Direct Tumor Irradiation Potentiates Adoptive NK Cell Targeting Against Parental and Stemlike Cancer in Human Liver Cancer Models

PURPOSE

Radiation therapy (RT) has been shown to effectively induce the expression of intercellular adhesion molecule-1 (ICAM-1), which is recognized by lymphocyte function-associated antigen 1 (LFA-1) expressed on natural killer (NK) cells. However, the potential synergistic antitumor immune response of tumor irradiation and administered NK cells has not been explored in intractable human liver cancers. Furthermore, NK cell targeting against both parental and cancer stemness has never been investigated.

METHODS AND MATERIALS

Highly activated ex vivo NK cells were administered into the human liver tumor-bearing mice. Tumor direct RT was optimized according to tumor bearing site. HepG2 and Hep3B ICAM-1 knockout cells were generated using CRISPR/CAS9. Stemness tumor spheres were generated. NK cell cytolysis against parental and tumor sphere was evaluated using flow cytometry and real-time cytotoxicity assay.

RESULTS

A combination of adoptive NK cell therapy with RT significantly improved therapeutic efficacy over monotherapies against subcutaneous, orthotopic, and metastatic human liver tumor models. Direct tumor irradiation potentiated NK cell recognition and conjugation against liver cancer through the LFA-1/ICAM-1 axis. Suppression of immune synapse formation on NK cells using high-affinity LFA-1 inhibitors or ICAM-1 knockout liver cancer induced "outside-in" signal blocking in NK cells, resulting in failure to eliminate liver tumor despite the combination therapy. NK cells effectively recognized and targeted triple-high epithelial cell adhesion molecule+CD133+CD24+ liver cancer expressing upregulated ICAM-1 in the irradiated tumor microenvironment, which led to prevention of the initiation of metastasis, improving survival in a metastatic model. In addition, the LFA-1/ICAM-1 axis interruption between NK cells and stemness liver tumor spheres significantly diminished NK cell cytolysis. Consistent with our preclinical data, the LFA-1/ICAM-1 axis correlated with survival outcomes in patients with metastatic cancer from the The Cancer Genome Atlas databases.

CONCLUSIONS

NK cells in combination with tumor irradiation can provide synergistic therapeutic effects for NK cell recognition and elimination against both parental and stemlike liver cancer through LFA-1/ICAM-1.

GSK3β Interacts With CRMP2 and Notch1 and Controls T-Cell Motility

The trafficking of T-cells through peripheral tissues and into afferent lymphatic vessels is essential for immune surveillance and an adaptive immune response. Glycogen synthase kinase 3β (GSK3β) is a serine/threonine kinase and regulates numerous cell/tissue-specific functions, including cell survival, metabolism, and differentiation. Here, we report a crucial involvement of GSK3β in T-cell motility. Inhibition of GSK3β by CHIR-99021 or siRNA-mediated knockdown augmented the migratory behavior of human T-lymphocytes stimulated via an engagement of the T-cell integrin LFA-1 with its ligand ICAM-1. Proteomics and protein network analysis revealed ongoing interactions among GSK3β, the surface receptor Notch1 and the cytoskeletal regulator CRMP2. LFA-1 stimulation in T-cells reduced Notch1-dependent GSK3β activity by inducing phosphorylation at Ser9 and its nuclear translocation accompanied by the cleaved Notch1 intracellular domain and decreased GSK3β-CRMP2 association. LFA-1-induced or pharmacologic inhibition of GSK3β in T-cells diminished CRMP2 phosphorylation at Thr514. Although substantial amounts of CRMP2 were localized to the microtubule-organizing center in resting T-cells, this colocalization of CRMP2 was lost following LFA-1 stimulation. Moreover, the migratory advantage conferred by GSK3β inhibition in T-cells by CHIR-99021 was lost when CRMP2 expression was knocked-down by siRNA-induced gene silencing. We therefore conclude that GSK3β controls T-cell motility through interactions with CRMP2 and Notch1, which has important implications in adaptive immunity, T-cell mediated diseases and LFA-1-targeted therapies.

LFA-1-dependent HuR nuclear export and cytokine mRNA stabilization in T cell activation

Lymphokine gene expression is a precisely regulated process in T cell-mediated immune responses. In this study we demonstrate that engagement of the beta(2) integrin LFA-1 in human peripheral T cells markedly extends the half-life of TNF-alpha, GM-CSF, and IL-3 mRNA, as well as a chimeric beta-globin mRNA reporter construct containing a strongly destabilizing class II AU-rich element from the GM-CSF mRNA 3'-untranslated region. This integrin-enhanced mRNA stability leads to augmented protein production, as determined by TNF-alpha ELISPOT assays. Furthermore, T cell stimulation by LFA-1 promotes rapid nuclear-to-cytoplasmic translocation of the mRNA-stabilizing protein HuR, which in turn is capable of binding an AU-rich element sequence in vitro. Abrogation of HuR function by use of inhibitory peptides, or marked reduction of HuR levels by RNA interference, prevents LFA-1 engagement-mediated stabilization of T cell TNF-alpha or IFN-gamma transcripts, respectively. Thus, HuR-mediated mRNA stabilization, stimulated by integrin engagement and controlled at the level of HuR nuclear export, is critically involved in T cell activation.

The hepatitis C envelope 2 protein inhibits LFA-1-transduced protein kinase C signaling for T-lymphocyte migration

BACKGROUND & AIMS

The ability of viruses to escape the host immune response represents a globally important problem related to a wide variety of pathogens. Hepatitis C is one of the major causes of liver disease worldwide. Clearance rates of this virus are low, and this condition normally involves a chronic inflammatory process. This raises a possibility that the virus may have developed mechanisms enabling it to evade T-cell-mediated immune surveillance. The aim of this study was to investigate the effect of the hepatitis C envelope protein E2 on LFA-1-stimulated T-cell migration and macrophage inflammatory protein (MIP-1alpha, MIP-1beta) secretion.

METHODS

T cells were stimulated through the leukocyte function-associated molecule-1 (LFA-1) receptor by incubating with either intracellular adhesion molecule 1 (ICAM-1)-Fc fusion protein or anti-LFA-1 immobilized on 8-well chamber slides. Subcellular localization of protein kinase C (PKC)-beta, CD81, and LFA-1 was determined by immunofluorescence analysis. Lipid raft formation was assessed using the Cellomics Kineticscan reader. MIP-1alpha and MIP-1beta levels were detected by enzyme-linked immunosorbent assay.

