A novel integrin involved in thymocyte-thymic epithelial cell interactions

ALCAM Deficiency Alleviates LPS-Induced Acute Lung Injury by Inhibiting Inflammatory Response

We investigated the effects and underlying mechanisms of activated leukocyte adhesion molecule (ALCAM) on acute lung injury (ALI) by using lipopolysaccharide (LPS)-induced ALI animal model and LPS-induced inflammation in vitro. In LPS-stimulated mice, ALCAM deficiency relieved lung injury, which manifested as reduced pathological changes in the lung tissue, reduced pulmonary edema, and reduced vascular permeability. Furthermore, we demonstrated that ALCAM deficiency reduced the infiltration of inflammatory cells, including neutrophil, eosinophil, and macrophages; the release of inflammatory cytokines, including IL-1β, IL-6, TNF-α, and COX2; and reduced the protein level of TLR4/NF-κB pathway (TLR4, MyD88, p-IkBɑ, and p-NF-κB p65). We also demonstrated that ALCAM deficiency reduced the expression of oxidative stress-related proteins (Nrf-2, HO-1, and NQO-1) and endoplasmic reticulum stress-related proteins (CHOP, GRP78, ATF-6, and p-eIF2ɑ). In addition, in LPS-induced inflammation in vitro, ALCAM overexpression promoted inflammatory response, oxidative stress, and ER stress. We established that ALCAM deficiency can suppress the ALI process by reducing inflammatory response, oxidative stress, and endoplasmic reticulum stress.

Activated Leukocyte Cell Adhesion Molecule Stimulates the T-Cell Response in Allergic Asthma

RATIONALE

The activated leukocyte cell adhesion molecule (ALCAM) is a cluster of differentiation 6 ligand that is important for stabilizing the immunological synapse and inducing T-cell activation and proliferation.

OBJECTIVES

In this study, we investigated the role of ALCAM in the development of inflammation in allergic asthma.

METHODS

An ovalbumin (OVA)-induced allergic asthma model was established in wild-type (WT) and ALCAM-deficient (ALCAM^-/-) mice. T-cell proliferation was evaluated in cocultures with dendritic cells (DCs). Bone marrow-derived dendritic cells (BMDCs) from WT and ALCAM^-/- mice were cultured and adoptively transferred to OT-II mice for either OVA sensitization or challenge. An anti-ALCAM antibody was administered to assess its therapeutic potential. ALCAM concentrations in the sputum and serum of children with asthma were quantified by ELISA.

MEASUREMENTS AND MAIN RESULTS

Inflammatory responses were lower in ALCAM^-/- mice than in WT mice, and T cells cocultured with DCs from ALCAM^-/- mice showed reduced proliferation relative to those cocultured with DCs from WT mice. A decreased inflammatory response was observed upon adoptive transfer of BMDCs from ALCAM^-/- mice as compared with that observed after transfer of BMDCs from WT mice. In addition, anti-ALCAM antibody-treated mice showed a reduced inflammatory response, and sputum and serum ALCAM concentrations were higher in children with asthma than in control subjects.

CONCLUSIONS

ALCAM contributes to OVA-induced allergic asthma by stimulating T-cell activation and proliferation, suggesting it as a potential therapeutic target for allergic asthma.

Phagocytic cells of the thymic reticulum interact with thymocytes via extracellular matrix ligands and receptors

We previously showed that, in the context of thymic epithelial cells, thymocyte migration is partially controlled by extracellular matrix (ECM)-mediated interactions. Herein we evaluated whether these interactions could be involved in cell migration related events in the context of non-epithelial cells of the thymic microenvironment, the phagocytic cells of the thymic reticulum (PTR). We first showed, by immunocytochemistry, cytofluorometry, and RT-PCR, that PTR produce ECM components, including fibronectin and laminin, and express the corresponding integrin-type receptors, VLA-4, VLA-5, and VLA-6. Thymocytes adhere onto PTR monolayers, with immature CD4(+)CD8(+) cells being predominant. Importantly, such an adhesion is partially mediated by ECM ligands and receptors, since it was impaired by anti-ECM or anti-ECM receptor antibodies. Conjointly, our data reveal that the ECM-dependence for thymocyte adhesion onto the thymic microenvironment is not restricted to the epithelial cells, being also seen when they encounter non-epithelial phagocytic cells.

