Characterization of the function of intercellular adhesion molecule (ICAM)-3 and comparison with ICAM-1 and ICAM-2 in immune responses

ICAMs in Immunity, Intercellular Adhesion and Communication

Interactions among leukocytes and leukocytes with immune-associated auxiliary cells represent an essential feature of the immune response that requires the involvement of cell adhesion molecules (CAMs). In the immune system, CAMs include a wide range of members pertaining to different structural and functional families involved in cell development, activation, differentiation and migration. Among them, β2 integrins (LFA-1, Mac-1, p150,95 and αDβ2) are predominantly involved in homotypic and heterotypic leukocyte adhesion. β2 integrins bind to intercellular (I)CAMs, actin cytoskeleton-linked receptors belonging to immunoglobulin superfamily (IgSF)-CAMs expressed by leukocytes and vascular endothelial cells, enabling leukocyte activation and transendothelial migration. β2 integrins have long been viewed as the most important ICAMs partners, propagating intracellular signalling from β2 integrin-ICAM adhesion receptor interaction. In this review, we present previous evidence from pioneering studies and more recent findings supporting an important role for ICAMs in signal transduction. We also discuss the contribution of immune ICAMs (ICAM-1, -2, and -3) to reciprocal cell signalling and function in processes in which β2 integrins supposedly take the lead, paying particular attention to T cell activation, differentiation and migration.

Investigation of the clinical utility of adhesion molecules in the management of thyroid nodules

To better understand the relationship among cell adhesion molecules (CAM) and investigate the clinical diagnostic and prognostic application of ICAM-1 (ICAM1), LFA-1 (ITGAL), and L-selectin (SELL) proteins and mRNA corresponding expression in thyroid cancer. Gene expression was evaluated by RT-qPCR, and protein expression was evaluated by immunohistochemistry. We evaluated 275 patients (218 women, 57 men, 48.4 ± 14.5 years old), including 102 benign and 173 malignant nodules. The 143 papillary thyroid carcinoma (PTC) and 30 follicular thyroid carcinoma (FTC) patients were managed according to current guidelines and followed-up for 78.7 ± 54.2 months. Malignant and benign nodules differed concerning mRNA (p = 0.0027) and protein (p = 0.0020 for nuclear) expression of L-selectin and ICAM-1 (mRNA: p = 0.0001 and protein: p = 0.0014) and protein expression of LFA-1 (p = 0.0168), but not mRNA expression of LFA-1 (p = 0.2131). SELL expression was more intense in malignant tumors (p = 0.0027). ICAM1 (p = 0.0064) and ITGAL (p = 0.0244) mRNA expression was higher in tumors with lymphocyte infiltrate. ICAM-1 expression correlated with younger age at diagnosis (p = 0.0312) and smaller tumor size (p = 0.0443). Also, LFA-1 expression correlated with higher age at diagnosis (p = 0.0376) and was more intense at stage III and IV (p = 0.0077). In general, the protein expression of the 3 CAM decreased as the process of cellular dedifferentiation occurred. We suggest that the SELL and ICAM1 genes and L-selectin and LFA-1 protein expression may help confirm malignancy and assist in the histological characterization of follicular patterned lesions, but we were unable to correlate these CAMs with patient outcomes.

Intercellular Adhesion Molecule-1-Induced Posttraumatic Brain Injury Neuropathology in the Prefrontal Cortex and Hippocampus Leads to Sensorimotor Function Deficits and Psychological Stress

Intercellular adhesion molecule-1 (ICAM-1) promotes adhesion and transmigration of circulating leukocytes across the blood-brain barrier (BBB). Traumatic brain injury (TBI) causes transmigrated immunocompetent cells to release mediators [function-associated antigen (LFA)-1 and macrophage-1 antigen (Mac-1)] that stimulate glial and endothelial cells to express ICAM-1 and release cytokines, sustaining neuroinflammation and neurodegeneration. Although a strong correlation exists between TBI-mediated inflammation and impairment in functional outcome following brain trauma, the role of ICAM-1 in impairing functional outcome by inducing neuroinflammation and neurodegeneration after TBI remains inconclusive. The experimental TBI was induced in vivo by fluid percussion injury (FPI; 10 and 20 psi) in wild-type (WT) and ICAM-1-/- mice and in vitro by stretch injury (3 psi) in brain endothelial cells. We manipulate ICAM-1 pharmacologically and genetically and conducted several biochemical analyses to gain insight into the mechanisms underlying ICAM-1-mediated neuroinflammation and performed rotarod, grid-walk, sucrose preference, and light-dark tests to assess functional outcome. TBI-induced ICAM-1-mediated neuroinflammation and cell death occur via LFA-1 or Mac-1 signaling pathways that rely on oxidative stress, matrix metalloproteinase (MMP), and vascular endothelial growth factor (VEGF) pathways. The deletion or blocking of ICAM-1 resulted in a better outcome in attenuating neuroinflammation and cell death as marked by the markers such as NF-kB, IL-1β, TNF-α, cleaved-caspase-3 (cl-caspase-3), Annexin V, and by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and Trypan blue staining. ICAM-1 deletion in TBI improves sensorimotor, depression, and anxiety-like behavior with significant upregulation of norepinephrine (NE), dopamine (DA) D1 receptor (DAD1R), serotonin (5-HT)1AR, and neuropeptide Y (NPY). This study could establish the significance of ICAM-1 as a novel therapeutic target against the pathophysiology to establish functional recovery after TBI.

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.

Decreased expression of the β2 integrin on tumor cells is associated with a reduction in liver metastasis of colorectal cancer in mice

BACKGROUND

Lymphocyte Function-Associated Antigen-1 (LFA-1; CD18/CD11a) is one of the main adhesion molecules used by immune cells to infiltrate the liver under inflammatory conditions. Recently, the expression of this integrin has also been reported on several solid tumors, including colorectal cancer. However, its functional role in the metastatic progression to the liver remains unknown. Using in vitro assays and an experimental orthotopic in vivo model of liver metastasis, we aimed to elucidate the role of tumor LFA-1 in the metastatic progression by means of the partial depletion of the β₂ subunit of LFA-1, required for integrin activation, firm adhesion and signaling.

METHODS

To do so, we evaluated the effects of β₂ reduction on the murine colon carcinoma C26 cell line on their pro-metastatic features in vitro and their metastatic potential in vivo in a mouse model of colon carcinoma metastasis to the liver.

RESULTS

The reduction in β₂ integrin expression correlated with a slower proliferation, and a reduced adhesion and migration of C26 cells in an in vitro setting. Additionally, tumor cells with a reduced in β₂ integrin expression were unable to activate the liver sinusoidal endothelial cells (LSECs). This resulted in a recovery of the cytotoxic potential of liver lymphocytes which is compromised by LSECs activated by C26 cells. This was related to the abrogation of RNA expression of inflammatory and angiogenic cytokines by C26 cells after their activation with sICAM-1, the main ligand of β₂α_L. Furthermore, in vivo tumor cell retention and metastasis were profoundly reduced, along with a decrease in the recruitment and infiltration of myeloid derived suppressor cells (MDSCs) and lymphocytes to the liver.

CONCLUSION

Taken together, our findings uncovered the modulatory role for the tumor β₂ subunit of the LFA-1 integrin in the metastatic progression of colorectal cancer to the liver by impairing activation of liver endothelium and thus, the local immune response in the liver. Besides, this integrin also showed to be critical in vivo for tumor cell retention, cytokine release, leukocyte recruitment and metastasis development. These data support a therapeutical potential of the integrin LFA-1 as a target for the treatment of colorectal liver metastasis.

