Overlapping and selective roles of endothelial intercellular adhesion molecule-1 (ICAM-1) and ICAM-2 in lymphocyte trafficking

ICAMs in Immunity, Intercellular Adhesion and Communication

Interactions among leukocytes and leukocytes with immune-associated auxiliary cells represent an essential feature of the immune response that requires the involvement of cell adhesion molecules (CAMs). In the immune system, CAMs include a wide range of members pertaining to different structural and functional families involved in cell development, activation, differentiation and migration. Among them, β2 integrins (LFA-1, Mac-1, p150,95 and αDβ2) are predominantly involved in homotypic and heterotypic leukocyte adhesion. β2 integrins bind to intercellular (I)CAMs, actin cytoskeleton-linked receptors belonging to immunoglobulin superfamily (IgSF)-CAMs expressed by leukocytes and vascular endothelial cells, enabling leukocyte activation and transendothelial migration. β2 integrins have long been viewed as the most important ICAMs partners, propagating intracellular signalling from β2 integrin-ICAM adhesion receptor interaction. In this review, we present previous evidence from pioneering studies and more recent findings supporting an important role for ICAMs in signal transduction. We also discuss the contribution of immune ICAMs (ICAM-1, -2, and -3) to reciprocal cell signalling and function in processes in which β2 integrins supposedly take the lead, paying particular attention to T cell activation, differentiation and migration.

LFA-1/ICAM-1 Adhesion Pathway Mediates the Homeostatic Migration of Lymphocytes from Peripheral Tissues into Lymph Nodes through Lymphatic Vessels

Lymphocyte function-associated antigen-1 (LFA-1) and its endothelial ligand intercellular adhesion molecule-1 (ICAM-1) are important for the migration of lymphocytes from blood vessels into lymph nodes. However, it is largely unknown whether these molecules mediate the homeostatic migration of lymphocytes from peripheral tissues into lymph nodes through lymphatic vessels. In this study, we find that, in naive mice, ICAM-1 is expressed on the sinus endothelia of lymph nodes, but not on the lymphatic vessels of peripheral tissues. In in vivo lymphocyte migration assays, memory CD4+ T cells migrated to lymph nodes from peripheral tissues much more efficiently than from blood vessels, as compared to naive CD4+ T cells. Moreover, ICAM-1 deficiency in host mice significantly inhibited the migration of adoptively transferred wild-type donor lymphocytes from peripheral tissues, but not from blood vessels, into lymph nodes. The migration of LFA-1-deficient donor lymphocytes from peripheral tissues into the lymph nodes of wild-type host mice was also significantly reduced as compared to wild-type donor lymphocytes. Furthermore, the number of memory T cells in lymph nodes was significantly reduced in the absence of ICAM-1 or LFA-1. Thus, our study extends the functions of the LFA-1/ICAM-1 adhesion pathway, indicating its novel role in controlling the homeostatic migration of lymphocytes from peripheral tissues into lymph nodes and maintaining memory T cellularity in lymph nodes.

Intercellular Adhesion Molecule 1: More than a Leukocyte Adhesion Molecule

Intercellular adhesion molecule 1 (ICAM-1) is a transmembrane protein in the immunoglobulin superfamily expressed on the surface of multiple cell populations and upregulated by inflammatory stimuli. It mediates cellular adhesive interactions by binding to the β2 integrins macrophage antigen 1 and leukocyte function-associated antigen 1, as well as other ligands. It has important roles in the immune system, including in leukocyte adhesion to the endothelium and transendothelial migration, and at the immunological synapse formed between lymphocytes and antigen-presenting cells. ICAM-1 has also been implicated in the pathophysiology of diverse diseases from cardiovascular diseases to autoimmune disorders, certain infections, and cancer. In this review, we summarize the current understanding of the structure and regulation of the ICAM1 gene and the ICAM-1 protein. We discuss the roles of ICAM-1 in the normal immune system and a selection of diseases to highlight the breadth and often double-edged nature of its functions. Finally, we discuss current therapeutics and opportunities for advancements.

Manipulating adrenergic stress receptor signalling to enhance immunosuppression and prolong survival of vascularized composite tissue transplants

BACKGROUND

Vascularized composite tissue allotransplantation (VCA) to replace limbs or faces damaged beyond repair is now possible. The resulting clear benefit to quality of life is a compelling reason to attempt this complex procedure. Unfortunately, the high doses of immunosuppressive drugs required to protect this type of allograft result in significant morbidity and mortality giving rise to ethical concerns about performing this surgery in patients with non-life-threatening conditions. Here we tested whether we could suppress anti-graft immune activity by using a safe β2 -adrenergic receptor (AR) agonist, terbutaline, to mimic the natural immune suppression generated by nervous system-induced signalling through AR.

METHODS

A heterotopic hind limb transplantation model was used with C57BL/6 (H-2b) as recipients and BALB/c (H-2d) mice as donors. To test the modulation of the immune response, graft survival was investigated after daily intraperitoneal injection of β2 -AR agonist with and without tacrolimus. Analyses of immune compositions and quantification of pro-inflammatory cytokines were performed to gauge functional immunomodulation. The contributions to allograft survival of β2 -AR signalling in donor and recipient tissue were investigated with β2 -AR-/- strains.

RESULTS

Treatment with the β2 -AR agonist delayed VCA rejection, even with a subtherapeutic dose of tacrolimus. β2 -AR agonist decreased T-cell infiltration into the transplanted grafts and decreased memory T-cell populations in recipient's circulation. In addition, decreased levels of inflammatory cytokines (IFN-γ, IL-6, TNF-α, CXCL-1/10 and CCL3/4/5/7) were detected following β2 -AR agonist treatment, and there was a decreased expression of ICAM-1 and vascular cell adhesion molecule-1 in donor stromal cells.

CONCLUSIONS

β2 -AR agonist can be used safely to mimic the natural suppression of immune responses, which occurs during adrenergic stress-signalling and thereby can be used in combination regimens to reduce the dose needed of toxic immunosuppressive drugs such as tacrolimus. This strategy can be further evaluated for feasibility in the clinic.

Endothelial cells of pulmonary origin display unique sensitivity to the bacterial endotoxin lipopolysaccharide

Acute respiratory distress syndrome (ARDS) is a major clinical problem without available therapies. Known risks for ARDS include severe sepsis, SARS-CoV-2, gram-negative bacteria, trauma, pancreatitis, and blood transfusion. During ARDS, blood fluids and inflammatory cells enter the alveoli, preventing oxygen exchange from air into blood vessels. Reduced pulmonary endothelial barrier function, resulting in leakage of plasma from blood vessels, is one of the major determinants in ARDS. It is, however, unknown why systemic inflammation particularly targets the pulmonary endothelium, as endothelial cells (ECs) line all vessels in the vascular system of the body. In this study, we examined ECs of pulmonary, umbilical, renal, pancreatic, and cardiac origin for upregulation of adhesion molecules, ability to facilitate neutrophil (PMN) trans-endothelial migration (TEM) and for endothelial barrier function, in response to the gram-negative bacterial endotoxin LPS. Interestingly, we found that upon LPS stimulation, pulmonary ECs showed increased levels of adhesion molecules, facilitated more PMN-TEM and significantly perturbed the endothelial barrier, compared to other types of ECs. These observations could partly be explained by a higher expression of the adhesion molecule ICAM-1 on the pulmonary endothelial surface compared to other ECs. Moreover, we identified an increased expression of Cadherin-13 in pulmonary ECs, for which we demonstrated that it aids PMN-TEM in pulmonary ECs stimulated with LPS. We conclude that pulmonary ECs are uniquely sensitive to LPS, and intrinsically different, compared to ECs from other vascular beds. This may add to our understanding of the development of ARDS upon systemic inflammation.