Antigenic profile of human thymus in concurrence with "Clusters of Thymic Epithelial Staining" classification

We examined the expression of various CD coded or not yet defined antigens in human thymus samples using indirect immunoperoxidase and immunoflourescent techniques. Data obtained are presented in concurrence with Clusters of Thymic Epithelial Staining (CTES) classification for various monoclonal antibodies recognizing CD antigens (CD1, CD1a, CD6, CD9, CD14, CD16, CD29, CD30, CD32, CD44, CD45RB, CD47, CD48, CD49a, CD49b, CD49c, CD49d, CD49e, CD49f, CD51, CD53, CD54, CD56, CD57, CD63, CD85, CD95, CD98, CD102, CD103, CD106, CD109, CD146, CD147, CD148, CD151, CD152, CD158a, CD158b, CD164, CD165, CD166) and for monoclonal antibodies 1B10, 5G7, A4, BD46, BLTZ, HP1C5, IND.64, M72, WU947 whose specifities are not yet defined. Some of the mAbs such as CD49f, IND.64 and BD46 are detected as good markers for specific cell types or compartments. Significance of the presence of these antigens on thymic epithelial cells at certain locations is briefly discussed.

Thymocyte Contact or Monoclonal Antibody-Mediated Clustering of 3β1 or 6β4 Integrins Activate Interleukin-6 (IL-6) Transcription Factors (NF-κB and NF-IL6) and IL-6 Production in Human Thymic Epithelial Cells

T-cell precursors develop within the thymus in contact with multiple supportive elements, among which thymic epithelial cells (TEC) are known to exert a dominant role in their homing, survival, and functional differentiation. All these functions are supported by cell-cell contacts and cytokine release. Signaling events triggered in lymphoid cells by adhesion to TEC are well characterized, but little is known about the opposite phenomenon. To address this issue, we derived cultures of TEC from human normal thymus. TEC monolayers were cocultured with thymocytes and immunostained with monoclonal antibodies (MoAbs) to integrin  (2, 3, 4, and 6) and β (β1 and β4) chains. Optical and confocal analysis showed that integrins were polarized on TEC at discrete surface locations: 6β4 lined the basal surface of TEC monolayers, whereas 3β1 was found mostly at TEC-TEC contacts; it is noteworthy that both 3β1 and 6β4 became highly enriched also at the boundaries with adherent thymocytes. Functional studies performed with MoAbs anti-β1 and -β4 integrins showed that β1, and, to a much lower extent, β4 heterodimers are involved in the TEC-thymocyte adhesion. Thymocyte contact or MoAb-mediated ligation of 3, 6, β1, and β4 integrins was investigated as a potential inducer of intracellular signaling in TEC. Thymocyte adhesion or cross-linking of MoAbs bound to integrins clustered at the TEC/thymocyte contact sites led to activation of interleukin-6 (IL-6) gene transcription factors, namely NF-IL6 serine phosphorylation and NF-κB nuclear targeting, as well as to increased IL-6 secretion. We propose that integrin clustering occurring during TEC-thymocyte contacts modulates in TEC the gene expression of a cytokine involved in thymocyte growth and functional differentiation.

Thymocyte Contact or Monoclonal Antibody-Mediated Clustering of 3β1 or 6β4 Integrins Activate Interleukin-6 (IL-6) Transcription Factors (NF-κB and NF-IL6) and IL-6 Production in Human Thymic Epithelial Cells

