Involvement of the CDw50 molecule in allorecognition

A survey of endogenous retrovirus (ERV) sequences in the vicinity of multiple sclerosis (MS)-associated single nucleotide polymorphisms (SNPs)

Although multiple sclerosis (MS) is one of the most common central nervous system diseases in young adults, little is known about its etiology. Several human endogenous retroviruses (ERVs) are considered to play a role in MS. We are interested in which ERVs can be identified in the vicinity of MS associated genetic marker to find potential initiators of MS. We analysed the chromosomal regions surrounding 58 single nucleotide polymorphisms (SNPs) that are associated with MS identified in one of the last major genome wide association studies. We scanned these regions for putative endogenous retrovirus sequences with large open reading frames (ORFs). We observed that more retrovirus-related putative ORFs exist in the relatively close vicinity of SNP marker indices in multiple sclerosis compared to control SNPs. We found very high homologies to HERV-K, HCML-ARV, XMRV, Galidia ERV, HERV-H/env62 and XMRV-like mouse endogenous retrovirus mERV-XL. The associated genes (CYP27B1, CD6, CD58, MPV17L2, IL12RB1, CXCR5, PTGER4, TAGAP, TYK2, ICAM3, CD86, GALC, GPR65 as well as the HLA DRB1*1501) are mainly involved in the immune system, but also in vitamin D regulation. The most frequently detected ERV sequences are related to the multiple sclerosis-associated retrovirus, the human immunodeficiency virus 1, HERV-K, and the Simian foamy virus. Our data shows that there is a relation between MS associated SNPs and the number of retroviral elements compared to control. Our data identifies new ERV sequences that have not been associated with MS, so far.

RUNX3 regulates intercellular adhesion molecule 3 (ICAM-3) expression during macrophage differentiation and monocyte extravasation

The adhesion molecule ICAM-3 belongs to the immunoglobulin gene superfamily and functions as a ligand for the β2 integrins LFA-1, Mac-1 and α_dβ₂. The expression of ICAM-3 is restricted to cells of the hematopoietic lineage. We present evidences that the ICAM-3 gene promoter exhibits a leukocyte-specific activity, as its activity is significantly higher in ICAM-3+ hematopoietic cell lines. The activity of the ICAM-3 gene promoter is dependent on the occupancy of RUNX cognate sequences both in vitro and in vivo, and whose integrity is required for RUNX responsiveness and for the cooperative actions of RUNX with transcription factors of the Ets and C/EBP families. Protein analysis revealed that ICAM-3 levels diminish upon monocyte-derived macrophage differentiation, monocyte transendothelial migration and dendritic cell maturation, changes that correlate with an increase in RUNX3. Importantly, disruption of RUNX-binding sites led to enhanced promoter activity, and small interfering RNA-mediated reduction of RUNX3 expression resulted in increased ICAM-3 mRNA levels. Altogether these results indicate that the ICAM-3 gene promoter is negatively regulated by RUNX transcription factors, which contribute to the leukocyte-restricted and the regulated expression of ICAM-3 during monocyte-to-macrophage differentiation and monocyte extravasation.

Treatment of patients with progressive unresectable metastatic melanoma with a heterologous polyvalent melanoma whole cell vaccine

