Babesia bovis: expression of adhesion molecules in bovine umbilical endothelial cells stimulated with plasma from infected cattle / Babesia bovis: expressão de moléculas de adesão em células endoteliais de cordão umbilical de bovinos estimuladas com plasma de bovinos infectados

Ten male, 12-month-old Jersey with intact spleens, serologically and parasitologically free from Babesia were housed individually in an arthropod-free isolation system from birth and throughout entire experiment. The animals were randomly divided into two groups. Five animals (group A) were intravenously inoculated with 6.6 X10(7) red blood cells parasitized with pathogenic sample of Babesia bovis (passage 7 BboUFV-1), for the subsequent "ex vivo" determination of the expression of adhesion molecules. Five non-inoculated animals (group B) were used as the negative control. The expression of the adhesion molecules ICAM-1, VCAM, PECAM-1 E-selectin and thrombospondin (TSP) was measured in bovine umbilical vein endothelial cells (BUVECs). The endothelial cells stimulated with a pool of plasma from animals infected with the BboUFV-1 7th passage sample had a much more intense immunostaining of ICAM-1, VCAM, PECAM-1 E-selectin and TSP, compared to the cells which did not received the stimulus. The results suggest that proinflammatory cytokines released in the acute phase of babesiosis may be involved in the expression of adhesion molecules thereby implicating them in the pathophysiology of babesiosis caused by B. bovis.

Dez bezerros machos, da raça Jersey, com 1 ano de idade com baços "in situ", sorológica e parasitologicamente livres de Babesia, foram mantidos em baias individuais no isolamento a prova de artrópodes do Depto de Veterinária desde o nascimento e ao longo de toda a experimentação. Os animais foram divididos aleatoriamente em dois grupos. Cinco animais (grupo A) foram inoculados por via intravenosa com 6,6 x10(7) hemácias parasitados com amostra patogênica de Babesia bovis (BboUFV - 1 7ª passagem) , para a determinação subseqüente "ex vivo" da expressão de moléculas de adesão . Cinco animais não inoculados (Grupo B ) foram utilizados como controlo negativo . A expressão de moléculas de adesão ICAM - 1, VCAM , PECAM - 1, E - selectina e trombospondina ( TSP ) foi medida em células endoteliais da veia umbilical de bovinos (BUVECs). As células endoteliais estimuladas com um pool de plasma proveniente de animais infectados com BboUFV - 1 7ª passagem tinham uma imunocoloração muito mais intensa de ICAM - 1 , VCAM , PECAM - 1 de E - selectina e de TSP , em comparação com as células que não receberam o estímulo . Os resultados sugerem que as citocinas pró-inflamatórias liberados na fase aguda da babesiose pode estar envolvida na expressão de moléculas de adesão , implicando , assim, elas na fisiopatologia da babesiose causada por B. bovis.

E2F1 renders prostate cancer cell resistant to ICAM-1 mediated antitumor immunity by NF-κB modulation.

BACKGROUND: E2F1 is the gatekeeper of the cell cycle controlling an analogous balance between proliferation and cell death. E2F1 expression is elevated in advanced prostate cancer. However, it is still unclear that the roles and mechanisms of E2F1 on prostate cancers. METHODS: Targeted knockdown by interferon RNA was applied on two prostate cancer and Hela cell lines to examine the inverse correlation expression of E2F1 and ICAM-1. ICAM-1 promoter reporter and ChIP assays were used for analysis of the molecular basis of transcriptional regulation of E2F1 on ICAM-1. Co-IP assays were employed for testing the protein interaction between E2F1 and NF-κB. Tumor xenograft mice model with E2F1 and ICAM-1-knockdown prostate cancer cells were used to investigate the effects of E2F1 and ICAM-1 on antitumor immunity. RESULTS: E2F1 knockdown by a specific short hairpin RNA increased gene transcription and protein expression of ICAM-1. By using wild type and a series of mutant ICAM-1 promoter luciferase constructs, the NF-κB binding sites were found to be important for E2F1 regulation of ICAM-1 promoter. Targeted knockdown of E2F1 did not affect expression and phosphorylation of NF-κB and IκBα, but facilitated NF-κB binding to the ICAM-1 promoter, subsequently induced ICAM-1 transcription and production in prostate carcinoma cells. Furthermore, knockdown of E2F1 inhibited tumor growth of prostate cancer in vivo through increasing the susceptibility of tumor cells to ICAM-1-mediated anti-tumor immunity including enhancement of monocyte adhesion, leucocytes infiltration, as well as cytotoxicity against tumor cells. CONCLUSIONS: E2F1 knockdown inhibited prostate tumor growth in vitro and in vivo through sensitizing tumor cells to ICAM-1 mediated anti-immunity by NF-κB modulation, highlighting the potential of E2F1 as a therapeutic target.