HIV-1 Vpu Downmodulates ICAM-1 Expression, Resulting in Decreased Killing of Infected CD4+ T Cells by NK Cells

HIV-1 Vpu is known to alter the expression of numerous cell surface molecules. Given the ever-increasing list of Vpu targets identified to date, we undertook a proteomic screen to discover novel cell membrane proteins modulated by this viral protein. Plasma membrane proteome isolates from Vpu-inducible T cells were subjected to stable isotope labeling of amino acids in cell culture (SILAC)-based mass spectrometry analysis, and putative targets were validated by infection of primary CD4⁺ T cells. We report here that while intercellular adhesion molecule 1 (ICAM-1) and ICAM-3 are upregulated by HIV-1 infection, expression of Vpu offsets this increase by downregulating these molecules from the cell surface. Specifically, we show that Vpu is sufficient to downregulate and deplete ICAM-1 in a manner requiring the Vpu transmembrane domain and a dual-serine (S52/S56) motif necessary for recruitment of the beta-transducin repeat-containing E3 ubiquitin protein ligase (β-TrCP) component of the Skp, Cullin, F-box (SCF^β-TrCP) E3 ubiquitin ligase. Vpu interacts with ICAM-1 to induce its proteasomal degradation. Interestingly, the E3 ubiquitin ligase component β-TrCP-1 is dispensable for ICAM-1 surface downregulation yet is necessary for ICAM-1 degradation. Functionally, Vpu-mediated ICAM-1 downregulation lowers packaging of this adhesion molecule into virions, resulting in decreased infectivity. Importantly, while Vpu-mediated downregulation of ICAM-3 has a limited effect on the conjugation of NK cells to HIV-1-infected CD4⁺ T cells, downregulation of ICAM-1 by Vpu results in a reduced ability of NK cells to bind and kill infected T cells. Vpu-mediated ICAM-1 downregulation may therefore represent an evolutionary compromise in viral fitness by impeding the formation of cell-to-cell contacts between immune cells and infected T cells at the cost of decreased virion infectivity.IMPORTANCE The major barrier to eradicating HIV-1 infection is the establishment of treatment-resistant reservoirs early in infection. Vpu-mediated ICAM-1 downregulation may contribute to the evasion of cell-mediated immunity during acute infection to promote viral dissemination and the development of viral reservoirs. By aiding the immune system to clear infection prior to the development of reservoirs, novel treatments designed to disrupt Vpu-mediated ICAM-1 downregulation may be beneficial during acute infection or as a prophylactic treatment.

Concerning immune synapses: a spatiotemporal timeline

The term “immune synapse” was originally coined to highlight the similarities between the synaptic contacts between neurons in the central nervous system and the cognate, antigen-dependent interactions between T cells and antigen-presenting cells. Here, instead of offering a comprehensive molecular catalogue of molecules involved in the establishment, stabilization, function, and resolution of the immune synapse, we follow a spatiotemporal timeline that begins at the initiation of exploratory contacts between the T cell and the antigen-presenting cell and ends with the termination of the contact. We focus on specific aspects that distinguish synapses established by cytotoxic and T helper cells as well as unresolved issues and controversies regarding the formation of this intercellular structure.

Leukocytes Crossing the Endothelium: A Matter of Communication

Leukocytes cross the endothelial vessel wall in a process called transendothelial migration (TEM). The purpose of leukocyte TEM is to clear the causing agents of inflammation in underlying tissues, for example, bacteria and viruses. During TEM, endothelial cells initiate signals that attract and guide leukocytes to sites of tissue damage. Leukocytes react by attaching to these sites and signal their readiness to move back to endothelial cells. Endothelial cells in turn respond by facilitating the passage of leukocytes while retaining overall integrity. In this review, we present recent findings in the field and we have endeavored to synthesize a coherent picture of the intricate interplay between endothelial cells and leukocytes during TEM.

RUNX3 regulates intercellular adhesion molecule 3 (ICAM-3) expression during macrophage differentiation and monocyte extravasation

The adhesion molecule ICAM-3 belongs to the immunoglobulin gene superfamily and functions as a ligand for the β2 integrins LFA-1, Mac-1 and α_dβ₂. The expression of ICAM-3 is restricted to cells of the hematopoietic lineage. We present evidences that the ICAM-3 gene promoter exhibits a leukocyte-specific activity, as its activity is significantly higher in ICAM-3+ hematopoietic cell lines. The activity of the ICAM-3 gene promoter is dependent on the occupancy of RUNX cognate sequences both in vitro and in vivo, and whose integrity is required for RUNX responsiveness and for the cooperative actions of RUNX with transcription factors of the Ets and C/EBP families. Protein analysis revealed that ICAM-3 levels diminish upon monocyte-derived macrophage differentiation, monocyte transendothelial migration and dendritic cell maturation, changes that correlate with an increase in RUNX3. Importantly, disruption of RUNX-binding sites led to enhanced promoter activity, and small interfering RNA-mediated reduction of RUNX3 expression resulted in increased ICAM-3 mRNA levels. Altogether these results indicate that the ICAM-3 gene promoter is negatively regulated by RUNX transcription factors, which contribute to the leukocyte-restricted and the regulated expression of ICAM-3 during monocyte-to-macrophage differentiation and monocyte extravasation.

Human neutrophils interact with both 6-sulfo LacNAc+ DC and NK cells to amplify NK-derived IFN{gamma}: role of CD18, ICAM-1, and ICAM-3

The role of neutrophils as key players in the regulation of innate and adaptive immune responses is increasingly being recognized. We report that human neutrophils establish a network with both natural killer (NK) cells and 6-sulfo LacNAc(+) dendritic cells (slanDCs), which ultimately serves to up-regulate NK-derived interferonγ (IFNγ). This network involves direct reciprocal interactions and positive amplification loops mediated by cell-derived cytokines. Accordingly, we show that after lipopolysaccharide + interleukin-2 (IL-2) or IL-15/IL-18 stimulation, neutrophils directly interact with and potentiate the activity of both slanDCs and NK cells. On the one hand, neutrophils augment the release of IL-12p70 by slanDCs via a CD18/ intercellular adhesion molecule-1 (ICAM-1) interaction that stimulates activated NK cells to produce IFNγ. IFNγ further potentiates the interaction between neutrophils and slanDCs and the release of slanDC-derived IL-12p70, thus creating a positive feedback loop. On the other hand, neutrophils directly co-stimulate NK cells via CD18/ICAM-3, leading to the production of IFNγ. Colocalization of neutrophils, NK cells, and slanDCs, as well as of IL-12p70 and IFNγ, in inflamed tissues of Crohn disease and psoriasis provides strong evidence for a novel cellular and cytokine cooperation within the innate immune system in which neutrophils act as amplifiers of NK cell/slanDC-mediated responses.

A distinct profile of serum levels of soluble intercellular adhesion molecule-1 and intercellular adhesion molecule-3 in mycosis fungoides and Sézary syndrome

BACKGROUND

Cell adhesion molecules (CAMs) play a pivotal role in cutaneous localization of T cells. Tissue-selective localization of T lymphocytes to the skin is crucial for immune surveillance and in the pathogenesis of skin disorders.

