purposes.

A Liver Capsular Network of Monocyte-Derived Macrophages Restricts Hepatic Dissemination of Intraperitoneal Bacteria by Neutrophil Recruitment

The liver is positioned at the interface between two routes traversed by pathogens in disseminating infection. Whereas blood-borne pathogens are efficiently cleared in hepatic sinusoids by Kupffer cells (KCs), it is unknown how the liver prevents dissemination of peritoneal pathogens accessing its outer membrane. We report here that the hepatic capsule harbors a contiguous cellular network of liver-resident macrophages phenotypically distinct from KCs. These liver capsular macrophages (LCMs) were replenished in the steady state from blood monocytes, unlike KCs that are embryonically derived and self-renewing. LCM numbers increased after weaning in a microbiota-dependent process. LCMs sensed peritoneal bacteria and promoted neutrophil recruitment to the capsule, and their specific ablation resulted in decreased neutrophil recruitment and increased intrahepatic bacterial burden. Thus, the liver contains two separate and non-overlapping niches occupied by distinct resident macrophage populations mediating immunosurveillance at these two pathogen entry points to the liver.

CXCR4 identifies transitional bone marrow premonocytes that replenish the mature monocyte pool for peripheral responses

It is well established that Ly6C^hi monocytes develop from common monocyte progenitors (cMoPs) and reside in the bone marrow (BM) until they are mobilized into the circulation. In our study, we found that BM Ly6C^hi monocytes are not a homogenous population, as current data would suggest. Using computational analysis approaches to interpret multidimensional datasets, we demonstrate that BM Ly6C^hi monocytes consist of two distinct subpopulations (CXCR4^hi and CXCR4^lo subpopulations) in both mice and humans. Transcriptome studies and in vivo assays revealed functional differences between the two subpopulations. Notably, the CXCR4^hi subset proliferates and is immobilized in the BM for the replenishment of functionally mature CXCR4^lo monocytes. We propose that the CXCR4^hi subset represents a transitional premonocyte population, and that this sequential step of maturation from cMoPs serves to maintain a stable pool of BM monocytes. Additionally, reduced CXCR4 expression on monocytes, upon their exit into the circulation, does not reflect its diminished role in monocyte biology. Specifically, CXCR4 regulates monocyte peripheral cellular activities by governing their circadian oscillations and pulmonary margination, which contributes toward lung injury and sepsis mortality. Together, our study demonstrates the multifaceted role of CXCR4 in defining BM monocyte heterogeneity and in regulating their function in peripheral tissues.

Neutrophils Self-Regulate Immune Complex-Mediated Cutaneous Inflammation through CXCL2

Deposition of immune complexes (ICs) in tissues triggers acute inflammatory pathology characterized by massive neutrophil influx leading to edema and hemorrhage, and is especially associated with vasculitis of the skin, but the mechanisms that regulate this type III hypersensitivity process remain poorly understood. Here, using a combination of multiphoton intravital microscopy and genomic approaches, we re-examined the cutaneous reverse passive Arthus reaction and observed that IC-activated neutrophils underwent transmigration, triggered further IC formation, and transported these ICs into the interstitium, whereas neutrophil depletion drastically reduced IC formation and ameliorated vascular leakage in vivo. Thereafter, we show that these neutrophils expressed high levels of CXCL2, which further amplified neutrophil recruitment and activation in an autocrine and/or paracrine manner. Notably, CXCL1 expression was restricted to tissue-resident cell types, but IC-activated neutrophils may also indirectly, via soluble factors, modulate macrophage CXCL1 expression. Consistent with their distinct cellular origins and localization, only neutralization of CXCL2 but not CXCL1 in the interstitium effectively reduced neutrophil recruitment. In summary, our study establishes that neutrophils are able to self-regulate their own recruitment and responses during IC-mediated inflammation through a CXCL2-driven feed forward loop.