Targeting intercellular adhesion molecule-1 (ICAM-1) to reduce rhinovirus-induced acute exacerbations in chronic respiratory diseases

The chronic respiratory non-communicable diseases, asthma and chronic obstructive pulmonary disease (COPD) are among the leading causes of global mortality and morbidity. Individuals suffering from these diseases are particularly susceptible to respiratory infections caused by bacterial and/or viral pathogens, which frequently result in exacerbation of symptoms, lung function decline, frequent hospital emergency visits and increased socioeconomic burden. Human rhinoviruses (HRV) remain the major viral pathogen group implicated in exacerbations of both asthma and COPD. The rhinoviral entry into the host lung epithelium is facilitated primarily by the adhesion site (“receptor”) intercellular adhesion molecule-1 (ICAM-1), coincidentally expressed on the respiratory epithelium in these conditions. Multiple observations of increased airway ICAM-1 protein in asthmatics, smokers and smoking-related COPD have been recorded in the literature. However, the lack of robust therapies for COPD in particular has triggered a renewed interest in assessing receptor antagonism-based anti-viral strategies for treatment of intercurrent viral infections in those with pre-existing chronic lung diseases. Given the crucial role ICAM-1 plays in facilitating HRV adhesion and, thus, transmissibility to the host respiratory system, as well as the up-regulation of ICAM-1 by smoking, we summarize the role of HRV in smoking-induced COPD and especially highlight the role of ICAM-1 in epithelial viral adhesion and chronic lung disease progression. Further, the review also sheds light specifically on evolving precision therapeutic strategies in blocking ICAM-1 for preventing viral adhesion and exacerbations of COPD.

FVIII regulates the molecular profile of endothelial cells: functional impact on the blood barrier and macrophage behavior

Hemophilia A is an inherited X-linked recessive bleeding disorder caused by deficient activity of blood coagulation factor VIII (FVIII). In addition, hemophilia patients show associated diseases including osteopenia, altered inflammation and vascular fragility which may represent the consequence of recurrent bleeding or may be related to the direct FVIII deficiency. Nowadays, recombinant FVIII is proposed to treat hemophilia patients with no circulating FVIII inhibitor. Initially described as a coenzyme to factor IXa for initiating thrombin generation, there is emerging evidence that FVIII is involved in multiple biological systems, including bone, vascular and immune systems. The present study investigated: (i) the functional activities of recombinant human FVIII (rFVIII) on endothelial cells, and (ii) the impact of rFVIII activities on the functional interactions of human monocytes and endothelial cells. We then investigated whether rFVIII had a direct effect on the adhesion of monocytes to the endothelium under physiological flow conditions. We observed that direct biological activities for rFVIII in endothelial cells were characterized by: (i) a decrease in endothelial cell adhesion to the underlying extracellular matrix; (ii) regulation of the transcriptomic and protein profiles of endothelial cells; (iii) an increase in the vascular tubes formed and vascular permeability in vitro; and (iv) an increase in monocyte adhesion activated endothelium and transendothelial migration. By regulating vascular permeability plus leukocyte adhesion and transendothelial migration, the present work highlights new biological functions for FVIII.

Immune Responses to IAV Infection and the Roles of L-Selectin and ADAM17 in Lymphocyte Homing

Influenza A virus (IAV) infection is a global public health burden causing up to 650,000 deaths per year. Yearly vaccination programmes and anti-viral drugs currently have limited benefits; therefore, research into IAV is fundamental. Leukocyte trafficking is a crucial process which orchestrates the immune response to infection to protect the host. It involves several homing molecules and receptors on both blood vessels and leukocytes. A key mediator of this process is the transmembrane glycoprotein L-selectin, which binds to vascular addressins on blood vessel endothelial cells. L-selectin classically mediates homing of naïve and central memory lymphocytes to lymph nodes via high endothelial venules (HEVs). Recent studies have found that L-selectin is essential for homing of activated CD8⁺ T cells to influenza-infected lungs and reduction in virus load. A disintegrin and metalloproteinase 17 (ADAM17) is the primary regulator of cell surface levels of L-selectin. Understanding the mechanisms that regulate these two proteins are central to comprehending recruitment of T cells to sites of IAV infection. This review summarises the immune response to IAV infection in humans and mice and discusses the roles of L-selectin and ADAM17 in T lymphocyte homing during IAV infection.

The Micro-Immunotherapy Medicine 2LEID Exhibits an Immunostimulant Effect by Boosting Both Innate and Adaptive Immune Responses

This study aimed at evaluating the effects of the micro-immunotherapy medicine (MIM) 2LEID, both in vitro and in vivo, on several components of the innate and adaptive immune system. MIM increased the phagocytic activity of macrophages, and it augmented the expression of the activation markers CD69 and HLA-DR in NK cells and monocytes/macrophages, respectively. The effect of MIM was evaluated in a model of respiratory infection induced by influenza A virus administration to immunocompetent mice in which it was able to improve neutrophil recruitment within the lungs (p = 0.1051) and slightly increased the circulating levels of IgM (p = 0.1655). Furthermore, MIM stimulated the proliferation of CD3-primed T lymphocytes and decreased the secretion of the immunosuppressive cytokine IL-10 in CD14⁺-derived macrophages. Human umbilical vein endothelial cells were finally used to explore the effect of MIM on endothelial cells, in which it slightly increased the expression of immune-related markers such as HLA-I, CD137L, GITRL, PD-L1 and ICAM-1. In conclusion, the present study suggests that MIM might be a promising nonspecific (without antigen specificity) immunostimulant drug in preventing and early treating respiratory infections, but not only exclusively, as it would gently support several facets of the immune system and host defenses.

Transforming growth factor (TGF)-β1 and interferon (IFN)-γ differentially regulate ICAM-1 expression and adhesion of Toxoplasma gondii to human trophoblast (BeWo) and uterine cervical (HeLa) cells

Toxoplasma gondii is a parasite able to infect various cell types, including trophoblast cells. Studies have demonstrated that interleukin (IL)-10, transforming growth factor (TGF)-β1 and interferon (IFN)-γ are involved in the susceptibility of BeWo trophoblast cells to T. gondii infection. Furthermore, T. gondii is able to adhere to the plasma membrane of host cells through intercellular adhesion molecule (ICAM)-1. Thus, the present study aimed to assess the role of IL-10, TGF-β1 and IFN-γ in the expression of ICAM-1 in BeWo and HeLa cells and to analyze the role of ICAM-1 in the adhesion and invasion of T. gondii to these cells under the influence of these cytokines. For this purpose, BeWo and HeLa cells were treated or not, before and after T. gondii infection, with rIL-10, rTGF-β1 or rIFN-γ. For the BeWo cells, rIL-10 and rTGF-β1 favored susceptibility to infection, but only rTGF-β1 and rIFN-γ increased ICAM-1 expression, and TNF-α release. On the other hand, rIFN-γ downregulated the expression of ICAM-1 triggered by T. gondii in HeLa cells, leading to control of the infection. Moreover, we observed that upregulation of ICAM-1, mediated by cytokine's stimulation, in BeWo and HeLa cells resulted in a high number rate of both parasite adhesion and invasion to these cells, which were strongly reduced after ICAM-1 neutralization. Likewise, the blockage of ICAM-1 molecule also impaired T. gondii infection in human villous explants. Taken together, these findings demonstrate that TGF-β1 and IFN-γ differentially regulate ICAM-1 expression, which may interfere in the adhesion/invasion of T. gondii to BeWo and HeLa cells for modulating susceptibility to infection.

Lymph Node Stromal Cell-Intrinsic MHC Class II Expression Promotes MHC Class I-Restricted CD8 T Cell Lineage Conversion to Regulatory CD4 T Cells

MHC class I (MHC-I)-restricted CD4⁺ T cells have long been discovered in the natural repertoire of healthy humans as well as patients with autoimmune diseases or cancer, but the exact origin of these cells remains to be fully characterized. In mouse models, mature peripheral CD8⁺ T cells have the potential to convert to CD4⁺ T cells in the mesenteric lymph nodes. This conversion can produce a unique population of MHC-I-restricted CD4⁺ T cells including Foxp3⁺ regulatory T cells termed MHC-I-restricted CD4⁺Foxp3⁺ T (CI-T_reg) cells. In this study we examined the cellular and molecular elements that promote CD8-to-CD4 lineage conversion and the development of CI-T_reg cells in mice. Using adoptive transfer and bone marrow chimera experiments, we found that the differentiation of CI-T_reg cells was driven by lymph node stromal cell (LNSC)-intrinsic MHC-II expression as opposed to transcytosis of MHC-II from bone marrow-derived APCs. The lineage conversion was accompanied by Runx3 versus ThPOK transcriptional switch. This finding of a new role for LNSCs in vivo led us to develop an efficient tissue culture method using LNSCs to generate and expand CI-T_reg cells in vitro. CI-T_reg cells expanded in vitro with LNSCs effectively suppressed inflammatory tissue damage caused by pathogenic CD4⁺ T cells in mouse models of colitis. This study identified a novel role of MHC-II expressed by LNSCs in immune regulation and the potential utilization of LNSCs to generate novel subsets of immune regulatory cells for therapeutic applications.

