CD18 Gene Research Articles

Targeted disruption of the CD18 or ICAM-1 gene inhibits choroidal neovascularization.

To investigate the role of the leukocyte adhesion molecules CD18 and intercellular adhesion molecule (ICAM)-1 in the development of choroidal neovascularization (CNV). Laser photocoagulation was used to induce CNV in wild-type C57BL/6J mice and species-specific counterparts with targeted homozygous disruption of the CD18 or ICAM-1 gene. Expression of CD18 and ICAM-1 after laser injury was assessed by immunostaining. CNV responses were compared on the basis of en masse volumetric measurements obtained by confocal microscopy 2 weeks after laser injury and by determination of fluorescein angiographic leakage at 1, 2, and 4 weeks after laser injury. The site of laser injury showed upregulation of ICAM-1 and invasion by CD18-positive leukocytes within 1 day of laser injury. Significantly fewer lesions exhibited fluorescein leakage defined to be pathologically significant in CD18-deficient mice at weeks 1, 2, and 4 weeks and in ICAM-1-deficient mice at 1 and 4 weeks, compared with the control. There were a significantly greater number of lesions without fluorescein leakage in CD18-deficient mice than in the other two groups at all time points. The volume of CNV in CD18- and ICAM-1-deficient mice was significantly less than in wild type. These data suggest a nonredundant role for leukocyte adhesion to vascular endothelium in the development of laser-induced choroidal neovascularization.

During differentiation of the monocytic cell line U937, Pur alpha mediates induction of the CD11c beta 2 integrin gene promoter.

CD11c is a member of the beta(2) integrin family of adhesion molecules that, together with CD18, forms a heterodimeric receptor on the surface of myeloid, NK, dendritic, and certain leukemic, lymphoma, and activated lymphoid cells. Monocytic differentiation is associated with an induction of both CD11c and CD18 gene expression. The resulting CD11c/CD18 receptor mediates firm adhesion to the vascular endothelium, transendothelial migration, chemotaxis, and phagocytosis. Monocytic differentiation can be mimicked in vitro by treatment of the promonocytic cell line U937 with PMA. Recently, we reported that in U937 cells, expression of the CD11c gene is controlled by an unidentified transcription factor that binds ssDNA. This finding suggested that DNA secondary structure plays an important role in controlling the CD11c gene and prompted us to search for additional ssDNA-binding activities with which this gene interacts. In this study, we report that in U937 cells, expression of the CD11c gene is mediated by the ssDNA-binding protein Puralpha. During PMA-induced differentiation, the ability of Puralpha to activate the CD11c promoter in U937 cells increases, as does that of Sp1. Together, these increases in the functional activity of both Puralpha and Sp1 combine to induce CD11c expression.

A prospective evaluation of the CD14 and CD18 gene polymorphisms and risk of stroke.

Genetic polymorphisms of the CD14 lipopolysaccharide receptor gene (CD14) and the CD18 leukocyte adhesion molecule gene (CD18) have recently been hypothesized to be risk factors for atherothrombosis. However, no prospective data on subsequent risk of stroke are available. The present investigation was conducted to examine the possible association between the CD14 C(-260)T and CD18 codon 441 gene polymorphisms and the incidence of stroke in a large, prospective, matched case-control sample from the Physicians' Health Study. In the Physicians' Health Study, 14 916 apparently healthy men were followed over a 12-year period for stroke. Using a nested case-control study design, 338 study participants who developed stroke (cases) and 338 age- and smoking-matched study participants who remained free of reported disease during follow-up (controls) were evaluated. Both polymorphisms were determined by polymerase chain reaction with subsequent and respective restriction fragment length polymorphism gel electrophoresis. All observed genotype frequencies were in Hardy-Weinberg equilibrium. The allele and genotype distributions of the polymorphisms tested were similar among cases and controls, such that the relative risk of future stroke was 0.87 for CD14 C(-260)T (95% CI=0.69 to 1.11; P=0.27) and 0.99 for CD18 codon 441 (95% CI=0.77 to 1.28; P=0.96) assuming an additive mode of inheritance. No evidence of association was observed assuming dominant or recessive model, and similar null results were observed in subgroup analysis restricted to thromboembolic events In this large, prospective study, we found little evidence that the two previously described polymorphisms in the CD14 and CD18 genes are associated with risks of future stroke.