Tumor stroma and chemokines control T-cell migration into melanoma following Temozolomide treatment

The infiltration of T lymphocytes within tumors is associated with better outcomes in cancer patients, yet current understanding of factors that influence T-lymphocyte infiltration into tumors remains incomplete. In our study, Temozolomide (TMZ), a chemotherapeutic drug used to treat metastatic melanoma, induced T-cell infiltration into transplanted melanoma and into genitourinary (GU) tumors in mice developing spontaneous melanoma. In contrast, TMZ treatment did not increase T-cell infiltration into cutaneous tumors, despite similar increases in the expression of the (C-X-C) chemokines CXCL9 and CXCL10 in all sites after TMZ exposure. Our findings reveal that the matrix architecture of the GU tumor stroma, and its ability to present CXCL9 and CXCL10 after TMZ treatment played a key role in favouring T-cell infiltration. We subsequently demonstrate that modifications of these key elements by combined collagenase and TMZ treatment induced T-cell infiltration into skin tumors. T cells accumulating within GU tumors after TMZ treatment exhibited T helper type-1 effector and cytolytic functional phenotypes, which are important for control of tumor growth. Our findings highlight the importance of the interaction between tumor stroma and chemokines in influencing T-cell migration into tumors, thereby impacting immune control of tumor growth. This knowledge will aid the development of strategies to promote T-cell infiltration into cancerous lesions and has the potential to markedly improve treatment outcomes.

Visualization of bone marrow monocyte mobilization using Cx3cr1gfp/+Flt3L-/- reporter mouse by multiphoton intravital microscopy

Monocytes are innate immune cells that play critical roles in inflammation and immune defense. A better comprehension of how monocytes are mobilized and recruited is fundamental to understand their biologic role in disease and steady state. The BM represents a major "checkpoint" for monocyte homeostasis, as it is the primary site for their production and release. Our study determined that the Cx3cr1(gfp/+) mouse strain is currently the most ideal model for the visualization of monocyte behavior in the BM by multiphoton intravital microscopy. However, we observed that DCs are also labeled with high levels of GFP and thus, interfere with the accuracy of monocyte tracking in vivo. Hence, we generated a Cx3cr1(gfp/+)Flt3L(-/-) reporter mouse and showed that whereas monocyte numbers were not affected, DC numbers were reduced significantly, as DCs but not monocytes depend on Flt3 signaling for their development. We thus verified that mobilization of monocytes from the BM in Cx3cr1(gfp/+)Flt3L(-/-) mice is intact in response to LPS. Collectively, our study demonstrates that the Cx3cr1(gfp/+)Flt3L(-/-) reporter mouse model represents a powerful tool to visualize monocyte activities in BM and illustrates the potential of a Cx3cr1(gfp/+)-based, multifunctionality fluorescence reporter approach to dissect monocyte function in vivo.

Neutrophil mobilization via plerixafor-mediated CXCR4 inhibition arises from lung demargination and blockade of neutrophil homing to the bone marrow

The CXCR4 antagonist plerixafor augments frequency of circulating neutrophils via release from the lung and prevents neutrophil homing to the bone marrow.

Blood neutrophil homeostasis is essential for successful host defense against invading pathogens. Circulating neutrophil counts are positively regulated by CXCR2 signaling and negatively regulated by the CXCR4–CXCL12 axis. In particular, G-CSF, a known CXCR2 signaler, and plerixafor, a CXCR4 antagonist, have both been shown to correct neutropenia in human patients. G-CSF directly induces neutrophil mobilization from the bone marrow (BM) into the blood, but the mechanisms underlying plerixafor-induced neutrophilia remain poorly defined. Using a combination of intravital multiphoton microscopy, genetically modified mice and novel in vivo homing assays, we demonstrate that G-CSF and plerixafor work through distinct mechanisms. In contrast to G-CSF, CXCR4 inhibition via plerixafor does not result in neutrophil mobilization from the BM. Instead, plerixafor augments the frequency of circulating neutrophils through their release from the marginated pool present in the lung, while simultaneously preventing neutrophil return to the BM. Our study demonstrates for the first time that drastic changes in blood neutrophils can originate from alternative reservoirs other than the BM, while implicating a role for CXCR4–CXCL12 interactions in regulating lung neutrophil margination. Collectively, our data provides valuable insights into the fundamental regulation of neutrophil homeostasis, which may lead to the development of improved treatment regimens for neutropenic patients.