OBJECTIVE

To detect the profile of soluble CAMs in patients with cutaneous T-cell lymphoma (CTCL), we investigated the levels of intercellular adhesion molecule-1 (ICAM-1, soluble ICAM-1 [sICAM-1]); intercellular adhesion molecule-3 (sICAM-3); vascular cell adhesion molecule-1 (sVCAM-1); and E-selectin (sE-selectin) in sera from patients with T-cell-mediated skin diseases.

METHODS

Serum levels of the 4 CAMs were measured by enzyme-linked immunosorbent assay in 42 participants including 11 patients with early stages of CTCL; 7 with advanced stages of CTCL including Sézary syndrome; 12 with inflammatory skin diseases (psoriasis and atopic dermatitis); 8 with skin diseases that may evolve into CTCL; and healthy individuals. Levels were correlated with biological parameters known as prognostic factors in non-Hodgkin lymphomas.

RESULTS

In patients with CTCL, significantly increased levels of sICAM-1 and sICAM-3 were found when compared with healthy individuals and patients with inflammatory dermatosis. Soluble E-selectin and sVCAM-1 levels were not increased. There were significant positive correlations between sICAM-1 and sICAM-3 levels and each of them with beta2-microglobulin levels.

LIMITATIONS

Limited number of patients was a limitation.

CONCLUSION

There is a distinct profile of soluble CAMs in patients with CTCL. However, future studies with a larger group of patients are needed to confirm these findings. We propose that high sICAM-1 and sICAM-3 levels have important implications in the context of immune response and immune surveillance in these patients.

Intercellular adhesion molecule 1 (ICAM-1), but not ICAM-2 and -3, is important for dendritic cell-mediated human immunodeficiency virus type 1 transmission

Dendritic cells (DCs) play a critical role in cell-to-cell-mediated transmission of human immunodeficiency virus type 1 (HIV-1). Interactions between intercellular adhesion molecules (ICAMs) and their ligands facilitate DC-T-cell contact. The interaction between ICAM-1 on DCs and leukocyte function-associated molecule 1 (LFA-1) on CD4(+) T cells has been proposed to be important for DC-mediated HIV-1 transmission. Given that DCs and T cells express multiple ICAMs and binding ligands, the relative importance of ICAMs in DC-mediated HIV-1 transmission remains to be defined. Here, we examine the role of ICAM-1, -2, and -3 in DC-mediated HIV-1 transmission to various types of target cells including primary CD4(+) T cells. The expression levels of ICAMs and their ligands on immature and mature DCs and various types of HIV-1 target cells were measured by flow cytometry. Blocking ICAM-1 in DCs with specific monoclonal antibodies and small interfering RNA impaired DC-mediated HIV-1 transmission. DC-mediated viral transmission was significantly inhibited when both ICAM-1 on DCs and LFA-1 on CD4(+) T cells were blocked. However, blockade of ICAM-1 on target cells did not significantly inhibit DC-mediated HIV-1 transmission. Ectopic expression and antibody blocking suggest that DC-mediated HIV-1 transmission to primary CD4(+) T cells is independent of ICAM-2 and ICAM-3. Taken together, our data clarified the role of ICAMs in DC-mediated HIV-1 transmission to CD4(+) T cells.

Leukocyte integrins and their ligand interactions

Although critical for cell adhesion and migration during normal immune-mediated reactions, leukocyte integrins are also involved in the pathogenesis of diverse clinical conditions including autoimmune diseases and chronic inflammation. Leukocyte integrins therefore have been targets for anti-adhesive therapies to treat the inflammatory disorders. Recently, the therapeutic potential of integrin antagonists has been demonstrated in psoriasis and multiple sclerosis. However, current therapeutics broadly affect integrin functions and, thus, yield unfavorable side effects. This review discusses the major leukocyte integrins and the anti-adhesion strategies for treating immune diseases.

Adhesion molecule interactions facilitate human immunodeficiency virus type 1-induced virological synapse formation between T cells

Human immunodeficiency virus type 1 (HIV-1) can spread between CD4+ T cells by using a virological synapse (VS). The VS assembly is a cytoskeleton-driven process dependent on HIV-1 envelope glycoprotein (Env)-receptor engagement and is hypothesized to require adhesion molecule interactions. Here we demonstrate that leukocyte function-associated antigen 1 (LFA-1), intercellular adhesion molecule 1 (ICAM-1), and ICAM-3 are enriched at the VS and that inhibition of these interactions influences conjugate formation and reduces VS assembly. Moreover, CD4+ T cells deficient in LFA-1 or with modified LFA-1 function were less able to support VS assembly and cell-cell transfer of HIV-1. Thus, cognate adhesion molecule interactions at the VS are important for HIV-1 spread between T cells.

Loop 1 structure of the leishmanial ICAM-L molecule is crucial for parasite binding and infection of host macrophages

The binding of each intercellular adhesive molecule (ICAM) molecule fragment from Leishmania amazonensis (ICAM-L) to host macrophages was investigated using an indirect immunofluorescent sandwich technique, based on the observation that ICAM-L can block the uptake of L. amazonensis on the macrophage surface and all prepared ICAM-L fragments can react with rabbit anti-ICAM-L antiserum. The ICAM-L fragments lacking the loop 1 (LI) structure failed to bind to macrophages, and the disruption of the LI structure by mercaptoethanol led to the failure of binding. The fragments containing the LI structure functioned similarly to ICAM-L, by temporarily retarding host cell growth and cell cycle progression, and inhibiting the Leishmania infection of host macrophages. These results suggest that LI constitutes the main determinant of the ICAM-L molecule in binding to, and infection of, host macrophages.

ICAM-3 influences human immunodeficiency virus type 1 replication in CD4(+) T cells independent of DC-SIGN-mediated transmission

We investigated the role of ICAM-3 in DC-SIGN-mediated human immunodeficiency virus (HIV) infection of CD4(+) T cells. Our results demonstrate that ICAM-3 does not appear to play a role in DC-SIGN-mediated infection of CD4(+) T cells as virus is transmitted equally to ICAM-3(+) or ICAM-3(-) Jurkat T cells. However, HIV-1 replication is enhanced in ICAM-3(-) cells, suggesting that ICAM-3 may limit HIV-1 replication. Similar results were obtained when SIV replication was examined in ICAM-3(+) and ICAM-3(-) CEMx174 cells. Furthermore, while ICAM-3 has been proposed to play a co-stimulatory role in T cell activation, DC-SIGN expression on antigen presenting cells did not enhance antigen-dependent activation of T cells. Together, these data indicate that while ICAM-3 may influence HIV-1 replication, it does so independent of DC-SIGN-mediated virus transmission or activation of CD4(+) T cells.

Activation of LFA-1 by ionomycin is independent of calpain-mediated talin cleavage

Activation of calpains by calcium flux leading to talin cleavage is thought to be an important process of LFA-1 activation by inside-out signalling. Here, we tested the effects of the calcium ionophore ionomycin and calpain inhibitor calpeptin on LFA-1-mediated adhesion of a T cell hybridoma line, cytotoxic T cells and primary resting T cells. Ionomycin activated LFA-1-mediated adhesion of all three types of T cells, and calpeptin inhibited the effects of ionomycin. However, calpeptin also inhibited activation of LFA-1 by PMA, which did not induce calcium flux. Cleavage of talin was undetectable in ionomycin-treated T cells. Furthermore, treatment with ionomycin and calpeptin induced apoptosis of T cells. Inhibitors of phosphatidyl Inositol-3 kinase inhibited activation of LFA-1 by ionomycin, but not by PMA, whereas the protein kinase C inhibitor inhibited the effects of PMA, but not ionomycin. Thus, activation of LFA-1 by ionomycin is independent of calpain-mediated talin cleavage.