Beta2 integrins are required for skin homing of primed T cells but not for priming naive T cells.

Beta2 integrins are of critical importance for leukocyte extravasation through vascular endothelia and for T cell activation. To elucidate the role of beta2 integrins in T cell-mediated immune responses, allergic contact dermatitis (ACD), irritant dermatitis, and delayed-type hypersensitivity (DTH) were assessed in mice lacking the beta2 integrin subunit, CD18. ACD and DTH responses, but not edema formation, were severely suppressed in CD18(-/-) mice. Extravasation of CD18(-/-) T cells into eczematous skin lesions was greatly impaired, whereas migration of Langerhans cell precursors and dendritic cells was normal in CD18(-/-) mice. CD18(-/-)lymph nodes (LNs) contained an abnormal population of CD3(-)CD44(high) lymphocytes and showed evidence of widespread T cell activation. T cells from regional LNs of sensitized CD18(-/-) mice proliferated in response to hapten challenge, and subcutaneous injection of sensitized syngeneic LN cells directly into ears of hapten-challenged naive recipients restored the defective ACD in CD18(-/-) mice, suggesting that CD18 is not required for priming of naive T cells but is indispensable for T cell extravasation. Thus, a dysfunction of T cells, in addition to granulocytes, may contribute to the pathophysiology of leukocyte adhesion deficiency type I, which arises from mutations in the human CD18 gene.

Association of a CD18 gene polymorphism with a reduced risk of restenosis after coronary stenting

Inflammatory mechanisms play an important role in the process of restenosis after percutaneous coronary interventions, with cell adhesion molecules, including Mac-1 (CD11b/CD18), as key mediators. A single nucleotide polymorphism, 1323C/T, located in exon 11 of the CD18 gene has been previously described, but its functional and clinical significances have not yet been studied. We assessed whether an association exists between this polymorphism and restenosis after coronary stenting. Clinical and angiographic measures of restenosis were evaluated over 1 year after coronary stent placement in 1,207 consecutive patients. Angiographic restenosis was defined as a ≥50% diameter stenosis at follow-up angiography. Determination of the CD18 1323C/T genotype was based on the polymerase chain reaction technique. The frequency of the T allele was 0.34 and its presence reduced the 1-year risk of a major adverse cardiac event (death, myocardial infarction, target vessel revascularization) by 29% (p = 0.011). Carriers of the T allele had a significantly lower risk of angiographic restenosis compared with noncarriers (odds ratio 0.71, 95% confidence interval 0.55 to 0.92). The incidence of restenosis decreased as a function of the number of T alleles: 38.1% in patients with genotype CC, 31.7% in patients with genotype CT, and 26.0% in patients with genotype TT (p = 0.004). Thus, the 1323T allele of the CD18 gene is associated, in a gene dose-dependent manner, with a lower incidence of angiographic restenosis after coronary stenting. This finding suggests that Mac-1 is involved in the development of restenosis after coronary stent placement.

PCR screening and allele frequency estimation of bovine leukocyte adhesion deficiency in Holstein and Gir cattle in Brazil

Bovine leukocyte adhesion deficiency (BLAD) is a disease known to affect the Holstein cattle breed throughout the world. Eighty-eight Holstein dairy cows and 88 Gir dairy bulls were genotyped by PCR for the CD18 BLAD alelle. The frequency of the BLAD mutant allele and the BLAD-carrier prevalence in Brazilian Holstein cows were 2.8 and 5.7%, respectively. No mutant allele was found in any of the 88 Gir animals. We conclude that the CD18 gene mutation is prevalent in Brazilian Holstein cattle and absent or present at a very low frequency in Gir cattle.

The expression of LFA-1 is increased on down's syndrome (Trisomy 21) Platelets

Abstract We have previously demonstrated the presence of lymphocyte function associated antigen-1 (LFA-1) on human platelets. The genes encoding the CD18 (LFA-1 β chain) and CD11a (LFA-1 α chain) are located on chromosomes 21 and 16 respectively. Down syndrome patients are known to have a substantial overexpression of LFA-1 on lymphoid cells, probably due to the extra copy of CD18 gene in Trisomy 21 (T21). However, on some cells (monocytic and granulocytic), the effect of T21 was not clear. In this study, we looked for a possible difference in LFA-1 expression between T21 and normal donor platelets, using comparative flow cytometry analysis and Western blot. Using this approach, we show that the expression of the common β subunit LFA-1 was constitutively increased on platelets from 5 to 7 T21 patients. The expression of the α chain on resting and thrombin-activated platelets from children or adults with T21 compared to age-matched controls, showed a similarly increased expression to that of the β chain. These data indicate that a trisomy-dependent constitutive effect on the expression of CD18 on platelets occurs in Down's syndrome, and that this also increases CD11a expression, which therefore leads to the overexpression of LFA-1. This alteration may be related to the higher incidence of cardiovascular disease in such patients.

