Differential roles of VLA-4(CD49d/CD29) and LFA-1(CD11a/CD18) integrins and E- and P-selectin during developing and established active or adoptively transferred adjuvant arthritis in the rat

Response of Circulating Inflammatory Markers to Intermittent Hypoxia-Hyperoxia Training in Healthy Elderly People and Patients with Mild Cognitive Impairment

Intermittent hypoxia-hyperoxia training (IHHT) is a non-pharmacological therapeutic modality for management of some chronic- and age-related pathologies, such as Alzheimer’s disease (AD). Our previous studies demonstrated significant improvement of cognitive function after IHHT in the patients with mild cognitive impairment (MCI). The present study further investigated the effects of IHHT on pro-inflammatory factors in healthy elderly individuals and patients with early signs of AD. Twenty-nine subjects (13 healthy subjects without signs of cognitive impairment syndrome and 16 patients diagnosed with MCI; age 52 to 76 years) were divided into four groups: Healthy+Sham (n = 7), Healthy+IHHT (n = 6), MCI+Sham (n = 6), and MCI+IHHT (n = 10). IHHT was carried out 5 days per week for 3 weeks (total 15 sessions), and each daily session included 4 cycles of 5-min hypoxia (12% FIO2) and 3-min hyperoxia (33% FIO2). Decline in cognitive function indices was observed initially in both MCI+Sham and MCI+IHHT groups. The sham training did not alter any of the parameters, whereas IHHT resulted in improvement in latency of cognitive evoked potentials, along with elevation in APP110, GDF15 expression, and MMP9 activity in both healthy subjects and those with MCI. Increased MMP2 activity, HMGB1, and P-selectin expression and decreased NETs formation and Aβ expression were also observed in the MCI+IHHT group. There was a negative correlation between MoCA score and the plasma GDF15 expression (R = −0.5799, p < 0.05) before the initiation of IHHT. The enhanced expression of GDF15 was also associated with longer latency of the event-related potentials P330 and N200 (R = 0.6263, p < 0.05 and R = 0.5715, p < 0.05, respectively). In conclusion, IHHT upregulated circulating levels of some inflammatory markers, which may represent potential triggers for cellular adaptive reprogramming, leading to therapeutic effects against cognitive dysfunction and neuropathological changes during progression of AD. Further investigation is needed to clarify if there is a causative relationship between the improved cognitive function and the elevated inflammatory markers following IHHT.

Not Just an Adhesion Molecule: LFA-1 Contact Tunes the T Lymphocyte Program

The α_Lβ₂ integrin LFA-1 is known to play a key role in T lymphocyte migration, which is necessary to mount a local immune response, and is also the main driver of autoimmune diseases. This migration-triggering signaling process in T cells is tightly regulated to permit an immune response that is appropriate to the local trigger, as well as to prevent deleterious tissue-damaging bystander effects. Emerging evidence shows that, in addition to prompting a diverse range of downstream signaling cascades, LFA-1 stimulation in T lymphocytes modulates gene-transcription programs, including genetic signatures of TGF-β and Notch pathways, with multifactorial biological outcomes. This review highlights recent findings and discusses molecular mechanisms by which LFA-1 signaling influence T lymphocyte differentiation into the effector subsets Th1, Th17, and induced regulatory T cells. We argue that LFA-1 contact with a cognate ligand, such as ICAM-1, independent of the immune synapse activates a late divergence in T cells' effector phenotypes, hence fine-tuning their functioning.

Neutrophils and arthritis: Role in disease and pharmacological perspectives

The inflammatory response in the joint can induce an intense accumulation of leukocytes in the tissue that frequently results in severe local damage and loss of function. Neutrophils are essential cells to combat many pathogens, but their arsenal can contribute or aggravate articular inflammation. Here we summarized some aspects of neutrophil biology, their role in inflammation and indicated how the modulation of neutrophil functions could be useful for the treatment of different forms of arthritis.

