Leukocyte adhesion molecules deficiency: its structural basis, pathophysiology and implications for modulating the inflammatory response

Cafeteria diet-induced obesity remodels immune response in acute Trypanosoma cruzi infection

BACKGROUND

Obesity is a global problem associated with several conditions, including hypertension, diabetes, arthritis and cardiovascular diseases. With the increase in the prevalence of obesity in recent years, mostly in developing countries, it is important to study its impact on various diseases, including infectious illnesses, such as Chagas disease, caused by the protozoan Trypanosoma cruzi. Considering that a diet rich in salt, sugar, and fat is associated with obesity, this study aimed to evaluate the influence of cafeteria diet (CAF)-induced obesity on immune responses in T. cruzi-infected rats.

METHODS

Male Wistar Hannover rats were provided with water and food ad libitum (chow group). The CAF-fed groups received a normal rodent diet or CAF. The animals were intraperitoneally infected with 105 trypomastigote forms of the Y strain of T. cruzi present in the whole blood from a previously infected mouse.

RESULTS

CAF-fed rats showed a significant increase in visceral adipose tissue weight compared to chow-fed rats. A significant reduction in CD3+ CD4+ helper splenic T cells was observed in obese-infected rats compared to non-obese-infected rats, as well as CD11b and macrophages. In addition, macrophages from obese animals displayed reduced RT1b levels compared to those from control animals. Moreover, INF-γ, an important factor in macrophage activation, was reduced in obese-infected rats compared with their counterparts.

CONCLUSIONS

These results indicate that a CAF can impair the cell-mediated immune response against T. cruzi.

The complement receptor C5aR2 regulates neutrophil activation and function contributing to neutrophil-driven epidermolysis bullosa acquisita

Introduction

The function of the second receptor for the complement cleavage product C5a, C5aR2, is poorly understood and often neglected in the immunological context. Using mice with a global deficiency of C5aR2, we have previously reported an important role of this receptor in the pathogenesis of the neutrophil-driven autoimmune disease epidermolysis bullosa acquisita (EBA). Based on in vitro analyses, we hypothesized that the absence of C5aR2 specifically on neutrophils is the cause of the observed differences. Here, we report the generation of a new mouse line with a LysM-specific deficiency of C5aR2.

Methods

LysM-specific deletion of C5aR2 was achieved by crossing LysM^cre mice with tdTomato-C5ar2^fl/fl mice in which the tdTomato-C5ar2 gene is flanked by loxP sites. Passive EBA was induced by subcutaneous injection of rabbit anti-mouse collagen type VII IgG. The effects of targeted deletion of C5ar2 on C5a-induced effector functions of neutrophils were examined in in vitro assays.

Results

We confirm the successful deletion of C5aR2 at both the genetic and protein levels in neutrophils. The mice appeared healthy and the expression of C5aR1 in bone marrow and blood neutrophils was not negatively affected by LysM-specific deletion of C5aR2. Using the antibody transfer mouse model of EBA, we found that the absence of C5aR2 in LysM-positive cells resulted in an overall amelioration of disease progression, similar to what we had previously found in mice with global deficiency of C5aR2. Neutrophils lacking C5aR2 showed decreased activation after C5a stimulation and increased expression of the inhibitory Fcγ receptor FcγRIIb.

Discussion

Overall, with the data presented here, we confirm and extend our previous findings and show that C5aR2 in neutrophils regulates their activation and function in response to C5a by potentially affecting the expression of Fcγ receptors and CD11b. Thus, C5aR2 regulates the finely tuned interaction network between immune complexes, Fcγ receptors, CD11b, and C5aR1 that is important for neutrophil recruitment and sustained activation. This underscores the importance of C5aR2 in the pathogenesis of neutrophil-mediated autoimmune diseases.

Nanoparticles for Targeted Brain Drug Delivery: What Do We Know?

The blood-brain barrier (BBB) is a barrier that separates the blood from the brain tissue and possesses unique characteristics that make the delivery of drugs to the brain a great challenge. To achieve this purpose, it is necessary to design strategies to allow BBB passage, in order to reach the brain and target the desired anatomic region. The use of nanomedicine has great potential to overcome this problem, since one can modify nanoparticles with strategic molecules that can interact with the BBB and induce uptake through the brain endothelial cells and consequently reach the brain tissue. This review addresses the potential of nanomedicines to treat neurological diseases by using nanoparticles specially developed to cross the BBB.

Insight into the LFA-1/SARS-CoV-2 Orf7a Complex by Protein-Protein Docking, Molecular Dynamics, and MM-GBSA Calculations

In the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) genome, open reading frames (ORFs) encode for viral accessory proteins. Among these, Orf7a structurally resembles the members of the immunoglobulin (Ig) superfamily and intracellular adhesion molecules (ICAMs), in particular. ICAMs are involved in integrin binding through lymphocyte function-associated antigen 1 (LFA-1). Based on such considerations and on previous findings on SARS-CoV, it has been postulated that the formation of the LFA-1/Orf7a complex could contribute to SARS-CoV-2 infectivity and pathogenicity. With the current work, we aim at providing insight into this macromolecular assembly, taking advantage of the recently reported SARS-CoV-2 Orf7a structure. Protein-protein docking, molecular dynamics (MD) simulations, and a Molecular Mechanical-Generalized Born Surface Area (MM-GBSA)-based stage were enrolled to provide refined models.

PLCε1 mediates one-lung ventilation injury by regulating the p38/RhoA/NFκB activation loop

BACKGROUND

Phospholipase C epsilon-1 (PLCε1) might be a novel and potential target in treating inflammatory conditions. In the present study, we aimed to clarify whether PLCε1 is involved in lung injury caused by one-lung ventilation (OLV) and to elucidate the potential molecular mechanism of PLCε1-mediated signaling pathway on OLV induced inflammatory response and injury.