Unresectable metastatic melanoma has no elective treatment. Neither chemotherapy, intravenous IL-2 nor biochemotherapy clearly improves the overall survival. Recent assays with therapeutic vaccines have been recently yielded promising results. Here, we describe the application, clinical tolerance and antitumoural activity of a heterologous polyvalent melanoma whole cell vaccine in patients with metastatic melanoma. Twenty-eight AJCC stage III/IV melanoma patients with progressive unresectable metastatic disease were treated with our heterologous polyvalent melanoma whole cell vaccine between July 1, 1998 and July 1, 2002. All patients had already been unsuccessfully treated with high doses of IFN-alpha2 and/or polychemotherapy and/or biochemotherapy and/or perfusion of extremities, or could not receive other treatments due to their age or underlying illness. Twenty-three were assessable. The vaccine was constituted by 10 melanoma cell lines, derived from primary, lymph node and metastatic melanomas. Prior to intradermal inoculation, the cells were irradiated and mixed with BCG, and 50% were treated with DNFB. After a median follow-up of 19 months, 26% of patients responded: 3 CR (18, 16+, and 26+ months), 2 PR (8 and 22 months) and 1 MR (36+ months). The median survival of the whole group was 20.2 months. None of the 28 patients initially included in the study presented significant toxicity. This vaccination program had specific antitumoural activity in advanced metastatic melanoma patients and was well tolerated. The clinical responses and the median survival of our group of patients, together with the low toxicity of our polyvalent vaccine, suggest that this approach could be applied to earlier metastatic melanoma patients.

Pathogens target DC-SIGN to influence their fate DC-SIGN functions as a pathogen receptor with broad specificity

Dendritic cells (DC) are vital in the defense against pathogens. To sense pathogens DC express pathogen recognition receptors such as toll-like receptors (TLR) and C-type lectins that recognize different fragments of pathogens, and subsequently activate or present pathogen fragments to T cells. It is now becoming evident that some pathogens subvert DC functions to escape immune surveillance. HIV-1 targets the DC-specific C-type lectin DC-SIGN to hijack DC for viral dissemination. HIV-1 binding to DC-SIGN protects HIV-1 from antigen processing and facilitates its transport to lymphoid tissues, where DC-SIGN promotes HIV-1 infection of T cells. Recent studies demonstrate that DC-SIGN is a more universal pathogen receptor that also recognizes Ebola, cytomegalovirus and mycobacteria. Mycobacterium tuberculosis targets DC-SIGN by a mechanism that is distinct from that of HIV-1, leading to inhibition of the immunostimulatory function of DC and pathogen survival. Thus, a better understanding of DC-SIGN-pathogen interactions and their effects on DC function is necessary to combat infections.

A novel adhesion pathway that regulates dendritic cell trafficking and T cell interactions

Dendritic cells (DC) are present in essentially every tissue, where they operate at the interface of innate and acquired immunity by recognizing pathogens and presenting pathogen-derived peptides to T cells. Cell-cell interactions between DC, T cells and endothelial cells are crucial to all immunological processes. Recently, several C-type lectin receptors have been characterized that are abundantly expressed on the surface of DC. It is now becoming clear that these lectin receptors serve not only as antigen-receptors recognizing pathogens, but they may also function as adhesion receptors and/or signaling molecules. In particular the DC specific C-type lectin DC-SIGN (CD209) regulates adhesion processes, such as DC trafficking by interacting with ICAM-2 and T cell synapse formation, upon binding of ICAM-3. C-type lectins such as DC-SIGN contain a lectin domain that recognizes in a Ca2+-dependent manner carbohydrates such as mannose-containing structures presented on the glycoproteins ICAM-2 and ICAM-3. Although the integrin LFA-1 is a counter-receptor for both ICAM-2 and ICAM-3, on DC, DC-SIGN is the high affinity adhesion receptor for ICAM-2/-3. Here we discuss how the heterogeneity of mannose-residues exposed on cellular proteins and pathogens regulates specific binding of a repertoire of DC-expressed C-type lectins that contribute to the diversity of immune responses created by DC.

Cutting edge: CCR4 mediates antigen-primed T cell binding to activated dendritic cells

The binding of a T cell to an Ag-laden dendritic cell (DC) is a critical step of the acquired immune response. Herein, we address whether a DC-produced chemokine can induce the arrest of T cells on DC under dynamic flow conditions. Ag-primed T cells and a T cell line were observed to rapidly ( approximately 0.5 s) bind to immobilized DC at low shear stress (0.1-0.2 dynes/cm(2)) in a pertussis toxin-sensitive fashion. Quantitatively, Ag-primed T cells displayed 2- to 3-fold enhanced binding to DC compared with unprimed T cells (p < 0.01). In contrast to naive T cells, primed T cell arrest was largely inhibited by pertussis toxin, neutralization of the CC chemokine, macrophage-derived chemokine (CCL22), or by desensitization of the CCL22 receptor, CCR4. Our results demonstrate that DC-derived CCL22 induces rapid binding of activated T cells under dynamic conditions and that Ag-primed and naive T cells fundamentally differ with respect to chemokine-dependent binding to DC.