Leukocyte integrins: role in leukocyte recruitment and as therapeutic targets in inflammatory disease

Infection or sterile inflammation triggers site-specific attraction of leukocytes. Leukocyte recruitment is a process comprising several steps orchestrated by adhesion molecules, chemokines, cytokines and endogenous regulatory molecules. Distinct adhesive interactions between endothelial cells and leukocytes and signaling mechanisms contribute to the temporal and spatial fine-tuning of the leukocyte adhesion cascade. Central players in the leukocyte adhesion cascade include the leukocyte adhesion receptors of the β2-integrin family, such as the αLβ2 and αMβ2 integrins, or of the β1-integrin family, such as the α4β1-integrin. Given the central involvement of leukocyte recruitment in different inflammatory and autoimmune diseases, the leukocyte adhesion cascade in general, and leukocyte integrins in particular, represent key therapeutic targets. In this context, the present review focuses on the role of leukocyte integrins in the leukocyte adhesion cascade. Experimental evidence that has implicated leukocyte integrins as targets in animal models of inflammatory disorders, such as experimental autoimmune encephalomyelitis, psoriasis, inflammatory bone loss and inflammatory bowel disease as well as preclinical and clinical therapeutic applications of antibodies that target leukocyte integrins in various inflammatory disorders are presented. Finally, we review recent findings on endogenous inhibitors that modify leukocyte integrin function, which could emerge as promising therapeutic targets.

Neutrophils in local and systemic antibody-dependent inflammatory and anaphylactic reactions

Neutrophils are notorious for their efficacy in microbial killing. Various mechanisms, such as phagocytosis, production of ROS, cytokines/chemokines and lipid mediators, degranulation of antimicrobials and enzymes, as well as NETosis contribute to this capacity. However, every incidence of neutrophil activation bears a risk to cause damage to the host. Several distinct steps, i.e., adhesion to endothelial cells, transmigration, chemotaxis, cytokine stimulation, and TLR signaling, are thought to control the extent of neutrophil activation. In the absence of a microbial stimulus, other pathways can induce neutrophil activation, among which FcR-induced activation when neutrophils encounter ICs. In these situations (inflammation, autoimmunity, allergy), neutrophils may act as primary or secondary effectors of immune reactions. In the presence of circulating ICs, neutrophils can indeed get stimulated directly in the bloodstream and trigger an immune response. Upon deposition of antibody complexes inside of tissues, neutrophils are first recruited and primed before being highly activated to amplify the ongoing inflammation. This review focuses on the engagement, activation, and responses of neutrophils to antibody ICs, inside of tissues or in the vasculature.

A (99m)Tc-labeled dual-domain cytokine ligand for imaging of inflammation

INTRODUCTION

Interleukin (IL)-1 and IL-18 are potent proinflammatory cytokines in inflammation-related diseases. Their actions are regulated by IL-1 receptor antagonist (IL-1ra) and IL-18 binding protein (IL-18bp). This study was designed to (99m)Tc-radiolabel an IL-1ra and IL-18bp dual-domain cytokine ligand, IL-18bp-Fc-IL-1ra, for specific inflammation targeting.

METHODS

The (99m)Tc-IL-18bp-Fc-IL-1ra was obtained by direct labeling via 2-iminothiolane reduction. Competitive binding of (99m)Tc-labeled and unlabeled IL-18bp-Fc-IL-1ra to rat polymorphonuclear leukocytes was assessed in vitro. A mouse ear edema model was used to evaluate specific targeting properties of (99m)Tc-IL-18bp-Fc-IL1ra in vivo. The correlation between (99m)Tc-IL-18bp-Fc-IL-1ra uptake and (111)In-labeled polymorphonuclear neutrophil infiltration was studied using ischemic-reperfused rat hearts.

RESULTS

Direct (99m)Tc-labeling yielded a stable dual-domain cytokine radioligand with radiochemical purity greater than 95% after gel filtration. Competitive binding studies showed specific targeting of (99m)Tc-IL-18bp-Fc-IL-1ra to inflammatory cells. The (99m)Tc-IL-18bp-Fc-IL-1ra uptake was 1.80±0.17 % injected dose per gram (%ID/g) in the inflamed ear without blocking, whereas uptake in the presence of IL-18bp-Fc-IL-1ra was 1.09±0.08 %ID/g (P<.05). The amounts of IL-1β and IL-18 were significantly increased in the inflamed ears compared to the vehicle controls. A significant correlation of (99m)Tc-IL-18bp-Fc-IL-1ra with (111)In-labeled neutrophil distribution was observed in the ischemic-reperfused hearts (P<.001).