METHODS

Male Sprague-Dawley (SD) rats were divided into wide-type (PLCε1-WT) group and PLCε1-KO group, and were treated with OLV for 0.5 h, 1 h, and 2 h respectively. Observation of lung tissue injury in rats was performed by Hematoxylin and eosin (HE) staining and Wet/dry (W/D) radios. In addition, pulmonary microvascular endothelial cells (PMVECs) transfected with PLCε1-si RNA, were stimulated by lipopolysaccharide (LPS). To explore the possible roles of PLCε1 in the OLV induced inflammatory injury and the involved pathway underlying, the lung tissue and bronchoalveolar lavage fluids (BALF) of OLV rats, as well as the PMVECs were prepared for further analysis. Enzyme-linked immunoassay (ELISA) was used to detect the expression of pro-inflammatory factors. The activities of related pathway proteins (NF-κB, phospho-p38, p38, phospho-ERK1/2, ERK1/2, RhoA and ROCK) were also detected by reverse transcription quantitative polymerase chain reaction (RT-qPCR) and western blot analysis.

RESULTS

Compared to the PLCε1-WT rats, PLCε1-KOrats exhibited marked alleviation of lung inflammation as shown by great reduction in lung wet/dry weight ratios, decreases in the expressions of pro-inflammatory mediators, and declines in the number of neutrophils and the protein concentration in bronchoalveolar lavage fluid (BALF). Moreover, the increased expressions of RhoA and NF-κB p65 mRNA induced by OLV were significantly inhibited in PLCε1-KO rats. In LPS treated PMVECs, PLCε1-si RNA transfection ones also showed the decrease expression of proinflammatory mediators, reduction in p38 phosphorylation levels and downregulation of RhoA/ROCK signaling activation. Co-cultured with PLCε1-si RNA and BTRB796 (p38 inhibitors) in LPS-stimulated PMVECs resulted in a significant reduction in RhoA and NF-κB activity. In addition, treatment with either ROCK inhibitor (Y-27632) or dominant negative mutant of RhoA (RhoT19 N) significantly reduced the expression of NF-κB in PLCε1-si RNA treated PMVECs.

CONCLUSION

The results indicated that PLCε1 played an important role in the inflammatory response induced by OLV. Moreover, through promoting p38/RhoA/ROCK activation loop, PLCε1 promoted NF-κB activation and thereby increased the expressions of inflammatory mediators, which induced the PMVECs inflammation and subsequent injury. The results of this study provide a potential therapeutic target for the reduction of inflammatory response in patients with OLV.

Clinical and Genetic Spectrum of a Large Cohort of Patients With Leukocyte Adhesion Deficiency Type 1 and 3: A Multicentric Study From India

Leukocyte adhesion deficiency (LAD) syndrome is a group of inborn errors of immunity characterized by a defect in the cascade of the activation and adhesion leading to the failure of leukocyte to migrate to the site of tissue injury. Three different types of LAD have been described. The most common subtype is LAD type 1 (LAD1) caused due to defects in the ITGβ2 gene. LAD type 2 (LAD2) is caused by mutations in the SLC35C1 gene leading to a generalized loss of expression of fucosylated glycans on the cell surface and LAD type 3 (LAD3) is caused by mutations in the FERMT3 gene resulting in platelet function defects along with immunodeficiency. There is a paucity of data available from India on LAD syndromes. The present study is a retrospective analysis of patients with LAD collated from 28 different centers across India. For LAD1, the diagnosis was based on clinical features and flow cytometric expression of CD18 on peripheral blood leukocytes and molecular confirmation by Sanger sequencing. For patients with LAD3 diagnosis was largely based on clinical manifestations and identification of the pathogenic mutation in the FERMT3 gene by next-generation Sequencing. Of the total 132 cases diagnosed with LAD, 127 were LAD1 and 5 were LAD3. The majority of our patients (83%) had CD18 expression less than 2% on neutrophils (LAD1°) and presented within the first three months of life with omphalitis, skin and soft tissue infections, delayed umbilical cord detachment, otitis media, and sepsis. The patients with CD18 expression of more than 30% (LAD1⁺) presented later in life with skin ulcers being the commonest manifestation. Bleeding manifestations were common in patients with LAD3. Persistent neutrophilic leukocytosis was the characteristic finding in all patients. 35 novel mutations were detected in the ITGβ2 gene, and 4 novel mutations were detected in the FERMT3 gene. The study thus presents one of the largest cohorts of patients from India with LAD, focusing on clinical features, immunological characteristics, and molecular spectrum.

Plasma membrane receptors of tissue macrophages: functions and role in pathology

The cells of the mononuclear phagocyte system (MPS) constitute a dispersed organ, which is distributed throughout the body. Macrophages in different tissues display distinctive mosaic phenotypes as resident and recruited cells of embryonic and bone marrow origin, respectively. They help to maintain homeostasis during development and throughout adult life, yet contribute to the pathogenesis of many disease processes, including inflammation, innate and adaptive immunity, metabolic disorders, and cancer. Heterogeneous tissue macrophage populations display a wide variety of surface molecules to recognise and respond to host, microbial, and exogenous ligands in their environment; their receptors mediate the uptake and destruction of effete and dying host cells and pathogens, as well as contribute trophic and secretory functions within every organ in the body. Apart from local cellular interactions, macrophage surface molecules and products serve to mobilise and coordinate systemic humoral and cellular responses. Their use as antigen markers in pathogenesis and as potential drug targets has lagged in clinical pathology and human immunotherapy. In this review, we summarise the properties of selected surface molecules expressed on macrophages in different tissues and disease processes, to provide a functional basis for diagnosis, further research, and treatment. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Gastrointestinal Disorders Associated with Primary Immunodeficiency Diseases

There are now 354 inborn errors of immunity (primary immunodeficiency diseases (PIDDs)) with 344 distinct molecular etiologies reported according to the International Union of Immunological Sciences (IUIS) (Clin Gastroenterol Hepatol 11: p. 1050-63, 2013, Semin Gastrointest Dis 8: p. 22-32, 1997, J Clin Immunol 38: p. 96-128, 2018). Using the IUIS document as a reference and cross-checking PubMed ( www.ncbi.nlm.nih.pubmed.gov ), we found that approximately one third of the 354 diseases of impaired immunity have a gastrointestinal component [J Clin Immunol 38: p. 96-128, 2018]. Often, the gastrointestinal symptomatology and pathology is the heralding sign of a PIDD; therefore, it is important to recognize patterns of disease which may manifest along the gastrointestinal tract as a more global derangement of immune function. As such, holistic consideration of immunity is warranted in patients with clinically significant gastrointestinal disease. Here, we discuss the manifold presentations and GI-specific complications of PIDDs which could lead patients to seek advice from a variety of clinician specialists. Often, patients with these medical problems will engage general pediatricians, surgeons, gastroenterologists, rheumatologists, and clinical immunologists among others. Following delineation of the presenting concern, accurate and often molecular diagnosis is imperative and a multi-disciplinary approach warranted for optimal management. In this review, we will summarize the current state of understanding of PIDD gastrointestinal disease involvement. We will do so by focusing upon gastrointestinal disease categories (i.e., inflammatory, diarrhea, nodular lymphoid hyperplasia, liver/biliary tract, structural disease, and oncologic disease) with an intent to aid the healthcare provider who may encounter a patient with an as-yet undiagnosed PIDD who presents initially with a gastrointestinal symptom, sign, or problem.

