Stimulation through CD50 (ICAM-3) induces both activation and programmed cell death of human thymocytes

Identification and characterization of human thymic cortical dendritic macrophages that may act as professional scavengers of apoptotic thymocytes

We identify and characterize a special type of macrophage in the human thymic cortex that may act as professional scavengers of apoptotic thymocytes. These are large cells with clear cytoplasm, evenly distributed exclusively in the thymic cortex, and usually contain degraded nuclei in their cytoplasm. They are distinct from ordinary macrophages (OM) in the thymic cortex in expressing fascin, an actin-bundling protein specific for dendritic cells (DC), and in lacking lysozyme (LZM) and CD68. They are also different from DC in lacking major histocompatibility complex (MHC)-class II molecules. To distinguish them from OM and DC, we called them thymic cortical dendritic macrophages (TCDM). Both TCDM and OM are positive for DC-SIGN (CD209) and HAM56, whereas fascin(hi) MHC-class II(hi) medullary DC (mDC) are negative for these antigens. TCDM exhibit either dendritic or plump feature depending on cases examined. Plump TCDM usually contain several degraded nuclei, while dendritic TCDM contain one or two. These degraded nuclei are positive for active caspase-3 (aCasp-3), indicating that they are apoptotic thymocytes. In contrast to TCDM, LZM(hi) CD68(hi) OM are smaller round cells, distributed unevenly throughout the thymus, and do not contain apoptotic thymocytes at all. TCDM tend to adhere to capillaries with their dendrites or they make extensive contacts covering a large portion of the capillaries. Electron microscopic analysis confirmed the extensive contact between TCDM and capillaries and indicated that TCDM possess extremely electron-lucent, abundant cytoplasm with numerous tubulovesicular structures and secondary lysosomes. The finding of numerous condensed nuclei in most of the TCDM indicates that these cells represent a special type of fixed macrophages in the human thymic cortex, and that they play a central role in the clearance of apoptotic thymocytes.

Subtyping obsessive-compulsive disorder: clinical and immunological findings in child and adult onset

It has been suggested that certain kinds of childhood OCD with specific clinical, biological and immunological characteristics may form a subgroup of OCD. We study the presence of these characteristics in child onset OCD and propose that the disorder be considered as a subtype of adult OCD. Forty adult patients with OCD were divided in two groups according to time of disease onset: 18 early onset and 21 late. Both sets were compared with a control group of 14 psychiatric patients. Child onset OCD was associated with higher mean ASLO titers, higher frequencies of history of tic disorders and tonsillitis in childhood and compulsive symptoms. No differences were found in D8/17 antibody titers or in other autoimmune parameters. The findings suggest that child onset OCD can be considered as a subgroup of adult OCD, although more specific biological markers are needed to identify it.

Engagement of ICAM-3 provides a costimulatory signal for human immunodeficiency virus type 1 replication in both activated and quiescent CD4+ T lymphocytes: implications for virus pathogenesis

Human immunodeficiency virus type 1 (HIV-1) replication is regulated by several extracellular signals. We demonstrate that intercellular adhesion molecule 3 (ICAM-3) acts as a costimulating molecule to increase HIV-1 transcription and viral production, a process allowing productive infection of quiescent CD4+ T lymphocytes. The present work suggests an important role for ICAM-3 in HIV-1 replication.

Molecular mechanisms involved in CD43-mediated apoptosis of TF-1 cells. Roles of transcription Daxx expression, and adhesion molecules

CD43 (leukosialin, sialophorin), an abundant leukocyte surface sialoglycoprotein, regulates leukocyte adhesion and transmits activating signals in T cells and dendritic cells. Immobilized anti-CD43 monoclonal antibody (mAb) MEM-59 has been previously shown to induce apoptosis of hematopoietic progenitors. In this study we show that it also triggers apoptosis of the myeloid progenitor-derived cell line TF-1. The kinetics of the MEM-59-induced apoptosis were unusually slow, with the first apoptotic cells appearing 36-48 h after their contact with the immobilized antibody; in 5 days, 90% of the cells were dead. CD43-mediated apoptosis was enhanced by coimmobilized anti-CD45 mAb and partly suppressed by coimmobilized anti-CD50 (ICAM-3) or anti-CD99 mAb. The MEM-59-triggered apoptosis of TF-1 cells was also inhibited by the overexpression of an apoptotic regulator, Daxx. CD43-mediated apoptosis was preceded by the repression of the DNA binding activity of the transcription factor AP-1. DNA array screening revealed that the expression of several genes encoding apoptosis-regulating proteins, including 14-3-3 proteins and the granulocyte macrophage colony-stimulating factor (GM-CSF) receptor beta-subunit, was repressed in TF-1 cells bound to immobilized MEM-59. The down-regulation of 14-3-3 proteins and GM-CSF receptor beta was accompanied by translocation of the proapoptotic protein Bad to the mitochondria. These results suggest that engagement of CD43 may, presumably through the repressing transcription, initiate a Bad-dependent apoptotic pathway.