CD18 in monogenic and polygenic inflammatory processes of the skin

The beta 2 integrin family (CD11/CD18) of leukocyte adhesion molecules plays a key role in inflammation. Absence of the common chain (CD18) leads to leukocyte adhesion deficiency-1 (LAD1) in humans. We here summarize data of two genetically defined mice models of beta 2 integrin deficiency, one with a CD18 null mutation (CD18-/-), and the other one with a hypomorphic CD18 mutation (CD18hypo). Firstly, we focus on the underlying mechanism of a severely impaired wound healing in CD18-/- mice, outlining a scenario in which a defective extravasation and phagocytosis of CD18-/- neutrophils results in delayed myofibroblast-dependent wound contraction owing to a deficient transforming growth factor-beta 1 release. Based on this, we have identified a potential therapy that fully rescued the impaired wound healing in CD18-/- mice. Secondly, we expand on a CD18hyp0 PL/J mouse model closely resembling human psoriasis. Apart from common clinical and pathophysiological features, this psoriasiform dermatitis also depends on the presence of activated CD4+ T cells. We here recapitulate the influence of a reduced CD18 gene expression on T-cell function, also with regard to CD18 gene-dose effects, and its contribution to the pathogenesis of this disease. Taken together, these unique features make this model a valuable tool for investigations into the pathogenesis of human psoriasis--including its polygenic base--and future preclinical studies.

A novel flow-cytometry-based assay for quantification of affinity and avidity changes of integrins

Cell adhesion plays an important role in cell-cell contact formation and cell migration. Thus, the assessment of cellular adhesiveness is one important feature when studying cell-mediated immune responses. The interaction of lymphocytes with other cell types such as antigen-presenting cells or vascular-endothelial cells occurs via adhesion molecules including L-selectin, VCAM-1 or ICAM-1. There are principally two mechanisms by which cell adhesion can be enhanced: namely changes in the affinity or avidity of receptor interactions. Conventional plate-based adhesion assays detect both forms. However, they do not permit discrimination between affinity- and avidity-mediated changes in the adhesiveness. Moreover, analysis of cell subpopulations requires cell separation prior to performance of the adhesion assay. Conventional flow-cytometry-based tests make it possible to determine changes in the affinity of integrins at the single cell level. However, they fail to quantify avidity-mediated adhesiveness. Here we describe a novel flow-cytometry-based assay, which allows the detection of both integrin-mediated affinity as well as avidity changes at the single cell level. This opens up the possibility of precisely characterizing the adhesive capacity of subpopulations in heterogeneous cell populations.

ICAM-2 mediates neutrophil transmigration in vivo: evidence for stimulus specificity and a role in PECAM-1-independent transmigration

ICAM-2 has been implicated in leukocyte transmigration in vitro, but there is little in vivo evidence to support this. To address this, neutrophil migration was investigated in ICAM-2-deficient mice (KO) and in wild-type (WT) mice treated with an anti-ICAM-2 blocking monoclonal antibody (mAb) (3C4). In a peritonitis model, IL-1beta-induced accumulation of neutrophils was significantly reduced in mice treated with 3C4 (51% inhibition) and in KO mice (41% inhibition). In contrast, TNF-alpha- or thioglycolate-induced responses were not suppressed in KO mice. Analysis of IL-1beta-induced leukocyte responses in cremasteric venules of KO animals by intravital microscopy indicated a defect in transmigration (44% inhibition) but not rolling or adhesion. As found before, TNF-alpha-induced leukocyte transmigration was unaltered in the KO mice. WT mice treated with the anti-ICAM-2 mAb also exhibited a selective reduction in leukocyte transmigration in response to IL-1beta while an anti-ICAM-1 mAb inhibited both leukocyte adhesion and transmigration. Interestingly, mAb 3C4 significantly suppressed IL-1beta-induced neutrophil transmigration in PE-CAM-1 KO animals in the peritonitis model but not in the cremaster muscle. The findings provide direct evidence for the involvement of ICAM-2 in neutrophil transmigration in vivo, though this role appears to be stimulus specific. Furthermore, ICAM-2 appears capable of mediating PECAM-1-independent leukocyte transmigration.

Efficacy of the fully human monoclonal antibody MOR102 (#5) against intercellular adhesion molecule 1 in the psoriasis-severe combined immunodeficient mouse model

BACKGROUND

Psoriasis is considered as a chronic immune-mediated disease characterized by inflammation and proliferation of the epidermis.

OBJECTIVES

Targeting intercellular adhesion molecule 1 (ICAM-1) is an attractive therapeutic option as this molecule is critically involved in leucocyte adhesion and extravasation as well as in lymphocyte activation.

METHODS

We have selected the fully human monoclonal antibody MOR102 (#5) against ICAM-1 from the Human Combinatorial Antibody Library (HuCAL). This antibody, as human IgG4 [corrected] was tested for its ability to interfere with lymphocyte activation and adhesion in vitro as well as for its antipsoriatic efficacy in vivo using the psoriasis-severe combined immunodeficient (SCID) mouse model.

RESULTS

The antibody demonstrated efficient inhibition of lymphocyte adhesion to ICAM-1 in vitro, with an IC(50) of approximately 0.4 microg mL(-1) (3 nmol L(-1)). In addition, MOR102 (#5) reduced lymphocyte proliferation in mixed lymphocyte cultures by approximately 50%. The in vivo efficacy of MOR102 (#5) was tested on grafts derived from lesional skin of patients with chronic plaque-stage psoriasis transplanted on to SCID mice. Intraperitoneal injection of 10 mg kg(-1) of MOR102 (#5) antibody every alternate day over a period of 4 weeks resulted in reconstitution of orthokeratotic differentiation and a significant (P < 0.05) reduction in epidermal thickness as well as marked reduction in the inflammatory infiltrate. Therapeutic activity may be related to the targeting of ICAM-1 on keratinocytes and thus preventing efficient activation of local T cells.

CONCLUSIONS

Based on the efficacy of the fully human monoclonal antibody MOR102 (#5) shown in vitro as well as in vivo in the psoriasis-SCID mouse model, initiation of clinical studies is indicated.

Molecular mechanics and dynamics of leukocyte recruitment during inflammation

Discovery of new genes and proteins directly supporting leukocyte adhesion is waning, whereas there is heightened interest in the cell mechanics and receptor dynamics that lead from transient tethering via selectins to affinity shifts and adhesion strengthening through integrins. New optical tools enable real-time imaging of leukocyte rolling and arrest in parallel plate flow channels (PPFCs), and detection of single-molecule force spectroscopy provides an inner view of the intercellular adhesive contact region. Leukocyte recruitment during acute inflammation is triggered by ligation of G protein-coupled chemotactic receptors (GPCRs) and clustering of selectins. This, in turn, activates beta(2)-integrin (CD18), which facilitates cell capture and arrest in shear flow. This review provides a conceptual model for the molecular events supporting leukocyte recruitment.