ICAM-1 and ICAM-2 Are Differentially Expressed and Up-Regulated on Inflamed Pulmonary Epithelium, but Neither ICAM-2 nor LFA-1: ICAM-1 Are Required for Neutrophil Migration Into the Airways In Vivo

Neutrophil migration into the airways is an important process to fight infection and is mediated by cell adhesion molecules. The intercellular adhesion molecules, ICAM-1 (CD54) and ICAM-2 (CD102) are known ligands for the neutrophil integrins, lymphocyte function associated antigen (LFA)-1 (αLβ2; CD11a/CD18), and macrophage-1 antigen (Mac-1;αMβ2;CD11b/CD18) and are implicated in leukocyte migration into the lung. However, it is ill-defined how neutrophils exit the lung and the role for ICAMs in trans-epithelial migration (TEpM) across the bronchial or alveolar epithelium. We found that human and murine alveolar epithelium expressed ICAM-1, whilst the bronchial epithelium expressed ICAM-2, and both were up-regulated during inflammatory stimulation in vitro and in inflammatory lung diseases such as cystic fibrosis. Although β2 integrins interacting with ICAM-1 and -2 mediated neutrophil migration across human bronchial epithelium in vitro, neither ICAM-2 nor LFA-1 binding of ICAM-1 mediated murine neutrophil migration into the lung or broncho-alveolar space during LPS-induced inflammation in vivo. Furthermore, TEpM of neutrophils themselves resulted in increased epithelial junctional permeability and reduced barrier function in vitro. This suggests that although β2 integrins interacting with ICAMs may regulate low levels of neutrophil traffic in healthy lung or early in inflammation when the epithelial barrier is intact; these interactions may be redundant later in inflammation when epithelial junctions are disrupted and no longer limit TEpM.

Long-term physical training in adolescent sprint and middle distance swimmers alters the composition of circulating T and NK cells which correlates with soluble ICAM-1 serum concentrations

Purpose

It remains unknown how different training intensities and volumes chronically impact circulating lymphocytes and cellular adhesion molecules. First, we aimed to monitor changes in NK and T cells over a training season and relate these to training load. Second, we analyzed effects of training differences between swimmers on these cells. Finally, we examined if changes in lymphocytes were associated with sICAM-1 concentrations.

Methods

We analyzed weekly training volume, training intensity, proportions of T and NK cells and serum sICAM-1 in eight sprint (SS) and seven middle-distance swimmers (MID) at three points over a 16-week training period: at the start (t₀), after 7 weeks of increased training load (t₇) and after 16 weeks, including 5-day taper (t₁₆).

Results

Training volume of all swimmers was statistically higher and training intensity lower from t₀–t₇ compared to t₇–t₁₆ (p = 0.001). Secondly, training intensity was statistically higher in SS from t₀–t₇ (p = 0.004) and t₇–t₁₆ (p = 0.015), while MID had a statistically higher training volume from t₇–t₁₆ (p = 0.04). From t₀–t₇, NK (p = 0.06) and CD45RA⁺CD45RO⁺CD4⁺ cells (p < 0.001) statistically decreased, while CD45RA⁻CD45RO⁺CD4⁺ cells (p = 0.024) statistically increased. In a subgroup analysis, SS showed statistically larger increases in NK cells from t₇–t₁₆ than MID (p = 0.012). Lastly, sICAM-1 concentrations were associated with changes in CD45RA⁻CDRO⁺CD4⁺ cells (r = − 0.656, p = 0.08).

Conclusion

These results indicate that intensified training in swimmers resulted in transient changes in T and NK cells. Further, NK cells are sensitive to high training volumes. Lastly, sICAM-1 concentrations may be associated with the migration and maturation of CD4⁺ cells in athletes.

Effects of hyperbaric oxygen therapy on the healing of thermal burns and its relationship with ICAM-1: A case-control study

Background

The damaging effects of thermal burns need to be managed holistically in order to create a suitable environment for wound healing. The purpose of our study was to investigate the effects of hyperbaric oxygen therapy (HBOT) on the healing of thermal burns and its relationship with intercellular adhesion molecule 1 (ICAM-1).

Methods

Twenty patients with thermal burns were randomly divided into two groups: the group to receive HBOT and the control group. Levels of the ICAM-1 mRNA gene and ICAM-1 serum along with the degree of wound epithelialization were examined before and after treatment. Laboratory and physical findings between the groups were compared.

Results

In the HBOT group compared with the control group, thermal wound complications were significantly reduced (p = .006), while length of stay in hospital was substantially reduced (p = .001). ICAM-1 serum levels strongly correlated with ICAM-1 mRNA gene expression (R² = 0.909, p < .001). The expression of the ICAM-1 mRNA gene (12.32 ± 1.31 vs. 10.79 ± 1.38) and ICAM-1 serum level (231.46 ± 37.20 vs. 158.23 ± 68.30) in patients with at least a 50% burn area exceeded those of patients with a smaller burn area. HBOT significantly decreased (p < .05) the expression of the ICAM-1 mRNA gene and ICAM-1 serum level (p = .004). The number of HBOT sessions strongly correlated with ICAM-1 serum level (p = .043) but poorly correlated with ICAM-1 mRNA gene expression (p = .22). The expression of the gene, however, strongly correlated with ICAM-1 serum level (r = −0.988, p < .001).

Conclusion

HBOT can reduce thermal wound complications, length of stay in hospitals due to thermal burns, ICAM-1 mRNA gene expression, and ICAM-1 serum level.

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Thermal burns are serious injuries with detrimental effects that require prompt treatment.

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The inflammatory process that occurs due to burns increases the production of ICAM-1.

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HBOT works by increasing the pressure of oxygen such that it can directly diffuse into various tissues.

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The effects of increased oxygen supply include angiogenesis, increased fibroblast proliferation, and reduced tissue edema.

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HBOT can reduce thermal wound complications, and length of stay in hospitals.

Lymphatic Valves Separate Lymph Flow Into a Central Stream and a Slow-Moving Peri-Valvular Milieu

The lymphatic system plays a pivotal role in the transport of fats, waste, and immune cells, while also serving as a metastatic route for select cancers. Using live imaging and particle tracking, we experimentally characterized the lymph flow field distal from the inguinal lymph node in the vicinity of normal bileaflet and malformed unileaflet intraluminal valves. Particle tracking experiments demonstrated that intraluminal lymphatic valves concentrate higher velocity lymph flow in the center of the vessel, while generating adjacent perivalvular recirculation zones. The recirculation zones are characterized by extended particle residence times and low wall shear stress (WSS) magnitudes in comparison to the rest of the lymphangion. A malformed unileaflet valve skewed lymph flow toward the endothelium on the vessel wall, generating a stagnation point and a much larger recirculation zone on the opposite wall. These studies define physical consequences of bileaflet and unileaflet intraluminal lymphatic valves that affect lymph transport and the generation of a heterogeneous flow field that affects the lymphatic endothelium nonuniformly. The characterized flow fields were recreated in vitro connecting different flow environments present in the lymphangion to a lymphatic endothelial cell (LEC) pro-inflammatory phenotype. Unique and detailed insight into lymphatic flow is provided, with potential applications to a variety of diseases that affect lymph transport and drug delivery.

Bayesian correlation is a robust gene similarity measure for single-cell RNA-seq data

Assessing similarity is highly important for bioinformatics algorithms to determine correlations between biological information. A common problem is that similarity can appear by chance, particularly for low expressed entities. This is especially relevant in single-cell RNA-seq (scRNA-seq) data because read counts are much lower compared to bulk RNA-seq. Recently, a Bayesian correlation scheme that assigns low similarity to genes that have low confidence expression estimates has been proposed to assess similarity for bulk RNA-seq. Our goal is to extend the properties of the Bayesian correlation in scRNA-seq data by considering three ways to compute similarity. First, we compute the similarity of pairs of genes over all cells. Second, we identify specific cell populations and compute the correlation in those populations. Third, we compute the similarity of pairs of genes over all clusters, by considering the total mRNA expression. We demonstrate that Bayesian correlations are more reproducible than Pearson correlations. Compared to Pearson correlations, Bayesian correlations have a smaller dependence on the number of input cells. We show that the Bayesian correlation algorithm assigns high similarity values to genes with a biological relevance in a specific population. We conclude that Bayesian correlation is a robust similarity measure in scRNA-seq data.