RESULTS

We report that the hepatitis C envelope protein E2 can dramatically inhibit T-lymphocyte motility and chemokine release induced via LFA-1 integrin ligation. We have demonstrated a novel T-lymphocyte-directed viral inhibitory mechanism involving the PKC-beta enzyme as a definitive intracellular target. E2-CD81 interaction stimulates translocation of PKC-beta to lipid rafts, thereby preventing its association with the centrosome and microtubule cytoskeleton, which is crucial to the process of T-cell migration.

CONCLUSIONS

These studies identify a mechanism whereby the hepatitis C virus can evade the host immune response by inhibition of T-cell migration.

Enhanced T-lineage acute lymphoblastic leukaemia cell survival on bone marrow stroma requires involvement of LFA-1 and ICAM-1

The bone marrow (BM) microenvironment supports leukaemia cell survival and proliferation. The roles played by adhesive receptor interactions in the survival of T-lineage acute lymphoblastic leukaemia (T-ALL) cells on BM stromal cells are not well understood. Recently, we have developed an assay that partially recapitulates the BM microenvironment using HS-5 BM stromal cells. In this assay, the magnitude of ex vivo T-ALL lymphoblast survival predicts patient outcome. We examined the molecular basis for cell-cell adhesive events leading to T-ALL lymphoblast survival on HS-5 and on donor-derived BM stroma. Lympho cyte function-associated antigen-1 (LFA-1) on T-ALL cell lines bound intercellular adhesion molecule-1 (ICAM-1) on HS-5 monolayers, and survival was inhibited 85-98% with monoclonal antibodies directed against LFA-1 or ICAM-1. We compared these results with patient-derived T-ALL lymphoblasts co-cultured on either HS-5 BM or normal BM monolayers and found that LFA-1 and ICAM-1 were required, but not alone sufficient for ex vivo leukaemic cell survival. On normal BM stroma, but not HS-5 monolayers, two additional adhesion molecules, vascular cell adhesion molecule-1 (VCAM-1) and E-selectin, were highly expressed and contributed to T-ALL cell survival. This is the first report to demonstrate the importance of LFA-1/ICAM-1-mediated adhesion as a critical event in a cascade of cell surface receptor-ligand interactions that regulate T-ALL survival in the BM microenvironment.

Effects of IL-8, Gro-alpha, and LTB(4) on the adhesive kinetics of LFA-1 and Mac-1 on human neutrophils

Firm adhesion of rolling neutrophils on inflamed endothelium is dependent on beta(2) (CD18)-integrins and activating stimuli. LFA-1 (CD11a/CD18) appears to be more important than Mac-1 (CD11b/CD18) in neutrophil emigration at inflammatory sites, but little is known of the relative binding characteristics of these two integrins under conditions thought to regulate firm adhesion. The present study examined the effect of chemoattractants on the kinetics of LFA-1 and Mac-1 adhesion in human neutrophils. We found that subnanomolar concentrations of interleukin-8, Gro-alpha, and leukotriene B(4) (LTB(4)) induced rapid and optimal rates of LFA-1-dependent adhesion of neutrophils to intercellular adhesion molecule (ICAM)-1-coated beads. These optimal rates of LFA-1 adhesion were transient and decayed within 1 min after chemoattractant stimulation. Mac-1 adhesion was equally rapid initially but continued to rise for >/=6 min after stimulation. A fourfold higher density of ICAM-1 on beads markedly increased the rate of binding to LFA-1 but did not change the early and narrow time window for the optimal rate of adhesion. Using well-characterized monoclonal antibodies, we showed that activation of LFA-1 and Mac-1 by Gro-alpha was completely blocked by anti-CXC chemokine receptor R2, but activation of these integrins by interleukin-8 was most effectively blocked by anti-CXC chemokine receptor R1. The topographical distribution of beads also reflected significant differences between LFA-1 and Mac-1. Beads bound to Mac-1 translocated to the cell uropod within 4 min, but beads bound to LFA-1 remained bound to the lamellipodial regions at the same time. These kinetic and topographical differences may indicate distinct functional contributions of LFA-1 and Mac-1 on neutrophils.

A primate model of renal ischemia-reperfusion injury for preclinical evaluation of the antileukocyte function associated antigen 1 monoclonal antibody odulimonab

PURPOSE

We established a primate model to investigate the effects of the antileukocyte function associated antigen 1 (CD 11a) mAb odulimomab (Imtix-Sangstad, Lyon, France) for preventing renal ischemia-reperfusion injury.

MATERIALS AND METHODS

We randomly divided 34 Macaca cynomolgus monkeys into groups 1 and 2, which received a renal autograft after 2 hours of cold ischemia, and groups 3 and 4, which received the autograft after 24 hours of cold ischemia. Before cold ischemia all harvested kidneys were subjected to 30 to 45 minutes of warm ischemia. Groups 1 and 3 monkeys were treated with an antileukocyte function associated antigen 1 mAb before cold ischemia and then for 3 days, while groups 2 and 4 monkeys received an IgG1 isotype control. In all groups renal function was investigated before warm ischemia and 72 hours after reperfusion. Serum creatinine and the leukocyte count were determined daily. Histological studies were done and lactoferrin was measured in the autotransplanted kidney 72 hours after reperfusion.

RESULTS

A decrease in renal function was shown after 2 hours of cold ischemia with tubular necrosis and mild cell infiltration, while after 24 hours of cold ischemia there was severe renal failure with tubular and glomerular necrosis, and leukocyte infiltration. A significant improvement in renal function and decrease in kidney lactoferrin content was evident in group 1 compared to group 2 at 72 hours, while no significant difference was noted in groups 3 and 4. No difference in histological patterns was evident in treated and untreated animals.

CONCLUSIONS

This study provides evidence for the validity of this ischemia-reperfusion injury model in primates. The protective effects of antileukocyte function associated antigen 1 mAb on renal injury was not as dramatic as in rodent models but a significant improvement in renal function was observed in treated animals after 2 hours of cold ischemia.

Statins selectively inhibit leukocyte function antigen-1 by binding to a novel regulatory integrin site

The beta2 integrin leukocyte function antigen-1 (LFA-1) has an important role in the pathophysiology of inflammatory and autoimmune diseases. Here we report that statin compounds commonly used for the treatment of hypercholesterolemia selectively blocked LFA-1-mediated adhesion and costimulation of lymphocytes. This effect was unrelated to the statins' inhibition of 3-hydroxy-3-methylglutaryl coenzyme-A reductase; instead it occurred via binding to a novel allosteric site within LFA-1. Subsequent optimization of the statins for LFA-1 binding resulted in potent, selective and orally active LFA-1 inhibitors that suppress the inflammatory response in a murine model of peritonitis. Targeting of the statin-binding site of LFA-1 could be used to treat diseases such as psoriasis, rheumatoid arthritis, ischemia/reperfusion injury and transplant rejection.