Human embryonic stem cells and their differentiated derivatives are less susceptible to immune rejection than adult cells

Differentiated cell types derived from human embryonic stem cells (hESCs) may serve in the future to treat various human diseases. A crucial step toward their successful clinical application is to examine the immune response that might be launched against them after transplantation. We used two experimental platforms to examine the in vivo leukocyte response toward hESCs. First, immunocompetent and immunodeficient mouse strains were used to identify T cells as the major component that causes xenorejection of hESCs. Second, mice that were conditioned to carry peripheral blood leukocytes from human origin were used to test the human leukocyte alloresponse toward undifferentiated and differentiated hESCs. Using this model, we have detected only a minute immune response toward undifferentiated as well as differentiated hESCs over the course of 1 month, although control adult grafts were repeatedly infiltrated with lymphocytes and destroyed. Our data show that the cells evade immune destruction due to a low immunostimulatory potential. Nevertheless, a human cytotoxic T lymphocyte clone that was specifically prepared to recognize two hESC lines could lyse the cells after major histocompatibility complex class I (MHC-I) induction. Although MHC-I levels in hESCs are sufficient for rejection by cytotoxic T cells, our data suggest that the immunostimulatory capacity of the cells is very low. Thus, immunosuppressive regimens for hESC-based therapeutics could be highly reduced compared with conventional organ transplantation because direct allorejection processes of hESCs and their derivatives are considerably weaker.

An atomic resolution view of ICAM recognition in a complex between the binding domains of ICAM-3 and integrin alphaLbeta2

Within the Ig superfamily (IgSF), intercellular adhesion molecules (ICAMs) form a subfamily that binds the leukocyte integrin alphaLbeta2. We report a 1.65-A-resolution crystal structure of the ICAM-3 N-terminal domain (D1) in complex with the inserted domain, the ligand-binding domain of alphaLbeta2. This high-resolution structure and comparisons among ICAM subfamily members establish that the binding of ICAM-3 D1 onto the inserted domain represents a common docking mode for ICAM subfamily members. The markedly different off-rates of ICAM-1, -2, and -3 appear to be determined by the hydrophobicity of residues that surround a metal coordination bond in the alphaLbeta2-binding interfaces. Variation in composition of glycans on the periphery of the interfaces influences on-rate.

T-Cell Modulation for the Treatment of Chronic Plaque Psoriasis with Efalizumab (Raptiva™): Mechanisms of Action

Psoriasis is a chronic, incurable, auto-immune disorder with cutaneous manifestations. New evidence on the central role of the immune system in the pathogenesis of psoriasis increasingly provides insight into pathogenic steps that can be modulated to provide disease control. Numerous biological therapies are in various stages of clinical development, with expectation of providing enhanced safety and efficacy over currently available psoriasis therapies. Efalizumab, a recombinant humanized monoclonal IgG1 antibody, is a novel targeted T-cell modulator that inhibits multiple steps in the immune cascade that result in the production and maintenance of psoriatic plaques, including initial T-cell activation and T-cell trafficking into sites of inflammation, including psoriatic skin, with subsequent reactivation in these sites. This article reviews the pharmacodynamic, pharmacokinetic and clinical effects observed during phase I, II and III efalizumab trials in patients with moderate to severe chronic plaque psoriasis.

Membranes as messengers in T cell adhesion signaling

Talin and RapL are components of molecular pathways that regulate the avidity of the integrin lymphocyte function-associated antigen 1 (LFA-1) for its ligand, intercellular adhesion molecule 1. In this review, we discuss recent advances in our understanding of LFA-1 affinity regulation and signaling and discuss a scenario for how Talin and Rap1 might act in synergy to achieve regulation of LFA-1 that is tailored to the specific functional requirements of different situations. Speedy delivery of signals may be crucial, and membrane trafficking from endosomes and the Golgi apparatus seem to be essential in delivering the messages from spatially segregated surface receptors.

CD2 engagement induces dendritic cell activation: implications for immune surveillance and T-cell activation

We have shown previously that primary dendritic cells and monocytes express equal levels of CD14 but are distinguishable by the presence of CD2 on dendritic cells. CD2 is known to mediate the activation of T and natural killer (NK) cells through its interaction with CD58. CD2 epitopes recognized by anti-T111, -T112, and -T113 monoclonal antibodies (mAbs) are present on dendritic cells. Here we show that CD2 engagement significantly increases class II, costimulatory (CD40, CD80, CD86), adhesion (CD54, CD58), and CCR7 molecule expression on primary dendritic cells. Conversely, minimal or no change in the expression of the above antigens occurs on monocyte-derived dendritic cells, because these molecules are already maximally expressed. However, both kinds of dendritic cells release interleukin-1beta (IL-1beta) and IL-12 after CD2 engagement. Lastly, interference with dendritic cell CD2-T-cell CD58 engagement decreases naive CD4+CD45RA+ T-cell proliferation. Collectively, our results suggest another role of the CD2-CD58 pathway that allows nonimmune and immune cells to interact directly with dendritic cells and initiate innate and adaptive immune responses.

The critical cytoplasmic regions of the alphaL/beta2 integrin in Rap1-induced adhesion and migration

Rap1 is a potent inside-out signal that increases LFA-1 adhesive activity. In this study, we have defined the cytoplasmic region of the alphaL and beta2 integrin that are required for Rap1-stimulated adhesion and subsequent migration on ICAM-1. Human LFA-1 bearing truncated and point-mutated alphaL and beta2 cytoplasmic regions were reconstituted in mouse IL-3-dependent proB cells, BAF/3. Truncation of the alphaL, but not beta2 subunit cytoplasmic region, abolished Rap1V12-dependent adhesion to ICAM-1. The alanine substitution of two lysine residues (K1097/K1099) in the alphaL subunit was found to be critical in adhesion induced by Rap1V12, but not PMA. This mutation suppressed Rap1V12-induced LFA-1 conformation changes and ligand-binding affinity. The K1097/K1099 mutation also impaired binding to ICAM-1 induced by TCR cross-linking or SDF-1. In contrast, the alanine substitution for tyrosine in the beta2 subunit endocytosis motif inhibited internalization of LFA-1, and severely impaired detachment at the cell rear, which resulted in long-elongated cell shapes. This result demonstrates that internalization of LFA-1 is a critical step in the deadhesion process. Our study revealed novel requirements of amino acid residues of the LFA-1 cytoplasmic region in the response to the inside-out signaling and the subsequent deadhesion process.

The immunological synapse: integrins take the stage

Adhesive interactions play important roles in coordinating T-cell migration and activation, specifically in the formation of the immunological synapse (IS), a specialized cell-cell junction. Recent demonstrations show several molecules implicated in T-cell signaling, including Vav, ADAP, and Rap-1, have major roles in integrin regulation and place adhesion molecules at center stage in addressing the question: what are the signals involved in the formation of the IS and full T-cell activation? This review focuses on the role of integrins as an essential system for both physical adhesion and signaling in T-cell activation. The role of integrins appears to be quite distinct from classical costimulation and has been largely overlooked due to the ubiquitous use of serum in lymphocyte functional assays. Each major signal transduction pathway has branches leading to the nucleus and others that feed back on cytoskeletal and membrane regulation at the IS.