DAMPs and NETs in Sepsis

Sepsis is a deadly inflammatory syndrome caused by an exaggerated immune response to infection. Much has been focused on host response to pathogens mediated through the interaction of pathogen-associated molecular patterns (PAMPs) and pattern recognition receptors (PRRs). PRRs are also activated by host nuclear, mitochondrial, and cytosolic proteins, known as damage-associated molecular patterns (DAMPs) that are released from cells during sepsis. Some well described members of the DAMP family are extracellular cold-inducible RNA-binding protein (eCIRP), high mobility group box 1 (HMGB1), histones, and adenosine triphosphate (ATP). DAMPs are released from the cell through inflammasome activation or passively following cell death. Similarly, neutrophil extracellular traps (NETs) are released from neutrophils during inflammation. NETs are webs of extracellular DNA decorated with histones, myeloperoxidase, and elastase. Although NETs contribute to pathogen clearance, excessive NET formation promotes inflammation and tissue damage in sepsis. Here, we review DAMPs and NETs and their crosstalk in sepsis with respect to their sources, activation, release, and function. A clear grasp of DAMPs, NETs and their interaction is crucial for the understanding of the pathophysiology of sepsis and for the development of novel sepsis therapeutics.

Toxoplasma gondii causes increased ICAM-1 and serotonin expression in the jejunum of rats 12 h after infection

OBJECTIVE

To analyze the remodeling dynamics of total collagen, type I and III, the expression of ICAM-1 and 5-HT in the jejunum of rats.

METHODS

Twenty-eight Wistar rats were randomly assigned to two experimental groups: the control group (CG, n = 7) and the infected group (receiving 5,000 sporulated T. gondii oocysts - ME49 strain, genotype II, n = 21). Seven infected rats each at 6 (G6), 12 (G12), and 24 (G24) hours post infection were sacrificed and segments of jejunum were collected for standard histological, histochemical, and immunohistochemistry processing techniques.

RESULTS

The infection promoted ICAM-1 and 5-HT expression, type III collagen, and total mast cell increases. However, it also caused a reduction in the area occupied by type I collagen fibers, and in submucosa thickness, and caused ganglion and peri-ganglion alterations.

CONCLUSION

The structural damage caused by toxoplasmic infection is intense during the first 24 h post inoculation. At peak dissemination, from 12 to 24 h, there is an increase in ICAM-1 and 5-HT expression, with intense migration of mast cells to the site of infection. There was also a reduction in submucosa thickness, and an effective loss of extracellular matrix (ECM) organization, which included changes in the dynamics of type I and III total collagen deposition.

Chemokines and integrins independently tune actin flow and substrate friction during intranodal migration of T cells

Although much is known about the physiological framework of T cell motility, and numerous rate-limiting molecules have been identified through loss-of-function approaches, an integrated functional concept of T cell motility is lacking. Here, we used in vivo precision morphometry together with analysis of cytoskeletal dynamics in vitro to deconstruct the basic mechanisms of T cell migration within lymphatic organs. We show that the contributions of the integrin LFA-1 and the chemokine receptor CCR7 are complementary rather than positioned in a linear pathway, as they are during leukocyte extravasation from the blood vasculature. Our data demonstrate that CCR7 controls cortical actin flows, whereas integrins mediate substrate friction that is sufficient to drive locomotion in the absence of considerable surface adhesions and plasma membrane flux.

Indole-3-carbinol is a potent inhibitor of ischemia-reperfusion-induced inflammation

BACKGROUND

Ischemia-reperfusion (I/R) induces tissue inflammation, which is characterized by an increased leukocyte-endothelial cell interaction and leukocyte transmigration. These processes are mediated by the activation of the nuclear factor (NF)κB signaling pathway, resulting in an elevated expression of specific adhesion molecules. The phytochemical indole-3-carbinol (I3C) has been shown to exert anti-inflammatory effects by interfering with NFκB signal transduction. The aim of the present study was to investigate whether I3C is capable of counteracting the pathogenesis of I/R injury.

MATERIALS AND METHODS

We investigated the inhibitory effect of I3C on endothelial surface protein expression during hypoxia and reoxygenation by flow cytometry. Moreover, the subcellular localization of NFκB was analyzed by immunofluorescence and Western blot. Adhesion protein levels on leukocytes after tumor necrosis factor-α stimulation were determined using flow cytometry. Finally, leukocyte-endothelial cell interaction and leukocyte transmigration during I/R was investigated in dorsal skinfold chambers of BALB/c mice by means of repetitive intravital fluorescence microscopy and immunohistochemistry.

RESULTS

I3C suppressed the expression of E-selectin and intercellular adhesion molecule-1 on human dermal microvascular endothelial cells by reducing the transcriptional activity of NFκB. Furthermore, surface protein levels of macrophage-1 antigen as well as activated lymphocyte function-associated antigen-1 were markedly reduced on I3C-treated leukocytes. In vivo, I3C treatment decreased the numbers of adherent and transmigrated leukocytes. This was associated with a reduced macromolecular leakage when compared with vehicle-treated controls.

CONCLUSIONS

These novel results indicate that I3C reduces the expression of endothelial and leukocytic adhesion proteins, resulting in attenuated leukocyte-endothelial cell interactions during I/R. Accordingly, dietary supplements containing I3C may be beneficial for the treatment of I/R-induced inflammation.

The main rhinovirus respiratory tract adhesion site (ICAM-1) is upregulated in smokers and patients with chronic airflow limitation (CAL)

BACKGROUND

ICAM-1 is a major receptor for ~60% of human rhinoviruses, and non-typeable Haemophilus influenzae, two major pathogens in COPD. Increased cell-surface expression of ICAM-1 in response to tobacco smoke exposure has been suggested. We have investigated epithelial ICAM-1 expression in both the large and small airways, and lung parenchyma in smoking-related chronic airflow limitation (CAL) patients.

METHODS

We evaluated epithelial ICAM-1 expression in resected lung tissue: 8 smokers with normal spirometry (NLFS); 29 CAL patients (10 small-airway disease; 9 COPD-smokers; 10 COPD ex-smokers); Controls (NC): 15 normal airway/lung tissues. Immunostaining with anti-ICAM-1 monoclonal antibody was quantified with computerized image analysis. The percent and type of cells expressing ICAM-1 in large and small airway epithelium and parenchyma were enumerated, plus percentage of epithelial goblet and submucosal glands positive for ICAM- 1.

RESULTS

A major increase in ICAM-1 expression in epithelial cells was found in both large (p < 0.006) and small airways (p < 0.004) of CAL subjects compared to NC, with NLFS being intermediate. In the CAL group, both basal and luminal areas stained heavily for ICAM-1, so did goblet cells and sub-mucosal glands, however in either NC or NLFS subjects, only epithelial cell luminal surfaces stained. ICAM-1 expression on alveolar pneumocytes (mainly type II) was slightly increased in CAL and NLFS (p < 0.01). Pack-years of smoking correlated with ICAM-1 expression (r = 0.49; p < 0.03).

CONCLUSION

Airway ICAM-1 expression is markedly upregulated in CAL group, which could be crucial in rhinoviral and NTHi infections. The parenchymal ICAM-1 is affected by smoking, with no further enhancement in CAL subjects.

Oral Mucosal Immunity and HIV/SIV Infection

Human Immunodeficiency Virus (HIV) transmission through genital and rectal mucosa has led to intensive study of mucosal immune responses to HIV and to the development of a vaccine administered locally. However, HIV transmission through the oral mucosa is a rare event. The oral mucosa represents a physical barrier and contains immunological elements to prevent the invasion of pathogenic organisms. This particular defense differs between micro-compartments represented by the salivary glands, oral mucosa, and palatine tonsils. Secretory immunity of the salivary glands, unique features of cellular structure in the oral mucosa and palatine tonsils, the high rate of oral blood flow, and innate factors in saliva may all contribute to the resistance to HIV/Simian Immunodeficiency Virus (SIV) oral mucosal infection. In the early stage of HIV infection, humoral and cellular immunity and innate immune functions in oral mucosa are maintained. However, these particular immune responses may all be impaired as a result of chronic HIV infection. A better understanding of oral mucosal immune mechanisms should lead to improved prevention of viral and bacterial infections, particularly in immunocompromised persons with Acquired Immune Deficiency Syndrome (AIDS), and to the development of a novel strategy for a mucosal AIDS vaccine, as well as vaccines to combat other oral diseases, such as dental caries and periodontal diseases.