CONCLUSION

Targeting proinflammatory cytokines with (99m)Tc-IL-18bp-Fc-IL-1ra may provide a suitable approach for specific detection of inflammatory sites.

Participation of Mac-1, LFA-1 and VLA-4 integrins in the in vitro adhesion of sickle cell disease neutrophils to endothelial layers, and reversal of adhesion by simvastatin

BACKGROUND

Pharmacological approaches to inhibit increased leukocyte adhesive interactions in sickle cell disease may represent important strategies for the prevention of vaso-occlusion in patients with this disorder. We investigated, in vitro, the adhesion molecules involved in endothelial-sickle cell disease neutrophil interactions and the effect of simvastatin on sickle cell disease neutrophil adhesion to tumor necrosis factor-α-activated endothelial monolayers (human umbilical vein endothelial cells), and neutrophil chemotaxis.

DESIGN AND METHODS

Sickle cell disease patients in steady state and not on hydroxyurea were included in the study. Endothelial cells treated, or not, with tumor necrosis factor-α and simvastatin were used for neutrophil adhesion assays. Neutrophils treated with simvastatin were submitted to interleukin 8-stimulated chemotaxis assays.

RESULTS

Sickle cell disease neutrophils showed greater adhesion to endothelial cells than control neutrophils. Adhesion of control neutrophils to endothelial cells was mediated by Mac-1 under basal conditions and by the Mac-1 and LFA-1 integrins under inflammatory conditions. In contrast, adhesion of sickle cell disease neutrophils to endothelium, under both basal and tumor necrosis factor-α-stimulated conditions, was mediated by Mac-1 and LFA-1 integrins and also by VLA-4. Under stimulated inflammatory conditions, simvastatin significantly reduced sickle cell disease neutrophil adhesion, and this effect was reversed by inhibition of nitric oxide synthase. Furthermore, intercellular adhesion molecule-1 expression was significantly abrogated on tumor necrosis factor-α-stimulated endothelium incubated with simvastatin, and statin treatment inhibited the interleukin-8-stimulated migration of both control and sickle cell disease neutrophils.

CONCLUSIONS

The integrins Mac-1, LFA-1 and, interestingly, VLA-4 mediate the adhesion of sickle cell disease leukocytes to activated endothelial cell layers, in vitro. Our data indicate that simvastatin may be able to reduce endothelial activation and consequent leukocyte adhesion in this in vitro model; future experiments and clinical trials may determine whether simvastatin therapy could be employed in patients with sickle cell disease, with beneficial effects on vaso-occlusion.

Molecular regulators of leucocyte chemotaxis during inflammation

A fundamental feature of any immune response is the movement of leucocytes from one site in the body to another to provide effector functions. Therefore, elucidating the molecular mechanisms underlying the migration of leucocytes from the blood to tissues is critical to our understanding of immune function during inflammation. The classic steps of leucocyte trafficking involve leucocyte tethering and rolling on vessel walls of the vasculature, followed by firm adhesion to the endothelium. Recent evidence suggests that upon adhering, leucocytes crawl within the vessels before transmigrating across vessel walls and crawling into targeted tissues. The directed nature of the crawling events is orchestrated by a complex array of soluble factors and molecular regulators in combination with the local intravascular and extracellular environment. In fact, this process is known as chemotaxis and orientates cell movement in relation to the ligand gradient. Several signalling pathways have been proposed to be involved in this gradient-sensing and amplification process, but the best studied, discussed in detail here, is the phosphatidylinositol 3-kinase pathway. Substantial progress has been made in understanding how cells roll and adhere in blood vessels; however, how cells crawl in blood vessels, emigrate, and then crawl in tissues has received much less attention. Therefore, the focus of this review is to provide recent insights into molecular mechanisms and cellular processes that mediate leucocyte crawling in blood vessels and tissues during the inflammatory response.