Cell adhesion and polarity during immune interactions

Intercellular interactions are critical for a coordinated function of different cell types involved in the immune response. Here we review the cellular and molecular events occurring during cell-cell immune contacts. Cognate naïve CD4+ T lymphocyte-dendritic cell (DC) and primed T cell-antigen-presenting B lymphocyte interactions are discussed. The engagement of cytotoxic T lymphocytes (CTL) or natural killer cells (NK) with their targets is analyzed and compared to the process of T cell-antigen-presenting cell (APC) conjugate formation. The immunological synapse, a complex cluster of molecules organized at the contact area of cell conjugates, exhibits common features but shows some differences depending on cell types involved. Cellular interactions occur in sequential stages that involve dramatic changes in cell polarity and dynamic redistribution of cell membrane receptors. The role of membrane microdomains, adaptor molecules and the cytoskeleton in the regulation of the molecular reorganization at cell-cell contacts is also discussed.

Intercellular adhesion molecule-1/LFA-1 ligation favors human Th1 development

Th cell polarization toward Th1 or Th2 cells is strongly driven by exogenous cytokines, in particular IL-12 or IL-4, if present during activation by Ag-presenting dendritic cells (DC). However, additional Th cell polarizing mechanisms are induced by the ligation of cell surface molecules on DC and naive Th cells. In the present study, the role of LFA-1/ICAM-1 ligation in human Th cell polarization was investigated. Triggering of LFA-1 on anti-CD3/CD28 stimulated naive Th cells with immobilized Fc-ICAM-1, in the absence of DC and exogenous cytokines, induced a marked shift toward Th1 cell development, accompanied by a dose-dependent decrease in GATA-3 expression and a dose-dependent increase in T-bet expression. Th1 polarization by LFA-1 ligation could be demonstrated only under low cytokine conditions, as it was largely overruled by IL-12 or IL-4. This IL-12-independent Th1-driving mechanism appears to be operated by certain subsets of effector DC. Maturation of DC by poly(I:C), a synthetic dsRNA, used as an in vitro model for viral infections, leads to the generation of Th1-driving effector DC (DC1), which express elevated levels of ICAM-1 but produce only low levels of IL-12p70. Blocking the ICAM-1/LFA-1 interaction in cocultures of these DC with naive Th cells attenuated their Th1-driving capacity. The molecular mechanism by which LFA-1 signaling supports Th1 differentiation is blocked by specific inhibitors of extracellular signal-regulated kinase phosphorylation. The present data indicate the existence of an IL-12-independent, extracellular signal-regulated kinase-mediated mechanism, through which high ICAM-1-expressing DC1 can drive Th1 polarization. This mechanism may be operational during viral infections.

Role of ICAM-3 in the initial interaction of T lymphocytes and APCs

Antigen-independent adhesive interactions between T lymphocytes and antigen-presenting cells (APCs) are essential for scanning for specific antigens on the APC surface and for initiating the immune response. Here we show, through time-lapse imaging of live cells, that the intercellular adhesion molecule 3 (ICAM-3, also known as CD50) is clustered specifically at the region of the T lymphocyte surface that initiates contact with APCs. We describe the role of ICAM-3 in T cell-APC conjugate formation before antigen recognition, in early intracellular signaling and in cytoskeletal rearrangement. Our data indicate that ICAM-3 is important in the initial scanning of the APC surface by T cells and, therefore, in generating the immune response.

CD18 activation epitopes induced by leukocyte activation

The cell surface adhesion molecule LFA-1 coordinates leukocyte trafficking and is a costimulatory molecule for T cell activation. We developed a panel of mAbs that recognize activation epitopes on the CD18 subunit, and show that stimulation of T lymphocytes appears to be accompanied by a conformational change in a subpopulation of LFA-1 that does not require ligand binding. Activation epitope up-regulation requires divalent cations, is sensitive to cellular signal transduction events, and correlates with cell adhesion. In addition, the stimulated appearance of these activation epitopes is absent in cell lines from patients with leukocyte adhesion deficiency-1/variant that has previously been shown to be defective in LFA-1 activation. Thus, these activation epitope Abs can be used to dissect signal transmission to CD18. Evidence suggests that these CD18 activation epitopes are induced early in cellular activation and are independent of actin rearrangement necessary for avid adhesion. We have also determined that function-blocking CD18 Abs inhibit the induction of activation epitopes. One activation epitope Ab binds to a site on CD18 distinct from that of the blocking Abs, indicating that the blocking Abs suppress a conformational change in LFA-1. We also find that these neoepitopes are present on rLFA-1 with high affinity for ICAM-1 and their binding is modulated in parallel with the affinity of LFA-1 for ICAM-1. Collectively, these neoepitope Abs identify a subpopulation of LFA-1 most likely with high affinity for ICAM-1 and necessary for LFA-1 function.

Ultrastructure and function of dimeric, soluble intercellular adhesion molecule-1 (ICAM-1)

Previous studies have demonstrated dimerization of intercellular adhesion molecule-1 (ICAM-1) on the cell surface and suggested a role for immunoglobulin superfamily domain 5 and/or the transmembrane domain in mediating such dimerization. Crystallization studies suggest that domain 1 may also mediate dimerization. ICAM-1 binds through domain 1 to the I domain of the integrin alpha(L)beta(2) (lymphocyte function-associated antigen 1). Soluble C-terminally dimerized ICAM-1 was made by replacing the transmembrane and cytoplasmic domains with an alpha-helical coiled coil. Electron microscopy revealed C-terminal dimers that were straight, slightly bent, and sometimes U-shaped. A small number of apparently closed ring-like dimers and W-shaped tetramers were found. To capture ICAM-1 dimerized at the crystallographically defined dimer interface in domain 1, cysteines were introduced into this interface. Several of these mutations resulted in the formation of soluble disulfide-bonded ICAM-1 dimers (domain 1 dimers). Combining a domain 1 cysteine mutation with the C-terminal dimers (domain 1/C-terminal dimers) resulted in significant amounts of both closed ring-like dimers and W-shaped tetramers. Surface plasmon resonance studies showed that all of the dimeric forms of ICAM-1 (domain 1, C-terminal, and domain 1/C-terminal dimers) bound similarly to the integrin alpha(L)beta(2) I domain, with affinities approximately 1.5--3-fold greater than that of monomeric ICAM-1. These studies demonstrate that ICAM-1 can form at least three different topologies and that dimerization at domain 1 does not interfere with binding in domain 1 to alpha(L)beta(2).

Novel cyclic peptide inhibits intercellular adhesion molecule-1-mediated cell aggregation

