Beta2-Integrins and Interacting Proteins in Leukocyte Trafficking, Immune Suppression, and Immunodeficiency Disease

Beta2-integrins are complex leukocyte-specific adhesion molecules that are essential for leukocyte (e.g., neutrophil, lymphocyte) trafficking, as well as for other immunological processes such as neutrophil phagocytosis and ROS production, and T cell activation. Intriguingly, however, they have also been found to negatively regulate cytokine responses, maturation, and migratory responses in myeloid cells such as macrophages and dendritic cells, revealing new, and unexpected roles of these molecules in immunity. Because of their essential role in leukocyte function, a lack of expression or function of beta2-integrins causes rare immunodeficiency syndromes, Leukocyte adhesion deficiency type I, and type III (LAD-I and LAD-III). LAD-I is caused by reduced or lost expression of beta2-integrins, whilst in LAD-III, beta2-integrins are expressed but dysfunctional because a major integrin cytoplasmic regulator, kindlin-3, is mutated. Interestingly, some LAD-related phenotypes such as periodontitis have recently been shown to be due to an uncontrolled inflammatory response rather than to an uncontrolled infection, as was previously thought. This review will focus on the recent advances concerning the regulation and functions of beta2-integrins in leukocyte trafficking, immune suppression, and immune deficiency disease.Peer reviewe

A beta2-Integrin/MRTF-A/SRF Pathway Regulates Dendritic Cell Gene Expression, Adhesion, and Traction Force Generation

beta2-integrins are essential for immune system function because they mediate immune cell adhesion and signaling. Consequently, a loss of beta2-integrin expression or function causes the immunodeficiency disorders, Leukocyte Adhesion Deficiency (LAD) type I and III. LAD-III is caused by mutations in an important integrin regulator, kindlin-3, but exactly how kindlin-3 regulates leukocyte adhesion has remained incompletely understood. Here we demonstrate that mutation of the kindlin-3 binding site in the b2-integrin (TTT/AAA-b2-integrin knock-in mouse/KI) abolishes activation of the actin-regulated myocardin related transcription factor A/serum response factor (MRTF-A/SRF) signaling pathway in dendritic cells and MRTF-A/SRF-dependent gene expression. We show that Ras homolog gene family, member A (RhoA) activation and filamentous-actin (F-actin) polymerization is abolished in murine TTT/AAA-b2-integrin KI dendritic cells, which leads to a failure ofMRTF-A to localize to the cell nucleus to coactivate genes together with SRF. In addition, we show that dendritic cell gene expression, adhesion and integrin-mediated traction forces on ligand coated surfaces is dependent on the MRTF-A/SRF signaling pathway. The participation of b2-integrin and kindlin-3-mediated cell adhesion in the regulation of the ubiquitous MRTF-A/SRF signaling pathway in immune cells may help explain the role of b2-integrin and kindlin-3 in integrin-mediated gene regulation and immune system function.Peer reviewe

Mice Lacking beta2-Integrin Function Remain Glucose Tolerant in Spite of Insulin Resistance, Neutrophil Infiltration and Inflammation

Beta2-integrins are important in leukocyte trafficking and function, and are regulated through the binding of cytoplasmic proteins, such as kindlin-3, to their intracellular domain. Here, we investigate the involvement of beta2-integrins in the regulation of metabolic disease using mice where the kindlin-3 binding site in the beta2-integrin cytoplasmic tail has been mutated (TTT/AAA-beta2-integrin knock-in (KI) mice), leading to expressed but dysfunctional beta2-integrins and significant neutrophilia in vivo. Beta2-integrin KI mice fed on a high fat diet showed normal weight gain, and normal accumulation of macrophages and lymphocytes in white adipose tissue (WAT) and liver, but increased neutrophil numbers especially in WAT. In addition, beta2-integrin KI mice fed on a high fat diet showed significantly increased peripheral insulin resistance in response to high-fat feeding. However, this was associated with improved glucose disposal following glucose load. Interestingly, beta2-integrin KI neutrophils produced more elastase in vitro, in response to stimulation. Beta2-integrin KI mice displayed variability of tissue inflammatory status, with liver and WAT exhibiting little or no difference in inflammation compared to high fat fed controls, whereas skeletal muscle demonstrated a raised inflammatory profile in association with higher elastase levels and diminished signalling through the IRS1-PKB pathway. In conclusion, although expression of dysfunctional beta2-integrins increased neutrophil production and infiltration into tissue, skeletal muscle was the most affected tissue exhibiting evidence of higher neutrophil activity and insulin resistance. Thus, beta2-integrins modulate glucose homeostasis during high fat feeding predominantly through actions on skeletal muscle to affect metabolic phenotype in vivo.Peer reviewe