Protein Kinase CK2 Regulates Leukocyte-Endothelial Cell Interactions during Ischemia and Reperfusion in Striated Skin Muscle

BACKGROUND

Ischemia and reperfusion (I/R) causes tissue injury by inflammatory processes. This involves the upregulation of endothelial surface proteins by phospho-regulated signaling pathways, resulting in enhanced interactions of leukocytes with endothelial cells. Recently, we found that protein kinase CK2 is a crucial regulator of leukocyte-mediated inflammation. Therefore, in this study we investigated the involvement of CK2 in leukocyte-endothelial cell interactions during I/R injury.

METHODS

We first analyzed the inhibitory action of (E)-3-(2,3,4,5-tetrabromophenyl)acrylic acid (TBCA) and CX-4945 on CK2 kinase activity and the viability of human dermal microvascular endothelial cells (HDMEC). To mimic I/R conditions in vitro, HDMEC were exposed to hypoxia and reoxygenation and the expression of adhesion molecules was analyzed by flow cytometry. Moreover, we analyzed in vivo the effect of CK2 inhibition on leukocyte-endothelial cell interactions in the dorsal skinfold chamber model of I/R injury by means of repetitive intravital fluorescence microscopy and immunohistochemistry.

RESULTS

We found that TBCA and CX-4945 suppressed the activity of CK2 in HDMEC without affecting cell viability. This was associated with a significant downregulation of E-selectin and intercellular adhesion molecule (ICAM)-1 after in vitro hypoxia and reoxygenation. In vivo, CX-4945 treatment significantly decreased the numbers of adherent and transmigrated leukocytes in striated muscle tissue exposed to I/R.

CONCLUSION

Our findings indicate that CK2 is involved in the regulation of leukocyte-endothelial cell interactions during I/R by mediating the expression of E-selectin and ICAM-1.

Ultrasound-guided imaging of junctional adhesion molecule-A-targeted microbubbles identifies vulnerable plaque in rabbits

Identification of vulnerable atherosclerotic plaques by imaging the molecular characteristics is intensively studied recently, in which verification of specific markers is the critical step. JAM-A, a junctional membrane protein, is involved in the plaque formation, while it is unknown whether it can serve as a marker for vulnerable plaques. Vulnerable and stable plaques were created in rabbits with high cholesterol diet with or without partial ligation of carotid artery respectively. Significant higher JAM-A expression was found in vulnerable plaques than that in stable plaques. Furthermore, JAM-A was not only expressed in the endothelium, but also abundantly expressed in CD68-positive area. Next, JAM-A antibody conjugated microbubbles (MBJAM-A) or control IgG-conjugated microbubbles (MBC) were developed by conjugating the biotinylated antibodies to the streptavidin modified microbubbles, and visualization by contrast-enhance ultrasound (CEUS). Signal intensity of MBJAM-A was substantially enhanced and prolonged in the vulnerable plaque and some of the MBJAM-A was found colocalized with CD68 positive macrophages. In addition, cell model revealed that MBJAM-A were able to be phagocytized by activated macrophages. Taken together, we have found that increase of JAM-A serves as a marker for vulnerable plaques and targeted CEUS would be possibly a novel non-invasive molecular imaging method for plaque vulnerability.

Lung ICAM-1 and ICAM-2 support spontaneous intravascular effector lymphocyte entrapment but are not required for neutrophil entrapment or emigration inside endotoxin-inflamed lungs

The pulmonary vasculature constitutively expresses the integrin lymphocyte function-associated antigen-1 ligands intercellular adhesion molecule (ICAM)-1 and -2. In this study, effector T cells were temporarily entrapped by the lung vasculature on their way to inflamed lymph nodes, and this entrapment was strongly reduced in ICAM-1 and -2 double-deficient mice (79 and 86% reduction for CD8(+) and CD4(+) effectors, respectively, compared with wild-type mice). Although the pulmonary vasculature has been suggested to be masked by the heparan sulfate-containing glycocalyx, which is susceptible to heparanase-mediated shedding, lung and lymphocyte heparanase have been found to be unnecessary for this entrapment. Systemic LPS induced rapid neutrophil entrapment in the lung vasculature, but in contrast to T-cell entrapment, this sequestration was ICAM-1, ICAM-2, and heparanase independent. Furthermore, neutrophil migration into the bronchoalveolar space induced by LPS inhalation and LPS-induced leakage of red blood cells into this space were not dependent on lung ICAMs or heparanase activity. Nevertheless, heparanase was critical for neutrophil accumulation in smoke-exposed lungs. Our results indicate that, whereas T cells use ICAM-1 and -2 for temporary pulmonary entrapment, neutrophils get sequestered and extravasate into inflamed lungs independent of ICAMs. This is the first demonstration that the pulmonary vasculature is differentially recognized by T cells and neutrophils.-Petrovich, E., Feigelson, S. W., Stoler-Barak, L., Hatzav, M., Solomon, A., Bar-Shai, A., Ilan, N., Li, J.-P., Engelhardt, B., Vlodavsky, I., Alon, R. Lung ICAM-1 and ICAM-2 support spontaneous intravascular effector lymphocyte entrapment but are not required for neutrophil entrapment or emigration inside endotoxin-inflamed lungs.

Regulation of allergic lung inflammation by endothelial cell transglutaminase 2

Tissue transglutaminase 2 (TG2) is an enzyme with multiple functions, including catalysis of serotonin conjugation to proteins (serotonylation). Previous research indicates that TG2 expression is upregulated in human asthma and in the lung endothelium of ovalbumin (OVA)-challenged mice. It is not known whether endothelial cell TG2 is required for allergic inflammation. Therefore, to determine whether endothelial cell TG2 regulates allergic inflammation, mice with an endothelial cell-specific deletion of TG2 were generated, and these mice were sensitized and challenged in the airways with OVA. Deletion of TG2 in endothelial cells blocked OVA-induced serotonylation in lung endothelial cells, but not lung epithelial cells. Interestingly, deletion of endothelial TG2 reduced allergen-induced increases in respiratory system resistance, number of eosinophils in the bronchoalveolar lavage, and number of eosinophils in the lung tissue. Endothelial cell deletion of TG2 did not alter expression of adhesion molecules, cytokines, or chemokines that regulate leukocyte recruitment, consistent with other studies, demonstrating that deletion of endothelial cell signals does not alter lung cytokines and chemokines during allergic inflammation. Taken together, the data indicate that endothelial cell TG2 is required for allergic inflammation by regulating the recruitment of eosinophils into OVA-challenged lungs. In summary, TG2 functions as a critical signal for allergic lung responses. These data identify potential novel targets for intervention in allergy/asthma.

In vivo TCR Signaling in CD4(+) T Cells Imprints a Cell-Intrinsic, Transient Low-Motility Pattern Independent of Chemokine Receptor Expression Levels, or Microtubular Network, Integrin, and Protein Kinase C Activity

Intravital imaging has revealed that T cells change their migratory behavior during physiological activation inside lymphoid tissue. Yet, it remains less well investigated how the intrinsic migratory capacity of activated T cells is regulated by chemokine receptor levels or other regulatory elements. Here, we used an adjuvant-driven inflammation model to examine how motility patterns corresponded with CCR7, CXCR4, and CXCR5 expression levels on ovalbumin-specific DO11.10 CD4⁺ T cells in draining lymph nodes. We found that while CCR7 and CXCR4 surface levels remained essentially unaltered during the first 48–72 h after activation of CD4⁺ T cells, their in vitro chemokinetic and directed migratory capacity to the respective ligands, CCL19, CCL21, and CXCL12, was substantially reduced during this time window. Activated T cells recovered from this temporary decrease in motility on day 6 post immunization, coinciding with increased migration to the CXCR5 ligand CXCL13. The transiently impaired CD4⁺ T cell motility pattern correlated with increased LFA-1 expression and augmented phosphorylation of the microtubule regulator Stathmin on day 3 post immunization, yet neither microtubule destabilization nor integrin blocking could reverse TCR-imprinted unresponsiveness. Furthermore, protein kinase C (PKC) inhibition did not restore chemotactic activity, ruling out PKC-mediated receptor desensitization as mechanism for reduced migration in activated T cells. Thus, we identify a cell-intrinsic, chemokine receptor level-uncoupled decrease in motility in CD4⁺ T cells shortly after activation, coinciding with clonal expansion. The transiently reduced ability to react to chemokinetic and chemotactic stimuli may contribute to the sequestering of activated CD4⁺ T cells in reactive peripheral lymph nodes, allowing for integration of costimulatory signals required for full activation.