Structural study of N-linked oligosaccharides of human intercellular adhesion molecule-3 (CD50)

The N-linked oligosaccharides were released from purified human intercellular adhesion molecule (ICAM)-3 by hydrazinolysis. Approximately 6 mol of oligosaccharides were released from 1 mol of ICAM-3. The oligosaccharides reduced with NaB[3H]4 were separated into neutral and acidic fractions by paper electrophoresis. Most of the acidic oligosaccharides were converted to neutral ones by digestion with sialidase, indicating that they are sialyl derivatives. The neutral and sialidase-treated acidic oligosaccharides were fractionated by serial lectin column chromatography followed by Bio-Gel P-4 column chromatography. Structural studies of each oligosaccharide by sequential exo- and endo-glycosidase digestion and by methylation analysis revealed that N-linked oligosaccharides of ICAM-3 are mainly of tri- and tetra-antennary complex-type, about 60% of which contain two to three poly N-acetyllactosamine chains terminated with the type 1 structure and those without the type 1 structure per oligosaccharide. In addition, a small amount of the high mannose-type oligosaccharide with six alpha-mannose residues, which could act as a ligand for the dendritic cell-specific ICAM-3 grabbing nonintegrin, was detected.

Identification of DC-SIGN, a novel dendritic cell-specific ICAM-3 receptor that supports primary immune responses

Contact between dendritic cells (DC) and resting T cells is essential to initiate a primary immune response. Here, we demonstrate that ICAM-3 expressed by resting T cells is important in this first contact with DC. We discovered that instead of the common ICAM-3 receptors LFA-1 and alphaDbeta2, a novel DC-specific C-type lectin, DC-SIGN, binds ICAM-3 with high affinity. DC-SIGN, which is abundantly expressed by DC both in vitro and in vivo, mediates transient adhesion with T cells. Since antibodies against DC-SIGN inhibit DC-induced proliferation of resting T cells, our findings predict that DC-SIGN enables T cell receptor engagement by stabilization of the DC-T cell contact zone.

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.

Intracellular Cytokine Profile of Cord and Adult Blood Lymphocytes

Umbilical cord blood (CB) transplantation is thought to be associated with a reduced risk of severe graft-versus-host-disease (GVHD) compared with bone marrow transplantation (BMT). The cytokine cascade is known to be important in the pathogenesis of GVHD; however, previous studies investigating the cytokine secretion pattern of CB cells have been contradictory because of variations in experimental techniques. In this study, the cytokine profile of cord and adult blood lymphocytes and lymphocyte subsets has been assessed at the single-cell level by flow cytometry, using CD4/CD8 and CD45RA/CD45RO markers. Cord and adult blood mononuclear cells were stimulated with phorbol 12-myristate 13-acetate (PMA) and ionomycin in the presence of monensin. After 4 to 24 hours of incubation, interleukin-2 (IL-2), IL-4, interferon-γ (IFN-γ), and tumor necrosis factor-α (TNF-α) production was measured by three-color flow cytometry. The results show that cord blood lymphocytes (CBL) produce less IL-2, IL-4, IFN-γ, and TNF-α than adult peripheral blood lymphocytes (ABL). Further subset analysis showed that in CBL the majority of cytokine producing cells were CD4+CD45RA+, whereas in ABL the cytokine-producing cells were both CD4+CD45RO+ and CD8+CD45RO+. These results suggest that the reduced incidence of GVHD in CB transplantation may partly due to the altered cytokine profile seen in CBL.