Lights, camera, and action: vertebrate skin sets the stage for immune cell interaction with arthropod-vectored pathogens

Despite increasing studies targeted at host-pathogen interactions, vector-borne diseases remain one of the largest economic health burdens worldwide. Such diseases are vectored by hematophagous arthropods that deposit pathogens into the vertebrate host's skin during a blood meal. These pathogens spend a substantial amount of time in the skin that allows for interaction with cutaneous immune cells, suggesting a window of opportunity for development of vaccine strategies. In particular, the recent availability of intravital imaging approaches has provided further insights into immune cell behavior in living tissues. Here, we discuss how such intravital imaging studies have contributed to our knowledge of cutaneous immune cell behavior and specifically, toward pathogen and tissue trauma from the arthropod bite. We also suggest future imaging approaches that may aid in better understanding of the complex interplay between arthropod-vectored pathogens and cutaneous immunity that could lead to improved therapeutic strategies.

Cutting edge: the NLRP3 inflammasome links complement-mediated inflammation and IL-1β release

The complement system is a potent component of the innate immune response, promoting inflammation and orchestrating defense against pathogens. However, dysregulation of complement is critical to several autoimmune and inflammatory syndromes. Elevated expression of the proinflammatory cytokine IL-1β is often linked to such diseases. In this study, we reveal the mechanistic link between complement and IL-1β secretion using murine dendritic cells. IL-1β secretion occurs following intracellular caspase-1 activation by inflammasomes. We show that complement elicits secretion of both IL-1β and IL-18 in vitro and in vivo via the NLRP3 inflammasome. This effect depends on the inflammasome components NLRP3 and ASC, as well as caspase-1 activity. Interestingly, sublethal complement membrane attack complex formation, but not the anaphylatoxins C3a and C5a, activated the NLRP3 inflammasome in vivo. These findings provide insight into the molecular processes underlying complement-mediated inflammation and highlight the possibility of targeting IL-1β to control complement-induced disease and pathological inflammation.

Abstract 1508: TNF-receptor 2 plays a critical role in liver metastasis by regulating sinusoidal endothelial VCAM-1 expression, LY6G+ leukocyte recruitment and transendothelial migration

The hepatic microenvironment can play an important role in promoting liver metastasis. We and others have shown that when metastatic carcinoma cells enter the liver, a rapid inflammatory response mediated by TNF-α is triggered, enabling tumor transendothelial migration and metastasis. TNF-α binds to the cell surface through two receptors; the p55/p60 TNFR1 and the p75/p80 TNFR2. To elucidate the roles of these receptors in the inflammatory cascade and in liver colonization by tumor cells, we used mice with tnfr1, tnfr2 and combined tnfr1/tnfr2 gene deficiencies and investigated parameters of the host response and the outcome of metastasis in these mice using the highly metastatic mouse colon carcinoma MC-38 and lung carcinoma H-59 cells. We found that experimental liver metastasis following intrasplenic/portal inoculation of the tumor cells was markedly reduced in TNFR2−/− and even further in TNFR1−/−/TNFR2−/- female mice as compared to wild-type controls but no reduction was observed in TNFR1−/− mice. To identify the underlying mechanism(s), we investigated changes in the liver microenvironment following tumor inoculation using a combination of immunohistochemistry, confocal microscopy, qRT-PCR, and cytokine/chemokines profiling. We found that while in wild-type and TNFR1−/- mice, VCAM-1 expression on the sinusoidal endothelium was significantly upregulated within 16 hr post tumor injection, it was unchanged in TNFR2−/− and double negative female mice. In addition, qRT-PCR analysis revealed that the production of the neutrophil chemokine CXCL1, while upregulated in control mice, was suppressed in TNFR2−/− mice. These changes were associated with a parallel decrease in Ly6G+ neutrophil recruitment into extravascular, pro-metastatic niches 16-48 hr post tumor inoculation. Interestingly, these reductions were not observed in male TNFR2−/− mice and correspondingly, their metastatic burden was not reduced relative to control mice. Taken together, the results suggest that TNFR2 plays a critical and gender-specific role in Ly6G+ cell recruitment into the tumor-microenvironment by regulating sinusoidal endothelial VCAM-1 expression and chemokine production. In turn, the recruitment of these cells into extravascular pro-metastatic niches appears to promote liver metastasis. Supported by grant MOP-80201 from the Canadian Institute for Health Research. (to PB) and by a McGill Integrated Cancer Research Training Program fellowship (to BH).

