A peptide inhibitor of vascular adhesion protein-1 (VAP-1) blocks leukocyte-endothelium interactions under shear stress

Vascular adhesion protein-1 (VAP-1) is an endothelial adhesion molecule mediating leukocyte interactions with blood vessels during leukocyte extravasation. Molecularly VAP-1 is a cell-surface-expressed ecto-enzyme belonging to the group of semicarbazide-sensitive amine oxidases (SSAO; EC 2.4.6.3), which deaminate primary amines. Here we asked whether peptides displaying a suitable free amine group could be a substrate or inhibitor of SSAO and thus regulate VAP-1-mediated leukocyte adhesion. On the basis of a molecular model of VAP-1, we designed synthetic peptides that fit to the substrate channel of VAP-1. One of these lysine-containing peptides effectively inhibits VAP-1-dependent lymphocyte rolling and firm adhesion to primary endothelial cells under physiologically relevant shear conditions. The same peptide inhibits the SSAO activity of endothelial and recombinant VAP-1 in a selective and long-lasting manner. We also show that all enzymatically active VAP-1 is displayed on the cell surface. Our results suggest that, in addition to soluble amines, specific cell-surface-bound molecules containing free NH(2) groups in a suitable position may modulate the enzymatic activity of SSAO. Moreover, the inhibitory peptide diminishes leukocyte interactions with endothelial cells under conditions of shear, and thus it may be useful to treat inflammatory conditions.     

Identical expression of ELAM-1, VCAM-1, and ICAM-1 in sarcoidosis and usual interstitial pneumonitis

Extravasation of leucocytes in tissues is mediated by leucocyte—endothelial cell interactions in which adhesion molecules play an important role. Until now, two pathways have been unravelled, i.e., the LFA-1/ICAM-1 and the VLA-4/VCAM-1 pathways. ELAM-1 has been shown to be involved in granulocyte accumulation and recently also in lymphocyte migration. The role of HECA-452 is under investigation. In this study we have investigated the expression of the above-mentioned adhesion molecules in lung tissue of patients with pulmonary sarcoidosis and usual interstitial pneumonitis (UIP), and in mediastinal lymph nodes of patients with sarcoidosis. ICAM-1 (CD54) was broadly distributed on the endothelium of all the vessels found in sarcoidosis and UIP. VCAM-1 was present on the endothelium of the venules, capillaries, and arterioles in both sarcoidosis and UIP. ELAM-1 reacted with endothelial cells lining venules and capillaries in chronic progressive sarcoidosis and in the active phase of UIP but not in the stationary phases of both diseases. HECA-452 activity could be detected only on high endothelial venules within sarcoid lymph nodes. In lung tissues, macrophages bearing the ICAM-1 antigen were present in sarcoid tissue but not in the interstitium and alveolar space of UIP. LFA-1 (CD11a/CD18) and VLA-4 (CD49d/CD29) were present on all leucocytes found but seemed to be more highly expressed on lymphocytes in sarcoidosis. These findings suggest that the LFA-1/ICAM-1 and VLA-4/VCAM-1 pathways are involved in leucocyte migration in both types of lung disease, while in the active phases of sarcoidosis and UIP, ELAM-1 is also involved.     

Differential effects of interleukin 12 and interleukin 10 on superantigen-induced expression of cutaneous lymphocyte-associated antigen (CLA) and alphaEbeta7 integrin (CD103) by CD8+ T cells

At both cutaneous and mucosal sites, interleukin (IL)-10, IL-12 and transforming growth factor (TGF)-beta are important regulators of chronic inflammatory disease, where cutaneous lymphocyte-associated antigen (CLA) and alphaE integrin (CD103) may be expressed. Stimulation with streptococcal pyrogenic exotoxin C (SpeC) increased the expression of CD103 by CD8+ but not CD4+ T cells. While adding IL-12 augmented the expression of CLA, superantigen-induced expression of CD103 was markedly suppressed by IL-12, which could be reversed by TGF-beta. Antibodies against TGF-beta inhibited, and a combination of anti-TGF-beta and IL-12 completely abrogated the induced CD103 expression. IL-10 strongly decreased the frequency of CLA+ and although not increasing the frequency of CD103+CD8+ T cells, the amount of CD103 expressed per cell was markedly increased. Thus, the expression of CLA and CD103 may be antagonistically regulated by IL-10 and IL-12 and the balance between these cytokines could influence the T cell migration of inflammatory cells into epithelial tissues.     