Transfected HEK293 cells expressing functional recombinant intercellular adhesion molecule 1 (ICAM-1)--a receptor associated with severe Plasmodium falciparum malaria.

Intercellular adhesion molecule 1 (ICAM-1) is a membrane-bound glycoprotein expressed on endothelial cells and cells of the immune system. Human ICAM-1 mediates adhesion and migration of leucocytes, and is implicated in inflammatory pathologies, autoimmune diseases and in many cancer processes. Additionally, ICAM-1 acts as receptor for pathogens like human rhinovirus and Plasmodium falciparum malaria parasites. A group of related P. falciparum erythrocyte membrane protein 1 (PfEMP1) domains, the DBLß, mediates ICAM-1 binding of P. falciparum-infected erythrocytes. This ICAM­1-binding phenotype has been suggested to be involved in the development of cerebral malaria. However, more studies identifying cross-reactive antibody and ICAM-1-binding epitopes and the establishment of a clinical link between DBLß expression and e.g. cerebral malaria are needed before the DBLß domains can be put forward as vaccine candidates and go into clinical trials. Such studies require availability of functional recombinant ICAM-1 in large quantities. In this study, we compared recombinant ICAM-1 expressed in HEK293 and COS-7 cells with mouse myeloma NS0 ICAM-1 purchased from a commercial vendor in terms of protein purity, yield, fold, ability to bind DBLß, and relative cost. We present a HEK293 cell-based, high-yield expression and purification scheme for producing inexpensive, functional ICAM­1. ICAM-1 expressed in HEK293 is applicable to malaria research and can also be useful in other research fields.

Surface engineering of microparticles by novel protein transfer for targeted antigen/drug delivery.

Biodegradable microparticles can function as an adjuvant by targeting antigens to professional antigen presenting cells such as dendritic cells and macrophages. To enhance targeting of microparticles, we have developed a novel method of attaching immunostimulatory molecules such as B7-1 to the surface of albumin microparticles utilizing the glycosylphosphatidyl inositol (GPI) anchor. GPI-B7-1 attaches to the surface of albumin microparticles in a protein transfer mediated process and is functionally active. This protein transfer was dependent on the concentration of the GPI-anchored protein, and independent of temperature and incubation time. Results show that the binding of the GPI-anchored protein is specifically occurring through an interaction between the GPI-anchor and the albumin microparticle surface. Stability studies indicate that the GPI-anchored protein can remain attached to the surface of the microparticle up to 7 days, with storage at 4 degrees C providing the optimal stability. Finally, we were able to simultaneously attach two different GPI-anchored proteins, GPI-B7-1 and GPI-ICAM-1, to the microparticles, demonstrating the capability of attaching more than one GPI-anchored protein to the microparticle surface. This novel method of attaching proteins to the surface of microparticles has potential implications in using microparticles as an antigen delivery device in vaccines as well as in targeted drug delivery.

Cross-linking of CD54 on Burkitt lymphoma cell line Raji and Ramos induces FasL expression by reactive oxygen species and apoptosis of adjacent cells in Fas/FasL interaction.