The association of CD18 alleles with anti-myeloperoxidase subtypes of ANCA-associated systemic vasculitides.

Wegener granulomatosis (WG), microscopic polyangiitis (MP), and Churg Strauss syndrome (CSS) are rare systemic autoimmune disorders. Common features are anti-neutrophil cytoplasmic antibodies (ANCA) in patient sera. Whereas WG patients show mainly anti-proteinase 3 ANCA, MP and CSS patients typically present anti-myeloperoxidase (MPO) ANCA. ANCA play an important role in the pathogenesis in the vessel wall by activating polymorphonuclear cells (PMN) and increased adhesivity between PMN and endothelial cells via adhesion molecules. Here we investigated major adhesion molecules as predisposition factors via common polymorphisms in or in the vicinity of the candidate genes ICAM-1, e-selectin, PLAUR, CD11b, and CD18. A restriction fragment-length polymorphism in exon 11 of the CD18 gene was associated with MPO-ANCA(+) systemic vasculitis. Our data indicate that a common variant of the CD18 gene confers increased risk for CSS and MP, supporting that genetic factors are involved in the etiology and pathogenesis of ANCA-associated systemic vasculitides.

CD18-mediated neutrophil recruitment contributes to the pathogenesis of reperfused but not nonreperfused stroke.

Neutrophil (PMN) recruitment mediated by increased expression of intercellular adhesion molecule-1 expression (ICAM-1, CD54) in the cerebral microvasculature contributes to the pathogenesis of tissue injury in stroke. However, studies using blocking antibodies against the common beta2-integrin subunit on the PMN, the counterligand for ICAM-1 (CD18), have demonstrated equivocal efficacy. The current study tested the hypothesis that mice deficient in CD18 would be protected in the setting of reperfused but not nonreperfused stroke. Two groups of mice were studied, those whose PMNs could express CD18 (CD18 +/+) and those mice hypomorphic for the CD-18 gene (CD18 -/-). PMNs obtained from CD18 -/- or CD18 +/+ mice were fluorescently labeled and tested for binding to murine brain endothelial monolayers. Using a murine model of focal cerebral ischemia in which an occluding suture placed in the middle cerebral artery (MCA) is removed after 45 minutes (transient ischemia, reperfused stroke) or left in place (permanent ischemia, nonreperfused stroke), cerebral infarct volumes (% ipsilateral hemisphere by TTC staining), cerebral blood flow (CBF, % contralateral hemisphere by laser-Doppler flowmetry), and survival (%) were examined 24 hours after the initial ischemic event. Adoptive transfer studies used 111In-labeled PMNs (from either CD18 +/+ or CD18 -/- mice) to examine the relative accumulation of PMNs in the ischemic region. PMNs obtained from CD18 -/- mice exhibit reduced adhesivity (compared with CD18 +/+ PMNs) for both quiescent and cytokine-activated endothelial monolayers. CD18 -/- mice (n=14) subjected to transient focal cerebral ischemia demonstrated a 53% decrease in infarct volumes versus CD18 +/+ mice (n=26, P<0.05), improved penumbral CBF at 24 hours (1.8-fold, P=0.02), and a 3.7-fold decrease in mortality (P=0.02). However, when CD18 -/- mice (n=12) were subjected to permanent focal cerebral ischemia, no differences were noted in infarct volume, mortality, or CBF versus similarly treated CD18 +/+ mice (n=10). There was a greater accumulation of CD18 +/+ PMNs in the ischemic zone of CD18 +/+ animals than CD18 -/- animals subjected to reperfused stroke (82% increase, P=0.02), although there was no difference between groups when subjected to permanent MCA occlusion. Deficiency for the CD18 gene confers cerebral protection in a murine model of reperfused stroke, but this benefit does not extend to CD18-deficient animals subjected to permanent MCA occlusion. These data suggest that anti-PMN strategies should be targeted to reperfused stroke and may perhaps be used in conjunction with thrombolytic therapy that establishes reperfusion.