Pilus Adhesin RrgA Interacts with Complement Receptor 3, Thereby Affecting Macrophage Function and Systemic Pneumococcal Disease

10.1128/mBio.00535-12Pneumococcal pili have been shown to influence pneumococcal colonization, disease development, and the inflammatory response in mice. The role of the pilus-associated RrgA adhesin in pneumococcal interactions with murine and human macrophages was investigated. Expression of pili with RrgA enhanced the uptake of pneumococci by murine and human macrophages that was abolished by antibodies to complement receptor 3 (CR3) and not seen in CR3-deficient macrophages. Recombinant RrgA, but not pilus subunit RrgC, promoted CR3-mediated phagocytosis of coated beads by murine and human macrophages. Flow cytometry showed that purified CR3 binds pneumococcal cells expressing RrgA, and purified RrgA was shown to interact with CR3 and its I domain. In vivo, RrgA facilitated spread of pneumococci from the upper airways and peritoneal cavity to the bloodstream. Earlier onset of septicemia and more rapidly progressing disease was observed in wild-type mice compared to CR3-deficient mice challenged intranasally or intraperitoneally with pneumococci. Motility assays and time-lapse video microscopy showed that pneumococcal stimulation of macrophage motility required RrgA and CR3. These findings, together with the observed RrgA-dependent increase of intracellular survivors up to 10 h following macrophage infection, suggest that RrgA-CR3-mediated phagocytosis promotes systemic pneumococcal spread from local sites.IMPORTANCE Streptococcus pneumoniae is a major contributor to morbidity and mortality in infectious diseases globally. Symptomatology is mainly due to pneumococcal interactions with host cells leading to an inflammatory response. However, we still need more knowledge on how pneumococci talk to immune cells and the importance of this interaction. Recently, a novel structure was identified on the pneumococcal surface, an adhesive pilus found in about 30% of clinical pneumococcal isolates. The pilus has been suggested to be important for successful spread of antibiotic-resistant pneumococcal clones globally. Here we sought to identify mechanisms for how the pneumococcal pilin subunit RrgA contributes to disease development by interacting with host immune cells. Our data suggest a new way for how pneumococci may cross talk with phagocytic cells and affect disease progression. An increased understanding of these processes may lead to better strategies for how to treat these common infections.Peer reviewe

Caveolin-1 Influences LFA-1 Redistribution upon TCR Stimulation in CD8 T Cells

TCR stimulation by peptide-MHC complexes on APCs requires precise reorganization of molecules into the area of cellular contact to form an immunological synapse from where T cell signaling is initiated. Caveolin (Cav) 1, a widely expressed transmembrane protein, is involved in the regulation of membrane composition, cellular polarity and trafficking, and the organization of signal transduction pathways. The presence of Cav1 protein in T cells was identified only recently, and its function in this context is not well understood. We show that Cav1-knockout CD8 T cells have a reduction in membrane cholesterol and sphingomyelin, and upon TCR triggering they exhibit altered morphology and polarity, with reduced effector function compared with Cav1 wild-type CD8 T cells. In particular, redistribution of the b2 integrin LFA-1 to the immunological synapse is compromised in Cav1-knockout T cells, as is the ability of LFA-1 to form high-avidity interactions with ICAM-1. Our results identify a role for Cav1 in membrane organization and b2 integrin function in primary CD8 T cells.Peer reviewe

Optimal T cell activation and B cell antibody responses in vivo require the interaction between leukocyte function-associated antigen-1 and kindlin-3