CD54 is a cell surface adhesive glycoprotein, which is expressed in most cells. Interaction between CD54 and its ligands is involved in several cellular events including activation, proliferation, and cell death and also cell-to-cell adhesion. In the present study, we found that cross-linking of CD54 on Burkitt lymphoma cell lines, Raji and Ramos, induced apoptosis. We investigated that cross-linking of CD54 on Raji and Ramos using immobilized anti-CD54 mAb (clone 6.5B5) leads to apoptosis. CD54-induced apoptosis took place in association with an increase of intracellular reactive oxygen species (ROS) and a loss of the mitochondrial membrane potential and also the activation of caspases 3 and 9, resulting in the degradation of the proteolytic poly (ADP-ribose) polymerase. Pretreatment of each N-acetyl cystein and N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (a broad caspase inhibitor) blocked apoptosis. Cross-linking of CD54 immediately induced expression of fasL, which was inhibited by pretreatment of N-acetyl cystein. NOK-1 (antagonistic anti-fasL), ZB4 (antagonistic anti-fas), and N-benzyloxycarbonyl-Ile-Glu-Thr-Asp-fluoromethylketon (caspase 8 inhibitor) effectively rescued cells from apoptosis via adjacent fas-fasL interaction but did not block ROS generation. Taken together, it is concluded that engagement of CD54 on B lymphoma cell lines by anti-CD54 mAb may trigger fasL expression through ROS generation and may subsequently induce apoptosis in adjacent fas-fasL interaction.

Structures of the alpha L I domain and its complex with ICAM-1 reveal a shape-shifting pathway for integrin regulation.

The structure of the I domain of integrin alpha L beta 2 bound to the Ig superfamily ligand ICAM-1 reveals the open ligand binding conformation and the first example of an integrin-IgSF interface. The I domain Mg2+ directly coordinates Glu-34 of ICAM-1, and a dramatic swing of I domain residue Glu-241 enables a critical salt bridge. Liganded and unliganded structures for both high- and intermediate-affinity mutant I domains reveal that ligand binding can induce conformational change in the alpha L I domain and that allosteric signals can convert the closed conformation to intermediate or open conformations without ligand binding. Pulling down on the C-terminal alpha 7 helix with introduced disulfide bonds ratchets the beta 6-alpha 7 loop into three different positions in the closed, intermediate, and open conformations, with a progressive increase in affinity.

Changes in the immunologic phenotype of human malignant glioma cells after passaging in vitro.

Although immunotherapeutic strategies against glioblastomas have been promising both in vitro and in animal models, similar successes have not been realized in human clinical trials. One reason may be that immunotherapeutic strategies are based on prior studies that primarily have used human glioblastoma cell lines passaged in vitro, which may not accurately reflect the in vivo properties of glioblastoma cells. In this report, we used flow cytometry to quantify the expression of immunological cell surface molecules on human glioblastomas directly ex vivo (prior to any in vitro culturing) and after varying passages in vitro. Furthermore, we used ELISA to quantitate cytokine secretion after various passages in vitro. We demonstrate that in vitro culturing of established cell lines led to increases in the cell surface expression of MHC class I and ICAM-1 and secretion of IL-6 and TGF-beta(2). Furthermore, there were significant changes in the expression of MHC class I, MHC class II, B7-2, ICAM-1, and FasL when comparing ex vivo tumor cells to those after a single passage in vitro. After passaging once in vitro, there were also significant changes in the secretion of TGF-beta(2) and IL-10. This report indicates that in vitro culturing leads to significant changes in both cell surface molecules and secreted cytokines, which are known to affect the ability of immune cells to initiate an anti-tumor immune response. These changes in the immunological phenotype of glioblastomas after in vitro culturing may in part explain the limited success of immunotherapeutic strategies against glioblastomas in human clinical trials.

Expression of adhesion molecules in synovia of patients with treatment-resistant lyme arthritis.

