Deficiency of a surface membrane glycoprotein (Mo1) in man

INTEGRINS: A BEDSIDE TO BENCH TO BEDSIDE STORY

I provide a narrative of the path I took to discover the membrane receptors that mediate leukocyte adhesion, now known as β2 integrins or CD11/CD18. We followed this discovery with the first determination of the 3-D structures of integrins. The latter advance provided the foundation for understanding the unique features of integrins as divalent cation-dependent signaling receptors and as mechanosensitive conduits between the extracellular matrix and the intracellular cytoskeleton. Our structural studies are now opening new paths for taming overactive integrins in disease while minimizing the collateral damage associated with the faulty pharmacodynamics of current integrin inhibitory drugs.

CD11b agonists offer a novel approach for treating lupus nephritis

Lupus nephritis (LN) develops in more than a third of all systemic lupus erythematosus (SLE) patients and is the strongest predictor of morbidity and mortality. Increased circulating levels of type I interferon (IFN I) and anti-double stranded DNA (anti-dsDNA) and anti-RNA binding protein (anti-RNP) antibodies lead to increased glomerular injury via leukocyte activation and glomerular infiltration. Uncontrolled Toll-like receptor (TLR) signaling in leukocytes results in increased production of IFN I and anti-dsDNA antibodies. ITGAM gene codes for integrin CD11b, the α-chain of integrin heterodimer CD11b/CD18, that is highly expressed in leukocytes and modulates TLR-dependent pro-inflammatory signaling. Three nonsynonymous SNPs in the ITGAM gene strongly correlate with increased risk for SLE and LN and with IFN I levels. Here we review the literature on the role of CD11b on leukocytes in LN. We also incorporate conclusions from several recent studies that show that these ITGAM SNPs result in a CD11b protein that is less able to suppress TLR-dependent pro-inflammatory pathways in leukocytes, that activation of CD11b via novel small molecule agonists suppresses TLR-dependent pathways, including reductions in circulating levels of IFN I and anti-dsDNA antibodies, and that CD11b activation reduces LN in model systems. Recent data strongly suggest that integrin CD11b is an exciting new therapeutic target in SLE and LN and that allosteric activation of CD11b is a novel therapeutic paradigm for effectively treating such autoimmune diseases.

Methods for Assessing the Effects of Galectins on Leukocyte Trafficking and Clearance

Numerous protocols exist for investigating leukocyte recruitment and clearance both in vitro and in vivo. Here we describe an in vitro flow chamber assay typically used for studying the mechanisms underpinning leukocyte movement through the endothelium and zymosan-induced peritonitis, an acute in vivo model of inflammation that enables both leukocyte trafficking and clearance to be monitored. Insight is given as to how these models can be used to study the actions of galectins on the inflammatory process.

Neutrophils in innate immunity and systems biology-level approaches

The innate immune system is the first line of host defense against invading microorganisms. Polymorphonuclear leukocytes (PMNs or neutrophils) are the most abundant leukocyte in humans and essential to the innate immune response against invading pathogens. Compared to the acquired immune response, which requires time to develop and is dependent on previous interaction with specific microbes, the ability of neutrophils to kill microorganisms is immediate, nonspecific, and not dependent on previous exposure to microorganisms. Historically, studies of PMN-pathogen interaction focused on the events leading to killing of microorganisms, such as recruitment/chemotaxis, transmigration, phagocytosis, and activation, whereas postphagocytosis sequelae were infrequently considered. In addition, it was widely accepted that human neutrophils possessed limited capacity for new gene transcription and thus, relatively little biosynthetic capacity. This notion has changed dramatically within the past 20 years. Further, there is now more effort directed to understand the events occurring in PMNs after killing of microbes. Herein, we give an updated review of the systems biology-level approaches that have been used to gain an enhanced view of the role of neutrophils during host-pathogen interaction and neutrophil-mediated diseases. We anticipate that these and future systems-level studies will continue to provide information important for understanding, treatment, and control of diseases caused by pathogenic microorganisms. This article is categorized under: Physiology > Organismal Responses to Environment Physiology > Mammalian Physiology in Health and Disease Biological Mechanisms > Cell Fates.

Biology and structure of leukocyte β 2 integrins and their role in inflammation

Integrins comprise a large family of αβ heterodimeric cell adhesion receptors that are expressed on all cells except red blood cells and that play essential roles in the regulation of cell growth and function. The leukocyte integrins, which include members of the β ₁, β ₂, β ₃, and β ₇ integrin family, are critical for innate and adaptive immune responses but also can contribute to many inflammatory and autoimmune diseases when dysregulated. This review focuses on the β ₂ integrins, the principal integrins expressed on leukocytes. We review their discovery and role in host defense, the structural basis for their ligand recognition and activation, and their potential as therapeutic targets.

Cell surface topography is a regulator of molecular interactions during chemokine-induced neutrophil spreading

Adhesive interactions between neutrophils and endothelium involve chemokine-induced neutrophil spreading and subsequent crawling on the endothelium to sites of transmigration. We investigated the importance of cell topography in this process using immunofluorescence, scanning electron microscopy, and live-cell imaging using total internal reflectance microscopy to observe redistribution of key membrane proteins, both laterally and relative to surface topography, during neutrophil spreading onto glass coated with interleukin 8. During formation of the lamellipod, L-selectin is distributed on microvilli tips along the top of the lamellipodium, whereas the interleukin 8 receptors CXCR1 and CXCR2 and the integrin LFA-1 (αLβ2) were present at the interface between the lamellipodium and the substrate. Total internal reflection fluorescence imaging indicated that LFA-1 and both chemokine receptors redistributed into closer contact with the substrate as the cells spread onto the surface and remodeled their topography. A geometric model of the surface remodeling with nonuniform distribution of molecules and a realistic distribution of microvilli heights was matched to the data, and the fits indicated a 1000-fold increase in the concentration of chemokine receptors and integrins available for bond formation at the interface. These observations imply that topographical remodeling is a key mechanism for regulating cell adhesion and surface-induced activation of cells.