Differential effect on U937 cell differentiation by targeting transcriptional factors implicated in tissue- or stage-specific induced integrin expression

The inhibition of transcription factor functions was used to define their role in phorbol ester-induced cellular differentiation of a monocytic cell line, U937. We demonstrate a differential effect on cell adhesion and differentiation: antisense or competitive binding with double-stranded oligonucleotides antagonized the functions of AP-1, NF-κB, and PU.1 transcriptional factors. In the presence of phorbol 12-myristate 13-acetate (PMA), U937 cells attached to the plastic surface and cells were characterized by marked expression of β2-integrin molecules on the cell surface. We show that the in vivo differentiation of U937 cells appears to occur normally in the absence of AP-1 activity. In contrast, the addition to the cell culture of phosphorothioate oligonucleotides that contained the NF-κB or PU.1 binding sites significantly inhibited U937 differentiation. The absence of NF-κB led to pleiotropic effects with a clear reduction in the expression of integrin and other lineage-specific myeloid antigens on the cell surface. In contrast, the absence of PU.1 had a more restricted effect on integrin expresion on the cell surface, probably as a result of blockage of CD18 gene expression.

Partial Genomic Structure of the Bovine CD18 Gene and the Refinement of Test for Bovine Leukocyte Adhesion Deficiency

Partial Genomic Structure of the Bovine CD18 Gene and the Refinement of Test for Bovine Leukocyte Adhesion Deficiency

Map location, genomic organization and expression patterns of the human RED1 RNA editase.

A cDNA fragment containing sequences homologous to the rat RED1 RNA editase gene was recently identified on human chromosome 21. Here we report the location of this cDNA in distal 21q22.3 near the CD18 gene. We also report isolation of cDNA clones containing the complete coding region of the human RED1 gene, and use of this sequence to determine the genomic structure from overlapping cosmids. Human RED1 spans approximately 25 kb and is composed of 10 exons containing coding sequences. The two RNA binding domains are located within a single large, 935 nucleotide, exon 2. An alternatively processed exon 6 potentially interrupts the catalytic domain. Exon 10 is largely composed of the 3' untranslated region, which is unusually high in GC content and contains a segment that is > 90% identical with the 3' UT of the homologous rat gene. A survey of expression patterns reveals differential processing of the 5 and 8.5 kb transcripts in all sources examined. The difference in transcript size likely results from alternative processing in the 3' UT. Potential relevance of overexpression of RED1 to the development of the Down Syndrome phenotype is discussed.

Human Leukocyte Integrin CD18 Promoter Directs Low Levels of Expression of a Mutated Human CD4 Reporter Gene in Leukocytes of Transgenic Mice

The human leukocyte integrin CD18 molecule exists on the leukocyte surface in heterodimeric complexes with individual CD11 subunits, which mediate important leukocyte adhesion reactions. The CD18 subunit is developmentally regulated with the highest levels present on mature leukocytes of all lineages. To identify the regulatory sequences responsible for the tissue- and stage-specific expression of the CD18 subunit, we used 3.5 kb of regulatory sequence upstream from the human CD18 gene transcription start site to drive expression of a modified human CD4 reporter gene in transgenic mice. Despite the inclusion of Sp1 and PU.1 sites in the construct, and the generation of founder lines possessing multiple copies of the transgene, the reporter gene was expressed in low levels in the leukocytes of the transgenic mice. These studies indicate that although PU.1 and Sp1 sites are required for CD18 promoter activityin vitro,additional regulatory regions appear to be required for high levels of copy number dependent expressionin vivo.

GABP and PU.1 compete for binding, yet cooperate to increase CD18 (beta 2 leukocyte integrin) transcription.