The expression of adhesion molecules in synovium in patients with Lyme arthritis is surely critical in the control of Borrelia burgdorferi infection but may also have pathologic consequences. For example, molecular mimicry between a dominant T-cell epitope of B. burgdorferi outer surface protein A and an adhesion molecule, human lymphocyte function-associated antigen 1 (LFA-1), has been implicated in the pathogenesis of treatment-resistant Lyme arthritis. Using immunohistochemical methods, we examined synovial samples for expression of adhesion molecules in 29 patients with treatment-resistant Lyme arthritis and in 15 patients with rheumatoid arthritis or chronic inflammatory monoarthritis. In Lyme arthritis synovia, endothelial cells showed intense expression of P-selectin and vascular adhesion protein-1 (VAP-1). Expression of LFA-1 was also intense on infiltrating cells, particularly in lymphoid aggregates, and intercellular adhesion molecule-1 (ICAM-1) was markedly expressed on synovial lining and endothelial and infiltrating cells. Moderate expression of vascular cell adhesion molecule-1 (VCAM-1) was seen on synovial lining and endothelial cells, and mild expression of its ligand, very late antigen-4, was apparent in perivascular lymphoid infiltrates. Except for lesser expression of VCAM-1 in Lyme synovia, the levels of expression of these adhesion molecules were similar in the three patient groups. We conclude that certain adhesion molecules, including ICAM-1 and LFA-1, are expressed intensely in the synovia of patients with Lyme arthritis. Upregulation of LFA-1 on lymphocytes in this lesion may be critical in the pathogenesis of treatment-resistant Lyme arthritis.

In situ expression of intercellular adhesion molecule-1 (ICAM-1) mRNA in calves with acute Pasteurella haemolytica pneumonia.

The in situ expression of intercellular adhesion molecule-1 (ICAM-1) mRNA in normal and pneumonic lung tissues of Holstein calves with bovine leukocyte adhesion deficiency (BLAD) was compared with that of age-matched non-BLAD Holstein calves by in situ hybridization. Twenty-four Holstein calves (both BLAD and non-BLAD) were randomly assigned to one of two experimental groups and inoculated intrabronchially with Pasteurella haemolytica or pyrogen-free saline. Lung tissues were collected and fixed in 10% neutral formalin at 2 or 4 hours postinoculation (PI). The expression and distribution of ICAM-1 mRNA in the different cell types of the lung tissue was detected by in situ hybridization with a 307-base-pair bovine ICAM-1 riboprobe. In lungs of both non-BLAD and BLAD saline-inoculated calves, ICAM-1 expression was present in epithelial cells but occurred in <30% of cells in bronchi, bronchioles, and alveoli. ICAM-1 expression in vascular endothelial cells was present in <30% of cells in pulmonary arteries and veins. The expression of ICAM-1 was significantly greater (>60% of cells) in bronchiolar and alveolar epithelial cells and pulmonary endothelial cells of arteries and veins in both BLAD and non-BLAD calves inoculated with P. haemolytica. Bronchiolar epithelium had the highest intensity of mRNA expression and highest percentage of cells that were stained, whereas bronchial epithelium had the lowest intensity and percentage of cells stained. Most alveolar macrophages and neutrophils in infected lungs also expressed ICAM-1. ICAM-1 expression was generally increased in infected BLAD calves at 2 hours PI as compared with non-BLAD calves but not at 4 hours PI. The increased expression of ICAM-1 during acute P. haemolytica pneumonia in calves suggests that ICAM-1 is upregulated and may play a role in leukocyte infiltration. The extent of ICAM-1 expression in P. haemolytica-inoculated calves with BLAD was initially enhanced but otherwise similar to that in non-BLAD calves.

Jejuna of patients with insulin-dependent diabetes mellitus (IDDM) show signs of immune activation.