The origins of the molecular era of adhesion research

Recognition of the importance of cell adhesion grew steadily during the twentieth century as it promised answers to fundamental questions in diverse fields that included cell biology, developmental biology, tumorigenesis, immunology and neurobiology. However, the route towards a better understanding of its molecular basis was long and difficult, with many false starts. Major progress was made in the late 1970s to late 1980s with the identification of the major families of adhesion molecules, including integrins and cadherins. This in turn set the stage for the explosive growth in adhesion research over the past 25 years.

The leucocyte β2 (CD18) integrins: the structure, functional regulation and signalling properties

Leucocytes are highly motile cells. Their ability to migrate into tissues and organs is dependent on cell adhesion molecules. The integrins are a family of heterodimeric transmembrane cell adhesion molecules that are also signalling receptors. They are involved in many biological processes, including the development of metazoans, immunity, haemostasis, wound healing and cell survival, proliferation and differentiation. The leucocyte-restricted β2 integrins comprise four members, namely αLβ2, αMβ2, αXβ2 and αDβ2, which are required for a functional immune system. In this paper, the structure, functional regulation and signalling properties of these integrins are reviewed.

Neutrophils in innate host defense against Staphylococcus aureus infections

Staphylococcus aureus has been an important human pathogen throughout history and is currently a leading cause of bacterial infections worldwide. S. aureus has the unique ability to cause a continuum of diseases, ranging from minor skin infections to fatal necrotizing pneumonia. Moreover, the emergence of highly virulent, drug-resistant strains such as methicillin-resistant S. aureus in both healthcare and community settings is a major therapeutic concern. Neutrophils are the most prominent cellular component of the innate immune system and provide an essential primary defense against bacterial pathogens such as S. aureus. Neutrophils are rapidly recruited to sites of infection where they bind and ingest invading S. aureus, and this process triggers potent oxidative and non-oxidative antimicrobial killing mechanisms that serve to limit pathogen survival and dissemination. S. aureus has evolved numerous mechanisms to evade host defense strategies employed by neutrophils, including the ability to modulate normal neutrophil turnover, a process critical to the resolution of acute inflammation. Here we provide an overview of the role of neutrophils in host defense against bacterial pathogens and discuss strategies employed by S. aureus to circumvent neutrophil function.

Pyoderma gangrenosum-like lesions in leukocyte adhesion deficiency I treated with intravenous immunoglobulin

A 31-year-old Caucasian male with leukocyte adhesion deficiency I and a 20-year history of recurrent, painful cutaneous ulcerations on the extremities presented with fatigue and worsening pain in both legs. He had experienced minimal improvement in his leg ulcers from treatment with systemic steroids, numerous courses of systemic antibiotics, and brief trials of infliximab and mycophenolate mofetil. He was treated with monthly intravenous immunoglobulin infusions. Upon completion of six courses of intravenous immunoglobulin his ulcerations had nearly healed for the first time in a decade.

Mary Allen Engle Award: The glue of life--a career retrospective

The author was privileged to be an early contributor to the concept that cell adhesion molecules, the leukocyte (β2) integrins, play a pivotal role in the acute inflammatory process. For the author, this began with the development of a monoclonal antibody (anti-Mo1) that identified a differentiation antigen on the surface of human myeloid cells (including neutrophils, monocytes, and natural killer (NK) cells). Serendipitously, it was discovered that the Mo1 antigen was the heterodimeric glycoprotein (gp155,95) absent from the surface of neutrophils isolated from patients with adhesion defects in vitro and a syndrome characterized by chronic, life-threatening infections in vivo (a syndrome now termed leukocyte adhesion deficiency, type 1) (LAD-1). Collaborative efforts with other investigators (including members of the ACCA) revealed that patients with LAD-1 exhibited genetic mutations on chromosome 21 resulting in absent or diminished expression of a class of 4 surface adhesion molecules (now termed CD11a/CD18, CD11b/CD18, CD11c/CD18, and CD11d/CD18) known as the leukocyte or β2 family of integrins. Knowledge of the role of the β2 integrins in the acute inflammatory response led to the development of effective gene therapy strategies to treat LAD-1 in preclinical animal models and to the comprehensive testing of anti-integrin antibodies as anti-inflammatory agents to prevent organ damage as a complication of acute inflammation. This retrospective provides one illustration of the potential of bench-to-bedside research to generate new knowledge of clinical significance.