CD18 (beta 2 leukocyte integrin) is a leukocyte-specific adhesion molecule that plays a crucial role in immune and inflammatory responses. A 79-nucleotide fragment of the CD18 promoter is sufficient to direct myeloid transcription. The CD18 promoter is bound by the B lymphocyte- and myeloid-restricted ets factor, PU.1, and disruption of the PU.1-binding sites significantly reduces promoter activity. However, PU.1 alone cannot fully account for the leukocyte-specific and myeloid-inducible transcription of CD18. We identified a ubiquitously expressed nuclear protein complex of extremely low electrophoretic mobility that also binds to this region of the CD18 promoter. This binding complex is a heterotetramer composed of GABP alpha, and ets factor, and GABP beta, a subunit with homology to Drosophila Notch. GABP alpha competes with the lineage restricted factor, PU.1, for the same critical CD18 ets sites. The CD18 promoter is activated in myeloid cells by transfection with both GABP alpha and GABP beta together, but not by either factor alone. Transfection of non-hematopoietic cells with the two GABP subunits together with PU.1 is sufficient to activate CD18 transcription in otherwise non-permissive cells. Thus, GABP and PU.1 compete for the same binding sites but cooperate to activate CD18 transcription.

Improved Transfer of the Leukocyte Integrin CD18 Subunit Into Hematopoietic Cell Lines by Using Retroviral Vectors Having a Gibbon Ape Leukemia Virus Envelope

Leukocyte adherence deficiency (LAD) is an inherited immunodeficiency disease caused by defects in the CD18 leukocyte integrin subunit. Transduction of CD18 into hematopoietic cells from children with LAD represents a potential therapy for this disorder. In an attempt to maximize transfer and expression of CD18, we evaluated retroviral vectors with and without the neomycin selectable marker, with a modified tRNA primer binding site designed to prevent inhibition of gene expression, and with two different viral envelope proteins produced by using the amphotropic retrovirus packaging cell line PA317 or the gibbon ape leukemia virus packaging cell line PG13. The vectors were tested using transducing K562/CD11b cells and LAD Epstein-Barr virus (EBV) B cells and measuring levels of cell-surface CD11/CD18 expression by fluorescence-activated cell sorter analysis. The best results were obtained with vectors made using PG13 packaging cells, for which about 25% of the K562 cells exposed once to the vectors expressed surface CD11b/CD18 and about 25% of the LAD EBV B cells exposed three times over a 3-day period to the vectors expressed surface CD11a/CD18. In contrast, transduction of cells under similar conditions with retroviral vectors produced using PA317 producer cells yielded less than 2% of the K562 cells and less than 4% of the LAD EBV B cells expressing the CD11/CD18 heterodimer on the cell surface. The presence or absence of the neomycin resistance gene or the modified tRNA primer had no effect on CD18 gene transfer rate or expression level. The increase in transduction with PG13 vectors correlated with Northern blotting and reverse transcription-polymerase chain reaction studies that indicated that both K562 cells and the LAD EBV B cells express transcripts for the gibbon ape leukemia virus receptor at higher levels than for the amphotropic virus receptor. These findings indicate that the transduction efficiency of retroviral packaging cell lines correlates with receptor gene expression in the target cells and that vectors made using PG13 cells may be efficacious for gene therapy for LAD and other diseases in which gene transfer to hematopoietic cells is required.

The leukocyte integrin gene CD11c is transcriptionally regulated during monocyte differentiation

The leukocyte integrins, LFA-1, Mac-1 and p150,95, are heterodimeric proteins that consist of a distinct α and a common β subunit. The β subunit gene (CD18) is constitutively expressed on all leukocytes, however, the α subunit genes for LFA-1, Mac-1 and p150,95 (CD11a, CD11b and CD11c, respectively) show cell- and developmental stage-specific expression. We investigated the regulation of the CD11c gene in the promyeloblastic leukemic cell line, HL60, following differentiation along the monocytic pathway with phorbol 12-myristate 13-acetate (PMA). The steady-state level of CD11c mRNA increased markedly over 48 hr from the undetectable level present before differentiation. The half-life of CD11c MRNA in differentiated HL60 cells was not unusually long and similar to that of CD18 mRNA found in both undifferentiated and differentiated cells which suggested that altered mRNA stability did not account for the appearance of CD11c mRNA. Nuclear run-on analysis revealed that transcriptional activation during differentiation resulted in the appearance of CD11c mRNA. Inhibition of protein synthesis by cycloheximide in undifferentiated HL60 cells did not result in transcriptional activation of the CD11c gene. However, there was a significant increase (approximately eight-fold) in the steady-state level of CD18 mRNA which was not the result of transcriptional activation. Inhibition of protein synthesis in differentiated HL60 cells did not lead to significant changes in the steady-state levels of either CD11c or CD18 mRNAs. These findings indicated that the CD11c gene is regulated by transcriptional mechanisms which require prior protein synthesis. Transcriptional activation of the CD18 gene as a result of differentiation with PMA also requires protein synthesis. Further, in the absence of protein synthesis in undifferentiated HL60 cells, post-transcriptional mechanisms stabilize CD18 mRNA.