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.

Rat and rabbit plasma distribution of free and chylomicron-associated BIRT 377, a novel small molecule antagonist of LFA-1-mediated cell adhesion

PURPOSE

The objectives of this study are to determine the plasma distribution of free and chylomicron-associated BIRT 377 within rats and rabbits.

METHODS

For the rat studies free and chylomicron-associated BIRT 377 was incubated in plasma from CD 1 non-fasted rats for 60 minutes at 37 degrees C. Following incubation the plasma was separated into its lipoprotein and lipoprotein-deficient plasma (LPDP) fractions by three different methods and analyzed for BIRT 377 content by HPLC. For the rabbit studies New Zealand fasted white rabbits (3 kg; n=4) were administered an intravenous dose of free BIRT 377 (1 mg/kg). Following administration, serial blood samples were obtained and the plasma was analyzed for BIRT 377. The plasma conected at the 0.083-h time point was separated into each of its lipoprotein fractions and analyzed for BIRT 377.

RESULTS

37.8 +/- 1.2% of the original drug amount incubated in rat plasma was recovered within the lipoprotein-rich fraction. 41.5 +/- 0.4% of the original chylomicron-associated drug concentration incubated was recovered within the lipoprotein-rich fraction. The percentage of drug recovered within the TRL fraction was significantly greater following the incubation of chylomicron-associated BIRT 377 compared to free BIRT 377. In addition, BIRT 377 apparently follows a two-compartment pharmacokinetic model following single intravenous dose administration to rabbits.

CONCLUSIONS

These findings suggest that plasma lipoprotein binding of BIRT 377 is evident and may be a factor in evaluating the pharmacological fate of this drug when administered to patients that exhibit changes in their plasma lipoprotein lipid.

Chemokines stimulate human T lymphocyte transendothelial migration to utilize VLA-4 in addition to LFA-1

Lymphocyte infiltration in inflammation is induced by the dual actions of chemokines and cell adhesion molecules. The role of LFA-1 and VLA-4 in chemokine-induced T cell transendothelial migration (TEM) across cytokine-activated endothelium has not been examined. LFA-1, but not VLA-4, mediated blood T cell TEM to RANTES, macrophage inflammatory protein-1alpha (MIP-1alpha), and stromal cell-derived factor-1 (SDF-1), and across tumor necrosis factor alpha (TNF-alpha) or interferon-gamma (IFN-gamma) -stimulated endothelial cells (EC). Chemokine stimulation in combination with TNF-alpha activation of EC induced TEM, which was partially mediated by VLA-4. SDF-1 increased a beta1-integrin activation epitope on T cells and enhanced VLA-4-mediated adhesion. Thus, LFA-1 mediates TEM under most conditions, but VLA-4 can also mediate TEM, although, in contrast to LFA-1, this requires exogenous chemokines and EC activation. In addition, an LFA-1- and VLA-4-independent pathway of lymphocyte TEM can also be induced by SDF-1.

LFA-1 expression on target cells promotes human immunodeficiency virus type 1 infection and transmission

While CD4 and the chemokine receptors are the principal receptors for human immunodeficiency virus (HIV), other cellular proteins, such as LFA-1, are also involved in HIV infection. LFA-1 and its ligands, ICAM-1, ICAM-2, and ICAM-3, can be expressed on the cells infected by HIV, as well as on the HIV virions themselves. To examine the role of LFA-1 expressed on target cells in HIV infection, Jurkat-derived Jbeta2.7 T-cell lines that express either wild-type LFA-1, a constitutively active mutant LFA-1, or no LFA-1 were used. The presence of wild-type LFA-1 enhanced the initial processes of HIV infection, as well as the subsequent replication and transmission from cell to cell. In contrast, the constitutively active LFA-1 mutant failed to promote virus replication and spread, even though this mutant could help HIV enter cells and establish the initial infection. This study clearly demonstrates the contribution of LFA-1 in the different stages of HIV infection. Moreover, not only is LFA-1 expression important for initial HIV-cell interaction, subsequent replication, and transmission, but its activity must also be properly regulated.

Hydrogen peroxide induces LFA-1-dependent neutrophil adherence to cardiac myocytes

Adult cardiac myocytes express intercellular adhesion molecule (ICAM)-1 in response to cytokine stimulation. This allows stable adhesion of chemotactically stimulated but not unstimulated neutrophils. In the current study, we demonstrated that brief exposure of ICAM-1-expressing cardiac myocytes to H(2)O(2) promoted transient adhesive interactions between myocytes and neutrophils without added chemotactic factors. This transient adhesion differed in two ways from the stable adhesion promoted by exogenous chemotactic factors. It occurred more rapidly, peaking within 15 min, and it was dependent on leukocyte function-associated antigen (LFA)-1 (CD11a/CD18) on the neutrophil interacting with ICAM-1 on the myocyte. In contrast, chemotactic factor-induced adhesion peaked at 60 min and was dependent on Mac-1 (CD11b/CD18). The transient adhesion could be completely inhibited by platelet-activating factor (PAF)-receptor antagonists WEB-2086 and SDZ-64-412. These results indicate that canine neutrophils may utilize both LFA-1 and Mac-1 to adhere to adult cardiac myocytes, with LFA-1 triggered by a PAF-like activity induced in myocytes by H(2)O(2).

LFA-1- and ICAM-1-dependent homotypic aggregation of human thymocytes induced by JL1 engagement

Cell-cell adhesion is essential for the appropriate immune response, differentiation, and migration of lymphocytes. This important physiological event is reflected in vitro by homotypic cell aggregation. We have previously reported that a 120 kDa cell surface glycoprotein, JL1, is a unique protein specifically expressed by immature double positive (DP) human thymocytes which are in the process of positive and negative selections through the interaction between thymocyte and antigen-presenting cells (APCs). The function of the JL1 molecule, however, is yet to be identified. We show here that anti-JL1 monoclonal antibody (mAb) induced the homotypic aggregation of human thymocytes in a temperature- and Mg2+-dependent manner. It required an intact cytoskeleton and the interaction between leucocyte function associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) since it was blocked by cytochalasin B and D, and mAb against LFA-1 and ICAM-1 which are known to be involved in the aggregation of thymocytes. Translocation of phosphatidylserine (PtdSer) through the cell membrane was not detected, implying that the molecular mechanism of JL-1-induced homotypic aggregation is different from that of CD99-induced homotypic aggregation. In summary, JL1 is a cell surface molecule that induces homotypic adhesion mediated by the LFA-1 and ICAM-1 interaction and cytoskeletal reorganization. These findings suggest that JL1 may be an important regulator of thymocyte development and thymocyte-APC interaction.