Shedding of large functionally active CD11/CD18 Integrin complexes from leukocyte membranes during synovial inflammation distinguishes three types of arthritis through differential epitope exposure

CD18 integrins are adhesion molecules expressed on the cell surface of leukocytes and play a central role in the molecular mechanisms supporting leukocyte migration to zones of inflammation. Recently, it was discovered that CD11a/CD18 is shed from the leukocyte surface in models of inflammation. In this study, we show that shedding of human CD11/CD18 complexes is a part of synovial inflammation in rheumatoid arthritis and spondyloarthritis but not in osteoarthritis. In vivo and in vitro data suggest that the shedding is driven by TNF-α, which links the process to central events in the inflammatory response. The shed complexes contain multiple heterodimers of CD11/CD18, are variable in size, and differ according to the type of synovial inflammation. Furthermore, the differential structures determine the avidity of binding of the complexes to the ICAM-1. With the estimated concentrations of CD11/CD18 in plasma and synovial fluid a significant coverage of binding sites in ICAM-1 for CD18 integrins is expected. Based on cell adhesion experiments in vitro, we hypothesize that the large soluble complexes of CD11/CD18 act in vivo to buffer leukocyte adhesion by competing with the membrane-bound receptors for ICAM-1 binding sites. As reported here for synovial inflammation changes in the concentration or structure of these complexes should be considered as likely contributors to disease activity.

Role of neutrophils in innate immunity: a systems biology-level approach

The innate immune system is the first line of host defense against invading microorganisms. Polymorphonuclear leukocytes (PMNs or neutrophils) are the most abundant leukocyte in humans and essential to the innate immune response against invading pathogens. Compared with the acquired immune response, which requires time to develop and is dependent on previous interaction with specific microbes, the ability of neutrophils to kill microorganisms is immediate, non-specific, and not dependent on previous exposure to microorganisms. Historically, studies on PMN-pathogen interaction focused on the events leading to killing of microorganisms, such as recruitment/chemotaxis, transmigration, phagocytosis, and activation, whereas post-phagocytosis sequelae were infrequently considered. In addition, it was widely accepted that human neutrophils possessed limited capacity for new gene transcription and thus, relatively little biosynthetic capacity. This notion has changed dramatically within the past decade. Further, there is now more effort directed to understand the events occurring in PMNs after killing of microbes. Herein we review the systems biology-level approaches that have been used to gain an enhanced view of the role of neutrophils during host-pathogen interaction. We anticipate that these and future systems-level studies will ultimately provide information critical to our understanding, treatment, and control of diseases caused by pathogenic microorganisms.

Reactive oxygen intermediate-induced pathomechanisms contribute to immunosenescence, chronic inflammation and autoimmunity

Deregulation of reactive oxygen intermediates (ROI) resulting in either too high or too low concentrations are commonly recognized to be at least in part responsible for many changes associated with aging. This article reviews ROI-dependent mechanisms critically contributing to the decline of immune function during physiologic - or premature - aging. While ROI serve important effector functions in cellular metabolism, signalling and host defence, their fine-tuned generation declines over time, and ROI-mediated damage to several cellular components and/or signalling deviations become increasingly prevalent. Although distinct ROI-associated pathomechanisms contribute to immunosenescence of the innate and adaptive immune system, mutual amplification of dysfunctions may often result in hyporesponsiveness and immunodeficiency, or in chronic inflammation with hyperresponsiveness/deregulation, or both. In this context, we point out how imbalanced ROI contribute ambiguously to driving immunosenescence, chronic inflammation and autoimmunity. Although ROI may offer a distinct potential for therapeutic targeting along with the charming opportunity to rescue from deleterious processes of aging and chronic inflammatory diseases, such modifications, owing to the complexity of metabolic interactions, may carry a marked risk of unforeseen side effects.

The vessel wall and its interactions

Blood cell interactions with the vessel wall were first documented almost 170 years ago. Modern advances have revealed that leukocyte and platelet interactions with the endothelium are at the nexus of complex, dynamic cellular and molecular networks that, when dysregulated, may lead to pathological inflammation and thrombosis, which are major sources of morbidity and mortality in the Western world. In this review, we relate the history of blood cell interactions with the vasculature, discuss recent progress, and raise some unresolved questions awaiting the field.

The importance of the Mac-1, LFA-1 glycoprotein family in monocyte and granulocyte adherence, chemotaxis, and migration into inflammatory sites: insights from an experiment of nature

The Mac-1, LFA-1 (lymphocyte function-associated 1), p150,95 family of glycoproteins, which share a common beta subunit of Mr 95 000, are of widespread importance in leucocyte adhesion reactions. This paper focuses on the role of this glycoprotein family in granulocyte and monocyte adhesion and chemotaxis in vitro, and in migration into inflammatory sites in vivo. Most findings have been made with granulocytes, but results with monocytes are similar. Some studies have used leucocytes from patients exhibiting a severe or moderate deficiency in expression of this glycoprotein family, which is secondary to a defect in the common beta subunit. Patients are susceptible to bacterial infections and have defective pus formation and Rebuck skin-window tests, despite chronic granulocytosis. Granulocytes from such patients exhibit defective adherence to serum albumin and fibronectin-coated glass or plastic, defective orientation and directed migration in response to chemoattractants, and are defective in chemoattractant-stimulated aggregation and hyperadherence. Antibodies to the common beta subunit, to the Mac-1 alpha subunit, and to a lesser extent to the LFA-1 and p150,95 alpha subunits, inhibit many of the same functional responses by normal cells. In normal granulocytes and monocytes chemoattractants stimulate a five-fold increase in Mac-1 and p150,95 surface expression, by mobilization of a latent, presumably intracellular, pool. Cells from patients are deficient in up-regulation of these molecules but show normal up-regulation of other surface receptors, degranulation and oxidative burst. The hypothesis is presented that Mac-1 and p150,95 regulate or directly mediate the increase in granulocyte and monocyte adhesivity, which is essential for diapedesis, chemotaxis and migration into inflammatory sites.