T-cell precursors develop within the thymus in contact with multiple supportive elements, among which thymic epithelial cells (TEC) are known to exert a dominant role in their homing, survival, and functional differentiation. All these functions are supported by cell-cell contacts and cytokine release. Signaling events triggered in lymphoid cells by adhesion to TEC are well characterized, but little is known about the opposite phenomenon. To address this issue, we derived cultures of TEC from human normal thymus. TEC monolayers were cocultured with thymocytes and immunostained with monoclonal antibodies (MoAbs) to integrin  (2, 3, 4, and 6) and β (β1 and β4) chains. Optical and confocal analysis showed that integrins were polarized on TEC at discrete surface locations: 6β4 lined the basal surface of TEC monolayers, whereas 3β1 was found mostly at TEC-TEC contacts; it is noteworthy that both 3β1 and 6β4 became highly enriched also at the boundaries with adherent thymocytes. Functional studies performed with MoAbs anti-β1 and -β4 integrins showed that β1, and, to a much lower extent, β4 heterodimers are involved in the TEC-thymocyte adhesion. Thymocyte contact or MoAb-mediated ligation of 3, 6, β1, and β4 integrins was investigated as a potential inducer of intracellular signaling in TEC. Thymocyte adhesion or cross-linking of MoAbs bound to integrins clustered at the TEC/thymocyte contact sites led to activation of interleukin-6 (IL-6) gene transcription factors, namely NF-IL6 serine phosphorylation and NF-κB nuclear targeting, as well as to increased IL-6 secretion. We propose that integrin clustering occurring during TEC-thymocyte contacts modulates in TEC the gene expression of a cytokine involved in thymocyte growth and functional differentiation.

Antibody cross-linking of the thymocyte-specific cell surface molecule CTX causes abnormal mitosis and multinucleation of tumor cells

The thymocyte-specific cell surface molecule CTX is a developmentally regulated type I transmembrane protein of the immunoglobulin superfamily which, in the amphibian Xenopus, is exclusively expressed by a large fraction of cortical thymocytes and by different cell lines derived from independent spontaneous thymic tumors. Antibody cross-linking of CTX in vitro inhibits the growth of tumor cells and causes morphological alterations. Cells divide abnormally, accumulate in the G2/M phase of the cell cycle, and become multinucleated. This demonstrates, for the first time, that multinucleation can be induced by specifically cross-linking a cell surface molecule.

Cross-linking CTX, a novel thymocyte-specific molecule, inhibits the growth of lymphoid tumor cells in Xenopus

CTX, a new Xenopus Ig superfamily molecule present on some cortical thymocytes and lymphoid tumor cells, is expressed at the cell surface under six differently glycosylated isoforms as shown by two-dimensional gel analysis and by endo F glycosidase treatment. Following chemical cross-linking before immunoprecipitation, a large fraction of surface CTX forms non-covalently linked dimers at the cell surface. This finding, which is consistent with the presence of a J segment with diglycine beta bulge in the V region of the molecule, suggests that this dimer has the same conformation as a T-cell receptor (TCR) or an Ig molecule. The V8 digest patterns of the monomers and dimers are identical. While this suggests that the dimer is a homodimer of two CTX chains, it does not distinguish whether each CTX chain is encoded by the same or different gene loci. When tumor cells were added to culture wells that had been coated with the anti-CTX monoclonal antibody X71, 30-50% underwent rapid (within 30 min) morphological changes followed by growth inhibition as determined by a decrease in thymidine incorporation and by direct cell counting. No apoptosis, calcium flux or external calcium requirement was noted after cross-linking of CTX. These results suggest that CTX can function as a receptor, and that its interaction with a ligand influences the control of cell proliferation through a signalling pathway that is distinct from the TCR machinery.

Immunohistochemical study of skin lesions in acute and chronic graft versus host disease following bone marrow transplantation

Allogeneic bone marrow transplantation (BMT) is the therapy of choice for a variety of malignant and nonmalignant disorders; however, a major constraint to successful BMT is graft versus host disease (GVHD). Skin lesions are the earliest presentation of GVHD. Donor-derived cytotoxic T lymphocytes are the effector cells responsible for lesions in the skin and other tissues. Here we show that most skin-infiltrating lymphocytes, in all forms of GVHD, are memory T cells with a predominance of CD4+ cells in the dermis and CD8+ cells in the epidermis. Relatively little attention has been focused on the adhesive phenotype of keratinocytes in GVHD. In this study, immunohistochemical analyses of skin biopsies from BMT patients with acute or chronic GVHD were conducted, with particular emphasis on antigen-presenting cells (APCs) and on keratinocytes. The distribution of APCs in the epidermis (Langerhans' cells) was investigated. Keratinocytes were analyzed for the expression of human leukocyte antigen DR locus (HLA-DR) and of a novel integrin, alpha10.1.2 beta1, which is detected in the basal layer of normal epidermis. Langerhans' cells were decreased in all grades of acute GVHD, but the epidermal APC network was reconstituted in chronic GVHD. HLA-DR was expressed by keratinocytes in grade 2 and 3 acute GVHD lesions, but not in two of three chronic GVHD cases, and in the regression phase of acute GVHD. Integrin chains alpha10.1.2 and beta1 were detected in the epidermal basal cell layer of most GVHD cases but they were also expressed in suprabasal keratinocytes of both acute and chronic GVHD. This latter finding indicates that a proliferative response uncoupled from differentiation occurs in keratinocytes in the course of GVHD.