Transmission of HIV-1 infection between trophoblast placental cells and T-cells take place via an LFA-1-mediated cell to cell contact

HIV-1 vertical transmission is thought to mainly take place by virus crossing the placental barrier. However, the mechanism by which HIV-1-infects placental cells remains to be elucidated. We have found that purified cytotrophoblasts as well as trophoblastic cell lines are susceptible to infection by different HIV-1 isolates as detected by DNA-PCR and release of infectious virus, although with very low efficiency. Purified trophoblast or trophoblastic cell lines express low levels of chemokine receptors CCR-5 and CXCR-4 but not CD4 on the cell surface. To test if those molecules were used as receptors for HIV-1 infection, placental cells were pretreated with antibodies to CD4, CC-chemokines, C-X-C chemokines. None of those treatments inhibited HIV-1 infection. In contrast, we have found that HIV-1 infection of placental cells was increased in cocultures of infected T-cell blasts and placental cells. More interestingly, antibodies to beta(2) integrins and to LFA-1 were able to significantly block infection of placental cells. Cell surface expression of ICAM-1, an adhesion molecule involved in attachment of leukocytes to placenta, was upregulated in HIV-1-infected placental cells. Placental cells were able to transfer HIV-1 infection to T-cell blasts. This transmission required cell to cell contact and was also inhibited by anti-LFA-1 antibodies. In summary our results suggest that placental trophoblast could be infected by HIV-1 by a mechanism involving T cell to placental contact. Moreover, placental infection enhanced ICAM-1 expression and leukocyte adherence, an event which was required to transfer HIV-1 infection to T cells. This provides an explanation of the virus passing through the placental barrier during in utero HIV-1 vertical transmission.     

Interaction of nanobacteria with cultured mammalian cells

Nanobacteria were recently isolated from human blood and commercial fetal bovine serum (FBS) and were located in the -2 subgroup of proteobacteria based upon their 16S rRNA gene sequence. They can be cultured even in the absence of mammalian cells, and have extraordinary properties, like very slow growth rate and an impermeable cell wall, making their detection difficult by standard microbiological techniques. Since they are present in FBS, and thus in cell cultures, it is essential to clarify their effects on cultured mammalian cells. In this study, we show that four out of six nanobacterial isolates from different sera exerted a cytotoxic effect on 3T6 fibroblasts verified by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] viability assay, lactate dehygrogenase (LDH) release and by direct microscopy. The cytotoxic effect of nanobacteria was attenuated after they had been subcultured several times. The cytotoxic effect was similar with all tested murine and human fibroblastoid cell lines. Differential interference contrast and electron microscopy, and FITC staining with specific monoclonal antibodies indicated selective, possibly receptor-mediated adherence, followed by internalization and cytotoxicity in the 3T6 fibroblasts used as a model in these interaction studies. Thus, nanobacteria have a special way of invading mammalian cells: they trigger cells that are not normally phagocytic to engulf them. These organisms seem to be an important cause for cell vacuolization, poor thriving and unexpected cell lysis, problems frequently encountered in mammalian cell culture.     

Expression of adhesion molecules in primary B-cell gastric lymphoma and lymphoid follicles

To determine whether primary B-cell gastric lymphoma (GL) is one entity, we examined the expression of three adhesion molecules in the microvasculature of lymphomas. Stromal cells, including vascular endothelial cells, within lymphoid follicles of the gastric mucosa were also investigated. Twenty-two surgical specimens of GL were classified into low-grade malignant lymphoma arising from mucosa-associated lymphoid tissue (low-grade lymphoma, n=9), and high-grade malignant lymphoma with (secondary high-grade lymphoma, n=6) or without (primary high-grade lymphoma, n=7) a low-grade component. The proportion of venules positive for ELAM-1 or VCAM-1 was significantly higher (P<0.001) in primary high-grade lymphoma than in low-grade and secondary high-grade lymphomas. In gastric lymphoid follicles, the stromal cells of the germinal centre (GC) were positive for ICAM-1, ELAM-1, and VCAM-1, but the stromal cells of the marginal zone (MZ) were positive only for ICAM-1. We found two patterns of adhesion molecule expression in gastric lymphoid follicles, the MZ pattern and the GC pattern. Low-grade and secondary high-grade lymphomas, which had the MZ pattern, might be of MZ-cell lineage, but most primary high-grade lymphomas, which had the GC pattern, might be of follicular centre cell lineage.     