Peptides derived from ICAM-1 and LFA-1 modulate T cell adhesion and immune function in a mixed lymphocyte culture

BACKGROUND

The counter receptors intercellular adhesion molecule (ICAM)-1 and lymphocyte function-associated antigen (LFA)-1 are lymphocyte cell surface adhesion proteins the interaction of which can provide signals for T cell activation. This binding event is important in T cell function, migration, and general immune system regulation. The ability to inhibit this interaction with monoclonal antibodies has proved to be therapeutically useful for several allograft rejection and autoimmune disease models.

METHODS

Short peptides representing counter-receptor contact domains of LFA-1 and ICAM-1 were examined for their ability to inhibit T cell adhesion and T cell function.

RESULTS

Peptides encompassing amino acids Q1-C21 and D26-K50 of ICAM-1, I237-I261 and G441-G466 of the LFA-1 alpha-subunit, and D134-Q159 of the LFA-1 beta-subunit inhibited LFA-1/ICAM-1-dependent adhesion in a phorbol-12,13-dibutyrate-induced model of tonsil T cell homotypic adhesion. This inhibition was specific to the peptide sequence and occurred without stimulation of T cell proliferation. The peptides also were effective in preventing T cell function using a one-way mixed lymphocyte reaction model for bone marrow transplantation.

CONCLUSIONS

Our data suggest that these peptides or their derivatives may be useful as therapeutic modulators of LFA-1/ICAM-1 interaction during organ transplants.

Ubiquitin-proteasome system is involved in induction of LFA-1/ICAM-1-dependent adhesion of HL-60 cells

Membrane-permeable proteasome inhibitors, lactacystin (LC) and N-acetyl-Leu-Leu-norleucinal (ALLN), but not calpain inhibitor Z-Leu-leucinal (ZLL), prevented LFA-1/ICAM-1-dependent cellular adhesion of TPA-stimulated HL-60 cells. These proteasome inhibitors affected neither the induction of monocytic differentiation nor the accompanying protein-tyrosine phosphorylation. They suppressed the increase in the avidity of LFA-1 to ICAM-1 without changing the expression of these molecules. Immunoblotting using monoclonal antibody FK-1, which reacts specifically with polyubiquitinated proteins, demonstrated that the proteasome inhibitors caused the drastic accumulation of the polyubiquitinated proteins in the membrane fraction of TPA-treated HL-60 cells. This indicates that accompanying activation of LFA-1, TPA induces the polyubiquitination of the membrane proteins, which are rapidly degraded by proteasomes. These data taken together show that proteolysis mediated by the ubiquitin-proteasome system is a prerequisite for the induction of LFA-1-dependent adhesion of HL-60 cells.

A Ca2+ binding cyclic peptide derived from the alpha-subunit of LFA-1: inhibitor of ICAM-1/LFA-1-mediated T-cell adhesion

The objective of this work is to study the conformation of cyclic peptide (1), cyclo (1, 12) Pen1-Gly2-Val3-Asp4-Val5-Asp6-Gln7-+ ++Asp8-Gly9-Glu10-Thr11-Cys12, in the presence and absence of calcium. Cyclic peptide 1 is derived from the divalent cation binding sequence of the alpha-subunit of LFA-1. This peptide has been shown to inhibit ICAM-1-LFA-1 mediated T-cell adhesion. In order to understand the structural requirements for this biologically active peptide, its solution structure was studied by nuclear magnetic resonance (NMR), circular dichroism (CD) and molecular dynamics simulations. This cyclic peptide exhibits two types of possible conformations in solution. Structure I is a loop-turn-loop type of structure, which is suitable to bind cations such as EF hand proteins. Structure II is a more extended structure with beta-hairpin bend at Asp4-Val5-Asp6-Gln7. There is evidence that alterations in the conformation of LFA-1 upon binding to divalent cations cause LFA-1 to bind to ICAM-1. To understand this mechanism, the cation-binding properties of the peptide were studied by CD and NMR. CD studies indicated that the peptide binds to calcium and forms a 1 : 1 (peptide: calcium) complex at low calcium concentrations and multiple types of complexes at higher cation concentrations. NMR studies indicated that the conformation of the peptide is not significantly altered upon binding to calcium. The peptide can inhibit T-cell adhesion by directly binding to ICAM-1 or by disrupting the interaction of the alpha and beta-subunits of LFA-1 protein. This study will help us to understand the mechanism(s) of action of this peptide and will improve our ability to design a better inhibitor of T-cell adhesion.

Acquisition of interleukin-5 secretion by human naive T-helper cells is regulated by distinct signals from both the T-cell receptor/CD3 complex and CD2

We developed a human naive T-helper (Th) cell differentiation model with anti-CD3 monoclonal antibody (MoAb), using a B-cell line as source of costimulation. In this system, we examined the contribution of the T-cell receptor (TCR)/CD3-derived signals and that of lymphocyte function-associated antigen-1 (LFA-1) and CD2 in regulating Th-cell subset differentiation. We found that lowering the level of anti-CD3 MoAb decreased tumour necrosis factor-alpha (TNF-alpha) production, while increasing secretion of the Th2 cytokines, interleukin-5 (IL-5) and interleukin-13 (IL-13). Secretion of interferon-gamma (IFN-gamma) was not influenced by the strength of the anti-CD3 signal. Under conditions where Th0 cells are generated, co-culture with anti-CD2 F(ab')2 MoAb led to the generation of Th cells that secreted 30-35% less IL-5, while not affecting secretion of IFN-gamma or granulocyte-macrophage colony-stimulating factor (GM-CSF). By contrast, anti-CD18 MoAb F(ab')2 inhibited IFN-gamma and GM-CSF levels only in the primary stimulation, but did not affect cytokine levels after restimulation. Neither anti-CD2 nor anti-CD18 F(ab')2 MoAbs could alter cytokine secretion profiles of peripheral blood-derived memory/effector Th cells. Our results indicate that acquisition of IL-5 secretion capability by Th cells is regulated mainly by signals transduced by the TCR/CD3 complex and by the presence of interleukin-4 (IL-4), while the CD2/LFA-3 pathway plays an additional, but minor, role. These regulatory CD2-derived signals, however, are distinct from those generated by the TCR/CD3 complex.