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.

Human leukemic (HMC-1) mast cells are responsive to 1alpha, 25-dihydroxyvitamin D(3): selective promotion of ICAM-3 expression and constitutive presence of vitamin D(3) receptor

Expression levels of adhesion molecules on HMC-1 mast cells were examined prior to and following administration of 1alpha, 25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. While most receptors (including ICAM-1) remained unchanged by the treatment, solely ICAM-3 expression was promoted in a dose- and time-dependent fashion, peaking at 50 nM of 1,25(OH)(2)D(3) and 72 h, illustrating that like other myeloid cells, human mast cells are 1,25(OH)(2)D(3) responsive, yet in a highly selective manner. Flow cytometric results were confirmed by ELISA, by semiquantitative RT-PCR, and functionally by showing enhanced anti-ICAM-3 mediated homotypic aggregation of 1,25(OH)(2)D(3) pretreated cells. Since cellular responsiveness is conferred by the vitamin D(3) receptor (VDR), we examined human mast cells for its expression. VDR was constitutively present in both HMC-1 and skin mast cells by RT-PCR technique and in nuclear extracts of HMC-1 cells by Western blot analysis. Our data thus suggest that human mast cells are direct targets of 1, 25(OH)(2)D(3) action.

Antibody engagement of intercellular adhesion molecule 3 triggers apoptosis of normal and leukaemic myeloid marrow cells

Intercellular adhesion molecule 3 (ICAM-3, CD50) is an immunoglobulin (Ig) domain-containing cell-cell adhesion receptor that binds to the lymphocyte function antigen 1 (LFA-1; CD11a/CD18) integrin. It is constitutively expressed on haematopoietic precursors and differentiated leucocytes, as well as on most leukaemic cells. ICAM-3/LFA-1 binding during a lymphocyte-mediated cellular immune response has been well established; however, its role in the marrow compartment is unclear. In this study, marrow cells from normal and acute leukaemic donors, as well as leukaemic cell lines, were cultured in the presence of various monoclonal antibodies (mAbs) to ICAM-3, and apoptosis was subsequently measured by annexin V binding. Anti-ICAM-3 mAb ICR 1.1 engagement triggered increased percentages of apoptosis among normal and leukaemic marrow myeloid cells. Fab fragments of ICR 1.1 mimicked the intact mAb, suggesting that the apoptotic signal was independent of Fc receptor interactions and did not require bivalent epitope engagement. In addition, the apoptotic signal was found to be independent of ICAM-1/LFA-1 binding interactions, as well as Fas/FasL and tumour necrosis factor alpha (TNF-alpha)/TNF receptor-activated pathways, as neutralizing antibodies to CD11a/CD18, Fas and TNF-alpha failed to abrogate the response.

Macrophage Recognition of ICAM-3 on Apoptotic Leukocytes

Cells undergoing apoptosis are cleared rapidly by phagocytes, thus preventing tissue damage caused by loss of plasma membrane integrity. In this study, we show that the surface of leukocytes is altered during apoptosis such that the first Ig-like domain of ICAM-3 (CD50) can participate in the recognition and phagocytosis of the apoptotic cells by macrophages. Macrophage recognition of apoptotic cell-associated ICAM-3 was demonstrated both on leukocytes and, following transfection of exogenous ICAM-3, on nonleukocytes. The change in ICAM-3 was a consistent consequence of apoptosis triggered by various stimuli, suggesting that it occurs as part of a final common pathway of apoptosis. Alteration of ICAM-3 on apoptotic cells permitting recognition by macrophages resulted in a switch in ICAM-3-binding preference from the prototypic ICAM-3 counterreceptor, LFA-1, to an alternative macrophage receptor. Using mAbs to block macrophage/apoptotic cell interactions, we were unable to obtain evidence that either the alternative ICAM-3 counterreceptor αdβ2 or the apoptotic cell receptor αvβ3 was involved in the recognition of ICAM-3. By contrast, mAb blockade of macrophage CD14 inhibited ICAM-3-dependent recognition of apoptotic cells. These results show that ICAM-3 can function as a phagocytic marker of apoptotic leukocytes on which it acquires altered macrophage receptor-binding activity.