The roles of enteric viruses and food antigens as possible triggers in human insulin-dependent diabetes mellitus and the evidence that mucosal-associated homing receptors are important in both human and experimental diabetes prompted us to undertake an immunohistochemical study of intestinal specimens from patients with IDDM. We studied jejunal morphology and immunohistochemistry in 26 patients with IDDM, 13 of whom had the HLA-DQB1*0201 gene and therefore a higher risk of coeliac disease. The findings were compared with those in specimens from age-matched controls. Villous structure and the density of the intraepithelial lymphocytes were normal in every biopsy specimen. The extent of positivity with anti-DR and -DP antibodies in the villous epithelium was significantly greater in the specimens from patients than in those from controls (P = 0.0002 in both comparisons). The crypts were also more positive: for DR P = 0.0001, and for DP P = 0.002. The densities of T cells, CD4+, CD8+, and T cell receptor alpha/beta+ and gamma/delta+ cells in the epithelium and lamina propria were similar in patients and controls, but the patients had significantly more alpha 4/beta 7 integrin+ cells in the lamina propria (P = 0.006). No difference was seen between HLA-DQB1*0201-positive and -negative patients. These findings reflect a stage of inflammation in the structurally normal intestines of patients with IDDM and suggest secretion of inflammatory Th1-type cytokines in the intestine.

Novel phenotype associated with in vivo activated CTL precursors.

A previously undefined phenotype of CD8(+) cells that appears to represent in vivo activated CTL precursors (CTLP*) has been identified in the spleens of C57Bl/6 mice responding to a P815 tumor allograft. This population was first evident by the transient expression of very high levels of CD28 and CD44 on day 5 of the allograft response and reached maximal levels on days 7 and 8 before declining on day 9. A transient increase in CD69 expression was also observed on these cells on day 5. In contrast, CTL effectors (CTLE), identified by their CD8(+)CD44(hi)CD62LloCD45RBlo phenotype, were not appreciably detected in the spleen until day 8 and reached maximal levels on day 10. Further characterization of CTLP* on day 7 revealed that they represented blasting cells by increased light scatter and also expressed very high levels of CD54 but not CD122, CD152, or CD154. In addition, the cells had already up-regulated CD49d, asialo GM1, CD11a, and CD95L, and down-regulated their expression of CD62L. A small percentage of these cells also expressed CD25. Day 7 CTLP* sorted on the basis of their CD44(xhi) and CD54(xhi) phenotype did not exhibit cytolytic activity in a standard chromium release assay but became cytotoxic when they were cultured in the presence of exogenous murine IL-2 for 5 days. Granzyme B activity, however, was detected in CTLP* on day 7 at levels equivalent to CTLE on day 10. In order to establish a potential precursor relationship between CTLP* and CTLE, mice were treated with various doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a chemical that has been shown to dose-dependently suppress the in vivo generation of CTLE to P815 tumor cells by altering an early stage of CTLP activation. Results indicated that CTLP* were suppressed by TCDD on day 7 to the same degree that CTLE were suppressed on day 10. Importantly, for controls and for all doses of TCDD, there were approximately 12.5 CTLE on day 10 for every CTLP* detected on day 7. These results suggested that TCDD acted identically across all doses to inhibit the early stages of activation of CTLP but did not affect the final stages of differentiation and expansion to CTLE. This interpretation supports the previous observation that TCDD exposure had to occur within the first 3 days of the allograft response in order to induce suppression of CTLE activity. Taken together, these results support the conclusion that in vivo activated CTLP can be identified by their unique expression of very high levels of CD44, CD28, and/or CD54 prior to their full maturation and clonal expansion to functional CTLE.

Proteolytic cleavage of ICAM-1 by human neutrophil elastase.