The intercellular adhesion molecule (ICAM) family of proteins. New members and novel functions

Macromolecular adhesive associations between cells are important for transmitting spatial and temporal information that is critical for immune system function. One such group of proteins, the intercellular adhesion molecules (ICAMs), has grown as newly identified members are revealed. In addition, the functions of the ICAMs, in general, have begun to be better understood, including intracellular signaling events. This information has led to the design of novel therapeutic agents that may prove effective in a variety of disease states.

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.

Functional mapping of the cytoplasmic region of intercellular adhesion molecule-3 reveals important roles for serine residues

Intercellular adhesion molecule-3 (ICAM-3), a ligand for beta2 integrins, elicits a variety of activation responses in lymphocytes. We describe a functional mapping study that focuses on the 37-residue cytoplasmic region of ICAM-3. Carboxyl-terminal truncations delineated portions involved in T cell antigen receptor costimulation, homotypic aggregation, and cellular spreading. Truncation of the membrane distal 25 residues resulted in loss of T cell antigen receptor costimulation as determined by interleukin 2 secretion. Aggregation and cell spreading were sensitive to truncation of the membrane distal and proximal thirds of the cytoplasmic portion. Phosphoamino acid analysis revealed that ICAM-3 from activated cells contained phosphoserine and phosphopeptide mapping identified Ser489 as a site of phosphorylation in vivo. Mutation of Ser489 or Ser515 to alanine blocked interleukin 2 secretion, aggregation and cell spreading, while mutation of other serine residues affected only a subset of functions. Ser489 was a phosphorylation site in vitro for recombinant protein kinase Ctheta. Finally, treatment of Jurkat cells with chelerythrine chloride, a protein kinase C inhibitor, prevented ICAM-3-triggered spreading. This study delineates separable regions and amino acid residues within the cytoplasmic portion of ICAM-3 that are important for T cell function.

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

CD50 (ICAM-3) has been identified as the third CD11a/CD18 (LFA-1) counter receptor. We investigated the expression and possible role of this molecule in the induction of early and late activation events in human thymocytes. We observed that CD50 expression is acquired by early T cell progenitors (CD34+) and maintained during thymic development, reaching the highest levels in the most mature population of thymocytes (CD3high). Neither basal nor cytokine-induced expression of CD50 was observed on untransformed human thymic epithelial cell lines. Cross-linking of CD50 expressed on the surface of human thymocytes, by using mAbs recognizing epitopes not related to the CD11a binding site, transduced transmembrane signals leading to an increase of intracellular calcium concentration. This calcium mobilization was inhibited when CD50 was co-cross-linked with CD45, suggesting that tyrosine phosphorylation is also involved in CD50 signaling. The same anti-CD50 mAbs that were able to affect intracellular calcium levels were shown to induce CD69 but not CD25 expression on human thymocytes. This effect was preferentially observed on CD3low/CD3high thymocyte subpopulations. Cross-linking of CD50 also significantly increased activation-induced cell death of human thymocytes. These results support the idea that CD50 molecule can play a role in developing functionally mature T lymphocytes.

Expression of intercellular adhesion molecule-3 (ICAM-3/CD50) in malignant lymphoproliferative disorders and solid tumors

ICAM-3/CD50 is a recently described LFA-1 counter receptor that seems to play an important role in the initiation of immune responses. In this study we have examined the expression of ICAM-3/CD50 in a large series of human neoplasms including 101 Non-Hodgkin's lymphomas (NHL), 26 Hodgkin's disease, and 38 solid tumors to define the distribution patterns of this molecule in malignant neoplasms and their possible correlation with clinical and pathological characteristics of the patients. In NHL, ICAM-3/CD50 was expressed in almost all the tumors with a tendency to be lost in high grade lymphomas. Reed-Sternberg cells and their variants in Hodgkin's disease were always negative independently of the histological subtype of the disease. No expression was observed in tumor epithelial cells of the 38 solid tumors examined. Strong endothelial cell staining was observed in 31% of the NHL and 31% of Hodgkin's disease. ICAM-3 expression in these cases was restricted to small tumor vessels. ICAM-3 expression in endothelial cells of NHL was significantly more frequent in high grade (40%) than in low grade lymphomas (14%) (p = 0.012). In addition, tumor vessels were also positive in 29% of solid tumors independently of the histological type. No correlation was observed between ICAM-3 expression in tumor or endothelial cells and other clinical and pathological characteristics of the patients. These findings indicate that ICAM-3 expression in human tumors is restricted to hematological neoplasms with a tendency to be lost in high grade lymphomas and Hodgkin's disease. ICAM-3 is also expressed by endothelial cells from tumor-associated neovascularization in both lymphoid and solid tumors.