The determinants of susceptibility/resistance to adjuvant arthritis in rats

Adjuvant arthritis (AA) serves as an excellent model for human rheumatoid arthritis. AA is readily inducible in certain rat strains, but not in others. Susceptibility/resistance to AA is determined by multiple factors. Among the genetic factors, both MHC and non-MHC genes contribute to arthritis susceptibility, and specific quantitative trait loci show association with the severity of the disease. Differential T-cell proliferative and cytokine responses, as well as antibody responses, to heat-shock proteins are evident when comparing AA-susceptible and AA-resistant rats. In addition, neuroendocrine factors and the housing environment can further modulate arthritis susceptibility/severity in particular rat strains.

Role of adhesion molecules in synovial inflammation

PURPOSE OF REVIEW

The ability of cells to adhere to other cells and extracellular matrix (ECM) through cellular adhesion molecules (CAMs) is central to tissue remodeling and inflammation. This review discusses the potential role of CAMs in development of synovial inflammation through regulating the recruitment of inflammatory cells via endothelial-leukocyte interactions, the organization and activation of leukocytes in the synovial sublining, and the formation and behavior of the hyperplastic synovial lining.

RECENT FINDINGS

Over the past several years valuable insight has been gained into the role of cell-cell and cell-ECM adhesive interactions in synovial organization and inflammation. Recently, cadherin-11 was identified on fibroblast-like synoviocytes and has been demonstrated to play a central role in synovial lining organization. Furthermore, studies using animal models of inflammatory arthritis have demonstrated critical roles for E- and P-selectins, CD11a/CD18 [lymphocyte function-associated antigen (LFA)-1], alpha4beta1 integrin, and cadherin-11 in the development of synovial inflammation.

SUMMARY

Cell-cell and cell-ECM interactions through CAMs play an important role in synovial inflammation. Future studies of CAMs are needed to define more thoroughly their role in synovial inflammation and their potential as therapeutic targets in the treatment of rheumatoid arthritis and related inflammatory arthritic conditions.

The dynamics of articular leukocyte trafficking and the immune response to self heat-shock protein 65 influence arthritis susceptibility

INTRODUCTION

Adjuvant arthritis (AA) shares several features with human rheumatoid arthritis, and it can be induced in the Lewis (LEW) rat but not the Wistar Kyoto (WKY) rat (both RT.1(l)) by immunization with heat-killed Mycobacterium tuberculosis (Mtb). We set out to unravel the mechanisms underlying the differential susceptibility to AA of these MHC-compatible rat strains.

MATERIALS AND METHODS

We compared the levels of T-cell proliferative and cytokine response to the immunoregulatory self (rat) hsp65 (Rhsp65) after an arthritogenic (Mtb) challenge and the kinetics of migration of adoptively transferred, (111)Indium-labeled, Mtb-primed leukocytes into the hind paw joints of recipient rats.

RESULTS AND DISCUSSION

The WKY rats raised a significantly higher level of T-cell proliferative response coupled with a temporally opposite cytokine profile against the disease-regulating Rhsp65 compared to that of LEW rats. Moreover, the arthritogenic leukocytes accumulated into the joints of WKY rats at significantly lower numbers than that in LEW rats.

CONCLUSIONS

These results offer novel insights into the immune events influencing the pathogenesis of autoimmune arthritis.

Blockade of chemokine receptor CXCR3 inhibits T cell recruitment to inflamed joints and decreases the severity of adjuvant arthritis