Leukocyte adherence mediated by intercellular adhesion molecule-1 (ICAM-1) binding to leukocyte function-associated antigen (LFA-1) is required for proper inflammatory and immune function. Inhibition of ICAM-1\LFA-1 binding using monoclonal antibodies (mAb) has been shown to be efficacious at inhibiting lymphoma metastasis as well as leukocyte emigration into tissue in a number of inflammatory diseases such as ischemia-reperfusion injury, septic shock and rheumatoid arthritis. In this report, we describe the development and characterization of a small peptide antagonist of ICAM-1-dependent cell aggregation. By using repeated selection of a cyclic nonapeptide phage display library on purified ICAM-1, we identified phage that were competitively eluted with anti-ICAM-1 mAb. The peptide sequences were determined by nucleotide sequencing, and the peptide sequence (C*LLRMRSIC*) (IP01) that occurred most frequently was chosen for further study. Phage expressing this peptide sequence specifically bound ICAM-1 over a range of 5 x 10(6) to 1 x 10(8) phage/microL. A cyclic IP01 peptide, linear IP01 peptide, a cyclic nonapeptide with a scrambled IP01 sequence, and a random, cyclic nonapeptide were synthesized. The cyclic and linear IP01 peptides were able to inhibit ICAM-1-mediated cell aggregation at a concentration of 1 mM, whereas the random and scrambled peptide sequences did not alter aggregation. Cyclic IP01 had a half-maximal inhibitory concentration of approximately 970 microM. Cyclic IP01 did not inhibit cellular aggregation that was dependent on ICAM-2 or ICAM-3. Alanine substitutions in the cyclic IP01 identified at least four amino acids necessary for inhibition of ICAM-1 dependent cell aggregation; leucine 2, leucine 3, methionine 5, and arginine 6. Finally, we showed that cyclic IP01 can inhibit firm adhesion of neutrophils to endothelium, a critical event in inflammatory diseases, in an assay that recapitulates physiologic flow conditions. Homology of IP01 with the primary amino acid sequences of the alpha or beta subunit of LFA-1 was not identified. Thus, we identified a unique molecule that inhibits ICAM-1 dependent cell adhesion, but is not related to the primary sequence of the ICAM-1 ligand LFA-1. Due to the small size and ability to block cell-cell adhesion, IP01 may serve as a useful tool for study of ICAM-1 and LFA-1 biology as well as for the development of small molecule therapeutics.

Immunophenotypic characterization of normal blood CD56+lo versus CD56+hi NK-cell subsets and its impact on the understanding of their tissue distribution and functional properties

In the present study we have compared the immunophenotypic characteristics of the CD56+lo and CD56+hi NK-cell subsets in a group of normal healthy adults. Our results show that CD56+hi NK-cells display greater light-scatter properties than CD56+lo NK-cells at the same time they have higher levels of CD25 and CD122 IL-2 chains, together with a higher reactivity for HLA-DR and CD45RO and lower levels of CD45RA, supporting that, as opposed to the majority of the CD56+lo population, CD56+hi NK-cells might correspond to a subset of activated circulating NK-lymphocytes. Higher expression of the CD2 and CD7 costimulatory molecules found for the CD56+hi NK-cells would support their greater ability to respond to various stimuli. In addition, CD56+hi NK-cells expressed higher levels of several adhesion molecules such as CD2, CD11c, CD44, CD56, and CD62L compared to CD56+lo NK-cells, supporting a particular ability of these cells to migrate from blood to tissues and/or a potential advantage to form conjugates with target cells. Interestingly, CD56+lo and CD56+hi NK-cells showed a different pattern of expression of killer receptors that might determine different activation requirements for each of these NK-cell subsets. For instance, absence or low levels of CD16 expression might explain the lower antibody-dependent cytotoxicity activity of CD56+hi NK-cells. On the other hand, the virtual absence of expression of the CD158a and NKB1 immunoglobulin-like and the greater reactivity for the CD94 lectin-like killer receptors on CD56+hi in comparison to CD56+lo NK-cells might determine different MHC-class I specificities for both NK-cell subsets, a possibility that deserves further studies to be confirmed.

Inhibition of the adherence of T-lymphocytes to epithelial cells by a cyclic peptide derived from inserted domain of lymphocyte function-associated antigen-1

Tissue inflammation is characterized by aggravated leukocyte infiltration into the sites of inflammation. The mechanism requires the interactions of leukocyte adhesion-molecules and their ligands in the inflamed tissues. In this study, we demonstrate that a cyclic peptide cLAB.L [cyclol, 12-PenlTDGEATDSGC], derived from the "inserted" or I-domain of LFA-1 is able to inhibit the adherence of T-lymphocytes to the epithelial cell monolayers. This inhibition has been thought to involve the disruption of LFA-1/ICAM-1 interaction. The heterotypic adhesion of phorbol ester-activated Molt-3 cells and IFN-gamma-induced Caco-2 monolayers was inhibited upon treatment of the monolayers with monoclonal antibodies (MAbs) to adhesion molecules or with cLAB.L peptide. The adhesion can be inhibited by MAbs to ICAM-1, ICAM-2, and VCAM-1, and cLAB.L peptide in a concentration-dependent manner. However, none of the individual uses of these molecules led to a total inhibition. The inhibitory activity of cLAB.L is greatly reduced by low temperature and the absence of cell activation. Treatment of cLAB.L peptide may trigger an early event of apoptosis on activated but not on non-activated Molt-3 cells; no indication of peptide-induced apoptosis was found on Caco-2 cells. Taken together, data from this work suggest that cLAB.L may have applications to direct cell-targeted delivery during tissue inflammation.

Binding and internalization of an LFA-1-derived cyclic peptide by ICAM receptors on activated lymphocyte: a potential ligand for drug targeting to ICAM-1-expressing cells

PURPOSE

The interaction of cell-adhesion molecules LFA-1/ICAM-1 is critical for many inflammatory and immune responses. Blockades of this interaction using antibodies or peptide analogs are being developed as therapeutic approaches for inflammatory and autoimmune diseases. The aim of this study is to examine the binding and internalization mechanisms of LFA-1 peptide [cLAB.L or cyclo-(1,12)-PenITDGEATDSGC] mediated by ICAM receptors on the surface of lymphocytes.

METHODS

The binding and internalization of cLAB.L were evaluated using fluorescence-labeled cLAB.L on activated Molt-3 cells, measured by flow cytometry. Confocal fluorescence microscopy was also used to image the distribution of peptide binding and internalization.

RESULTS

The binding of FITC-cLAB.L exhibited bimodal cell distribution and was enhanced by Ca2+ and Mg2+. Marked differences in peptide binding were found between 37 and 4 degrees C, as well as between activated and non-activated cells. Unlabeled peptide, low temperature, and the absence of cell activation suppress the peptide binding. The presence of peptide in the cytoplasm was detected in 37 but not 4 degrees C binding. Peptide cLAB.L inhibited the binding of monoclonal antibodies to domain D1 of ICAM-1 and domain D1 of ICAM-3.

CONCLUSIONS

Peptide cLAB.L can bind to the D1-domain of ICAM-1 and, to a lesser extent, to ICAM-3 on activated T-cells. Peptide binding indicates responses to the multiple and dynamic states of activated receptor ICAMs, this peptide may also be internalized by ICAM receptors on T-cells. This work suggests that cLAB.L has a therapeutic potential to target drugs to ICAM-1 expressing cells including autoreactive lymphocytes and inflamed tissues.

Molecular, cellular and functional characterizations of a novel ICAM-like molecule of the immunoglobulin superfamily from Leishmania mexicana amazonensis

A molecule with two immunoglobulin (Ig) domains cloned from Leishmania mexicana amazonensis was characterized to have a sequence homology to the Ig domains of an ICAM-like molecule telencephalin, cloned from the brain of mammals, as well as to the variable domains of human immunoglobulin lambda light chain. The molecule therefore appears to be an ICAM-like molecule as well as a member of the immunoglobulin superfamily. We thus named it ICAM-L for Leishmania ICAM. The gene was coamplified with the ribonucleotide reductase M(2) subunit gene responsible for hydroxyurea resistance from hydroxyurea (Hu)-resistant Leishmania variants. As expected, an increase of the ICAM-L protein as well as an increase of the specific ICAM-L transcript of 2.1 kb was detected in the Hu-resistant variants with increasing doses of the drug used for resistance selection. Structurally, ICAM-L is more similar to the secretory adhesive molecules, such as 1Bgp and the link protein of the immunoglobulin superfamily, in that it lacks a transmembrane region and a GPI anchor sequence. Although ICAM-L was mainly localized in the nucleus of the parasite by confocal microscopy, however, detailed studies by electron microscopy and FACS analysis indicated that the protein was also localized on the surface of the parasite. The surface localization of the protein was furthered strengthened by the observations that anti-ICAM-L or ICAM-L itself can significantly block the binding of the parasite to macrophages. The blocking of the attachment of parasite to macrophages may indicate that ICAM-L functions as an intercellular adhesive molecule.