Lack of adhesion molecules in testicular diffuse centroblastic and immunoblastic B cell lymphomas as a contributory factor in malignant behaviour

Diffuse large B-cell lymphoma of the testis is a rare tumour, often with disseminated disease. According to the Kiel Classification, these lymphomas are of centroblastic or immunoblastic type, corresponding in the Working Formulation to malignant lymphoma, large cell non-cleaved and large cell immunoblastic, respectively. Adhesive cell-cell and cell-matrix interactions are generally assumed to play an important part in the metastatic process, and to find clues to the highly malignant biological behaviour of this tumour we examined expression of integrins and other adhesion molecules on the tumour cells and the presence of matrix proteins. Few adhesion molecules appeared to be expressed. CD44 was expressed in 10/12 lymphomas, CD49f/VLA-6 was positive in 5/12 cases, and CD49d/VLA-4, CD54 and CD62L were detectable in a small number (2–3) of lymphomas. All other adhesion molecules were lacking. This expression pattern is suggestive of a high metastatic potential: the tumour cells seem to be poorly attached to the extracellular matrix, to each other and to other cells (CD54-, CD11a-, CD58-). The adhesion molecules expressed, CD44, CD49f/VLA-6 and CD49d/VLA-4, have been reported to play a part in dissemination, mediating intravasation (CD49f/VLA-6) and extravasation (CD44, CD49d/VLA-4). This profile of adhesion molecules may explain, at least in part, the specific biological behaviour of these lymphomas with early and rapid dissemination.     

Immunolocalization of extracellular matrix proteins and integrins in sarcoid lymph nodes

 To improve our understanding of the role of extracellular matrix (ECM) proteins and integrins during the processes of granuloma formation in sarcoidosis, we examined the distribution of ECM proteins and the expression of integrins in sarcoid lymph nodes by immunohistochemical methods. We also examined the expression of transforming growth factor-β1 (TGF-β1), which is one of major regulators for synthesis of ECM proteins. Most ECM proteins were detected in the periphery of the granulomas in a concentric pattern, and fibronectin was diffusely detected from an early to a regressive stage. Compared with normal lymph nodes, most β1-integrin subfamilies (α1, α4, α5 and α6) were more strongly expressed on lymphocytes around the granulomas. Epithelioid cells exhibited strong expression of the α5 molecule. Fibroblasts exhibited the expression of the α2 and α5 molecules surrounding ECM proteins. The α5β1 molecule had a distribution similar to that of fibronectin. TGF-β1 was detected in epithelioid cells throughout the various evolutional stages and its expression was especially marked in mature granulomas. Interaction of fibronectin and the α5β1 molecule may have an important role in the process of formation of sarcoid granuloma. The expression of TGF-β1 may be involved in the regression of sarcoid granuloma by initiating fibrosis and atrophy of epithelioid cells. Received: 2 December 1997 / Accepted: 19 February 1998     

Activation of CD44 induces ICAM-1/LFA-1-independent,Ca2+, Mg2+, —independent adhesion pathway in lymphocyte-endothelial cell interaction

We have established an endothelial cell line KOP2.16 from pooled mouse lymph nodes. Resting lymphocytes avidly bound to KOP2.16 and migrated underneath the cytoplasm. The binding was partly mediated by VLA-4 and VCAM-1, but apparently independent of CD44 since anti-CD44 antibody examined failed to inhibit the binding. However, pretreatment of lymphocytes with anti-CD44 resulted in the rapid appearance of Ca²⁺-, Mg²⁺-independent, LFA-1/ICAM-1-, CD2/LFA-3,VLA-4/VCAM-l-independent lymphocyte binding, indicating that a novel adhesion pathway was induced by the anti-CD44 treatment. Interestingly, the elicited adhesion was observed only when anti-CD44 that block hyaluronate recognition of CD44 were used for lymphocyte pretreatment. Neither hyaluronate itself nor non-blocking anti-CD44 up-regulated the adhesion. Fab fragment of the blocking anti-CD44 did not induce the up-regulation unless cross-linked with a second antibody, indicating that cross-linking of surface CD44 is necessary for induction of a novel adhesion pathway. We propose that the agonistic anti-CD44 antibodies induce a novel adhesion pathway by mimicking ligand binding to CD44 on the lymphocyte surface and that non-hyaluronate ligand(s) is involved in regulation of adhesive function of CD44. Potential involvement of such a regulatory mechanism in lymphocyte homing is discussed.