T lymphocytes expressing the chemokine receptors, CCR2, CCR5, CXCR3, and CXCR6 are increased in inflamed tissues in rheumatoid arthritis. The role of CXCR3 in autoimmune arthritis induced in Lewis rats was investigated. CXCR3+ T cells migrated 2- to 3-fold more than CXCR3- T cells to inflamed joints in arthritic animals. CXCR3-expressing in vivo Ag-activated T lymphoblasts and in vitro-activated lymph node cells from arthritic animals were strongly recruited to the arthritic joints, and treatment with anti-CXCR3 mAb significantly inhibited this T cell recruitment by 40-60%. Immune T cells from the spleen and lymph nodes of actively immunized arthritic donors adoptively transferred arthritis to naive rats. Treatment with anti-CXCR3 mAb delayed the onset of arthritis and significantly reduced the severity of joint inflammation with a >50% decrease in the clinical arthritis score. Blockade of CXCR3 also significantly reduced the weight loss in the arthritic animals and inhibited neutrophil accumulation in the joints by 50-60%. There was a marked reduction in the leukocyte infiltration of the synovium in the presence of CXCR3 blockade and a decrease in the loss of articular cartilage of the joints. In conclusion, CXCR3 on T cells has an essential role in T cell recruitment to inflamed joints and the development of joint inflammation in adjuvant arthritis.

CD45RA T-cell activation without proliferation by a partial agonist monoclonal antibody to beta1 integrin

CD45RA T cells are fully co-activated by natural beta1 integrin ligands fibronectin (FN) and VCAM-1, as well as monoclonal antibody (mAb) 19H8, which binds a combinatorial epitope of the alpha4beta1 heterodimer. These integrin ligands stimulate CD3-dependent proliferation and the upregulation of early activation markers CD25 and CD69. However, beta1-specific antibody 33B6, which binds to a similar range of the predominant T-cell integrins as natural ligands FN (alpha4beta1 and alpha5beta1) and VCAM-1 (alpha4beta1), failed to costimulate proliferation in the CD45RA subset, while retaining the ability to costimulate early activation markers CD25 and CD69. After addition of exogenous human interleukin-2 to the culture media, 33B6 costimulation of proliferation is restored. These data provide evidence that a branch of the alpha4beta1 integrin-signaling pathway in CD45RA T cells can be independently regulated and exploited through the use of partial agonist ligands, including mAbs to the integrin heterodimer.

CXCR6 is expressed on T cells in both T helper type 1 (Th1) inflammation and allergen-induced Th2 lung inflammation but is only a weak mediator of chemotaxis

Numerous chemokine receptors are increased in number on T cells in inflamed tissues. Our objective was to examine CXCR6 expression on lymphocytes during immune and inflammatory reactions and its potential for mediating T-cell recruitment. The cDNA for rat CXCR6 was cloned and monoclonal antibodies (mAbs) to CXCR6 were developed. CXCR6 was present on 4-6% of CD4 and CD8 T cells in blood, normal lymph nodes (LNs) and the spleen, primarily on memory T cells. In vitro antigen re-stimulation of LN T cells from animals with autoimmune arthritis and experimental autoimmune encephalomyelitis (EAE) increased the proportion of CXCR6(+) T cells to 35-50% and anti-T-cell receptor (TCR) activation to 60-80%. In vivo, after antigen challenge of LNs there was only a small increase in CXCR6(+) T cells on the lymphoblasts in the LNs, and a much higher percentage of T cells were CXCR6(+) in virus-induced peritoneal exudates (approximately 47%) and in allergen-induced lung inflammation (33%). Chemotaxis of CXCR6-expressing inflammatory T cells to CXCL16 was poor, but that to CXCL10 was robust. We conclude that few T cells in normal and antigen-challenged LNs are CXCR6(+), whereas a high proportion of in vitro activated T cells and T cells from inflammatory sites are CXCR6(+), but these cells migrate poorly to CXCL16. This suggests that CXCR6 may contribute to T-cell positioning and activation, rather than recruitment. CXCR6 is also expressed on T cells not only in T helper type 1 (Th1) inflammation (arthritis and EAE) but also, as shown here, in Th2 inflammation, where it is increased after allergen challenge.