Molecular characterization of leukocyte adhesion deficiency in six patients

Leukocyte adhesion deficiency (LAD) is caused by defects in the CD18 gene, which codes for the common beta 2 subunit of the leukocyte integrins LFA-1, Mac-1 and p150,95. Failure to produce a functional beta 2 subunit results in the defective expression of all three leukocyte integrins, and the leukocytes of LAD patients have subnormal adhesion properties. Six patients with LAD were studied. Patient B was homozygous and carried a G284S mutation. A two-bp (GA) deletion at position 1256 (1256 delta GA) was found in the cDNA of patient C, who also had an abnormally large mRNA of 4.3 kb. Patients E and K were siblings and were heterozygous at the genomic level. One defective allele contained a mutation in intron 6/7 which created a preemptive 3' splice site. The resulting mRNA has 12 extra bases at the junction of exons 6 and 7, coding for four extra residues PSSQ in the protein. The same allele also carried a R586W mutation. The other allele was transcribed at a low level and was not characterized. Patient G carried a L149P mutation in one allele; again, the other allele was not characterized due to low transcription levels. Patient R carried two mutant alleles with G284S and R593C mutations respectively. The G284S mutation and the 1256 delta GA deletion have not been reported previously. CD18 cDNA carrying the abnormalities were cotransfected with normal CD11a or CD11b cDNA into COS cells. Expression of the LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18) antigens on COS cells was not detected, suggesting that these two mutations are sufficient to account for LAD.

Investigation of the polymorphic AvaII site by a PCR-based assay at the human CD18 gene locus.

The AvaII polymorphic site within the human CD18 gene was investigated in the Japanese population. A distinct distribution pattern is observed in this population. This polymorphism provides a new genetic marker for the long arm of chromosome 21 and should be a useful marker of leukocyte adhesion deficiency caused by mutations of the CD18 gene.

Restoration of Lytic Function in a Human Natural Killer Cell Line by Gene Transfection

NK cells can recognize and lyse target cells without restriction by the MHC. The molecular interaction responsible for NK cell recognition is poorly understood. It has been frequently suggested that the loss of β 2 integrin in immune competent cells may lead to dysfunction due to inadequate cell-cell interaction. We examined the role of lymphocyte functional adhesion molecule-1 in the function of a human natural killer leukemia cell line, YT-1. A mutant YT-1(-) cell subclone showed an absence of killing activity against a B lymphoma cell line, compared with that against a CD11a/CD18 positive parental cell line. YT-1(+) cells. We found that this loss of cytotoxicity was correlated with lack of surface expression of CD11a/CD18 molecules due to the mutation of the CD18 gene. Using gene transfer experiments, we provide strong evidence demonstrating that CD18 transfection to this mutant NK cell line. YT-1(-), restored the surface expression or CD11a/CD18, and this restoration was accompanied by reexpression of cytotoxic function.

Gene targeting yields a CD18-mutant mouse for study of inflammation.

CD18 is the common beta subunit for the heterodimeric leukocyte integrins that mediate many inflammatory cell adhesion responses including binding to intercellular adhesion molecules 1 and 2. CD18 deficiency in humans causes a severe granulocyte disorder with susceptibility to bacterial infections and high morbidity and mortality. Gene targeting was used to prepare an insertion mutation in the murine CD18 gene. The insertion mutation resulted in a hypomorphic rather than a null allele due to low expression from a cryptic promoter in the plasmid construct. Homozygous mutant mice are viable and fertile, demonstrate a mild granulocytosis, and have 2 or 16% of normal CD18 expression on granulocytes in the resting or activated state, respectively. Mutant mice show an impaired inflammatory response to a chemical peritonitis and delayed rejection of cardiac transplants. These CD18-mutant mice provide a model of the moderate form of the human disease and should be extremely valuable for in vivo analysis of the role of leukocyte integrin-dependent adhesion in inflammatory disease models.