Kindlin-3 is an important integrin regulator that is mutated in the rare genetic disorder, leukocyte adhesion deficiency type III, a disorder characterized by defective neutrophil trafficking and platelet function, leading to recurrent bacterial infections and bleeding. Kindlin-3 is also known to regulate T cell adhesion in vitro and trafficking in vivo, but whether the integrin/kindlin interaction regulates T or B cell activation in vivo is unclear. In this study, we used TTT/AAA β2-integrin knock-in (KI) mice and TCR-transgenic (OT-II) KI mice, in which the integrin/kindlin connection is disrupted, to investigate the role of the integrin/kindlin interaction in T cell activation. We show that basal T cell activation status in these animals in vivo is normal, but they display reduced T cell activation by wild-type Ag-loaded dendritic cells in vitro. In addition, T cell activation in vivo is reduced. We also show that basal Ab levels are normal in TTT/AAA β2-integrin KI mice, but B cell numbers in lymph nodes and IgG and IgM production after immunization are reduced. In conclusion, we show that the integrin/kindlin interaction is required for trafficking of immune cells, as well as for T cell activation and B cell Ab responses in vivo. These results imply that the immunodeficiency found in leukocyte adhesion deficiency type III patients, in addition to being caused by defects in neutrophil function, may be due, in part, to defects in lymphocyte trafficking and activation

Functional beta2-integrins restrict skin inflammation in vivo

Beta2-integrins and the important integrin regulator kindlin-3 are essential for leukocyte trafficking, but the role of beta2-integrins in regulating inflammation is still incompletely understood. Here, we have investigated skin inflammation in a mouse model where the kindlin-3 binding site in the beta2-integrin has been mutated (TTT/AAA-beta2-integrin knock-in), leading to expressed but dysfunctional integrins. We show that, surprisingly, neutrophil trafficking into the inflamed skin in a contact hypersensitivity model is normal in these mice, although trafficking of T cells and eosinophils into the skin is reduced. Instead, expression of dysfunctional integrins leads to increased mast cell and dendritic cell numbers in the skin, increased inflammatory cytokine production in the inflamed skin in vivo, and in mast cells in vitro. Furthermore, expression of dysfunctional integrins leads to increased dendritic cell activation and migration to lymph nodes and increased Th1 responses in vivo. Therefore, the kindlin-3/integrin interaction is important for trafficking of T cells and eosinophils but not absolutely required for neutrophil trafficking into the inflamed skin. Functional beta2-integrins also have a major role in restricting the immune response in the inflamed skin and lymph nodes in vivo, likely through effects on mast cell and dendritic cell numbers and activation

The efficacy of misoprostol vaginal insert compared with oral misoprostol in the induction of labor of nulliparous women:a randomized national multicenter trial

Abstract Introduction: Our objective was to compare the efficacy of a 200‐μg misoprostol vaginal insert vs oral misoprostol regarding the cesarean section rate and the time interval to vaginal delivery in nulliparous women with unfavorable cervix. Material and methods: In this prospective multicenter trial, 283 nulliparous women at term with Bishop score <6 were randomized to induction of labor with either a misoprostol vaginal insert (n = 140) or oral misoprostol (n = 143). In the oral misoprostol group, a 50‐μg dose of oral misoprostol was administered every 4 hours up to three times during the first day; during the second day, the dose was increased to 100‐μg every 4 hours up to three times during the first day, if necessary. Primary outcome was the cesarean section rate. Secondary outcomes were the time from induction of labor to vaginal delivery, the rate of other induction methods needed, labor augmentation with oxytocin and/or amniotomy, use of tocolytics and adverse neonatal and maternal events. Results: In the misoprostol vaginal insert group, median time to vaginal delivery was shorter (24.5 hours vs 44.2 hours, P < 0.001), whereas no difference was found in the cesarean section rate (33.8% vs 29.6%, odds ratio [OR] 1.21, 95% confidence interval [CI] 0.66–1.91, P = 0.67). Other induction methods and labor augmentation with oxytocin and/or amniotomy were less frequent in the misoprostol vaginal insert group (OR 0.32, 95% CI 0.18–0.59 and OR 0.56, 95% CI 0.32–0.99, respectively). Need for tocolysis and meconium‐stained amniotic fluid were more common in the misoprostol vaginal insert group (OR 3.63, 95% CI 1.12–11.79 and OR 2.38, 95% CI 1.32–4.29, respectively). Maternal and neonatal adverse events did not differ between groups. Conclusions: Misoprostol vaginal insert proved to shorten the time to vaginal delivery and to reduce the use of other methods of labor induction and augmentation, but it did not reduce the cesarean section rate compared with oral misoprostol. The benefit of more rapid delivery associated with misoprostol vaginal insert should be weighed against the greater risks for uterine hyperstimulation and meconium‐stained amniotic fluid