HTLV type IIIB infection of human thymic epithelial cells: viral expression correlates with the induction of NF-kappa B-binding activity in cells activated by cell adhesion

Productive infection by the LAV strain has been demonstrated in T cell precursors at different stages of intrathymic development, while viral replication in thymic epithelial cells is still controversial. In this article we show that epithelial cell cultures derived from the medullary component of normal thymus are infectable by HTLV-IIIB virus through cell-free and lymphoid-mediated transmission. Free virus inoculum results in the integration of proviral copies undergoing poor replication, whereas lymphoid-mediated transmission leads to substantial viral expression and the production of viral progeny able to secondary infect lymphoid cells. Interleukin 6 production and phenotype changes (increased expression of MHC class I and ICAM-1) were induced in TE cells by contact with free virus or by adhesion to infected lymphoid cells. By contrast, NF-kappa B-binding activity on the HIV-1 LTR kappa B enhancer element was upregulated only by contact with infected lymphoid cells, but not with virus. The viral replication observed in TE cells after lymphoid-mediated transmission correlates with the upregulation of NF-kappa B-binding activity. Interleukin 6 increased production and phenotype changes and increased NF-kappa B-binding activity were also induced by adhesion to uninfected lymphoid cells, demonstrating that lymphoepithelial cell contacts can activate TE cells. These results demonstrate that thymic epithelial cells are permissive to HIV infection and that viral replication in this cell lineage can be modulated by intracellular signals delivered by adhesive contacts.

The expression of VLA integrins in the human thymus

The integrin receptors are a family of transmembrane glycoproteins comprising non-covalent heterodimers. They interact with a wide variety of ligands including extracellular matrix glycoproteins, complement and other cells while their intracellular domains interact with the cytoskeleton. They participate in cell-matrix and cell-cell adhesion in many physiologically important processes including embryological development, hemostasis, thrombosis, wound healing, immune and nonimmune defense mechanisms, and oncogenic transformation. This investigation is focused on the histological distribution of the beta 1-integrins in the human thymus, using an indirect immunoperoxidase method. With the exception of VLA-4, none of the beta 1 integrins were expressed on thymocytes which were strongly positive in the cortex and perivascular compartment, somewhat weaker in the medulla. Thymic epithelial cells were positive for VLA-1, VLA-2, VLA-3 and VLA-6, but the distribution pattern of these molecules in epithelial cells at certain locations was quite different. VLA-1 was weakly expressed by both cortical and medullary epithelial cells. VLA-2 was strongly positive in cortical epithelial cells forming a dense framework at the peripheral cortex. VLA-3 and VLA-6 selectively stained a single flattened epithelial cell layer (perilobular epithelial cells) demarcating the peripheral cortex from the surrounding perivascular compartment. VLA-1,3,5,6 were also demonstrated in the endothelial cells and subendothelial layer of the thymic vasculature.

IN CONCLUSION

the distribution of integrins in human thymus tissues is of special interest. Such distribution shows that the VLA integrins may have different functions in different areas. The data presented in this study may be important in evaluating the functional role of the VLA integrins in thymocyte maturation in different compartments of the thymus.