The Inflammatory Response After Ischemic Stroke: Targeting β2 and β1 Integrins

Ischemic stroke is a leading cause of death and disability with limited therapeutic options. Resulting inflammatory mechanisms after reperfusion (removal of the thrombus) result in cytokine activation, calcium influx, and leukocytic infiltration to the area of ischemia. In particular, leukocytes migrate toward areas of inflammation by use of integrins, particularly integrins β1 and β2. Integrins have been shown to be necessary for leukocyte adhesion and migration, and thus are of immediate interest in many inflammatory diseases, including ischemic stroke. In this review, we identify the main integrins involved in leukocytic migration following stroke (α L β2, αDβ2, α4β1, and α5β1) and targeted clinical therapeutic interventions.

Early-onset inflammatory bowel disease as a model disease to identify key regulators of immune homeostasis mechanisms

Rare, monogenetic diseases present unique models to dissect gene functions and biological pathways, concomitantly enhancing our understanding of the etiology of complex (and often more common) traits. Although inflammatory bowel disease (IBD) is a generally prototypic complex disease, it can also manifest in an early-onset, monogenic fashion, often following Mendelian modes of inheritance. Recent advances in genomic technologies have spurred the identification of genetic defects underlying rare, very early-onset IBD (VEO-IBD) as a disease subgroup driven by strong genetic influence, pinpointing key players in the delicate homeostasis of the immune system in the gut and illustrating the intimate relationships between bowel inflammation, systemic immune dysregulation, and primary immunodeficiency with increased susceptibility to infections. As for other human diseases, it is likely that adult-onset diseases may represent complex diseases integrating the effects of host genetic susceptibility and environmental triggers. Comparison of adult-onset IBD and VEO-IBD thus provides beautiful models to investigate the relationship between monogenic and multifactorial/polygenic diseases. This review discusses the present and novel findings regarding monogenic IBD as well as key questions and future directions of IBD research.

Lung Epithelial Cell-Derived Microvesicles Regulate Macrophage Migration via MicroRNA-17/221-Induced Integrin β1 Recycling

Robust lung inflammation is one of the prominent features in the pathogenesis of acute lung injury (ALI). Macrophage migration and recruitment are often seen at the early stage of lung inflammatory responses to noxious stimuli. Using an acid inhalation-induced lung injury model, we explored the mechanisms by which acid exposure initiates macrophage recruitment and migration during development of ALI. The lung epithelium comprises a large surface area and functions as a first-line defense against noxious insults. We found that acid exposure induced a remarkable microvesicle (MV) release from lung epithelium as detected in bronchoalveolar lavage fluid. Significantly elevated RNA, rather than protein, was found in these epithelium-derived MVs after acid and included several highly elevated microRNAs, including microRNA (miR)-17 and miR-221. Acid-induced epithelial MV release promoted macrophage migration in vitro and recruitment into the lung in vivo and required, in part, MV shuttling of miR-17 and/or miR-221. Mechanistically, acid-induced epithelial MV miR-17/221 promoted β₁ integrin recycling and presentation back onto the surface of macrophages, in part via a Rab11-mediated pathway. Integrin β₁ is known to play an essential role in regulating macrophage migration. Taken together, acid-induced ALI results in epithelial MV shuttling of miR-17/221 that in turn modulates macrophage β₁ integrin recycling, promoting macrophage recruitment and ultimately contributing to lung inflammation.

Leukocyte integrin Mac-1 regulates thrombosis via interaction with platelet GPIbα

Inflammation and thrombosis occur together in many diseases. The leukocyte integrin Mac-1 (also known as integrin α_Mβ₂, or CD11b/CD18) is crucial for leukocyte recruitment to the endothelium, and Mac-1 engagement of platelet GPIbα is required for injury responses in diverse disease models. However, the role of Mac-1 in thrombosis is undefined. Here we report that mice with Mac-1 deficiency (Mac-1^−/−) or mutation of the Mac-1-binding site for GPIbα have delayed thrombosis after carotid artery and cremaster microvascular injury without affecting parameters of haemostasis. Adoptive wild-type leukocyte transfer rescues the thrombosis defect in Mac-1^−/− mice, and Mac-1-dependent regulation of the transcription factor Foxp1 contributes to thrombosis as evidenced by delayed thrombosis in mice with monocyte-/macrophage-specific overexpression of Foxp1. Antibody and small-molecule targeting of Mac-1:GPIbα inhibits thrombosis. Our data identify a new pathway of thrombosis involving leukocyte Mac-1 and platelet GPIbα, and suggest that targeting this interaction has anti-thrombotic therapeutic potential with reduced bleeding risk.

The binding of the leukocyte integrin Mac1 to the platelet receptor GPIbα is important for the physiological response to tissue injury. Here the authors show that this interaction also regulates thrombosis, without influencing bleeding time, which may provide clues for the development of new anti-thrombotic drugs.

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.

The many faces of Mac-1 in autoimmune disease

Mac-1 (CD11b/CD18) is a β2 integrin classically regarded as a pro-inflammatory molecule because of its ability to promote phagocyte cytotoxic functions and enhance the function of several effector molecules such as FcγR, uPAR, and CD14. Nevertheless, recent reports have revealed that Mac-1 also plays significant immunoregulatory roles, and genetic variants in ITGAM, the gene that encodes CD11b, confer risk for the autoimmune disease systemic lupus erythematosus (SLE). This has renewed interest in the physiological roles of this integrin and raised new questions on how its seemingly opposing biological functions may be regulated. Here, we provide an overview of the CD18 integrins and how their activation may be regulated as this may shed light on how the opposing roles of Mac-1 may be elicited. We then discuss studies that exemplify Mac-1's pro-inflammatory versus regulatory roles particularly in the context of IgG immune complex-mediated inflammation. This includes a detailed examination of molecular mechanisms that could explain the risk-conferring effect of rs1143679, a single nucleotide non-synonymous Mac-1 polymorphism associated with SLE.