ICAM-5--a novel two-facetted adhesion molecule in the mammalian brain

Cell adhesion is of utmost importance for normal development and cellular functions. ICAM-5 (intercellular adhesion molecule-5, telencephalin) is a member of the ICAM-family of adhesion proteins. These proteins bind to leukocyte beta(2)-integrins (CD11/CD18), but ICAM-5 is exceptional in several ways. It is solely expressed in the mammalian forebrain, appears at the time of birth, and is located in the soma and dendrites of neurons. It is structurally more complex than the others, and also shows homophilic adhesion. Recent studies show that it is important for the regulation of immunological activity in the brain and for the development of neuronal synapses and signal transmission.

Cellular and genetic basis of primary immune deficiencies

Knowledge of the genetic mutations of primary immune deficiency syndromes has grown significantly over the last 30 years. In this article the authors present an overview of the clinical aspects, laboratory evaluation, and genetic defects of primary immunodeficiencies, with an emphasis on the pathophysiology of the known molecular defects. This article is designed to give the primary pediatrician a general knowledge of this rapidly expanding field.

Intestinal epithelial pathobiology: past, present and future

The intestinal epithelium serves as one of man's primary interfaces with the outside world. Its importance is illustrated by the fact that the proper functioning of this interface is absolutely essential for human health, and even modest perturbations in its function may lead to diarrhoea, constipation, malnutrition, dehydration, infectious disease or chronic intestinal inflammatory diseases such as Crohn's disease and ulcerative colitis, collectively referred to as inflammatory bowel disease. Both pathogen-induced intestinal inflammation and the active flares of inflammatory bowel disease are histopathologically defined, their sequellae being mediated by neutrophils that migrate across the intestinal epithelium, forming a crypt abscess. Classically, the intestinal epithelium has been thought of primarily as a barrier, and indeed this is a very important aspect of its function, but the intestinal epithelium is also a highly interactive barrier. This chapter will summarize some of the basic research conducted over the past 15 years that has revealed basic insights into how the epithelium participates in the formation of a crypt abscess and how it plays a role in causing the characteristic clinical manifestations that ensue. In addition, the chapter will discuss how this research has resurrected the 'old', yet newly emerging, concept that physiological malfunction of the intestinal epithelium can be the primary defect that leads to the innate and adaptive immune dysregulation mediating inflammatory bowel disease.

The role of CD47 in neutrophil transmigration. Increased rate of migration correlates with increased cell surface expression of CD47

CD47, a cell surface glycoprotein, plays an important role in modulating neutrophil (PMN) migration across endothelial and epithelial monolayers. Here we show that anti-CD47 monoclonal antibodies (mAbs) delay PMN migration across collagen-coated filters or T84 epithelial monolayers toward the chemoattractant formylmethionylleucylphenylalanine (fMLP). Despite delayed transmigration by anti-CD47 mAbs, the numbers of PMN migrating across in either condition were the same as in the presence of control non-inhibitory mAbs. Cell surface labeling and immunoprecipitation demonstrated upregulation of CD47 to the PMN cell surface with kinetics similar to those of the transmigration response. Subcellular fractionation studies revealed redistribution of CD47 from intracellular compartments that co-sediment with secondary granules to plasma membrane-containing fractions after fMLP stimulation. Experiments performed to investigate potential signaling pathways revealed that inhibition of tyrosine phosphorylation with genistein reversed the anti-CD47-mediated PMN migration delay, whereas inhibition of phosphatidylinositol 3-kinase only partially reversed anti-CD47 effects that correlated with a rapid increase in PMN cell surface CD47. Analysis of the contribution of epithelial-expressed CD47 to PMN transmigration revealed that PMN migration across CD47-deficient epithelial monolayers (CaCO2) was significantly increased after stable transfection with CD47. These results suggest that cell surface CD47 and downstream tyrosine phosphorylation signaling events regulate, in part, the rate of PMN migration during the inflammatory response.

Registries of immunodeficiency patients and mutations

Immunodeficiencies form a distinct group of human hereditary diseases with several rare disorders. During recent years, information has been collected concerning immunodeficiency patients and mutations causing disorders. The large European (ESID) registry contains clinical data for some 7,000 patients. At present, international mutation databases have information for > 1,000 immunodeficiency patients, including X-linked chronic granulomatous disease (XCGD), Wiskott-Aldrich syndrome (WAS), and X-linked thrombocytopenia (XLT), X-linked hyper-IgM syndrome (XHIM), X-linked agammaglobulinemia (XLA), and X-linked severe combined immunodeficiency (XSCID). The databases are available on Internet. The mutation spectra of patients in these registries were compared. Mutational hotspots were found in CpG dinucleotides with a preference for selected flanking bases.