Specific association of CD63 with the VLA-3 and VLA-6 integrins

We screened monoclonal antibodies to cell-surface proteins and selected an antibody, called 6H1, that recognizes a putative integrin-associated protein. The 6H1 monoclonal antibody (mAb) indirectly coprecipitated alpha 3 beta 1 and/or alpha 6 beta 1, but not alpha 2 beta 1, or alpha 5 beta 1 from Brij 96 detergent lysates of multiple cell lines. Large scale purification using the 6H1 mAb yielded a single protein of 45-60 kDa with an amino-terminal sequence that exactly matched CD63. Confirming that the 6H1 mAb recognized the CD63 protein, 6H1 and a known anti-CD63 mAb yielded identical coprecipitation results and identical colocalization into lysosomal granules containing cathepsin D. Furthermore, we used an established anti-CD63 mAb to detect this protein in an alpha 3 beta 1 immunoprecipitate, and also we observed VLA-3 and CD63 colocalization in cellular "footprints." Notably, the cytoplasmic domain of alpha 3 was neither required nor sufficient for CD63 association, suggesting that it occurred elsewhere within the alpha 3 beta 1 complex. Knowledge of these specific CD63-alpha 3 beta 1 and CD63-alpha 6 beta 1 biochemical associations should lead to critical insights into the specialized functions of alpha 3 beta 1, alpha 6 beta 1, and CD63.

Cloning, mapping, and characterization of activated leukocyte-cell adhesion molecule (ALCAM), a CD6 ligand

Antibody-blocking studies have demonstrated the role of CD6 in thymocyte-thymic epithelial (TE) cell adhesion. Here we report that CD6 expressed by COS cells mediates adhesion to TE cells and that this interaction is specifically blocked with an anti-CD6 monoclonal antibody (mAb) or with a mAb (J4-81) that recognized a TE cell antigen. We isolated and expressed a cDNA clone encoding this antigen and show that COS cells transfected with this cDNA bind a CD6 immunoglobulin fusion protein (CD6-Rg). This antigen, which we named ALCAM (activated leukocyte-cell adhesion molecule) because of its expression on activated leukocytes, appears to be the human homologue of the chicken neural adhesion molecule BEN/SC-1/DM-GRASP. The gene was mapped to human chromosome 3q13.1-q13.2 by fluorescence in situ hybridization of cDNA probes to metaphase chromosomes. We prepared an ALCAM-Rg fusion protein and showed that it binds to COS cell transfectants expressing CD6, demonstrating that ALCAM is a CD6 ligand. The observations that ALCAM is also expressed by activated leukocytes and that both ALCAM and CD6 are expressed in the brain suggest that ALCAM-CD6 interactions may play a role in the binding of T and B cells to activated leukocytes, as well as in interactions between cells of the nervous system.

Identification and characterization of a 100-kD ligand for CD6 on human thymic epithelial cells

CD6 is a 130-kD glycoprotein expressed on the surface of thymocytes and peripheral blood T cells that is involved in TCR-mediated T cell activation. In thymus, CD6 mediates interactions between thymocytes and thymic epithelial (TE) cells. In indirect immunofluorescence assays, a recombinant CD6-immunoglobulin fusion protein (CD6-Rg) bound to cultured human TE cells and to thymic fibroblasts. CD6-Rg binding to TF and TE cells was trypsin sensitive, and 54 +/- 4% of binding was divalent cation dependent. By screening the blind panel of 479 monoclonal antibodies (mAbs) from the 5th International Workshop on Human Leukocyte Differentiation Antigens for expression on human TE cells and for the ability to block CD6-Rg binding to TE cells, we found one mAb (J4-81) that significantly inhibited the binding of CD6-Rg to TE cells (60 +/- 7% inhibition). A second mAb to the surface antigen identified by mAb J4-81, J3-119, enhanced the binding of CD6-Rg to TE cells by 48 +/- 5%. Using covalent cross-linking and trypsin digestion, we found that mAb J4-81 and CD6-Rg both bound to the same 100-kD glycoprotein (CD6L-100) on the surface of TE cells. These data demonstrate that a 100-kD glycoprotein on TE cells detected by mAb J4-81 is a ligand for CD6.