New approaches to blockade of alpha4-integrins, proven therapeutic targets in chronic inflammation

The recruitment of leukocytes into tissue is a pivotal step in inflammation. alpha4-Integrins are adhesion receptors on circulating leukocytes that mediate attachment to the endothelium and facilitate their migration into the inflamed tissue. This multistep process is mediated by the interaction of alpha4-integrins with their counter receptors VCAM-1 and MadCAM-1 that are expressed on endothelial cells. alpha4-Integrins act as both adhesive and signaling receptors. Paxillin, a signaling adaptor molecule, binds directly to the alpha4 cytoplasmic tail and its binding is important for cell migration. Blocking the adhesive functions of alpha4-integrins has been shown to be an effective therapeutic approach in the treatment of autoimmune diseases, but also carries the risk of defects in development, hematopoiesis and immune surveillance. Interfering with alpha4 signaling by inhibiting the alpha4-paxillin interaction decreases alpha4-mediated cell migration and adhesion to VCAM-1 and MadCAM under shear flow. These in vitro effects are accompanied by a selective impairment of leukocyte migration into inflammatory sites when the alpha4-paxillin interaction is blocked in vivo. Thus, blockade of alpha4-integrin signaling may offer a novel strategy for interfering with the functions of these receptors in pathological events while sparing important physiological functions.

Mechanisms of lymphocyte migration in autoimmune disease

The recruitment of leukocytes to inflamed tissues plays an essential role in combating infection and promoting wound healing. However, in autoimmune diseases such as multiple sclerosis and diabetes, leukocytes enter tissues and contribute to inappropriate inflammatory responses, which cause tissue injury and dysfunction. In diseases of this type, lymphocytes play critical roles in initiating and maintaining these aberrant inflammatory responses. The aim of this review is to examine the mechanisms whereby T-lymphocytes enter tissues in autoimmune diseases and to compare these mechanisms between various organs and diseases. An overview of the mechanisms of leukocyte recruitment and the techniques used to study leukocyte trafficking is provided, focusing on the use of intravital microscopy as a tool to assess the functional microvasculature in vivo. We also discuss the series of tissue homing events which allow naïve lymphocytes to first enter lymph nodes and undergo activation, then subsequently to home to the peripheral organ where their cognate antigen is present. Finally, we examine mechanisms of leukocyte recruitment in diseases such as multiple sclerosis, autoimmune diabetes, systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease and asthma.

Fundamentally different roles for LFA-1, Mac-1 and α4-integrin in neutrophil chemotaxis

Although the LFA-1, Mac-1 and α4 integrins are required for chemotaxis, it is unknown how they are regulated or what specific role they play. Previously we demonstrated that fMLP and IL-8 induce chemotaxis via the p38 MAPK and phosphoinositide 3-kinase (PI3K) pathways, respectively. Here we show that these chemoattractants also activate and use Mac-1 and LFA-1 in a differential manner during chemotaxis. Using integrin-specific substrata, we demonstrate that cell movement in response to IL-8 is mediated by Mac-1, whereas LFA-1 is required for directional migration. By contrast, chemotaxis to fMLP requires Mac-1 for cell movement, whereas LFA-1 and α4-integrin are required for directional migration. On serum protein, which contains ligands for LFA-1, Mac-1 and α4-integrin, chemotaxis to fMLP is dependent on Mac-1, whereas chemotaxis to IL-8 is dependent on LFA-1. These results suggest that Mac-1 is the dominant integrin involved in chemotaxis to fMLP, and LFA-1 is the dominant integrin involved in chemotaxis to IL-8. Consistent with these observations, higher quantities of high-affinity Mac-1 are found on cells chemotaxing to fMLP then on cells chemotaxing to IL-8. Moreover, a much larger quantity of clustered LFA-1 was found on cells migrating to IL-8 compared to cells moving towards fMLP. When cells are presented with competing gradients of fMLP and IL-8, they preferentially migrate towards fMLP and activate/utilize integrins in a manner identical to fMLP alone. Under the same conditions, p38 MAPK inhibition abolishes the preferential migration to fMLP; instead, the cells migrate preferentially towards IL-8. The activation and utilization of integrins under these conditions are consistent with patterns observed with IL-8 alone. Together, these data suggest that fMLP and IL-8 differentially activate integrins for use during chemotaxis, that p38 MAPK is a major mediator in the activation and utilization of integrins, and selective integrin activation occurs during chemotaxis between opposing gradients.