A functional granulocyte colony-stimulating factor receptor is required for normal chemoattractant-induced neutrophil activation

Granulocyte colony-stimulating factor (G-CSF) is a hematopoietic growth factor that is widely used to treat neutropenia. In addition to stimulating polymorphonuclear neutrophil (PMN) production, G-CSF may have significant effects on PMN function. Because G-CSF receptor (G-CSFR)-deficient mice do not have the expected neutrophilia after administration of human interleukin-8 (IL-8), we examined the effect of the loss of G-CSFR on IL-8-stimulated PMN function. Compared with wild-type PMNs, PMNs isolated from G-CSFR-deficient mice demonstrated markedly decreased chemotaxis to IL-8. PMN emigration into the skin of G-CSFR-deficient mice in response to IL-8 was also impaired. Significant chemotaxis defects were also seen in response to N-formyl-methionyl-leucyl-phenylalanine, zymosan-activated serum, or macrophage inflammatory protein-2. The defective chemotactic response to IL-8 does not appear to be due to impaired chemoattractant receptor function, as the number of IL-8 receptors and chemoattractant-induced calcium influx, actin polymerization, and release of gelatinase B were comparable to those of wild-type PMNs. Chemoattractant-induced adhesion of G-CSFR-deficient PMNs was significantly impaired, suggesting a defect in beta2-integrin activation. Collectively, these data demonstrate that selective defects in PMN activation are present in G-CSFR-deficient mice and indicate that G-CSF plays an important role in regulating PMN chemokine responsiveness.

Autoantibodies to leukocyte alphaMbeta2 integrin glycoproteins in HIV infection

HIV infection is often associated with polyclonal B-cell activation, autoantibodies, and clinically evident autoimmune disease. Because neutropenia and anti-neutrophil autoantibodies are common clinical features of HIV disease, we studied a series of HIV+ patients to determine whether anti-alphaMbeta2 integrin (MAC-1) specific anti-neutrophil autoantibodies occur in HIV disease, as we have shown to occur in patients with immune neutropenia not associated with HIV. Two new assays specific for anti-alphaMbeta2 IgG were developed to carry out these studies: an ELISA method using affinity-purified alphaMbeta2 integrin protein, and a flow cytometry method using subclones of the 293 human fetal kidney cell line, stably transfected with cDNAs for the alphaM and/or beta2 integrin subunits. In studies of the sera of 20 untreated HIV+ individuals, anti-alphaMbeta2 activity was detected in 9 (45%) by one or the other of these assays and in 5 (25%) by both assays. Seven of the 20 HIV+ study subjects had unexplained neutropenia, and of these, 6 (86%) were positive for anti-alphaMbeta2 autoantibodies. Our findings indicate that anti-alphaMbeta2 integrin autoantibodies are frequent in HIV+ individuals, particularly when unexplained neutropenia is also present, and raise the possibility that these autoantibodies may have a role in the acquired neutrophil dysfunction and increased risk of nonopportunistic bacterial infections observed in HIV disease.

Fcγ Receptor-Mediated Activation of Phospholipase D Regulates Macrophage Phagocytosis of IgG-Opsonized Particles

Receptors for the Fc portion of IgG (FcγRs) integrate the innate and acquired components of immunity by coupling the specific recognition of IgG Abs to the activation of phagocytic leukocytes. Knowledge of the molecular mechanisms that regulate phagocyte stimulation by FcγRs may permit therapeutic modulation to augment immunoprotective aspects and minimize damage to host tissues in diverse inflammatory diseases. Since phospholipase D (PLD) has been linked to the stimulation of cytotoxic leukocyte responses, we characterized FcγR-dependent activation of PLD in human macrophages. IgG-coated SRBCs (EIgG) stimulated a 9.4-fold increase in PLD activity compared with SRBCs treated with control Ab (p < 0.001), determined by formation of the PLD-specific product phosphatidylethanol in the presence of 0.5% ethanol. Levels of phosphatidic acid, the physiologic product of PLD-mediated catalyzis, were significantly increased in the absence of ethanol (6.4-fold, p < 0.001). PLD activity was also stimulated by immune complex-coated latex beads or cross-linking of Abs specific for FcγRI, FcγRII, or FcγRIII. Phagocytosis of EIgG was reduced by two inhibitors of PLD-mediated signaling, 2,3-diphosphoglycerate or 1-butanol. Addition of purified PLD restored control levels of phagocytosis in cells in which endogenous PLD was inhibited. The tyrosine kinase inhibitors genistein and herbimycin A caused concordant reductions in FcγR-stimulated PLD activity and phagocytosis. These studies demonstrate that FcγR-mediated phagocytosis is accompanied by tyrosine kinase-dependent activation of PLD and support the hypothesis that stimulation of PLD functions to regulate the ingestion of IgG-opsonized particles.

Pyoderma gangrenosum in a child with congenital partial deficiency of leucocyte adherence glycoproteins

Congenital deficiency of beta 2 integrin leucocyte adhesion molecules is a rare immunodeficiency and is often fatal. Neutrophils are unable to bind to ligands on the endothelium, and so cannot leave the circulation during inflammation or infection. When leucocyte adhesion deficiency (LAD) is caused by abnormally low expression of beta 2 integrins, it is termed LAD type 1. We describe a 5-year-old girl with a history of recurrent bacterial infections since early childhood who developed necrotic skin ulcers resembling pyoderma gangrenosum and a persistent circulating neutrophilia. Histologically, the lesions showed deep ulceration with a diffuse lymphohistiocytic infiltrate, but with a relative sparsity of neutrophils. Subsequent investigation revealed a complete absence of CD11a/CD18 beta 2 integrins on the surface of the patient's neutrophils, confirming the diagnosis of LAD type 1. The ulcers responded to treatment with oral prednisolone and colchicine.

Alternations of surface antigens on leukocytes after severe injury: correlation with infectious complications

OBJECTIVE

To investigate the alternations of surface antigens of leukocytes after severe injury and the correlation with clinical outcome.

SETTING

Emergency Department and Intensive Care Unit of a university hospital.