Anchorage-dependent binding of integrin I-domain to adhesion ligands

The dynamic interactions between leukocyte integrin receptors and ligands in the vascular endothelium, extracellular matrix, or invading pathogens result in leukocyte adhesion, extravasation, and phagocytosis. This work examined the mechanical strength of the connection between iC3b, a complement component that stimulates phagocytosis, and the ligand-binding domain, the I-domain, of integrin αMβ2. Single-molecule force measurements of αM I-domain-iC3b complexes were conducted by atomic force microscope. Strikingly, depending on loading rates, immobilization of the I-domain via its C-terminus resulted in a 1.3-fold to 1.5-fold increase in unbinding force compared with I-domains immobilized via the N-terminus. The force spectra (unbinding force versus loading rate) of the I-domain-iC3b complexes revealed that the enhanced mechanical strength is due to a 2.4-fold increase in the lifetime of the I-domain-iC3b bond. Given the structural and functional similarity of all integrin I-domains, our result supports the existing allosteric regulatory model by which the ligand binding strength of integrin can be increased rapidly when a force is allowed to stretch the C-terminus of the I-domain. This type of mechanism may account for the rapid ligand affinity adjustment during leukocyte migration.

Molecular characterization of leukocyte adhesion deficiency-I in Indian patients: identification of 9 novel mutations

PURPOSE

Leukocyte adhesion deficiency type-I (LAD-I) is caused by mutations in the ITGB2 gene, encoding the β2-subunit of β2-integrin (CD18) which leads to markedly reduced expression of CD18 on leukocytes resulting into recurrent life threatening infections. Here we aim to identify the molecular defects underlying LAD-I in Indian patients and correlate with the clinical presentation.

METHODS

Blood was collected from 30 patients and their parents for absolute neutrophil count, expression of CD18 and CD11 by flow cytometry and DNA extraction. PCR and DNA sequencing of the ITGB2 gene was done for mutation characterization.

RESULTS

Phenotypically, 22 patients were LAD-I(0), 1 was LAD-I(-) and 7 were LAD-I(+) showing no expression and reduced expression of CD18 respectively. Nine novel mutations in 15 patients and 11 known mutations in 16 patients were detected. Prenatal diagnosis was performed for 5 families.

CONCLUSION

In this study 30 patients were phenotypically and genotypically evaluated for a less known disease LAD-I. Unavailability of curative options to majority of the patients and high cost of supportive care emphasize the need to increase awareness about a suspicious case so that timely management can be given to the patient and prenatal diagnosis can be offered to their families.

New therapeutic approaches for protecting hematopoietic stem cells in aplastic anemia

Aplastic anemia (AA) is an immune-mediated and life-threatening form of acquired bone marrow failure (BMF), characterized by development and expansion of self-reactive T cells. These T cells cause continuous destruction of hematopoietic stem cells (HSCs), progenitors, and mature blood cells, leading to severe and if left untreated fatal marrow hypoplasia and pancytopenia. Standard treatment options for patients with AA include: (1) immunosuppressive therapy (IST) with anti-thymocyte globulin and cyclosporine A which targets self-reactive T cells, or (2) matched sibling or unrelated BM transplant (BMT). The IST treatment is often not effective due to poor response to therapy or disease relapse after IST. Also, BMT is not an option for many patients due to their age, comorbidities, and the lack of histocompatible donor. This necessitates development and testing of novel approaches to reduce severity of AA and to efficiently treat patients with refractory and relapsed AA. Immune-mediated AA was reproduced in animals, including mouse lymphocyte infusion models, which are used to study further etiology and pathophysiology of AA and test new drugs and approaches in treating and managing AA. In these mouse models the immune correlates and pathologic features of AA are strikingly similar to features of severe human AA. In this article we (a) briefly review standard and developing approaches for treating AA and (b) describe development and testing of novel treatment approach with a potential to safely reduce BM hypoplasia and significantly decrease the loss of HSCs in mouse lymphocyte infusion model of AA.

EM structure of the ectodomain of integrin CD11b/CD18 and localization of its ligand-binding site relative to the plasma membrane

One-half of the integrin α-subunit Propeller domains contain and extra vWFA domain (αA domain), which mediates integrin binding to extracellular physiologic ligands via its metal-ion-dependent adhesion site (MIDAS). We used electron microscopy to determine the 3D structure of the αA-containing ectodomain of the leukocyte integrin CD11b/CD18 (αMβ2) in its inactive state. A well defined density for αA was observed within a bent ectodomain conformation, while the structure of the ectodomain in complex with the Fab fragment of mAb107, which binds at the MIDAS face of CD11b and stabilizes the inactive state, further revealed that αA is restricted to a relatively small range of orientations relative to the Propeller domain. Using Fab 107 as probe in fluorescent lifetime imaging microscopy (FLIM) revealed that αA is positioned relatively far from the membrane surface in the inactive state, and a systematic orientation search revealed that the MIDAS face would be accessible to extracellular ligand in the inactive state of the full-length cellular integrin. These studies are the first to define the 3D EM structure of an αA-containing integrin ectodomain and to position the ligand-binding face of αA domain in relation to the plasma membrane, providing new insights into current models of integrin activation.

Phagocytosis is the main CR3-mediated function affected by the lupus-associated variant of CD11b in human myeloid cells

The CD11b/CD18 integrin (complement receptor 3, CR3) is a surface receptor on monocytes, neutrophils, macrophages and dendritic cells that plays a crucial role in several immunological processes including leukocyte extravasation and phagocytosis. The minor allele of a non-synonymous CR3 polymorphism (rs1143679, conversation of arginine to histidine at position 77: R77H) represents one of the strongest genetic risk factor in human systemic lupus erythematosus, with heterozygosity (77R/H) being the most common disease associated genotype. Homozygosity for the 77H allele has been reported to reduce adhesion and phagocytosis in human monocytes and monocyte-derived macrophages, respectively, without affecting surface expression of CD11b. Herein we comprehensively assessed the influence of R77H on different CR3-mediated activities in monocytes, neutrophils, macrophages and dendritic cells. R77H did not alter surface expression of CD11b including its active form in any of these cell types. Using two different iC3b-coated targets we found that the uptake by heterozygous 77R/H macrophages, monocytes and neutrophils was significantly reduced compared to 77R/R cells. Allele-specific transduced immortalized macrophage cell lines demonstrated that the minor allele, 77H, was responsible for the impaired phagocytosis. R77H did not affect neutrophil adhesion, neutrophil transmigration in vivo or Toll-like receptor 7/8-mediated cytokine release by monocytes or dendritic cells with or without CR3 pre-engagement by iC3b-coated targets. Our findings demonstrate that the reduction in CR3-mediated phagocytosis associated with the 77H CD11b variant is not macrophage-restricted but demonstrable in other CR3-expressing professional phagocytic cells. The association between 77H and susceptibility to systemic lupus erythematosus most likely relates to impaired waste disposal, a key component of lupus pathogenesis.