Human leukocyte elastase (HLE) participates in tissue destruction in a number of inflammatory disorders, including rheumatoid arthritis and cystic fibrosis. Since HLE has been shown to bind to Mac-1, and ICAM-1 plays a key role during the recruitment and the activation of leukocytes at inflamed sites, we investigated the capacity of HLE to cleave ICAM-1. Flow-cytometric analyses showed a dose-dependent cleavage of ICAM-1 by HLE on different human cell lines. The cleavage was completely inhibited by alpha1-antitrypsin, a natural HLE protease inhibitor. The ability of HLE to degrade ICAM-1 was further confirmed by electrophoretic analysis using a soluble form of ICAM-1 (D1-D5). Enzymatic removal of N-linked glycosylation did not significantly modulate ICAM-1 cleavage by HLE, while removal of sialic acid residues partially reduced the sensitivity of ICAM-1 to HLE. We further showed that sputum of cystic fibrosis patients contains high levels of HLE activity capable of cleavage of cell surface ICAM-1. The cleavage induced by incubation of cells with the sputum sample was totally inhibited by alpha1-antitrypsin and the specific peptidic HLE inhibitor N-methoxysuccinyl-Ala-Ala-Pro-Val-chloromethylketone. Moreover, the cleavage of ICAM-1 was concomitant to that of CD4 at the surface of the same cell, at the same amplitude, and at all HLE concentrations. The capacity of HLE to modulate the expression of ICAM-1 on the surface of leukocytes by proteolytic cleavage brings support to the hypothesis that overproduction of HLE can cause severe immunologic lung disorders by affecting intercellular adhesion.

A comparison of flow cytometry and immunohistochemistry in human colorectal cancers.

In human colorectal cancer it has been reported that some tumours lack the HLA-ABC antigens. This has been interpreted as reflecting tumour escape from the immune system. Earlier data have been obtained by immunohistochemistry. In this study, we compared the expression of HLA-ABC, HLA-DR, CD80 (B7-1) and CD54 (ICAM-1) in 20 tumours using both a conventional immunohistochemistry two-layer technique and multiparameter flow cytometry, gating on an epithelial cell marker. Colorectal cancer tissue used in flow cytometry was dissociated with collagenase, deoxyribonuclease and hyaluronidase. The intensity of expression of HLA-ABC, HLA-DR and CD80 was unaffected by the enzymes, but CD54 was decreased by 30%. The reproducibility of flow cytometry was good. Microscopy of sections revealed that about 5% of each tumour sample consisted of normal epithelium, but even after correction for this, flow cytometry was superior to immunohistochemistry in 33 out of 80 cases, and showed that tumours described as HLA-ABC negative by immunohistochemistry were in fact weakly positive for HLA-ABC. We conclude that flow cytometry and immunohistochemistry are complementary, and that flow cytometry is superior to immunohistochemistry for detecting antigens/epitopes present in low amounts.

Direct antigen presentation through binding of donor intercellular adhesion molecule-1 to recipient lymphocyte function-associated antigen-1 molecules in xenograft rejection.

Cellular interactions that lead to graft rejection were examined in a rat-to-mouse xenogeneic combination using species-specific monoclonal antibodies (mAbs) against donor and recipient intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-1 (LFA-1) molecules, respectively. Although both mAbs displayed moderate blocking activity in an in vitro mixed lymphocyte response assay, strong suppression was observed when anti-donor (rat) ICAM-1 mAb was combined with anti-recipient (mouse) LFA-1 mAb. Likewise, significant prolongation of islet xenograft survival was observed with these mAbs. Thus, 0.05 mg of anti-mouse LFA-1 mAb and anti-rat ICAM-1 mAb given on days 0 and 1 produced significant prolongation of graft survival over the control (51+/-20 days vs. 10+/-3 days, P<0.0001), but not when anti-mouse ICAM-1 mAb was combined with anti-mouse LFA-1 mAb (13+/-3 days). In this species combination, mouse T cells were able to proliferate in the presence of rat antigen-presenting cells (APCs) in a cell number-dependent manner, but not in the presence of mouse APCs. The binding assay showed that LFA-1 molecules on mouse T cells can bind immobilized rat ICAM-1 molecules. These results suggest that rat ICAM-1 molecules on APCs can interact with mouse LFA-1 molecules on T cells across a species barrier and that this binding generates the consequent immune responses leading to rejection. mAb treatment against these adhesion molecules of recipient as well as donor is crucial for preventing rejection in a xenogeneic transplantation model.

Identification of the binding site in intercellular adhesion molecule 1 for its receptor, leukocyte function-associated antigen 1.