PATIENTS

Patients with severe trauma (injury severity score > 16) were enrolled. Those who were transferred or had critical injuries were excluded.

MEASUREMENTS AND RESULTS

Polymorphonuclear cells (PMN) and mononuclear cells (MN) were isolated from patients on the 1st, 3rd and 7th day following injury. The mean fluorescent expressions of CD11b and CD16 of PMN, and CD25 of MN were measured and compared with those obtained from paralleled controls. Sixteen injured patients were included. The CD11b expressions of PMN increased on the 1st day and were still high on the 7th day. The CD16 expressions decreased on the 1st day and CD25 decreased on the 3rd day; both were still low on the 7th day. Six patients developed infectious complications. CD11b expression remained high and CD16 expression remained low on three measurements of the infectious patients, whereas both expressions recovered on the last measurement of non-infectious patients. CD25 expression remained low in both groups. Three infectious patients with pneumonia died from multiple organ failure.

CONCLUSIONS

Phenotypic alternations of leukocytes develop early after severe injury. The alternations may represent a state of activation of PMN and subsequent suppression of IL-2 related immunity. Persistent activation of PMN with enhanced CD11b and attenuated CD16 expression indicates the development of infectious complications and a poor prognosis can be anticipated if the infectious sites can not be controlled early.

Molecular events in neutrophil transepithelial migration

Neutrophil transepithelial migration is a central component of many inflammatory diseases of the gastrointestinal, respiratory and urinary tracts, and correlates with disease symptoms. In vitro modeling with polarized intestinal epithelial monolayers has shown that neutrophil transepithelial migration can influence crucial epithelial functions, ranging from barrier maintenance to electrolyte secretion. Studies have also demonstrated a dynamic involvement of the epithelium in modulating neutrophil transepithelial migration. Characterization of the molecular interactions between neutrophils and epithelial cells has revealed that transepithelial migration is dependent on the neutrophil beta 2 integrin CD11b/CD18, and does not appear to involve adhesive interactions with the selectins or intercellular adhesion molecule-1. Recent studies have implicated another transmembrane glycoprotein, CD47, as a crucial component of the transepithelial migration response. While the precise function of CD47 is not known, current evidence suggests that CD47-dependent events occur after CD11b/CD18-mediated neutrophil adhesion to the epithelium. This review will highlight key features of the current understanding of the molecular events important in neutrophil migration across epithelial surfaces.

Alloimmunization after granulocyte transfusions

BACKGROUND

Although granulocyte transfusions are recommended for neutropenic patients with bacterial infections that are unresponsive to antibiotic therapy, the presence of white cell (WBC) antibodies in the recipient can render these transfusions ineffective.

STUDY DESIGN AND METHODS

A 25-year-old man with chronic granulomatous disease experienced a pulmonary transfusion reaction while receiving granulocyte transfusions, and he was found to be immunized to neutrophil antigen NA2. A retrospective study of alloimmunization to HLA and neutrophil antigens in 18 patients with chronic granulomatous disease who had also received repeated granulocyte transfusions was then performed. Sera were tested in lymphocytotoxicity, granulocyte agglutination, granulocyte immunofluorescence, monoclonal antibody immonobilization of granulocyte antigen, and immunoprecipitation assays.

RESULTS

After the granulocyte transfusions, sera from 14 of the 18 patients contained WBC antibodies. Seven sera samples reacted in the lymphocytotoxicity, granulocyte immunofluorescence, and granulocyte agglutination assays; seven reacted in the lymphocytotoxicity and granulocyte immunofluorescence assays but not the granulocyte agglutination assay, and four did not react. When the monoclonal antibody immobilization of granulocyte antigen assay was used, three sera samples reacted with Fc gamma receptor III, three with the 58- to 64-kDa protein carrying the neutrophil antigen NB1, one with CD11a, and one with CD18. Antibodies from three patients immunoprecipitated a neutrophil protein of 60 kDa. Overall, antibodies to neutrophil antigens other than HLA could be detected in sera from eight patients. Transfusion reactions occurred in 11 of the 14 individuals with WBC antibodies and in none of the 4 without antibodies. Seven pulmonary reactions occurred in patients with WBC antibodies. The patients with WBC antibodies were given significantly more granulocyte concentrates (78 +/- 65 vs. 29 +/- 15 units, p < 0.05).

CONCLUSION

Recipients of granulocyte transfusions often become alloimmunized. Screening for WBC antibodies periodically during transfusions, after adverse reactions, or before subsequent transfusions is indicated. If WBC antibodies are present, no further granulocyte transfusions should be given unless the granulocytes are collected from HLA- and/or neutrophil antigen-compatible donors.

Apoptosis following interleukin-2 withdrawal from T cells: evidence for a regulatory role of CD18 (beta 2-integrin) molecules