CD43 (leukosialin, sialophorin) expression is differentially regulated by retinoic acids

CD43 (leukosialin, sialophorin), a cell-surface associated mucin that is constitutively expressed at high levels on most leukocytes, is thought to be involved in cell activation and adhesion. We here provide evidence that the vitamin A metabolites all-trans and 13-cis retinoic acid up-regulate CD43 on human leukemic (HMC-1) mast cells, as determined by flow cytometry, Western blot analysis, and by semiquantitative reverse transcriptase-polymerase chain reaction. Enhanced CD43 expression was accompanied by a strong increase in anti-CD43-mediated, LFA-1-dependent homotypic aggregation of HMC-1 cells, demonstrating that newly synthesized CD43 is functionally active in transmitting signals across the plasma membrane which result in enhanced cellular adhesion. CD43 expression was also enhanced in response to retinoic acids on isolated human skin mast cells and human monocytes, but not on cells of the basophilic cell line KU-812 and promyelocytic HL-60 cells, indicating that these agents might act in a cell-type specific manner. These combined result-point to a novel aspect in the regulation of CD43. Possibly, vitamin A metabolites act directly on the CD43 gene, since putative retinoic acid response elements have been detected within its regulatory regions.

Role of neutrophils in a rat model of gastric ulcer recurrence caused by interleukin-1 beta

The production of several cytokines such as interleukin (IL)-1 in gastric mucosa is increased in subjects infected with Helicobacter pylori, a bacterium associated with ulcer recurrence. This study was performed to determine whether the administration of IL-1 beta can cause recurrence of gastric ulcers in rats. Rats with healed ulcers received an injection of IL-1 beta (0.01 to 1 microgram/kg) or vehicle alone. Some rats received an injection of antiserum to rat neutrophils at the same time as 1 microgram/kg IL-1 beta or an injection of monoclonal antibodies against adhesion molecules (anti-intercellular adhesion molecule-1, anti-CD11a, and anti-CD11b) at 0, 12, and 24 hours after the initial injection. At this dose of IL-1 beta, the numbers of neutrophils and monocytes/macrophages infiltrating the scarred mucosa were higher at 12 and 24 hours than without injection of IL-1 beta. By 48 hours, seven of the eight bealed ulcers in the group treated with 1 microgram/kg IL-1 beta had recurred, as had one of the seven healed ulcers in the group given 0.1 microgram/kg IL-1 beta. No recurrence was found in the rats treated with 0.01 microgram/kg IL-1 beta or vehicle alone. Treatment with antiserum to neutrophils or antibodies to adhesion molecules inhibited both neutrophil infiltration into the scarred mucosa and the ulcer recurrence caused by IL-1 beta. These findings suggest possible mechanisms of recurrence of human peptic ulcers.

A protein kinase C inhibitor NA-382 prolongs the life span of AH66F-bearing rats as well as inhibiting leukocyte function-associated antigen-1 (LFA-1)-dependent adhesion of the cells

Rat ascites hepatoma AH66F is a high malignant tumor line, and AH66F-bearing rats died about 10 d after tumor inoculation. When treated with a protein kinase C (PKC) inhibitor, NA-382, the life span of AH66F-bearing rats was significantly prolonged, while a potent protein kinase A inhibitor, H-89, was not effective. In the adhesion assay, the adhesive ability to the mesentery-derived mesothelial cells (M-cells) of AH66F cells from rats injected with 10 mg/kg of NA-382 was significantly decreased, while the adhesion rate of the cells from the vehicle control group and from the H-89 (10 mg/kg)-treated group was about 50%. The adhesion of AH66F cells from the vehicle control group was curtailed to one half by leukocyte function-associated antigen-1 (LFA-1) beta-chain monoclonal antibody (WT.3), but that from the NA-382 group was not further influenced by WT.3. In flow cytometric analysis using WT.3, the expression of LFA-1 beta-chain on AH66F cells from the NA-382-treated group was also partially decreased, while that from the H-89-treated group was not changed. It was confirmed in vitro that after treatment with these protein kinase inhibitors for 48 h the expression of LFA-1 beta-chain in the cells was decreased by NA-382, but not by H-89. These results suggested that the PKC inhibitor prolongs the life span of AH66F-bearing rats through inhibition of LFA-1-dependent adhesion of the cells.

CD80 (B7.1) and CD54 (intracellular adhesion molecule-1) induce target cell susceptibility to promiscuous cytotoxic T cell lysis

Overexpression of B7 and intracellular adhesion molecule-1 (ICAM-1) on syngeneic cells triggered MHC-unrestricted lysis by MHC-restricted CD8+ CTL without TCR/CD3 engagement. Both CD28/B7 and LFA-1/ICAM-1 interactions were required for MHC-nonrestricted cytotoxicity. Cytotoxicity was measured in 4-h and 16- to 18-h cytotoxicity assays. B7-ICAM-1 overexpression triggered perforin- and Fas ligand-mediated lysis, while TNF-alpha was not elicited in MHC-unrestricted cytotoxicity. These results suggest that target cells may elicit MHC-unrestricted lysis from CTL through up-regulation of membrane adherence and costimulatory receptors.

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

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

Monocyte-derived macrophages prime peripheral T cells to undergo apoptosis by cell-cell contact via ICAM-1/LFA-1-dependent mechanism

We designed the present study to clarify the mechanism of superantigen-induced apoptosis of human mature T cells and to elucidate the pivotal roles of monocyte-derived macrophages in induction of T cell apoptosis. Exposure of unfractionated human peripheral blood mononuclear cells to SEA, SEB or PHA elicited apoptosis in T cells after 5-day culture. In purified T cell preparations, SEB was unable to induce apoptosis, but was inductive when the purified T cells were cocultured with monocyte-derived macrophages adhering to plastic culture dishes. Placing the T cells in the insert wells which physically separated them from the adhering macrophages resulted in a complete loss of SEB-induced apoptosis. The addition of blocking antibodies against LFA-1, ICAM-1 and CD2 to the cocultures significantly inhibited the SEB-induced T cell apoptosis. We concluded therefore that direct contact of macrophages with T cells is critical in SEB-induced T cell apoptosis, and that adhesion molecules such as LFA-1/ICAM-1 and CD2 may be involved in the mechanism of this effect.