High fat diet induces adhesion of platelets to endothelium in two models of dyslipidemia

Cardiovascular diseases (CVD) represent about 30% of all global deaths. It is currently accepted that, in the atherogenic process, platelets play an important role, contributing to endothelial activation and modulation of the inflammatory phenomenon, promoting the beginning and formation of lesions and their subsequent thrombotic complications. The objective of the present work was to study using immunohistochemistry, the presence of platelets, monocytes/macrophages, and cell adhesion molecules (CD61, CD163, and CD54), in two stages of the atheromatous process. CF-1 mice fed a fat diet were used to obtain early stages of atheromatous process, denominated early stage of atherosclerosis, and ApoE(-/-) mice fed a fat diet were used to observe advanced stages of atherosclerosis. The CF-1 mice model presented immunostaining on endothelial surface for all three markers studied; the advanced atherosclerosis model in ApoE(-/-) mice also presented granular immunostaining on lesion thickness, for the same markers. These results suggest that platelets participate in atheromatous process from early stages to advance d stages. High fat diet induces adhesion of platelets to endothelial cells in vivo. These findings support studying the participation of platelets in the formation of atheromatous plate.

ICAM-2 facilitates luminal interactions between neutrophils and endothelial cells in vivo

Intercellular adhesion molecule 2 (ICAM-2) is expressed on endothelial cells (ECs) and supports neutrophil extravasation. However, the full details of its role remain unknown, and the present study investigates the functional mechanisms of ICAM-2 in neutrophil–endothelial-cell interactions. Our initial studies showed expression of ICAM-2 at both EC junctions and on the EC body. In line with the observed expression profile analysis of neutrophil–vessel-wall interactions using real-time in vivo confocal microscopy identified numerous functional roles for ICAM-2 within the vascular lumen and at the stage of neutrophil extravasation. Functional or genetic blockade of ICAM-2 significantly reduced neutrophil crawling velocity, increased frequency of crawling with a disrupted stop-start profile, and prolonged interaction of neutrophils with EC junctions prior to transendothelial cell migration (TEM), collectively resulting in significantly reduced extravasation. Pharmacological blockade of the leukocyte integrin MAC-1 indicated that some ICAM-2-dependent functions might be mediated through ligation of this integrin. These findings highlight novel roles for ICAM-2 in mediating luminal neutrophil crawling and the effect on subsequent levels of extravasation.

Carnosol inhibits cell adhesion molecules and chemokine expression by tumor necrosis factor-α in human umbilical vein endothelial cells through the nuclear factor-κB and mitogen-activated protein kinase pathways

Inflammatory bowel diseases (IBD) are gastrointestinal disorders associated with chronic inflammatory processes. Carnosol has been demonstrated to possess anti-inflammatory properties. This study examined the suppressive effect of carnosol on the expression of cell adhesion molecules (CAMs) and chemokines in human umbilical vein endothelial cells (HUVECs) and the possible underlying mechanism. The effect of carnosol on CAM and chemokine expression in HUVECs was identified by western blotting and ELISA, respectively. nuclear factor (NF)-κB activation of HUVECs was analyzed using the TransAM NF-κB Family kit. The effect of carnosol on the tumor necrosis factor (TNF)-α-induced activation of the NF-κB and mitogen-activated protein kinase (MAPK) pathways, and was subsequently analyzed using western blotting. Carnosol not only inhibited TNF-α-induced protein expression of intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1 and E-selectin in HUVECs, but also suppressed interleukin (IL)-8 and monocyte chemoattractant protein (MCP)-1 expression. In addition, carnosol inhibited the TNF-α-induced phosphorylation of p-65 and IκB-α, as well as the activation of NF-κB. The same result was observed in TNF-α-stimulated phosphorylation of ERK1/2 and p-38. It was demonstrated that carnosol inhibited TNF-α-induced CAM and chemokine expression in HUVECs. The underlying mechanism may be associated with the blocking of the NF-κB and MAPK pathways. These results indicate that carnosol may be a novel therapeutic agent for targeting endothelial cells in IBDs.

Investigation of the monocyte diapedesis-related LFA-1 and JAM-A gene variants in Turkish coronary heart disease patients

Background

LFA-1/JAM-A interaction plays a significant role in early steps of leukocyte transendothelial migration (diapedesis) which takes part in atherosclerosis pathogenesis. In this population-based case–control study, the frequencies of JAM-A rs790056 and LFA-1 rs8058823 gene polymorphisms in patients with coronary heart disease (CHD) and healthy subjects were investigated and the correlations between the different genotypes and cardiovascular risk factors were analyzed.

Methods

The JAM-A and LFA-1 genotypes were determined in 153 patients with CHD and 124 controls by PCR–RFLP assay.

Results

In CHD patient group, the frequency of JAM-A rs790056 TT genotype and the frequency of T allele were higher when compared with the control group (p = 0.03 and p = 0.007,respectively). In patient groups, the frequency of LFA-1 rs8058823 AA genotype was higher (p = 0.000), and the frequency of AG genotype was lower when compared with the control group (p = 0.031). In the control group, LFA-1 rs8058823 G allele carriers had higher SBP than subjects with AA genotype (p = 0.038), whereas in the CHD patient group, G allele carriers had lower DBP than subjects with AA genotype (p = 0.007). The multivariate logistic regression analysis confirmed that the JAM-A rs790056 TT genotype (OR = 2.472, p = 0.045) and LFA-1 rs8058823 AA genotype (OR = 6.751, p = 0.000) were risk factors for CHD development.

Conclusion

These results suggest that the wild type genotypes and alleles of JAM-A rs790056 (TT genotype and T allele) and LFA-1 rs8058823 (AA genotype and A allele) were found to be risk factors for CHD, whereas rare genotypes and alleles were found to be higher in healthy controls thus being protective.

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JAM-A common genotype and allele were more frequent in CHD group than controls.

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LFA-1 common genotype was more frequent in CHD group than controls.

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LFA-1 rare allele had lower DBP than subjects with common genotype.

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JAM-A and LFA-1 common genotypes were risk factors for CHD development.

The integrin coactivator Kindlin-3 is not required for lymphocyte diapedesis

Kindlin-3 is an integrin-binding focal adhesion adaptor absent in patients with leukocyte and platelet adhesion deficiency syndrome and is critical for firm integrin-dependent leukocyte adhesion. The role of this adaptor in leukocyte diapedesis has never been investigated. In the present study, the functions of Kindlin-3 in this process were investigated in effector T lymphocytes trafficking to various lymphoid and nonlymphoid tissues. In vitro, Kindlin-3-deficient T cells displayed severely impaired lymphocyte function antigen-1-dependent lymphocyte adhesion but partially conserved very late antigen-4 adhesiveness. In vivo, the number of adoptively transferred Kindlin-3-deficient T effectors was dramatically elevated in the circulating pool compared with normal effectors, and the Kindlin-3 mutant effectors failed to enter inflamed skin lesions. The frequency of Kindlin-3-deficient T effectors arrested on vessel walls within inflamed skin-draining lymph nodes was also reduced. Strikingly, however, Kindlin-3-deficient effector T cells accumulated inside these vessels at significantly higher numbers than their wild-type lymphocyte counterparts and successfully extravasated into inflamed lymph nodes. Nevertheless, on entering these organs, the interstitial motility of these lymphocytes was impaired. This is the first in vivo demonstration that Kindlin-3-stabilized integrin adhesions, although essential for lymphocyte arrest on blood vessels and interstitial motility, are not obligatory for leukocyte diapedesis.