Warts and all: human papillomavirus in primary immunodeficiencies

Infection with human papillomavirus (HPV) is almost universal and eventually asymptomatic, but pathologic infection with HPV is severe, recurrent, and recalcitrant to therapy. It is also an underappreciated manifestation of primary immunodeficiency. Mutations in EVER1, EVER2, GATA2, CXCR4, and dedicator of cytokinesis 8 (DOCK8) are typically associated with extensive HPV infections, whereas several other primary immune defects result in severe HPV much less frequently. We review immunodeficiencies with severe HPV infections and the mechanisms underlying them.

Hormonal control of inflammatory responses

Almost any stage of inflammatory and immunological responses is affected by hormone actions. This provides the basis for the suggestion that hormones act as modulators of the host reaction against trauma and infection. Specific hormone receptors are detected in the reactive structures in inflamed areas and binding of hormone molecules to such receptors results in the generation of signals that influence cell functions relevant for the development of inflammatory responses. Diversity of hormonal functions accounts for recognized pro- and anti-inflammatory effects exerted by these substances. Most hormone systems are capable of influencing inflammatory events. Insulin and glucocorticoids, however, exert direct regulatory effects at concentrations usually found in plasma. Insulin is endowed with facilitatory actions on vascular reactivity to inflammatory mediators and inflammatory cell functions. Increased concentrations of circulating glucocorticoids at the early stages of inflammation results in downregulation of inflammatory responses. Oestrogens markedly reduce the response to injury in a variety of experimental models. Glucagon and thyroid hormones exert indirect anti-inflammatory effects mediated by the activity of the adrenal cortex. Accordingly, inflammation is not only merely a local response, but a hormone-controlled process.

The effect of tumour necrosis factor-alpha (TNF-alpha) muteins on human neutrophils in vitro

Tumour necrosis factor-α (TNF-α) has been implicated as an important inflammatory mediator. In vitro, TNF-α is reported to activate human polymorphonuclear neutrophils (PMN), inducing responses such as phagocytic activity, degranulation and oxidative metabolism. Biological responses to TNF-α are initiated by its binding to specific cell surface receptors, and various studies have shown that the major TNF receptor species on PMN is the 75 kDa receptor. To verify the suggestion that the receptor binding domain includes the region close to the N-terminus of the TNF-α molecule, four TNF-α derivatives termed muteins were constructed, using a synthetic cDNA fragment substituting the N-terminal 3–7 selected hydrophilic or hydrophobic amino acids in the original TNF-α genomic DNA. Binding of muteins to PMN was assessed using monoclonal antibodies recognizing either the 55 kDa (p55) or the 75 kDa (p75) TNF receptor subtypes. Blocking by muteins of anti-p75 antibody binding to PMN was as expected from their N-terminal amino acid composition and hydrophilic properties. Hydrophilic muteins competed well with anti-TNF receptor antibodies for binding to the p75 receptor. In contrast, hydrophobic muteins were unable to block anti-p75 binding. Similarly, degranulation, chemiluminescence or enhancement of the PMN response to specific stimuli by the muteins correlated with the hydrophilic properties of the muteins. The significance of these observations in relation to the molecular structure of TNF-α is discussed.

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.

Study of neutrophils isolated from peripheral blood of patients suffering from aggressive periodontitis at the cellular level: Receptors and cytoskeletal reorganization

BACKGROUND

Aggressive periodontitis (AgP) has been associated with polymorphonuclear leukocyte's (PMNL) dysfunction and periodontal pathogens possess variety of virulence factors that can impair PMNL's function. This study investigated the possible association between defective neutrophil adhesion and β(2) -integrin expression and defective neutrophil migration and actin polymerization level in the peripheral blood of neutrophils from the patients with AgP.

MATERIALS AND METHODS

A total of 30 individuals both male and female, age ranges between 13 - 48 years, were included in the study. Healthy controls (group I, n=10), chronic periodontitis (ChP) (group II, n=10), and AgP (group III, n=10), all without any systemic diseases and non-smokers, were recruited. Peripheral blood samples were taken and β(2) -integrin expression and actin polymerization levels were estimated by using fluorescence activated cell sorter analysis.

RESULTS

In AgP cases, both average values (β(2) -integrin and actin level) were significantly less than that of normal subjects (<0.001). But for ChP cases, only the average value of actin level is significantly lower than that of normal subjects (<0.025).

CONCLUSION

Lower β(2) -integrin expression in the AgP cases signifies lower neutrophil adhesion in AgP cases than normal, and the lower average value of actin polymerization for the AgP cases suggest lower migration capacity of neutrophils in AgP cases than normal.

Successful allogeneic stem cell transplantation with a reduced-intensity conditioning in a leukocyte adhesion deficiency type I patient

LAD-I is a rare, autosomal recessive, primary immunodeficiency in which phagocyte adhesion and chemotaxis are impaired. Multiple infections in the absence of pus accumulation and persistent elevated peripheral blood neutrophil counts are the hallmark of LAD-I. Allogeneic HSCT is the only treatment proved to be potentially curative for phagocyte adhesion impairment in LAD-I. Here, we report on a case of a 30-month-old girl with LAD-I, in whom peripheral blood stem cell from a genotypically identical sibling resulted in mixed chimerism.