Focal adhesion kinase-related fakB is regulated by the integrin LFA-1 and interacts with the SH3 domain of phospholipase C gamma 1

Signal transduction through integrin molecules expressed on platelets and nonlymphoid cells involves activation of the intracellular focal adhesion kinase ppI25FAK (FAK) to phosphorylate substrate proteins on tyrosine residues. Similar mechanisms are also functional in T-lymphocytes through the beta 1-integrin VLA-4. A putative FAK-related phosphoprotein (fakB) was identified that is responsive to intracellular signals induced through ligation of antigen receptors on both T- and B-lymphocytes, and whose induced tyrosine phosphorylation is augmented by TCR costimulation through the adhesion/costimulatory receptors CD2 and CD4. In this report, fakB is shown to respond to extracellular signals through the beta 2-integrin LFA-1 in the absence of primary signals through the TCR. Protein-protein complex formation was observed involving an association between fakB, phospholipase C gamma 1 (PLC gamma 1), and the tyrosine phosphoprotein pp35-36. Evidence is provided here that fakB interacts with PLC gamma 1 through its SH3 domain. The association between fakB and PLC gamma 1 does not appear to require T-cell activation, whereas the induced tyrosine phosphorylation of the protein complex components occurs following engagement of LFA-1. These data indicate that the beta2-integrin LFA-1 expressed on T-lymphocytes stimulates a novel, FAK-related molecule that may function in the interplay between adhesion receptors and intracellular signaling enzymes responsible for downstream second messenger generation.

Mechanisms underlying neutrophil adhesion to apical epithelial membranes

Crypt abscesses allow prolonged apposition of activated neutrophils to the epithelial surface of the colon. Adhesion of neutrophils to both the vascular endothelium and basolateral epithelial membrane share common effector molecules but are distinct processes. This study aimed to define the mechanisms that effect adhesion, independent of transmigration, to the apical epithelium. HT29 (cl 19A) cells were grown to confluency and incubated with neutrophils under conditions of: (i) neutrophil stimulation with phorbol-myristate-acetate; (ii) monolayer stimulation with interferon gamma, tumour necrosis factor alpha (IFN gamma, TNF alpha); and (iii) recent epithelial cell trypsinisation. These experiments were carried out in the presence of neutralising antibodies to CD18, CD11b, LFA-1, E-selectin, P-selectin, intracellular adhesion molecule 1 (ICAM-1), and ICAM-2; a novel CD11b/CD18 antagonist, neutrophil inhibitory factor (rNIF); adenosine receptor agonists (5'N-ethycarboxamido adenosine/N6-cylopentyladenosine (NECA/CPA)) and a platelet activating factor (PAF) receptor antagonist lexipafant. Adhesion of stimulated neutrophils to resting monolayers was Mac-1, CD18 dependent and ICAM-1, ICAM-2, E-selectin, P-selectin, PAF independent. Cytokine activated monolayers exhibited higher binding of neutrophils which was inhibited by rNIF and aCD18. Recently trypsinised monolayers bound neutrophils in a CD11b/CD18 and CD18 independent manner. Adenosine agonists failed to influence neutrophil adhesion under any condition. This study shows neutrophil adhesion to apical epithelial membranes is similar to that at the epithelial basolateral membrane, though different to that seen at the vascular endothelium. These results highlight regional differences in neutrophil adhesion molecule usage.

Differential dependence of TH-0, TH-1 and TH-2 CD4+ T cells on co-stimulatory activity provided by the accessory molecule LFA-1

BACKGROUND

The adhesion molecule LFA-1 contributes to the activation response of peripheral blood human CD4+ T cells. Less is known of its contribution to stimulation of long-term CD4+ T cell lines and clones or of its potential to co-stimulate CD4+ T cells of different functional phenotype.

OBJECTIVE

This study was therefore performed to investigate co-stimulatory properties of the LFA-1 (CD11a/CD18) complex in the activation of human CD4+ T cell lines and clones of TH-0, TH-1 and TH-2 subsets.

METHODS

Co-stimulatory activity was measured by cross-linking antibodies to CD11a or CD18 with anti-CD3 antibodies to plastic and then measuring the proliferative response of CD4+ T cells to these antibodies.

RESULTS

A house duct mite allergen-specific CD4+ T cell line (TH-2) demonstrated much greater dependence on both CD11a and CD18 than a mycobacterial antigen-specific CD4+ T cell line (TH-1). Co-stimulatory activity through LFA-1 was also provided to a house dust mite-specific CD4+ T cell clone (DE-9; TH-2) but not to an influenza haemagglutinin-specific CD4+ T cell clone (HA1-7; TH-0). In contrast, soluble antibodies to CD18 inhibited proliferative responses of both DE-9 and HA1.7 to an immunogenic challenge of antigen and to stimulation by anti-CD3 antibodies. However, the allergen-specific T cells were more susceptible to inhibition. Signal transduction was also observed from the T-cell receptor to LFA-1. Ligation of the T-cell receptor modulated the phenotypic expression of LFA-1 and ICAM-1 on both HA1.7 and DE-9. Phenotypic modulation was observed as a result of both activation and the induction of non-responsiveness.

CONCLUSION

These experiments indicate that CD4+ T cells of TH-2 functional phenotype may have a greater requirement for the co-stimulatory activity of LFA-1 than CD4+ T cells of TH-0 or TH-1 phenotypes.

Activation of natural killer cells by the mAb YTA-1 that recognizes leukocyte function-associated antigen-1

The mAb YTA-1, which brightly stains CD3-CD16+ large granular lymphocytes (LGL)/natural killer (NK) cells and CD8+ T cells by immunofluorescence, is specific for leukocyte function-associated antigen (LFA)-1. Some mAbs recognizing the LFA-1 alpha chain (CD11a) or LFA-1 beta chain (CD18) inhibited the binding of YTA-1 to peripheral blood mononuclear cells. YTA-1 mAb could be chemically cross-linked to 170 and 96 kDa molecules, whose molecular weights correspond to those of LFA-1 alpha and beta respectively. YTA-1 bound to COS-7 cells co-transfected with CD11a and CD18 cDNAs, but not to untransfected cells. Reactivities of YTA-1 to K562 cells transfected with LFA-1 alpha and beta (CD11a/CD18) cDNAs and to CHO cells transfected with Mac-1 (CD11b/CD18) or p150, 95 (CD11c/CD18) cDNAs strongly suggest that YTA-1 recognizes either LFA-1 alpha or an epitope formed by a combination of LFA-1 alpha and beta. Treatment of fresh CD3-CD16+ LGL with YTA-1 augmented cytolytic activity and induced proliferation. F(ab')2 fragments of YTA-1 augmented NK cytotoxicity, indicating that the NK activating signal was transmitted through LFA-1 without involvement of Fc gamma receptor III. In contrast, the other mAbs against LFA-1 could not activate NK cells. These results collectively indicate that YTA-1 recognizes a unique epitope of LFA-1, which is involved in activation of fresh NK cells.