Intercellular adhesion molecule 1 (ICAM-1, CD54) is a member of the Ig superfamily and is a counterreceptor for the beta 2 integrins: lymphocyte function-associated antigen 1 (LFA-1, CD11a/CD18), complement receptor 1 (MAC-1, CD11b/CD18), and p150,95 (CD11c/CD18). Binding of ICAM-1 to these receptors mediates leukocyte-adhesive functions in immune and inflammatory responses. In this report, we describe a cell-free assay using purified recombinant extracellular domains of LFA-1 and a dimeric immunoadhesin of ICAM-1. The binding of recombinant secreted LFA-1 to ICAM-1 is divalent cation dependent (Mg2+ and Mn2+ promote binding) and sensitive to inhibition by antibodies that block LFA-1-mediated cell adhesion, indicating that its conformation mimics that of LFA-1 on activated lymphocytes. We describe six novel anti-ICAM-1 monoclonal antibodies, two of which are function blocking. Thirty-five point mutants of the ICAM-1 immunoadhesin were generated and residues important for binding of monoclonal antibodies and purified LFA-1 were identified. Nineteen of these mutants bind recombinant LFA-1 equivalently to wild type. Sixteen mutants show a 66-2500-fold decrease in LFA-1 binding yet, with few exceptions, retain binding to the monoclonal antibodies. These mutants, along with modeling studies, define the LFA-1 binding site on ICAM-1 as residues E34, K39, M64, Y66, N68, and Q73, that are predicted to lie on the CDFG beta-sheet of the Ig fold. The mutant G32A also abrogates binding to LFA-1 while retaining binding to all of the antibodies, possibly indicating a direct interaction of this residue with LFA-1. These data have allowed the generation of a highly refined model of the LFA-1 binding site of ICAM-1.

Soluble ICAM-1 (sICAM-1) provokes PMN elastase release.

Elevated levels of soluble intercellular adhesion molecule-1 have been shown predictive of post-injury multiple organ failure. We hypothesized that sICAM-1 augments distant organ injury via its affect on the PMN and; thus, have examined neutrophil elastase and superoxide production in response to sICAM-1. To obtain soluble ICAM-1, Chinese Hamster Ovarian (CHO) cells were transfected with human ICAM-1 (cDNA vector CD1.8), lysed and centrifuged at 150,000g for 1 hr; supernatant was passed over an ICAM-1 affinity gradient, eluted with 0.1 mM glycine x HCl, and concentrated using an Amicon Spin-X filter. PMNs were incubated for 1 hr with sICAM-1 at 37 degrees C. Quiescent and PMA-activated PMNs served as negative and positive controls respectively. Elastase activity was measured by the cleavage of methoxy-succinyl-alalyl-alalyl-prolyl-valyl-p-nitroanilide. Superoxide production was determined by superoxide dismutase inhibitive ferricytochrome C reduction over a 5-60 min incubation. PMN incubation with sICAM-1 provoked marked increase in elastase release 10.43 +/- 2.90 (10(-6) U/hr) compared to control 1.64 +/- 0.57, and was equivalent to PMA-activated PMN elastase release 11.60 +/- 1.50 (10(-6) U/hr). In contrast, sICAM-1 alone did not promote spontaneous PMN superoxide production beyond buffer treated PMNs (0.25 +/- 0.09 nmole/2.5 x 10(5) PMN/min). In sum, sICAM-1 stimulates PMN elastase release in vitro. Clinically, this may represent a mechanism by which sICAM-1 participates in the genesis of post-injury multiple organ failure.

Competition between lymphocyte function-associated antigen 1 (CD11a/CD18) and Mac-1 (CD11b/CD18) for binding to intercellular adhesion molecule-1 (CD54).