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1508. doi:1538-7445.AM2012-1508

Gamma spectrum unfolding for a NaI monitor of radioactivity in aquatic systems

Spectrum unfolding is a powerful method that can enhance the readability of experimental energy spectra obtained by detectors of poor resolution. It is applied to the NaI-based monitor. The UMG 3.3 package is used for unfolding the experimental spectra with the response matrix obtained by MCNP4c2. The main parameter influencing the quality of the results is the chi(2). The goal of this study is to optimize the choice of this factor. The statistical accuracy of the technique is evaluated.

Prevalence of GBV-C/hepatitis G virus RNA and E2 antibody among subjects infected with human immunodeficiency virus type 1 after parenteral or sexual exposure

GB virus C (GBV-C) or hepatitis G virus (HGV) is transmitted by the parenteral route but the importance of sexual transmission needs to be ascertained. GBV-C/HGV infections were investigated using RNA and E2-antibody detection methods in 80 subjects infected by the human immunodeficiency virus type 1 (HIV-1) divided into 4 groups of 20 individuals each according to their main risk factor for HIV-1 infection: blood product recipients (group 1), intravenous drug users (group 2), homosexuals (group 3), or heterosexual exposure (group 4). The overall prevalence of GBV-C/HGV infection was 66.3%. No significant difference was observed in GBV-C/ HGV prevalence among the four groups: 75, 75, 55, and 60% in groups 1, 2, 3, and 4, respectively. Hepatitis C virus (HCV) antibodies, used as a control for parenteral exposure, were found in 70% and 90% of the subjects in groups 1 and 2 versus only 15% and 20% of the subjects in groups 3 and 4, respectively (P< .001). Similarly, coinfections with GBV-C/HGV and HCV were significantly associated with the parenteral route (P <.001). These data emphasized the usefulness of combining the detection of RNA and the E2 antibody to determine the actual prevalence of GBV-C/HGV infection. The high prevalence of the GBV-C/HGV markers among the HIV-1-infected subjects, especially those with sexual exposure, provides additional evidence that this route of transmission plays a key role in the epidemiology of GBV-C/HGV. The potential influence of GBV-C/HGV infection on the course of HIV-1 disease needs further evaluation.

Nitrogen balance and myofibrillar protein turnover in double muscled Belgian Blue bulls in relation to compensatory growth after different periods of restricted feeding

Nitrogen balance and myofibrillar protein breakdown were studied in 16 double-muscled Belgian Blue bulls during a low growth period (0.5 kg d−1) (LGP) of 4 mo (L4), 8 mo (L8), or 14 mo (L14) and the subsequent fattening period (rapid growth period, RGP). The control group (CG) was given a conventional fattening diet; the others received a low-energy, low-protein diet during LGP, and the same diet as the CG during RGP. Measurements were made halfway through the LGP, l mo after the beginning of the fattening period, and 1 mo before slaughter. Nitrogen balance was about half of CG (P < 0.001) during LGP, e.g., 50.8, 21.3, 25.8, and 23.8 g d−1, for CG, L4, L8, and L14, respectively. Between LGP and RGP, N balance increased by about 18 g N d−1 above the control in the compensating groups L4, L8 and L14. This was due to the higher digestibility and the higher metabolizability of the nitrogen in the fattening diet. Lower muscle protein accretion during the LGP resulted from decreased synthesis (P < 0.001) and degradation (P < 0.05) compared with the GC. When changing to RGP different evolution patterns were observed in the three formerly restricted groups, e.g. after a short restriction (L4) both synthesis and degradation rose during the RGP but declined towards the end. After a longer restriction (L8 and L14), synthesis and degradation increased and remained high. The magnitude of these increases was inversely proportional to the length of the restriction period. Key words: Belgian Blue bulls, compensatory growth, nitrogen balance, muscle, muscle protein breakdown

Phase II trial of spirogermanium in advanced non-small cell lung cancer. An Illinois Cancer Council Study

A phase II trial of spirogermanium was conducted in advanced previously untreated non-small cell lung cancer patients. The drug was given by intravenous infusion 3 times per week for 2 weeks, twice per week for the next 2 weeks, and then weekly. Starting dose was 125 mg/m2, and dose escalation of 25 mg/m2 per week was required in the absence of toxicity to a maximum dose of 200 mg/m2 per infusion. Fifteen eligible patients were treated, and no objective responses were seen. Primary toxicity was neurologic and reversible after withdrawal of the drug. We conclude that spirogermanium is not active against non-small cell lung cancer in the dosage used in this study.