Cytokine modulation of interactions between cultured human renal tubular and lymphoid blast cells

We examined the in vitro cytokine modulation of the interaction of cultured renal tubular epithelial cells (hKEC) with lymphoid effector cells, including mixed lymphocyte reaction (MLR)-derived blasts, Concanavalin A (Con A)-activated blast, and lymphokine-activated killer (LAK) cells. Blast adhesion to hKEC was augmented by treatment with either interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), or MLR supernatant. The augmented adhesion statistically correlated with intercellular adhesion molecule-1 (ICAM-1) upregulation on hKEC cells by the cytokines. Blocking of surface ICAM-1 on hKEC or of lymphocyte-function antigen-1 (LFA-1) on the blasts significantly inhibited adhesion. LFA-1 blocking on LAK or MLR blasts resulted in a significant inhibition in cytotoxic function. TNF-alpha and IL-1 beta treatments on hKEC increased the susceptibility to LAK cytotoxicity, whereas IFN-gamma and MLR supernatant treatment significantly reduced this susceptibility. Absorption of IFN-gamma from the MLR supernatant partially restored the susceptibility of LAK cytotoxicity. The combined data suggest the importance of cytokine regulation of LFA-1/ICAM-1 adhesion molecule in these cellular interactions. Although IFN-gamma augments attachment between hKEC and blastic effector cells, this cytokine endows hKEC with resistance to LAK cytotoxicity. Thus, it is clear that cytokine modulation is a complicated phenomenon involving both adhesion molecule regulation-dependent and independent mechanisms.

Treatment of murine lupus with monoclonal antibodies to lymphocyte function-associated antigen-1: dose-dependent inhibition of autoantibody production and blockade of the immune response to therapy

Monoclonal antibodies (mAb) to lymphocyte function-associated antigen-1 (LFA-1) have been used successfully in vivo to inhibit immune responses and to block inflammatory reactions. To determine whether these effects of anti-LFA-1 could retard autoimmune disease, we treated lupus-prone NZB/NZW F1 (B/W) mice with a rat mAb to LFA-1 (anti-CD11a). Mice received high-dose therapy (500 micrograms twice weekly), low-dose therapy (40 micrograms thrice weekly), or phosphate-buffered saline from age 5 months to age 10 months. Treatment with high doses of anti-CD11a suppressed both the immune response to the rat mAb and the production of autoantibodies to double-stranded DNA. In contrast, treatment with low doses of anti-CD11a elicited an immune response to the rat mAb and did not suppress autoantibody production. The immunosuppressive effects of high doses of anti-CD11a were not due to target cell depletion. In fact, treatment induced a marked lymphocytosis which involved all lymphocyte subsets equally. Despite inhibiting autoantibody production, high-dose therapy had only modest effects on longevity.

Involvement of adhesion molecules in human monocyte adhesion to and transmigration through endothelial cells in vitro

Although the accumulation of monocyte-derived foam cells in the subendothelium is a key step in early atherogenesis, the mechanism responsible for monocyte adhesion to and subsequent transmigration through endothelial cells (ECs) has not been defined fully. We investigated the kinetics and the role played by adhesion molecules in the adhesion and transmigration of human monocytes using an in vitro three-dimensional model system comprising ECs cultured on collagen gels. Monocyte adhesion to untreated EC layers increased with time, reached a maximum after 3 h, and then declined. Monocyte transmigration through untreated EC layers also increased with time and reached a plateau after 3-4 h. Prestimulation of ECs with interleukin-1 beta (IL-1 beta; 25 U/ml) for 4 h enhanced monocyte adhesion (40.7 +/- 1.4%) and transmigration (37.9 +/- 1.6%) significantly compared with the value for untreated EC layers. In unstimulated EC layers, anti-leukocyte function-associated antigen-1 (LFA-1) plus anti-intercellular adhesion molecule-1 (ICAM-1) monoclonal antibodies (mAbs) inhibited monocyte adhesion and transmigration significantly by 19% and 20%, respectively, whereas anti-very late antigen-4 (VLA-4) plus anti-vascular cell adhesion molecule-1 (VCAM-1) mAbs did not. In IL-1 beta-stimulated EC layers, anti-LFA 1 plus anti-ICAM-1 mAbs inhibited the adhesion and transmigration by 32% and 30%, respectively and anti-VLA-4 plus anti-VCAM-1 mAbs did so by 18% and 27%, respectively. These results suggest that the monocyte-EC interaction in unstimulated ECs is mediated, in part, by the LFA-1-ICAM-1 pathway and in IL-1 beta-stimulated ECs, in part, by both LFA-1-ICAM-1 and VLA-4-VCAM-1 pathways.

Differential, LFA-1-sensitive effects of antibodies to nectadrin, the heat-stable antigen, on B lymphoblast aggregation and signal transduction

Nectadrin, the heat-stable antigen (HSA), is a highly glycosylated GPI-linked glycoprotein that can undergo homophilic and heterophilic binding. In the present work we have examined short-term effects of nectadrin antibodies on splenic B lymphoblast aggregation and signal transduction. Monoclonal antibody 79 inhibited cell aggregation and induced an intracellular Ca++ signal in the absence of cross-linking. Both these effects were perturbed in the presence of LFA-1 antibodies. Nectadrin antibody M1/69 and polyclonal nectadrin antibodies stimulated cell aggregation, did not induce a Ca++ signal, and their effects were functionally independent of LFA-1. These results suggest that nectadrin may concomitantly mediate primary and activate secondary adhesion mechanisms whereby each of these processes may be related to a different signal transduction pathway.