Antigen and transforming growth factor Beta receptors contribute to long term functional and phenotypic heterogeneity of memory CD8 T cells

Pathogen-specific CD8 T cells provide a mechanism for selectively eliminating host cells that are harboring intracellular pathogens. The pathogens are killed when lytic molecules are injected into the cytoplasm of the infected cells and begin an apoptotic cascade. Activated CD8 T cells also release large quantities of pro-inflammatory cytokines that stimulate other immune cells in the local vicinity. As the alveoli are extraordinarily sensitive to cytokine induced damage, multiple layers of immune regulation limit the activities of immune cells that enter the lungs. These mechanisms include receptor-mediated signaling pathways in CD8 T cells that respond to peptide antigens and transforming growth factor β. Both pathways influence the functional and phenotypic properties of long-lived CD8 T cells populations in peripheral and lymphoid tissues.

A role for LFA-1 in delaying T-lymphocyte egress from lymph nodes

Lymphocytes use the integrin leukocyte function-associated antigen-1 (LFA-1) to cross the vasculature into lymph nodes (LNs), but it has been uncertain whether their migration within LN is also LFA-1 dependent. We show that LFA-1 mediates prolonged LN residence as LFA-1(-/-) CD4 T cells have significantly decreased dwell times compared with LFA-1(+/+) T cells, a distinction lost in hosts lacking the major LFA-1 ligand ICAM-1. Intra-vital two-photon microscopy revealed that LFA-1(+/+) and LFA-1(-/-) T cells reacted differently when probing the ICAM-1-expressing lymphatic network. While LFA-1(+/+) T cells returned to the LN parenchyma with greater frequency, LFA-1(-/-) T cells egressed promptly. This difference in exit behaviour was a feature of egress through all assessed lymphatic exit sites. We show that use of LFA-1 as an adhesion receptor amplifies the number of T cells returning to the LN parenchyma that can lead to increased effectiveness of T-cell response to antigen. Thus, we identify a novel function for LFA-1 in guiding T cells at the critical point of LN egress when they either exit or return into the LN for further interactions.

Endothelial cell PTP1B regulates leukocyte recruitment during allergic inflammation

Pulmonary eosinophilia is a consistent hallmark of allergic lung inflammation. Infiltration of eosinophils into ovalbumin (OVA)-challenged lungs is dependent on the adhesion molecule vascular cell adhesion molecule-1 (VCAM-1) on endothelial cells. Ligation of VCAM-1 activates endothelial cell protein tyrosine phosphatase 1B (PTP1B), which is required for VCAM-1-dependent leukocyte migration in vitro. To examine whether nonhematopoietic PTP1B modulates eosinophil recruitment in vivo, mice deficient in PTP1B were irradiated and received wild-type hematopoietic cells to generate chimeric PTP1B-/- mice. In response to OVA challenge, the chimeric PTP1B-/- mice had reduced eosinophilia in the lung tissue and bronchoalveolar lavage, indicating a role for PTP1B in nonhematopoietic cells during leukocyte recruitment. To determine whether endothelial cell PTP1B modulates eosinophil recruitment, mice with an inducible endothelial cell-specific PTP1B deletion (iePTP1B mice) were generated and the PTP1B deletion was induced after antigen sensitization before antigen challenge. In response to OVA challenge, the iePTP1B mice with the endothelial cell PTP1B deletion had an increased accumulation of eosinophils bound to the luminal surface of the endothelium in the lung vasculature and had a decrease in leukocyte recruitment into the lung tissue. In the iePTP1B mice, expression of adhesion molecules, cytokines, or chemokines that regulate leukocyte recruitment during inflammation was not altered, consistent with other studies that deletion of endothelial adhesion molecule signals does not alter lung cytokines and chemokines. In summary, these data suggest that VCAM-1 activation of PTP1B in the endothelium is necessary for eosinophil recruitment during allergic inflammation. Moreover, these studies provide a basis for targeting VCAM-1-dependent signaling pathways in allergy therapies.

Transepithelial migration of neutrophils into the lung requires TREM-1

Acute respiratory infections are responsible for more than 4 million deaths each year. Neutrophils play an essential role in the innate immune response to lung infection. These cells have an armamentarium of pattern recognition molecules and antimicrobial agents that identify and eliminate pathogens. In the setting of infection, neutrophil triggering receptor expressed on myeloid cells 1 (TREM-1) amplifies inflammatory signaling. Here we demonstrate for the first time that TREM-1 also plays an important role in transepithelial migration of neutrophils into the airspace. We developed a TREM-1/3-deficient mouse model of pneumonia and found that absence of TREM-1/3 markedly increased mortality following Pseudomonas aeruginosa challenge. Unexpectedly, TREM-1/3 deficiency resulted in increased local and systemic cytokine production. TREM-1/3-deficient neutrophils demonstrated intact bacterial killing, phagocytosis, and chemotaxis; however, histologic examination of TREM-1/3-deficient lungs revealed decreased neutrophil infiltration of the airways. TREM-1/3-deficient neutrophils effectively migrated across primary endothelial cell monolayers but failed to migrate across primary airway epithelia grown at the air-liquid interface. These data define a new function for TREM-1 in neutrophil migration across airway epithelial cells and suggest that it amplifies inflammation through targeted neutrophil migration into the lung.

Role of LFA-1 in the activation and trafficking of T cells: implications in the induction of chronic colitis

INTRODUCTION

We have previously demonstrated that adoptive transfer of naïve CD4(+) T cells devoid of lymphocyte function-associated antigen-1-deficient (LFA-1; CD11a/CD18) into recombination activating gene-1 (RAG-1) deficient (RAG(-/-) ) mice fails to induce chronic colitis whereas transfer of wild type (WT) T-cells induces unrelenting and chronic disease.

METHODS

The objectives of this study were to assess the role of lymphocyte function-associated antigen-1 (LFA-1) in enteric antigen (EAg)-induced activation of T cells in vitro and in vivo and to define the importance of this integrin in promoting trafficking of T cells to the mesenteric lymph nodes (MLNs) and colon.

RESULTS

We found that EAg-pulsed dendritic cells (DCs) induced proliferation of LFA-1-deficient (CD11a(-/-) ) CD4(+) T cells that was very similar to that induced using WT T cells, suggesting that LFA-1 is not required for activation/proliferation of T cells in vitro. Coculture of WT or CD11a(-/-) T cells with EAg-pulsed DCs induced the generation of similar amounts of interferon-gamma, interleukin (IL)-4, and IL-10, whereas IL-17A production was reduced ≈ 2-fold in cocultures with CD11a(-/-) T cells. Short-term (20-22 hours) trafficking studies demonstrated that while both WT and CD11a(-/-) T cells migrated equally well into the spleen, liver, lungs, small intestine, cecum, and colon, trafficking of CD11a(-/-) T cells to the MLNs was reduced by 50% when compared to WT T cells. When the observation period was extended to 3-7 days posttransfer, we observed ≈ 2-3-fold more WT T cells within the MLNs and colon than CD11a(-/-) T cells, whereas T-cell proliferation (as measured by CFSE dilution) was comparable in both populations.

CONCLUSIONS

Taken together, our data suggest that LFA-1 is not required for EAg-induced activation of CD4(+) T cells in vitro or in vivo but is required for trafficking of T cells to the MLNs and homing of colitogenic effector cells to the colon where they initiate chronic gut inflammation.

αL β2 integrin is indispensable for CD8+ T-cell recruitment in experimental pancreatic and hepatocellular cancer

Recruitment of activated leukocytes from peripheral blood into the tumor tissue is a crucial step of the immune response, which is controlled by the interaction between specific adhesion molecules such as endothelial ICAM-1 and leukocyte β(2) -integrins. Although attenuated expression of adhesion molecules on tumor endothelium has been proposed to represent a mechanism, which suppresses the intratumoral leukocyte infiltration, the relevance of adhesion molecules for leukocyte recruitment in tumor tissue is poorly understood. The present study is the first investigation of the role of ICAM-1 and β(2) -integrins in leukocyte recruitment in pancreatic and hepatocellular cancer in vivo, which was studied using knockout mice, intravital time-lapse microscopy and immunohistochemistry. We found that tumor tissue of both pancreatic and hepatocellular cancer was infiltrated with numerous active lymphoid and myeloid leukocytes, although the leukocyte extravasation rate in tumor blood vessels was very low. The knockout of LFA-1 (also known as α(L) β(2) integrin) strongly suppressed recruitment of CD8(+) T cells whereas no significant differences of leukocyte adhesion and infiltration were found in ICAM-1(-/-) and Mac-1(-/-) mice. Analysis of the interstitial leukocyte migration demonstrated that intratumoral leukocytes used haptokinetic type of migration, however, no significant differences of leukocyte migration between any knockout strains were found. We concluded that leukocyte recruitment in pancreatic and hepatocellular cancer is a slow-going process whose dynamics clearly contrasts to a high-speed leukocyte recruitment during acute inflammation. In contrast to acute inflammatory reaction, only LFA-1 controls recruitment of CD8(+) T-cells in both pancreatic and hepatocellular cancer, whereas ICAM-1 and Mac-1 are dispensable.