Human thymic epithelial cells express an endogenous lectin, galectin-1, which binds to core 2 O-glycans on thymocytes and T lymphoblastoid cells

Thymic epithelial cells play a crucial role in the selection of developing thymocytes. Thymocyte-epithelial cell interactions involve a number of adhesion molecules, including members of the integrin and immunoglobulin superfamilies. We found that human thymic epithelial cells synthesize an endogenous lectin, galectin-1, which binds to oligosaccharide ligands on the surface of thymocytes and T lymphoblastoid cells. Binding of T lymphoblastoid cells to thymic epithelial cells was inhibited by antibody to galectin-1 on the epithelial cells, and by two antibodies, T305 and 2B11, that recognize carbohydrate epitopes on the T cell surface glycoproteins CD43 and CD45, respectively. T lymphoblastoid cells and thymocytes bound recombinant galectin-1, as demonstrated by flow cytometric analysis, and lectin binding was completely inhibited in the presence of lactose. The degree of galectin-1 binding to thymocytes correlated with the maturation stage of the cells, as immature thymocytes bound more galectin-1 than did mature thymocytes. Preferential binding of galectin-1 to immature thymocytes may result from regulated expression of preferred oligosaccharide ligands on those cells, since we found that the epitope recognized by the T305 antibody, the core 2 O-glycan structure on CD43, was expressed on cortical, but not medullary cells. The level of expression of the UDP-GlcNAc:Gal beta 1,3GalNAc-R beta 1, 6GlcNAc transferase (core 2 beta 1, 6 GlcNAc transferase, or C2GnT), which creates the core 2 O-glycan structure, correlated with the glycosylation change between cortical and medullary cells. Expression of mRNA encoding the C2GnT was high in subcapsular and cortical thymocytes and low in medullary thymocytes, as demonstrated by in situ hybridization. These results suggest that galectin-1 participates in thymocyte-thymic epithelial cell interactions, and that this interaction may be regulated by expression of relevant oligosaccharide ligands on the thymocyte cell surface.

Characterization of human thymic epithelial cell surface antigens: phenotypic similarity of thymic epithelial cells to epidermal keratinocytes

Cellular interactions between developing thymocytes and cells of the thymic microenvironment are necessary for maturation of thymocytes into mature T cells. While much is known about the molecules on developing T cells that mediate these interactions, little is known about the surface molecules of human thymic epithelial (TE) cells. In this study, using a panel of 276 MAb including 255 MAb from the 5th International Workshop on Human Leukocyte Differentiation Antigens (HLDA-V), we have determined the expression of CD1 through CDw130 and other surface molecules on resting and IFN-gamma-activated cultured human TE cells and on resting epidermal keratinocytes (EK). We demonstrate the surface expression of 50 of the 161 molecules assayed for on TE cells, including a number of adhesion molecules, cytokine receptors, Apo-1, and MHC-encoded molecules. While activation of TE cells with IFN-gamma for 48 hr induced a greater than fivefold increase in the expression of four surface molecules (CD38, CD54, MHC class I, and MHC class II), it also induced a greater than 50% increase in the expression of 14 other surface molecules (CD12, CD29, CD40, CD44, CD47, CD49b, CD49c, CD49e, CD55, CD66, CD87, CD104, TE4, and STE3) and a decrease in the expression of three molecules (CDw65, CDw109, and STE2). In comparing the phenotype of TE cells to 83 other cell lines studied in HLDA-V, we found that TE cells were strikingly more similar to EK than to any of the other cell types tested.

cDNA cloning of mouse VLA-3 alpha subunit

cDNA clones for mouse VLA (very late antigen)-3 alpha subunit (alpha 3 integrin) were isolated and sequenced. The encoded mouse alpha 3 integrin subunit was composed of 1,053 amino acid residues. The results of sequence analysis revealed similar structural characteristics of other VLA alpha subunits. For example, the presence of a large extracellular domain including three putative metal binding sequences, a transmembrane domain, and a short cytoplasmic domain. A higher level of its message was detected in thymus than in kidney, stomach, spleen, liver, brain, or lung by Northern blotting analysis.