Stimulation through CD50 preferentially induces apoptosis of TCR1+ human peripheral blood lymphocytes

Apoptosis has an important role in several key immunological phenomena such as regulation of the immune response, and deletion of auto-reactive cells. This phenomenon is induced following the interaction of several cell membrane receptors with their respective ligands or after cell activation. We have studied the possible effect of signaling through CD50/ICAM-3 and CD69/AIM on apoptosis of peripheral blood lymphocytes. Apoptosis was assessed by both flow cytometry analysis (content of cell DNA and binding to annexin V), and detection of DNA fragmentation by agarose gel electrophoresis. We found that a stimulatory anti-CD50 mAb was able to induce a small but significant degree of apoptosis in resting peripheral blood mononuclear cells from most donors; this effect was dose-dependent and was evident as early as at 12 h, with a maximal induction at 48 h. Studies with T and non-T cells showed that only the former cell population was sensitive to the induction of apoptosis through CD50. Further experiments revealed that the anti-ICAM-3 mAb preferentially induced apoptosis of TCR gamma delta-bearing cells. In addition, we found a significant increase in Cai2+ in PBMC stimulated with an anti-CD50 mAb, suggesting the involvement of this signaling pathway in the induction of apoptosis through this adhesion receptor. In contrast, under our experimental conditions, stimulation through CD69 did not have any effect on the induction of apoptosis on either cultured T lymphoblasts or PMA-stimulated PBMC. Our findings suggest that the interaction of CD50 with its natural ligand LFA-1 results in the induction of apoptosis in a significant fraction of resting PBMC. This phenomenon may be involved in immune regulation, lymphocyte turnover and peripheral deletion of auto-reactive cells.

Coengagement of ICAM-3 and Fc Receptors Induces Chemokine Secretion and Spreading by Myeloid Leukocytes

ICAM-3 is expressed at high levels on myeloid leukocytes, but its function on these cells is unknown. We tested the hypothesis that it transduces outside-in proinflammatory signals using immobilized mAbs to engage ICAM-3 on freshly isolated human monocytes and neutrophils. Two immobilized Abs that recognize epitopes in the extracellular domain 1 of ICAM-3, which is critical for recognition by the αL/β2 integrin, potently induced secretion of MIP-1α, IL-8, and MCP-1 by monocytes and triggered IL-8 secretion by neutrophils. These chemokines are products of immediate-early genes that are induced when myeloid cells are activated. Chemokine secretion induced by “triggering” Abs was greater than that induced by isotype-matched immobilized Abs against ICAM-1, ICAM-2, PECAM-1, control Igs, or immobilized control proteins. Coengagement of ICAM-3 and Fc receptors (FcγRI or FcγRII) was required for maximal chemokine secretion by monocytes. Microscopy documented that there is also dramatic spreading of monocytes when surface ICAM-3 is engaged by immobilized Abs. Spreading was induced by Fab and F(ab′)2 fragments of triggering anti-ICAM-3 mAb, demonstrating direct outside-in signaling, but was not required for chemokine secretion. These experiments indicate that ICAM-3 may transmit outside-in signals when it is engaged by β2 integrins during myeloid cell-cell interactions in inflammatory lesions. Binding of Fc receptors by Ig in the local environment can amplify the responses.

Isolation of two CD50 (ICAM-3)-negative Jurkat T-cell clones and their application for analysis of CD50 function

The leukocyte differentiation antigen CD50 (intercellular adhesion molecule-3, ICAM-3), mediates cell-cell adhesion through its ligand LFA-1 and is a transducting receptor molecule during T-cell activation. Since CD50 homologues in other species have not yet been identified, the role of this molecule can only be analyzed in human cell models. Thus, to better study CD50 function in T cells, we have obtained two CD50-negative T-cell clones, named CAMY.1 and CAMY.2. These clones were derived from the Jurkat T-cell variant PPL.1. Data from analysis of protein expression, specific mRNA content and calcium mobilization assays have confirmed the absence of functional CD50 molecules on these two clones. Thus, CAMY.1 and CAMY.2 show no CD50 expression by phenotypical and immunoprecipitation analysis. CD50-specific mRNA content is undetectable by Northern blot analysis in these clones and, only, when RT-PCR was performed could specific mRNA be detected. Additionally, CD50 cross-linking on theses clones shows no increase in intracellular calcium. Transfection of CD50 cDNA on CAMY cells restores not only CD50 surface expression, but its functional ability to induce calcium mobilization, CD69 upregulation and cell morphological changes. The CAMY.1 and CAMY.2 clones provide useful model systems to analyze CD50 function in T cells.