Comprehensive analysis of lymph node stroma-expressed Ig superfamily members reveals redundant and nonredundant roles for ICAM-1, ICAM-2, and VCAM-1 in lymphocyte homing

Although it is well established that stromal intercellular adhesion molecule-1 (ICAM-1), ICAM-2, and vascular cell adhesion molecule-1 (VCAM-1) mediate lymphocyte recruitment into peripheral lymph nodes (PLNs), their precise contributions to the individual steps of the lymphocyte homing cascade are not known. Here, we provide in vivo evidence for a selective function for ICAM-1 > ICAM-2 > VCAM-1 in lymphocyte arrest within noninflamed PLN microvessels. Blocking all 3 CAMs completely inhibited lymphocyte adhesion within PLN high endothelial venules (HEVs). Post-arrest extravasation of T cells was a 3-step process, with optional ICAM-1-dependent intraluminal crawling followed by rapid ICAM-1- or ICAM-2-independent diapedesis and perivascular trapping. Parenchymal motility of lymphocytes was modestly reduced in the absence of ICAM-1, while ICAM-2 and alpha4-integrin ligands were not required for B-cell motility within follicles. Our findings highlight nonredundant functions for stromal Ig family CAMs in shear-resistant lymphocyte adhesion in steady-state HEVs, a unique role for ICAM-1 in intraluminal lymphocyte crawling but redundant roles for ICAM-1 and ICAM-2 in lymphocyte diapedesis and interstitial motility.

Extracellular adherence protein of Staphylococcus aureus suppresses disease by inhibiting T-cell recruitment in a mouse model of psoriasis

Psoriasis is a T-cell-mediated inflammatory disease. Previous studies focused on lymphocyte function-associated antigen 1 (LFA-1)-expressing T cells as a molecular target for therapeutic intervention. By contrast, information on therapeutic effects and the underlying mechanism of blocking the LFA-1 counter receptor, ICAM-1 is scarce. Here, we used the CD18 (beta2-integrin) hypomorphic (CD18hypo) mouse model of psoriasis to investigate the therapeutic role of extracellular adherence protein (Eap) of Staphylococcus aureus, which exerts antiinflammatory activities by interacting with the ICAM-1 function. We show that ICAM-1 is predominantly upregulated on endothelial cells in lesional skin of CD18hypo mice. In vitro Eap was found to disrupt cell-cell contacts between T cells and dendritic cells, and inhibit T-cell proliferation. By contrast, in vivo Eap rather blocked transmigration of T cells from vessels to inflamed skin of CD18hypo mice, but did not inhibit their proliferation and activation. Most importantly, Eap successfully suppressed the disease by blocking T-cell extravasation into the inflamed skin. Together, these data indicate that interaction between LFA-1 and ICAM-1 is causally involved in the pathogenesis of psoriasiform skin inflammation, and targeting ICAM-1 to selectively block T-cell extravasation by Eap without immune suppression may represent a potential therapeutic strategy for psoriasis.

Endothelial cell activation leads to neutrophil transmigration as supported by the sequential roles of ICAM-2, JAM-A, and PECAM-1

Leukocyte transmigration is mediated by endothelial cell (EC) junctional molecules, but the associated mechanisms remain unclear. Here we investigate how intercellular adhesion molecule-2 (ICAM-2), junctional adhesion molecule-A (JAM-A), and platelet endothelial cell adhesion molecule (PECAM-1) mediate neutrophil transmigration in a stimulus-dependent manner (eg, as induced by interleukin-1beta [IL-1beta] but not tumor necrosis factor-alpha [TNF-alpha]), and demonstrate their ability to act in sequence. Using a cell-transfer technique, transmigration responses of wild-type and TNF-alpha p55/p75 receptor-deficient leukocytes (TNFR(-/-)) through mouse cremasteric venules were quantified by fluorescence intravital microscopy. Whereas wild-type leukocytes showed a normal transmigration response to TNF-alpha in ICAM-2(-/-), JAM-A(-/-), and PECAM-1(-/-) recipient mice, TNFR(-/-) leukocytes exhibited a reduced transmigration response. Hence, when the ability of TNF-alpha to directly stimulate neutrophils is blocked, TNF-alpha-induced neutrophil transmigration is rendered dependent on ICAM-2, JAM-A, and PECAM-1, suggesting that the stimulus-dependent role of these molecules is governed by the target cell being activated. Furthermore, analysis of the site of arrest of neutrophils in inflamed tissues from ICAM-2(-/-), JAM-A(-/-), and PECAM-1(-/-) mice demonstrated that these molecules act sequentially to mediate transmigration. Collectively, the findings provide novel insights into the mechanisms of action of key molecules implicated in leukocyte transmigration.

Thermal facilitation of lymphocyte trafficking involves temporal induction of intravascular ICAM-1

OBJECTIVE

Fever is associated with improved survival, although its beneficial mechanisms are poorly understood. Previous studies indicate that the thermal element of fever augments lymphocyte migration across high endothelial venules (HEVs) of lymphoid organs by increasing the intravascular display of a gatekeeper trafficking molecule, intercellular adhesion molecule-1 (ICAM-1). Here, we evaluated the spatio-temporal relationship between the thermal induction of intravascular ICAM-1 and lymphocyte trafficking.

METHODS

Intravascular ICAM-1 density was quantified by immunofluorescence staining in mice exposed to fever-range whole-body hyperthermia (39.5+/-0.5 degrees C). ICAM-1-dependent lymphocyte trafficking was measured in short-term homing assays.

RESULTS

A linear relationship was observed between the duration of heat treatment and intravascular ICAM-1 density in HEVs with maximal responses requiring sustained (i.e., five hours) thermal stress. Circulating lymphocytes were found to sense incremental changes in ICAM-1 on HEVs, such that trafficking is proportional to the intravascular density of ICAM-1. We further identified a hydroxamate-sensitive shedding mechanism that restores ICAM-1 expression to homeostatic levels following the cessation of thermal stress.

CONCLUSIONS

The time-dependent response to thermal stress indicates that ICAM-1 density governs the efficiency of lymphocyte interactions with HEVs in vivo. These studies highlight the dynamic role of the microcirculation in promoting immune surveillance during febrile inflammatory responses.

CXCR3 ligands contribute to Th1-induced inflammation but not to homing of Th1 cells into the lung

Th1 cells are implicated in numerous pulmonary inflammatory disorders, and adoptive transfer of alloreactive Th1 cells mediates lung injury and inflammation in mice. In response to Th1-mediated immune injury, CXCR3 ligands IP10 and MIG are markedly induced. Because Th1 cells express high levels of CXCR3, their recruitment and activity may be influenced by CXCR3 ligands. To examine the role of CXCR3 ligands, the authors inhibited CXCR3-ligand interaction by 2 approaches: (1) antibody ablation of CXCR3 ligands IP10 (CXCL10/interferon-gamma -inducible 10-kDa protein) and MIG (CXCL9/monokine-induced by interferon-gamma), and (2) use of cxcr3(-/-) mice. Antibody neutralization of IP10 and MIG reduced Th1-cell mediated lung inflammation but did not alter Th1-cell influx in the lung. In contrast, a lack of CXCR3 on host cells had no effect on Th1 cells influx or acute inflammation. In vitro, ablation of endogenous IP10 and MIG inhibited antigen-mediated Th1-cell proliferation. These results suggest that the influx of alloreactive Th1 cells into the lung does not require CXCR3 ligands, but that these chemokines do affect Th1-cell proliferation and activity within the affected tissue. Other CXCR3(+) leukocytes do not contribute to acute alloimmune injury.