Following a successful immune response against invading microorganisms, the majority of activated T cells is eliminated, while a minor fraction survives as memory T cells. A decline in T lymphocyte growth factors such as interleukin-2 (IL-2) appears to play a role in the elimination of previously activated T cells. Thus, removal of IL-2 from proliferating T cells not only induces growth arrest, but triggers a massive cell death due to apoptosis. While the apoptotic response involves a series of well-described events, it remains less clear how apoptosis is regulated following IL-2 withdrawal. Here, we provide evidence that CD18 molecules (beta 2-integrins) play a regulatory role in the apoptotic response following removal of IL-2 from previously activated, antigen specific CD4+ T cell lines. Thus, CD18 mAb inhibited the apoptotic response to IL-2 deprivation, whereas mAb against other adhesion molecules (CD28, CD29, CD49d, CD80, CD86) did not. Secondly, IL-2 withdrawal resulted in a retarded apoptotic response in LFA-1 (CD11a/CD18) negative T cells obtained from a leukocyte adhesion deficiency (LAD) patient, as compared to LFA-1 positive T cell lines. Thirdly, co-culture of LFA-1 positive- and negative-T cells at different ratios induced apoptotic responses that were higher than expected, had the two lymphocyte populations not been interacting and significantly higher than that seen in pure LFA-1 negative T cells. Supernatants from LFA-1 positive T cell cultures undergoing apoptosis did not induce an enhanced apoptotic responses in LFA-1 negative T cells, and, reversely, culture supernatants from LFA-1 negative T cells did not rescue LFA-1 positive cells from undergoing apoptosis. The apoptotic response was partly blocked by IL-15, a newly identified T cell growth factor. Taken together, these findings suggest that CD18 molecules (beta 2-integrins) play a regulatory role in the apoptotic response following cytokine withdrawal, and that the regulation is mediated, at least partly, through T-T cell interactions. Thus, apoptotic death following IL-2 deprivation appears to be under "social" control by surrounding T cells.

Surface attachment of Salmonella typhimurium to intestinal epithelia imprints the subepithelial matrix with gradients chemotactic for neutrophils

During intestinal disease induced by Salmonella typhimurium transepithelial migration of neutrophils (PMN) rapidly follows attachment of the bacteria to the epithelial apical membrane. Among the events stimulated by these interactions is the release of chemotaxins that guide PMN through the subepithelial matrix and subsequently through the epithelium itself (McCormick, B.A., S.P. Colgan, C. Delp-Archer, S.I. Miller, and J.L. Madara. 1993. J. Cell Biol. 123:895-907). Given the substantial volume flow that normally characterizes matrix compartments underlying transporting epithelia, it is unclear how such transmatrix signaling is sustained. Here we show that when underlying matrices are isolated from biophysically confluent polarized monolayers of the human intestinal epithelial cell line T84, they fail to support substantial transmatrix migration of PMN unless an exogenous chemotactic gradient is imposed. In contrast, such matrices isolated from confluent monolayers apically colonized with S. typhimurium support spontaneous transmatrix migration of PMN. Such chemotactic imprinting of underlying matrices is resistant to volume wash and is paralleled by secretion of the known matrix-binding chemokine IL-8. Chemotactic imprinting of the matrix underlying S. typhimurium-colonized monolayers is dependent on epithelial protein synthesis, is directional implying the existence of a gradient, and is neutralized by antibodies either to IL-8 or to the IL-8 receptor on PMN. An avirulent S. typhimurium strain, PhoPc, which attaches to epithelial cells as efficiently as wild-type S. typhimurium, fails to induce basolateral secretion of IL-8 and likewise fails to imprint matrices. Together, these observations show that the epithelial surface can respond to the presence of a luminal pathogen and subsequently imprint the subepithelial matrix with retained IL-8 gradients sufficient to resist washout effects of the volume flow that normally traverses this compartment. Such data further support the notion that the primary role for basolateral secretion of IL-8 by the intestinal and likely other epithelia is recruitment of PMN through the matrix to the subepithelial space, rather than directing the final movement of PMN across the epithelium.

Observations of root surfaces from patients with early-onset periodontitis and leukocyte adhesion deficiency

The purpose of this investigation was to report observations of the root surfaces of teeth from 2 siblings with leukocyte adhesion deficiency (LAD). In previous publications, the clinical, radiographic and immunologic findings in the family were presented. 38 permanent teeth from the 2 siblings were prepared for microscopic examination, 11 for light microscopy (LM), and 27 for scanning electron microscopy (SEM). In addition, 8 healthy teeth obtained from 2 patients requiring extractions for orthodontic treatment served as controls. LM observations on healthy teeth revealed cementum with normal structural appearance which exhibited a mosaic or mogul-like pattern with SEM. In LAD specimens, cementum apical to the dentogingival junction exhibited resorption lacunae and areas of poor structural definition characterized by aplasia and hypoplasia (hypomineralization). Areas of hypoplasia presented as distinct irregular surfaces with a pebbly or globular-like appearance. Alteration in cementum formation and maturation may play a role in the etiology of early-onset periodontitis.

Identification of the complement iC3b binding site in the beta 2 integrin CR3 (CD11b/CD18)

The divalent cation-dependent interaction of the beta 2 integrin CR3 (CD11b/CD18) with the major complement opsonic C3 fragment iC3b is an important component of the central role of CR3 in inflammation and immune clearance. In this investigation we have identified the iC3b binding site in CR3. A recombinant fragment representing the CR3 A-domain, a 200-amino acid region in the ectodomain of the CD11b subunit, bound to iC3b directly and in a divalent cation-dependent manner. The iC3b binding site was further localized to a short linear peptide that also bound iC3b directly and inhibited iC3b binding to the A-domain as well as to CR3 expressed by human neutrophils. These data establish a major recognition function for the integrin A-domain and have important implications for development of novel antiinflammatory therapeutics.