Regulation of innate immune response to Candida albicans infections by αMβ2-Pra1p interaction

Candida albicans is a common opportunistic fungal pathogen and is the leading cause of invasive fungal diseases in immunocompromised individuals. The induction of cell-mediated immunity to C. albicans is one of the main tasks of cells of the innate immune system, and in vitro evidence suggests that integrin α(M)β₂ (CR3, Mac-1, and CD11b/CD18) is the principal leukocyte receptor involved in recognition of the fungus. Using α(M)β₂-KO mice and mutated strains of C. albicans in two models of murine candidiasis, we demonstrate that neutrophils derived from mice deficient in α(M)β₂ have a reduced ability to kill C. albicans and that the deficient mice themselves exhibit increased susceptibility to fungal infection. Disruption of the PRA1 gene of C. albicans, the primary ligand for α(M)β₂, protects the fungus against leukocyte killing in vitro and in vivo, impedes the innate immune response to the infection, and increases fungal virulence and organ invasion in vivo. Thus, recognition of pH-regulated antigen 1 protein (Pra1p) by α(M)β₂ plays a pivotal role in determining fungal virulence and host response and protection against C. albicans infection.

A novel 3' splice-site mutation and a novel gross deletion in leukocyte adhesion deficiency (LAD)-1

A patient was diagnosed with leukocyte adhesion deficiency-1. She was born in 1996 and her parents are not known to be related. Her leukocytes expressed less than 2% of the CD18 antigens relative to normal individuals. Molecular analysis revealed that she is a compound heterozygote. She inherited a 27,703bp deletion from her father (g.43201_PTTG1IP:10890del27703), spanning from intron 11 of the gene for the β2 integrin (ITGB2, CD18, NG_007270.2) to intron 2 of the gene for the Pituitary Tumor-Transforming Gene 1 Interacting Protein (PTTG1IP, NC_000021.8). The maternal allele has a g.23457C>A mutation at position -10 in intron 2 of the ITGB2 gene, resulting in the activation of a cryptic 3' splice site in intron 2 to include 43 intronic nucleotides (r.[59-43_59-1ins;59-10C>A]).

Exposure to in utero lipopolysaccharide induces inflammation in the fetal ovine skin

Inflammation is a defensive process by which the body responds to both localized and systemic tissue damage by the induction of innate and adaptive immunity. Literature from human and animal studies links inappropriate in utero inflammation to preterm parturition and fetal injury. The pathways by which such inflammation may cause labor, however, are not fully understood. Any proinflammatory agonist in the amniotic fluid will contact the fetal skin, in its entirety, but a potential role of the fetal skin in the pathways to labor have not previously been explored. We hypothesized that the fetal skin would respond robustly to the presence of intra-amniotic lipopolysaccharide (LPS) in our ovine model of in utero inflammation. In vitro and in utero exposure of fetal ovine keratinocytes or fetal skin to Escherichia coli LPS reliably induced significant increases in interleukin 1β (IL-1β), IL-6, tumor necrosis factor α (TNF-α), and IL-8 expression. We demonstrate that, in utero, this expression requires direct exposure with LPS suggesting that the inflammation is triggered directly in the skin itself, rather than as a secondary response to a systemic stimuli and that inflammation involves Toll-like receptor (TLR) regulation and neutrophil chemotaxis in concordance with an acute inflammatory reaction. We show that this response involves multiple inflammatory mediators, TLR regulation, and localized inflammatory cell influx characteristic of an acute inflammatory reaction. These novel data strongly suggests that the fetal skin acts as an important mediator of the fetal inflammatory response and as such may contribute to preterm birth.

IL-27/IFN-γ induce MyD88-dependent steroid-resistant airway hyperresponsiveness by inhibiting glucocorticoid signaling in macrophages

Inflammation and airway hyperresponsiveness (AHR) are hallmark features of asthma and often correlate with the severity of clinical disease. Although these features of asthma can be effectively managed with glucocorticoid therapy, a subgroup of patients, typically with severe asthma, remains refractory to therapy. The mechanisms leading to steroid resistance in severe asthmatics are poorly understood but may be related to the activation of innate host defense pathways. Previously, we have shown that IFN-γ-producing cells and LPS, two factors that are associated with severe asthma, induce steroid-resistant AHR in a mouse model. We now demonstrate that cooperative signaling induced by IFN-γ and LPS results in the production of IL-27 by mouse pulmonary macrophages. IL-27 and IFN-γ uniquely cooperate to induce glucocorticoid-resistant AHR through a previously unknown MyD88-dependent mechanism in pulmonary macrophages. Importantly, integrated signaling by IL-27/IFN-γ inhibits glucocorticoid-induced translocation of the glucocorticoid receptor to the nucleus of macrophages. Furthermore, expression of both IL-27 and IFN-γ was increased in the induced sputum of steroid-refractory asthmatics. These results suggest that a potential mechanism for steroid resistance in asthma is the activation of MyD88-dependent pathways in macrophages that are triggered by IL-27 and IFN-γ, and that manipulation of these pathways may be a therapeutic target.

Leukocyte adhesion deficiency type 1 presenting with recurrent pyoderma gangrenosum and flaccid scarring

We report an 11-year-old boy with a longstanding history of recurrent pyoderma gangrenosum and abnormal wound healing who eventually developed a fatal invasive fungal infection. This article emphasizes the importance to consider leukocyte adhesion deficiency type 1 in the differential diagnosis of patients with recurrent skin ulcers.

Integrin and chemokine receptor gene expression in implant-adherent cells during early osseointegration

The mechanisms of early cellular recruitment and interaction to titanium implants are not well understood. The aim of this study was to investigate the expression of pro-inflammatory cytokines, chemokines and adhesion markers during the first 24 h of implantation. Anodically oxidized and machined titanium implants were inserted in rat tibia. After 3, 12, and 24 h the implants were unscrewed and analyzed with quantitative polymerase chain reaction. Immunohistochemistry and scanning electron microscopy revealed different cell types, morphology and adhesion at the two implant surfaces. A greater amount of cells, as indicated by higher expression of small subunit ribosomal RNA (18S), was detected on the oxidized surface. Higher expression of CXC chemokine receptor-4 (at 12 h) and integrins, alphav (at 12 h), beta1 (at 24 h) and beta2 (at 12 and 24 h) was detected at the oxidized surfaces. Significantly higher tumor necrosis factor-alpha (at 3 h) and interleukin-1beta (at 24 h) expression was demonstrated for the machined surface. It is concluded that material surface properties rapidly modulate the expression of receptors important for the recruitment and adhesion of cells which are crucial for the inflammatory and regenerative processes at implant surfaces in vivo.