Structural study of N-linked oligosaccharides of human intercellular adhesion molecule-3 (CD50)

The N-linked oligosaccharides were released from purified human intercellular adhesion molecule (ICAM)-3 by hydrazinolysis. Approximately 6 mol of oligosaccharides were released from 1 mol of ICAM-3. The oligosaccharides reduced with NaB[3H]4 were separated into neutral and acidic fractions by paper electrophoresis. Most of the acidic oligosaccharides were converted to neutral ones by digestion with sialidase, indicating that they are sialyl derivatives. The neutral and sialidase-treated acidic oligosaccharides were fractionated by serial lectin column chromatography followed by Bio-Gel P-4 column chromatography. Structural studies of each oligosaccharide by sequential exo- and endo-glycosidase digestion and by methylation analysis revealed that N-linked oligosaccharides of ICAM-3 are mainly of tri- and tetra-antennary complex-type, about 60% of which contain two to three poly N-acetyllactosamine chains terminated with the type 1 structure and those without the type 1 structure per oligosaccharide. In addition, a small amount of the high mannose-type oligosaccharide with six alpha-mannose residues, which could act as a ligand for the dendritic cell-specific ICAM-3 grabbing nonintegrin, was detected.

Leukocyte CD11a expression and granulocyte activation during experimental myocardial ischemia and long lasting reperfusion

BACKGROUND

Myocardial ischemia and reperfusion are accompanied by leukocyte activation and expression of surface adhesion molecules, which induce pathological interactions between endothelial cells and circulating neutrophils, leading to tissue damage. While the dynamics of these processes have been well defined during acute reperfusion, there is very little information regarding long lasting reperfusion.

OBJECTIVES

To investigate neutrophil granulocyte (PMN) activation and the CD11a expression of leukocytes during myocardial ischemia and reperfusion for four weeks.

ANIMALS AND METHODS

The left anterior descending coronary artery was occluded for 1 h in six dogs, followed by reperfusion for four weeks. Peripheral blood samples were collected before the operation, at the end of ischemia, at 5 and 60 min of reperfusion, and on postoperative days 1, 2, 3, 7, 14, 21 and 28. Sham operation on four dogs served as control. Leukocyte expression of CD11a was measured by flow cytometry. Superoxide radical production of isolated PMNs was determined spectrophotometrically.

RESULTS

Granulocyte CD11a expression increased while the superoxide radical-producing capacity decreased significantly by the third postoperative day. Sham operation produced similar alterations in these parameters during the first postoperative week. From the second postoperative week, however, granulocyte radical production and adhesion molecule expression were higher in the ischemic animals.

CONCLUSIONS

The exhaustion of PMN radical production and maximal CD11a expression during the first postoperative week are probably due to the surgical trauma caused by thoracotomy, but increased granulocyte function during later reperfusion indicates prolonged healing of injured myocardium.

The second domain of intercellular adhesion molecule-1 (ICAM-1) maintains the structural integrity of the leucocyte function-associated antigen-1 (LFA-1) ligand-binding site in the first domain

The first domain of intercellular adhesion molecule-1 (ICAM-1) binds to the leucocyte function-associated antigen-1 (LFA-1) I domain, which contains the principal ligand-binding site of this leucocyte integrin. Whether the function of the second domain is also to directly bind LFA-1 has been unclear. Our data show that mutation in the hydrophilic EF loop of ICAM-1 domain 2 resulted in impaired binding of the isolated I domain when compared with wild-type ICAM-1. LFA-1 on T-cells also binds with reduced affinity to this ICAM-1 mutant. A hybrid construct containing the first domain of vascular cell-adhesion molecule-1 joined to domains 2-5 of ICAM-1 was unable to bind to the I domain, showing that there is no direct interaction between the second domain of ICAM-1 and the I domain. This construct was also not bound by LFA-1 expressed in T-cells. Function-blocking monoclonal antibodies that map to domain 2 of ICAM-1, implicating this domain in ligand binding, were found to act indirectly. In summary our data suggest that the second domain of ICAM-1 has a role in maintaining the structure of the LFA-1 ligand-binding site in the first domain of ICAM-1 but does not appear to have a direct role in ligand binding.

Activation of mitogen-activated protein kinase through alpha5/beta1 integrin is required for cell cycle progression of B progenitor cell line, Reh, on human marrow stromal cells

OBJECTIVE

Attachment to bone marrow (BM) stromal cells is crucial for the normal growth and development of B-cell progenitors (pro-B). However, the molecular mechanisms by which contact facilitates the proliferation of pro-B cells are not completely understood. This study was performed to investigate this interaction.

MATERIALS AND METHODS

A model pro-B cell line (Reh) and a human BM stromal cell line (KM102) were used. Flow cytomery was used for cell cycle analysis. Western Blotting and immunoprecipitation were utilized to examine the levels of cyclin-dependent kinase (cdk) and p27(Kip1).

RESULTS

Attachment to both KM102 and normal BM stromal cells significantly promoted the growth of Reh cells. Pretreatment of Reh cells with anti-integrin beta1 or alpha5 monoclonal antibody (mAb), but not alpha4 or ICAM-1 mAb, abrogated this enhancement of proliferation. Furthermore, stroma attachment resulted in shortening of the G(1) phase of cell cycle, significant increases cdk2 activity, degradation of cdk inhibitor p27-GST protein, and decrease in levels of p27(Kip1) protein. In addition, solid-phase cross-linking of alpha5 via immobilized antibody also resulted in extracellular signal-regulated (ERK)-2 kinase phosphorylation, increase in cdk2 activity, decrease in levels of p27(Kip1) protein, and enhanced proliferation that was inhibited by treatment with PD98059, a specific ERK inhibitor.

CONCLUSION

Integrin alpha5beta1-mediated stroma contact promotes the proliferation of B-cell progenitors through the activation of ERK-2, which in turn modulates cell cycle regulation machinery including induction of cdk2 activity and degradation of p27(Kip1) and contributing to acceleration of the G(1) phase of cell cycle progression.

CD8+ T cells are crucial for the ability of congenic normal mice to reject highly immunogenic sarcomas induced in nude mice with 3-methylcholanthrene

An attempt was made to identify the selection pressures put upon a growing tumour by CD8+ T cells. To this end tumours induced with 3-methylcholanthrene in T cell-deficient nude mice and in congenic T cell-competent nu/+ mice were transplanted to nu/+ recipients. The rejection rate of the sarcomas from nude mice was almost twice that of the sarcomas from nu/+ mice. Depletion of CD8+ T cells from nu/+ recipients prior to transplantation made them accept nude tumours that were consistently rejected by untreated nu/+ recipients. These findings suggest that a methylcholanthrene sarcoma during its growth in a T cell-competent host adapts to the T cell system through a selective elimination of highly immunogenic tumour cells that are susceptible to CD8+ T cell-mediated lysis.