MCP-1-stimulated monocyte attachment to laminin is mediated by beta 2-integrins

Migration of monocytes to sites of inflammation involves a series of attachments and detachments to extracellular matrix proteins. We examined the capacity of a chemokine, monocyte chemoattractant protein-1 (MCP-1), to regulate attachment of human monocytes to laminin, collagen I, collagen IV, or fibronectin. MCP-1 increased monocyte attachment to laminin in a dose- and time-dependent manner and stimulated a lesser increase to the other matrix proteins. Function-blocking monoclonal antibodies (MAbs) to the integrin beta 2-subunit (CD18), including Fab' fragments and alpha M (CD11b) blocked > 70% of attachment, whereas MAbs to the beta 1-integrin subunit reduced attachment by < 30%. This suggests that the CD11b/CD18 integrin is the predominant molecule involved in adhesion of MCP-1-stimulated monocytes to laminin. The association of CD11b with F-actin illustrated by confocal microscopy further supports this concept. In contrast, when monocytes were stimulated with the beta 1-stimulatory MAb TS2/16, monocyte adhesion to laminin occurred through beta 1-integrins. Thus MCP-1 can stimulate monocyte attachment to laminin, and this process is mediated through beta 2-integrins, principally CD11b/CD18.

Salmonella typhimurium attachment to human intestinal epithelial monolayers: transcellular signalling to subepithelial neutrophils

In human intestinal disease induced by Salmonella typhimurium, transepithelial migration of neutrophils (PMN) rapidly follows attachment of the bacteria to the epithelial apical membrane. In this report, we model those interactions in vitro, using polarized monolayers of the human intestinal epithelial cell, T84, isolated human PMN, and S. typhimurium. We show that Salmonella attachment to T84 cell apical membranes did not alter monolayer integrity as assessed by transepithelial resistance and measurements of ion transport. However, when human neutrophils were subsequently placed on the basolateral surface of monolayers apically colonized by Salmonella, physiologically directed transepithelial PMN migration ensued. In contrast, attachment of a non-pathogenic Escherichia coli strain to the apical membrane of epithelial cells at comparable densities failed to stimulate a directed PMN transepithelial migration. Use of the n-formyl-peptide receptor antagonist N-t-BOC-1-methionyl-1-leucyl-1- phenylalanine (tBOC-MLP) indicated that the Salmonella-induced PMN transepithelial migration response was not attributable to the classical pathway by which bacteria induce directed migration of PMN. Moreover, the PMN transmigration response required Salmonella adhesion to the epithelial apical membrane and subsequent reciprocal protein synthesis in both bacteria and epithelial cells. Among the events stimulated by this interaction was the epithelial synthesis and polarized release of the potent PMN chemotactic peptide interleukin-8 (IL-8). However, IL-8 neutralization, transfer, and induction experiments indicated that this cytokine was not responsible for the elicited PMN transmigration. These data indicate that a novel transcellular pathway exists in which subepithelial PMN respond to lumenal pathogens across a functionally intact epithelium. Based on the known unique characteristics of the intestinal mucosa, we speculate that IL-8 may act in concert with an as yet unidentified transcellular chemotactic factor(s) (TCF) which directs PMN migration across the intestinal epithelium.

Chemotaxis of polymorphonuclear neutrophils (PMN) in patients suffering from recurrent infection

PMN function was tested in patients suffering from recurrent infections. In 65 out of 240 patients lack of oxygen radical production or reduced chemotactic activity was found. In most cases the reduction was transient and associated with clinical impairments of the patients. Only a few patients had primary cellular defects. In one of those patients the expression of beta 2 integrins was reduced, while PMN of the other patients expressed beta 2 integrins normally. Thus, cellular defects other than the reduced expression of beta 2 integrins might also result in impaired chemotactic activity.

Defect of a complement receptor 3 epitope in a patient with systemic lupus erythematosus

Complement receptor 3 (CR3) is expressed on cells of the reticuloendothelial system and involved in the clearance of immune complexes. In this article a patient with a deficiency of the C3bi binding site of this receptor is described. Clinically this patient exhibited predominantly cutaneous manifestations of a systemic lupus erythematosus with an immune vasculitis and panniculitis. The deficiency of the CR3 epitope was demonstrated using flow cytometry. The functional relevance of this defect was demonstrated in a rosetting assay with C3bi-loaded erythrocytes. C3bi binding was found to be significantly decreased. Furthermore, there was an impairment of phagocytosis of opsonized Escherichia coli. The CR3 defect is not due to an autoantibody but is assumed to have a genetic basis. These data suggest that the defect of the CR3 may be involved in the pathogenesis of the immune vasculitis in this patient.

Familial genetic defect in a case of leukocyte adhesion deficiency

Leukocyte adhesion deficiency (LAD) is an inherited immunodeficiency disorder caused by CD18 subunit abnormality dependent defective expression of beta 2 integrins on the surface of leukocytes. On analysis of the CD18 molecular defect in a female Japanese patient with a severe deficiency LAD phenotype, neither CD11a nor CD18 molecules could be detected on the patient's EBV-transformed B lymphoblastoid cell line. The mRNA of the patient's B cells was normal in size, but was diminished in quantity, to approximately half normal levels. Sequencing of the CD18 cDNA of the patient revealed a C605 to T transition, resulting in a Pro178-->Leu substitution. This was heterozygous in the genomic DNA, and shown to be of maternal origin by family study. Only a few transcripts from the other allele without the Pro178-->Leu mutation were detectable. Northern blot analysis revealed reduced CD18 mRNA levels, not only in the patient, but also in the father and brother. These results indicate that our case is a compound heterozygote with two different mutant alleles: one causing a single amino acid substitution and the other causing defective expression of mRNA.