High-throughput screening based identification of small molecule antagonists of integrin CD11b/CD18 ligand binding

Binding of leukocyte specific integrin CD11b/CD18 to its physiologic ligands is important for the development of normal immune response in vivo. Integrin CD11b/CD18 is also a key cellular effector of various inflammatory and autoimmune diseases. However, small molecules selectively inhibiting the function of integrin CD11b/CD18 are currently lacking. We used a newly described cell-based high-throughput screening assay to identify a number of highly potent antagonists of integrin CD11b/CD18 from chemical libraries containing >100,000 unique compounds. Computational analyses suggest that the identified compounds cluster into several different chemical classes. A number of the newly identified compounds blocked adhesion of wild-type mouse neutrophils to CD11b/CD18 ligand fibrinogen. Mapping the most active compounds against chemical fingerprints of known antagonists of related integrin CD11a/CD18 shows little structural similarity, suggesting that the newly identified compounds are novel and unique.

Clinical significance of complement deficiencies

The complement system is composed of more than 30 serum and membrane-bound proteins, all of which are needed for normal function of complement in innate and adaptive immunity. Historically, deficiencies within the complement system have been suspected when young children have had recurrent and difficult-to-control infections. As our understanding of the complement system has increased, many other diseases have been attributed to deficiencies within the complement system. Generally, complement deficiencies within the classical pathway lead to increased susceptibility to encapsulated bacterial infections as well as a syndrome resembling systemic lupus erythematosus. Complement deficiencies within the mannose-binding lectin pathway generally lead to increased bacterial infections, and deficiencies within the alternative pathway usually lead to an increased frequency of Neisseria infections. However, factor H deficiency can lead to membranoproliferative glomerulonephritis and hemolytic uremic syndrome. Finally, deficiencies within the terminal complement pathway lead to an increased incidence of Neisseria infections. Two other notable complement-associated deficiencies are complement receptor 3 and 4 deficiency, which result from a deficiency of CD18, a disease known as leukocyte adhesion deficiency type 1, and CD59 deficiency, which causes paroxysmal nocturnal hemoglobinuria. Most inherited deficiencies of the complement system are autosomal recessive, but properidin deficiency is X-linked recessive, deficiency of C1 inhibitor is autosomal dominant, and mannose-binding lectin and factor I deficiencies are autosomal co-dominant. The diversity of clinical manifestations of complement deficiencies reflects the complexity of the complement system.

Regulation of integrin activity and signalling

The ability of cells to attach to each other and to the extracellular matrix is of pivotal significance for the formation of functional organs and for the distribution of cells in the body. Several molecular families of proteins are involved in adhesion, and recent work has substantially improved our understanding of their structures and functions. Also, these molecules are now being targeted in the fight against disease. However, less is known about how their activity is regulated. It is apparent that among the different classes of adhesion molecules, the integrin family of adhesion receptors is unique in the sense that they constitute a large group of widely distributed receptors, they are unusually complex and most importantly their activities are strictly regulated from the inside of the cell. The activity regulation is achieved by a complex interplay of cytoskeletal proteins, protein kinases, phosphatases, small G proteins and adaptor proteins. Obviously, we are only in the beginning of our understanding of how the integrins function, but already now fascinating details have become apparent. Here, we describe recent progress in the field, concentrating mainly on mechanistical and structural studies of integrin regulation. Due to the large number of articles dealing with integrins, we focus on what we think are the most exciting and rewarding directions of contemporary research on cell adhesion and integrins.

N-glycosylation of the I-like domain of beta1 integrin is essential for beta1 integrin expression and biological function: identification of the minimal N-glycosylation requirement for alpha5beta1

N-Glycosylation of integrin alpha5beta1 plays a crucial role in cell spreading, cell migration, ligand binding, and dimer formation, but the detailed mechanisms by which N-glycosylation mediates these functions remain unclear. In a previous study, we showed that three potential N-glycosylation sites (alpha5S3-5) on the beta-propeller of the alpha5 subunit are essential to the functional expression of the subunit. In particular, site 5 (alpha5S5) is the most important for its expression on the cell surface. In this study, the function of the N-glycans on the integrin beta1 subunit was investigated using sequential site-directed mutagenesis to remove the combined putative N-glycosylation sites. Removal of the N-glycosylation sites on the I-like domain of the beta1 subunit (i.e. the Delta4-6 mutant) decreased both the level of expression and heterodimeric formation, resulting in inhibition of cell spreading. Interestingly, cell spreading was observed only when the beta1 subunit possessed these three N-glycosylation sites (i.e. the S4-6 mutant). Furthermore, the S4-6 mutant could form heterodimers with either alpha5S3-5 or alpha5S5 mutant of the alpha5 subunit. Taken together, the results of the present study reveal for the first time that N-glycosylation of the I-like domain of the beta1 subunit is essential to both the heterodimer formation and biological function of the subunit. Moreover, because the alpha5S3-5/beta1S4-6 mutant represents the minimal N-glycosylation required for functional expression of the beta1 subunit, it might also be useful for the study of molecular structures.

Alveolar macrophage subpopulations in bronchoalveolar lavage and induced sputum of asthmatic and control subjects

BACKGROUND

Alveolar macrophages (AM) are the most numerous immune cells in the airways and are involved in the immunological homeostasis of the lung. Intriguingly, their role in asthma remains unclear probably, in part, because of their heterogeneity.

OBJECTIVE

To characterize AM population from bronchoalveolar lavage (BAL) and induced sputum (IS) of asthmatic and normal subjects using specific biomarkers.

METHODS

Non-asthmatic non-allergic and allergic mild asthmatic subjects were recruited for this study. AM were obtained from BAL and IS and cytospins were prepared. Immunocytochemistry was performed for nine cellular markers (CD68, RFD7, CD14, CD11b, CD83, CD64, CD80, CD86, and FIZZ1).

RESULTS

Asthmatic subjects had more AM RFD7(+) in BAL compared with IS, whereas control subjects had more AM RFD7(+) in IS than in BAL. Consequently, there was an increased number of AM RFD7(+) in BAL of asthmatic subjects compared with BAL of control subjects. AM CD11b(+) was higher in BAL than in IS in both groups. The expression of FIZZ1, marker of macrophage alternative activation, was similar in asthmatic and normal subjects.