Adhesion molecules involved in the binding and subsequent engulfment of thymocytes by a rat thymic epithelial cell line

A rat thymic epithelial cell (TEC) line (R-TNC.1) was established from a long-term TEC culture. Based on its ultrastructure, phenotype and cytokeratin profile, this line was characterized as a type of cortical TEC. R-TNC.1 cells had nursing activity which was manifested by the binding and subsequent engulfment of thymocytes. The role of adhesion molecules involved in these processes was studied extensively using a coculture of resting thymocytes and unstimulated or interferon-gamma (IFN-gamma)-stimulated R-TNC.1 cells. It was found that a number of adhesion molecules, such as CD2, CD4, CD8, LFA-1, CD18, ICAM-1 and Thy-1, was partly involved in the nursing activity. The effect of monoclonal antibodies (mAb) to these molecules depended on the incubation time and stimulation of R-TNC.1 cells. The inhibitory effect of mAb to CD2, LFA-1, CD18 and ICAM-1 on thymocyte engulfment was higher than their effect on thymocyte binding to the R-TNC.1 line. In addition, a LFA-1/CD18-dependent/ICAM-1-independent adhesion pathway was identified when unstimulated R-TNC.1 cells with minimal expression of ICAM-1 were used. The combination of inhibitory mAb did not completely abrogate the nursing activity of the R-TNC.1 line, suggesting the possible involvement of some other adhesion molecules.

Extracellular matrix components of the mouse thymus microenvironment. IV. Modulation of thymic nurse cells by extracellular matrix ligands and receptors

Extracellular matrix (ECM) proteins can influence cell migration and differentiation in a variety of cell systems. Within the thymus, these molecules are heterogeneously distributed, and their physiological role is poorly understood. This prompted us to carry out in vitro studies using the thymic nurse cell (TNC) model. We observed that fibronectin and laminin accelerate spontaneous in vitro release of thymocytes from TNC, whereas anti-ECM antibodies exhibited a blocking effect. Similar results were obtained with anti-ECM receptor reagents. Moreover, these antibodies abrogated in vitro reconstitution of TNC complexes and thymocyte adhesion to TNC-derived epithelial cultures. Our results indicate that lymphocyte traffic in TNC (comprising both entrance into and exit from the epithelial structure) is affected by interactions involving extracellular matrix ligands and receptors. In this respect, the dynamic analysis of thymic nurse cell complexes should be regarded as a relevant in vitro tool for functional studies of distinct adhesion molecules in intrathymic lymphocyte traffic.

Immunohistochemical localization of a novel beta 1 integrin in normal and pathologic squamous epithelia

The 10.1.2 MoAb reacts with a novel alpha chain that associates with the beta 1 integrin chain and is widely distributed among epithelial and endothelial cells of human adult and fetal tissues. In the epidermis and in other squamous epithelia, alpha 10.1.2 chains are expressed exclusively in the basal cell layer. Here we describe the immunohistochemical localization of alpha 10.1.2 in human epidermis, in other squamous epithelia, as well as in cultured keratinocytes. alpha 10.1.2 chain localization has also been investigated in a variety of non-neoplastic and neoplastic lesions of the skin, the uterine cervix, and the lung. We show that alpha 10.1.2 chains retain their basal keratinocyte localization in hyperplastic skin diseases and in benign tumors of the epidermis and that they are strongly expressed in basal cell carcinomas. In contrast, alpha 10.1.2 expression is decreased in keratinocytes that differentiate in vitro and is lost in epidermal dysplastic conditions, in the invading front of squamous cell carcinomas of the epidermis, in microinvasive cervical cancers, and in well-differentiated squamous lung tumors. These findings indicate that alpha 10.1.2 beta 1 integrin is downregulated during keratinocyte differentiation in vitro and in vivo. Moreover, lack of alpha 10.1.2 expression in basal cells of squamous epithelia is associated with early dysplastic changes and with the acquisition of invasive capacity.

Human thymic epithelial cells: adhesion molecules and cytokine production

The ability to culture human thymic epithelial cells has greatly facilitated studies of direct cell-cell interaction between thymic epithelial cells and T lymphocytes in vitro, as well as cytokine production and regulation of cytokine production. In vitro, human thymic epithelial cells bind to T lymphocytes via two adhesion pathways: CD2-lymphocyte function-associated antigen-3 and lymphocyte function-associated antigen-1-intercellular adhesion molecule-1. Cultured human thymic epithelial cells produce interleukins-1 alpha, -1 beta, -3, -6 and -8, granulocyte colony-stimulating factor, macrophage colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, leukemia inhibitory factor and transforming growth factor-alpha. Production of thymic epithelial cell-derived cytokines is regulated by both adhesion molecules (lymphocyte function-associated antigen-3) and soluble factors via both autocrine (interleukin-1 alpha, transforming growth factor-alpha) and paracrine (interleukin-4, interferon-gamma) pathways. Transforming growth factor-alpha and epidermal growth factor regulate various cytokine mRNA at a post-transcriptional level by increasing cytokine mRNA stability.