Both human integrin receptors Mac-1 (CD11b/CD18,CR3)and lymphocyte function-associated antigen (LFA)-1 (CD11a/CD18) have been demonstrated to bind human intercellular adhesion molecule-1 (ICAM-1) (CD54). Here we show that LFA-1 and Mac-1 can bind to ICAM-1 in the mouse as well. Interestingly, we observed that binding of murine LFA-1 dominates over Mac-1 for binding to ICAM-1. Using three different murine macrophage cell lines that express distinct levels of LFA-1 and Mac-1 on their cell surface, we could only detect Mac-1-dependent adhesion to ICAM-1 when little or no LFA-1 is expressed on the cell surface. When LFA-1 and Mac-1 are expressed at similar levels, the LFA-1/ICAM-1 interaction dominates over Mac-1/ICAM-1 interaction, indicating that there is a competition of LFA-1 and Mac-1 for ICAM-1 binding.

Immunopathogenesis of vernal keratoconjunctivitis.

We have analyzed the in situ distribution of immune cells in the conjunctival biopsy specimens obtained from patients with active vernal keratoconjunctivitis (VKC). We used immunohistochemical techniques and a panel of monoclonal and polyclonal antibodies. Our data point to a complex immunopathogenesis of the disease. Distinct components involved in IgE-mediated immune mechanisms, as well as humoral and cell mediated immune mechanisms were detected in the conjunctival tissues. In addition, we investigated the presence and distribution of adhesion molecules. In the normal conjunctiva, intercellular adhesion molecule-1 (ICAM-1) was expressed only on the vascular endothelium, lymphocyte function associated antigen-1 (LFA-1) and intercellular adhesion molecule-3 (ICAM-3) on epithelial and stromal mononuclear cells, and very late activation antigen-4 (VLA-4) on a few stromal mononuclear cells. Endothelial leukocyte adhesion molecule-1 (ELAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression was not detected. In VKC a marked increase of all these antigens was observed. Strong ICAM-1 expression was induced on the basal epithelial cells, and vascular endothelium. Furthermore, about 30% of the stromal mononuclear cells expressed ICAM-1. LFA-1 and ICAM-3 were expressed on the majority of infiltrating mononuclear cells. VLA-4 expression was noted on about 25% of the stromal mononuclear cells. ELAM-1 and VCAM-1 were induced on the vascular endothelial cells. Our results suggests that increased expression of adhesion molecules in VKC promotes the recruitment of inflammatory cells through blood vessels and the cell interaction between lymphocytes and antigen presenting cells, among lymphocytes, as well as between lymphocytes and epithelial cells.

Characterization of intercellular adhesion molecule-1 (ICAM-1)-augmented degranulation by cytotoxic T cells. ICAM-1 and anti-CD3 must be co-localized for optimal adhesion and stimulation.

Purified intercellular adhesion molecule-1 (ICAM-1), a ligand of the LFA-1, was used to analyze the contribution of ICAM-1 to the activation of CTL. ICAM-1 facilitates degranulation when co-immobilized with substimulatory amounts of anti-CD3. This facilitated response is most likely mediated through LFA-1, since Abs to this molecule significantly inhibit the response, Interestingly, when ICAM-1 and anti-CD3 are immobilized on separate beads and presented to the CTL, no ICAM-1-enhanced degranulation is observed. The ICAM-1 and anti-CD3 must be immobilized on the same surface to augment the response, suggesting that ICAM-1 either does not transmit signals into the cell or it transmits a very localized signal, since the ICAM-1 and anti-CD3 must be juxtaposed. Consistent with this finding, we demonstrate that ICAM-1 does not induce tyrosine phosphorylation or a Ca(2+)-flux in the CTL clone, but does potentiate these responses when co-immobilized with substimulatory anti-CD3. Finally ICAM-1 and anti-CD3 must be immobilized on the same bead for stable adhesion of CTL to ICAM-1. When ICAM-1 and anti-CD3 are immobilized on separate beads, there is only a transient, low level of adhesion to the ICAM-1 beads. Taken together, these results suggest that LFA-1 is acting principally as an adhesion molecule, with respect to ICAM-1, in CTL and that this adhesion is regulated through the TCR complex.