CONCLUSION

The expression of cellular markers on AM differs according to their localization in the lung. Subpopulations of AM may contribute to the inflammatory profile observed in asthmatic subjects.

Structural basis for the interaction of isoDGR with the RGD-binding site of alphavbeta3 integrin

Asparagine deamidation at the NGR sequence in the 5th type I repeat of fibronectin (FN-I5) generates isoDGR, an alphavbeta3 integrin-binding motif regulating endothelial cell adhesion and proliferation. By NMR and molecular dynamics studies, we analyzed the structure of CisoDGRC (isoDGR-2C), a cyclic beta-peptide mimicking the FN-I5 site, and compared it with NGR, RGD, or DGR-containing cyclopeptides. Docking experiments show that isoDGR, exploiting an inverted orientation as compared with RGD, favorably interacts with the RGD-binding site of alphavbeta3, both recapitulating canonical RGD-alphavbeta3 contacts and establishing additional polar interactions. Conversely, NGR and DGR motifs lack the fundamental pharmacophoric requirements for high receptor affinity. Therefore, unlike NGR and DGR, isoDGR is a new natural recognition motif of the RGD-binding pocket of alphavbeta3. These findings contribute to explain the different functional properties of FN-I5 before and after deamidation, and provide support for the hypothesis that NGR --> isoDGR transition can work as a molecular timer for activating latent integrin-binding sites in proteins, thus regulating protein function.

Neuroendocrine factors in the regulation of inflammation: excessive adiposity and calorie restriction

Acute inflammation is usually a self-limited life preserving response, triggered by pathogens and/or traumatic injuries. This transient response normally leads to removal of harmful agents and to healing of the damaged tissues. In contrast, unchecked or chronic inflammation can lead to persistent tissue and organ damage by activated leukocytes, cytokines, or collagen deposition. Excessive energy intake and adiposity cause systemic inflammation, whereas calorie restriction without malnutrition exerts a potent anti-inflammatory effect. As individuals accumulate fat and their adipocytes enlarge, adipose tissue undergoes molecular and cellular alterations, macrophages accumulate, and inflammation ensues. Overweight/obese subjects have significantly higher plasma concentrations of C-reactive protein and several cytokines, including IL-6, IL-8, IL-18, and TNF-alpha. Experimental animals on a chronic CR regimen, instead, have low levels of circulating inflammatory cytokines, low blood lymphocyte levels, reduced production of inflammatory cytokines by the white blood cells in response to stimulation, and cortisol levels in the high normal range. Recent data demonstrate that CR exerts a powerful anti-inflammatory effect also in non-human primates and humans. Multiple metabolic and neuroendocrine mechanisms are responsible for the CR-mediated anti-inflammatory effects, including reduced adiposity and secretion of pro-inflammatory adipokines, enhanced glucocorticoid production, reduced plasma glucose and advanced glycation end-product concentrations, increased parasympathetic tone, and increased ghrelin production. Measuring tissue specific effects of CR using genomic, proteomic, and metabolomic techniques in humans will foster the understanding of the complex biological processes involved in the anti-inflammatory and anti-aging effects of CR.

Leukocyte integrin Mac-1 promotes acute cardiac allograft rejection

BACKGROUND

In allograft rejection, recipient leukocytes and alloantibodies first target donor endothelial cells. Although the leukocyte integrin Mac-1 (alpha(Mbeta2), CD11b/CD18) facilitates cell-cell interactions among leukocytes and interactions between leukocytes and endothelial cells or platelets, its role in allograft survival and vasculopathy is incompletely defined.

METHODS AND RESULTS

This study examined parenchymal rejection and graft arterial disease after total allomismatched cardiac transplantation (BALB/c donor heart and B6 recipients) in wild-type (WT) and Mac-1-deficient (Mac-1(-/-)) recipients. Recipient Mac-1 deficiency attenuated parenchymal rejection and significantly prolonged cardiac allograft survival from 8.3+/-1.3 days in WT recipient allografts (n=18) to 13.8+/-2.3 days in Mac-1(-/-) recipient allografts (n=6; P<0.0001). Accumulation of neutrophils and macrophages significantly decreased in Mac-1(-/-) compared with WT recipients. Adoptive transfer of WT but not Mac-1(-/-) macrophages to Mac-1(-/-) recipients exacerbated parenchymal rejection and reduced allograft survival; in contrast, adoptive transfer of WT neutrophils did not affect graft survival. Mac-1(-/-) macrophages expressed significantly lower levels of costimulatory molecules both in vivo and in vitro, and mixed lymphocyte reaction using alloantigen-primed Mac-1(-/-) macrophages resulted in significantly lower antigen-presenting function than for WT macrophages. Tumor necrosis factor-alpha production also fell in cultures with Mac-1(-/-) macrophages. Despite attenuation of acute rejection, recipient Mac-1-deficiency did not prevent late graft arterial disease.

CONCLUSIONS

These studies demonstrate critical participation of Mac-1 in alloresponses during cellular allograft rejection. These observations establish a molecular target for modulating recipient responses to prolong graft survival.

Leukocyte adhesion deficiency type 1: an important consideration in the clinical differential diagnosis of prepubertal periodontitis. A case report and review of the literature

Leukocyte adhesion deficiency type 1 (LAD-1) is a rare, inherited immunodeficiency that affects 1 in 1 million people yearly and usually presents with recurrent, indolent bacterial infections of the skin, mouth, and respiratory tract and impaired pus formation and wound healing. Features of this disease result from mutations in the region of the CD18 gene, which is encoded on chromosome 21q22.3. This gene codes for the common subunit of the leukocyte integrins LFA-1, Mac 1, and p150,95. Failure to produce a functional subunit results in the defective expression of all 3 leukocyte integrins, and the leukocytes of LAD have subnormal adhesion properties. We present a case of the moderate-to-severe form of LAD in a 3-year-old girl who initially presented with generalized swelling and erythema of the gingiva, with slight tooth mobility and a nonhealing labial ulceration. Her medical history was significant for recurrent urinary tract infections. Periodontal pathogens, including Capnocytophaga, Eikenella corrodens, and Candida albicans, were cultured. The patient had a significantly elevated white blood cell count and absolute neutrophil count. The diagnosis of LAD was confirmed with flow cytometry, which revealed significantly decreased subunits. Twenty-four months after the diagnosis was made and after a series of granulocyte transfusions and bone marrow transplantations, she expired as the result of respiratory failure.