Thromboxane A2 receptor is highly expressed in mouse immature thymocytes and mediates DNA fragmentation and apoptosis

We have recently revealed that the thymus is the organ showing the highest expression of thromboxane (TX) A2 receptor in mice. In this study, thymic cell populations expressing the receptor were identified, and the effects of a TXA2 agonist on these cells were examined. Radioligand binding using a TXA2 receptor-specific radioligand revealed a single class of binding sites in the thymocytes with an affinity and specificity identical to those reported for the TXA2 receptor. The receptor density in these cells was comparable to that seen in blood platelets. This receptor is most highly expressed in CD4-8- and CD4+8+ immature thymocytes, followed by CD4+8- and CD4-8+ cells. The receptor density in splenic T cells was less than one fifth of that in CD4+8+ cells and no binding activity was detectable in splenic B cells. The addition of a TXA2 agonist, STA2, to thymocytes induced the disappearance of the CD4+8+ cells in a time- and concentration-dependent manner and caused DNA fragmentation. These changes were blocked by a specific TXA2 antagonist, S-145. These results demonstrate that TXA2 induces apoptotic cell death in immature thymocytes by acting on the TXA2 receptor on their cell surface and suggest a role for the TXA2/TXA2 receptor system in the thymic micro-environment.

Extracellular matrix proteins in intrathymic T-cell migration and differentiation?

Intrathymic T-cell migration and differentiation is not completely understood. Here, Wilson Savino and colleagues argue that certain interactions between differentiating thymocytes and thymic epithelial cells are mediated by extracellular matrix proteins and that these interactions influence intrathymic migration events and thymocyte differentiation.

Development of alpha beta T cells

Developing T cells in the thymus are subject to a screening process, through interactions with thymic stromal cells, from which T cells with appropriate T-cell receptors are selected. The recent generation of T-cell receptor transgenic mice and mice homozygous for disrupted T-cell receptor genes have now supplied tools that improve the prospect for a better understanding of the molecular mechanisms of this thymic selection process. In addition these model systems appear to indicate a role for a, not yet fully characterized, pre-T cell receptor complex in survival and further differentiation of pre-T cells.

The interactions of gamma delta T cells with extracellular matrix: receptor expression and utilization patterns

Purified populations and clones of human gamma delta T cells were examined for their ability to interact with extracellular matrix (ECM) components. The stimulation of these cells with phorbol ester induced cellular adhesion for ECM. The adhesion structures for fibronectin and collagen were shown to be members of the CD29 integrin family. The expression patterns of beta 1, beta 2 and beta 3 integrins by these cells were examined. The receptor expression and utilization patterns suggest that alpha beta, gamma delta T cells and B cells have similar repertoires of adhesion structure.

Novel factors from stromal cells: bone marrow and thymus microenvironments

The microenvironments contained within mammalian bone marrow and thymus play major roles in the life-long process of myeloid and lymphoid cell development and renewal. The cells that give architecture to these microenvironments are collectively referred to as stromal cells, and these cells grow as adherent cell types in cell culture. Stromal cells are predominantly a mixture of fibroblasts, cells of macrophage/dendritic lineages, epithelial and endothelial cells. There are at least three mechanisms that govern the interaction of stromal cells with hematopoietic and lymphoid cells: soluble factors, or cytokines, membrane-anchored growth factors and cell surface recognition molecules, such as integrins and selections. Little is known of the mechanisms that preserve the integrity of local microenvironments and how subpopulations of cells are transiently retained in microenvironments during various maturational states. Different lymphoid cells develop in bone marrow and thymus despite the similarities in stromal cells of these tissues. It remains a major quest to determine how the components of microenvironments of these organs regulate lineage-specific differentiation. The focus here is on stromal cells, the early development of myeloid cells and B lymphocytes in bone marrow and T lymphocytes in the thymus.