Intercellular adhesion molecule-1 on cultured human melanoma cells: influence of cytokines

Adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) and its counter-receptor, lymphocyte function associated antigen-1 (LFA-1), play very important roles in immune responses. In this study, the effects of cytokines on cultured human melanoma cells (MMG2) were examined, especially focussing on the expression of ICAM-1 on MMG2 and lymphocyte adhesion to MMG2. Both the expression of ICAM-1 and HLA-DR on MMG2 increased after treatment with IFN-gamma. ICAM-1 expression began to increase earlier than HLA-DR expression. TNF-alpha and IL-1 beta also increased the expression of ICAM-1 on MMG2. However, these cytokines did not increase the expression of HLA-DR. IFN-gamma had a dose dependent effect on lymphocyte adhesion to MMG2. Pretreatment of IFN-gamma treated MMG2 with 84H10 (anti-ICAM-1 antibody) or pretreatment of lymphocytes with either SPV-L7 (anti-LFA-1 alpha antibody) or IOT10 (anti-LFA-1 beta antibody) inhibited the lymphocyte adhesion to MMG2. These results suggest that ICAM-1 molecules induced on melanoma cells by IFN-gamma can interact with LFA-1 molecules on lymphocytes.

Adhesion of Subsets of Human Blood Mononuclear Cells to Endothelial Cells In Vitro, as Quantified by Flow Cytometry

Binding of leucocytes to endothelial cells (EC) is essential as an initial step in inflammatory responses. We present a rapid, non-radioactive method to measure adhesion of human lymphoid cells to EC using flow cytometry. Freshly isolated peripheral blood mononuclear cells (PBMC) were allowed to adhere to EC grown in 24-well plates. Non-adhering cells were removed, after which adhering cells and EC were dissociated using trypsin/EDTA. These samples were subsequently analysed by flow cytometry, using scatter properties to distinguish between adhering cells and EC. The ratio of the number of adhering leucocytes and EC was calculated to quantify adhesion. Results of the flow cytometric adhesion assay were comparable to those obtained with a conventional adhesion assay using chromium-labelled cells. We additionally show that by using the flow cytometric adhesion assay, adhesion of lymphocytes and monocytes present within the adhering PBMC can be quantified simultaneously. As a model, the contribution of LFA-1 (CD11a/CD18) and ICAM-1 (CD54) in adhesion of PBMC to EC was studied. It was found that adhesion of lymphocytes and monocytes is regulated differently by phorbol ester and that the relative contribution of LFA-1 and ICAM-1 differs for both cell types.

Human immunodeficiency virus-infected monocyte-derived macrophages express surface gp120 and fuse with CD4 lymphoid cells in vitro: a possible mechanism of T lymphocyte depletion in vivo

Monocyte-derived macrophages (MDM) infected in vitro with a macrophage-tropic strain of human immunodeficiency virus (HIV) fused with uninfected, CD4-expressing T lymphoblastoid cells, but not with a subclone of these cells lacking surface CD4. Infected MDM also fused with uninfected autologous and heterologous MDM. Recombinant soluble CD4 protein (rsCD4) (10 micrograms/ml) and full-length recombinant glycosylated gp120 (20 micrograms/ml) each inhibited fusion by 94-99%; the inhibition was dose-dependent. The N-terminal portion of gp120 did not inhibit syncytium formation. Fusion was also inhibited by a monoclonal antibody to an epitope which binds gp120 (S3.5), but not by antibody to an epitope not involved in gp120 binding (OKT4). HIV-infected MDM specifically bound fluorescein-conjugated rsCD4, and virus could be visualized budding from the surface of these cells. HIV-infected MDM express viral gp120 on their surface and fuse with CD4-bearing cells in a fashion similar to lymphoid cells. Macrophages may contribute to CD4 lymphocyte depletion in vivo by this fusion mechanism.

Late treatment with anti-LFA-1 (CD11a) antibody prevents cerebral malaria in a mouse model

CBA/Ca mice injected with Plasmodium berghei develop cerebral malaria (CM) characterized by ataxia and progressive paralysis leading to death 7-9 days after experimental infection. The development of cerebral symptoms is a function of the immune response in susceptible strains, and depends on cell-cell interactions involving T helper cells and mononuclear phagocytes. Here we ask whether antibodies to cell adhesion receptors of the immune system can influence the development of CM in this mouse model. When administrated on day 6 after infection, antibody to the leukocyte integrin leukocyte function-antigen-1 (LFA-1) but not antibodies to MAC-1, LECAM-1 (the MEL-14 antigen), alpha 4 integrin or ICAM-1 dramatically reduced the incidence of CM, leading to survival of most mice until the later onset of anemia. Anti-LFA-1 treatment did not result in a substantial decrease in the monocyte accumulation observed in cerebral vessels of susceptible mice. Its efficacy may be related to the broader roles of LFA-1 in cell-cell interactions important in the later pathogenic stages of the immune response to the parasite. Perturbation of immune cell function through interference with cell adhesion mechanisms may offer an important therapeutic tool in acute, life-threatening immune-mediated disorders.

Characterization of ICAM-2 and evidence for a third counter-receptor for LFA-1

In an endeavor to further characterize human intercellular adhesion molecule-2 (ICAM-2), two murine monoclonal antibodies (mAb) were generated to ICAM-2 transfected COS cells, and designated CBR-IC2/1 and CBR-IC2/2. Immunoprecipitated, reduced ICAM-2 migrated as a broad band of Mr 60,000 in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Treatment with N-glycanase revealed a peptide backbone of Mr 31,000, consistent with the size predicted from the cDNA. ICAM-2 had a broad distribution on hematopoietic cell lines and little expression on other cell lines, the sole exception being cultured endothelial cells which possess high levels of ICAM-2. Resting lymphocytes and monocytes expressed ICAM-2, while neutrophils did not. Staining of tissue sections with anti-ICAM-2 mAb confirmed their strong reactivity to vascular endothelium, but demonstrated a lack of ICAM-2 expression on other tissues. Small clusters of ICAM-2 positive cells were, however, seen in germinal centers. In contrast to ICAM-1 there was little or no induction of ICAM-2 expression on lymphocytes or cultured endothelium upon stimulation with inflammatory mediators. One of the two mAb, CBR-IC2/2, was found to totally inhibit binding of ICAM-2+ COS cells to purified lymphocyte function-associated antigen-1 (LFA-1). Using this mAb, LFA-1-dependent binding to both stimulated and unstimulated endothelium was found to be totally accounted for by ICAM-1 and ICAM-2. Homotypic aggregation of an Epstein-Barr virus-transformed B cell line, JY, was found to be solely ICAM-1 and ICAM-2-dependent, while in the case of the T cell lymphoma cell line, SKW3, anti- ICAM-2 mAb in conjunction with anti-ICAM-1 mAb could not inhibit the LFA-1-dependent aggregation. This suggests an additional LFA-1 ligand exists. Using a cell binding assay to purified LFA-1 in conjunction with anti-ICAM-1 and anti-ICAM-2 mAb, we have demonstrated that this putative third ligand for LFA-1 exists on SKW3 and other cell lines.