Localization of the binding site on intercellular adhesion molecule-3 (ICAM-3) for lymphocyte function-associated antigen 1 (LFA-1)

Intercellular adhesion molecule 3 (ICAM-3; CD50) is the predominant counter-receptor on resting T cells and monocytes for the leukocyte integrin, lymphocyte function-associated antigen 1 (LFA-1; CD11a/CD18), and may play an important role in the initial stages of the T cell-dependent immune response. Deletion of individual immunoglobulin superfamily (IgSF) domains of ICAM-3 and ICAM-3 IgSF domain chimeras with CD21 showed there is a single LFA-1 binding site in ICAM-3 and that IgSF domain 1 is necessary and sufficient for LFA-1 binding. Epitope mapping and functional studies performed with 17 anti-ICAM-3 monoclonal antibodies demonstrated that only some monoclonal antibodies, with epitopes wholly within domain 1 of ICAM-3, were able to block binding of ICAM-3 bearing cells to purified LFA-1, in agreement with the data obtained from the domain deletion mutants and CD21 chimeras. Analysis of a panel of 45 point mutants of domain 1 of ICAM-3 identified five residues that may contact LFA-1 as part of the binding site, Asn23, Ser25, Glu37, Phe54, and Gln75. These five residues are predicted by molecular modeling, based on the structure of vascular cell adhesion molecule 1 (VCAM-1), to cluster in two distinct locations on domain 1 of ICAM-3 on the BED face (Asn23 and Ser25) and on the C strand or CD loop (E37), the E strand (F54), and the FG loop (Q75). The residues, Asn23 and Ser25, comprise a consensus N-linked glycosylation site.

The ICAM-3/LFA-1 interaction is critical for epidermal Langerhans cell alloantigen presentation to CD4+ T cells

Intercellular adhesion molecule (ICAM)-3 is a recently described member of the immunoglobulin superfamily and, as such, is closely related to ICAM-1 and ICAM-2. All three ICAMS are cognate for the counter-receptor lymphocyte function associated antigen-1 (LFA-1, CD11a/CD18). Unlike ICAM-1 and ICAM-2, ICAM-3 is constitutively expressed at high levels on resting leucocytes. We investigated the expression and function of ICAM-3 in normal skin (n = 5), as well as its expression in psoriasis (n = 4), atopic eczema (n = 4), allergic (rhus) contact dermatitis (n = 3), and cutaneous T-cell lymphoma (CTCL, n = 2). Five-micrometre cryostat sections of skin were stained using monoclonal antibodies to ICAM-3 and a well characterized immunoperoxidase technique. In normal skin, ICAM-3 was expressed by all cutaneous leucocytes but most striking was the strong expression of ICAM-3 by Langerhans cells within both epidermis and dermis. This observation was confirmed by double-labelling with CD1a and negative staining with an IgG1 isotype control. In psoriasis, atopic eczema, allergic contact dermatitis, and CTCL, ICAM-3 was co-expressed on all CD1a+ cells, although, in psoriasis, the intensity of ICAM-3 expression was reduced. Functional blocking experiments were performed to determine whether the observed ICAM-3 expression on Langerhans cells was functionally important in antigen presentation. CD4+ T cells were prepared from peripheral blood and 10(5) CD4+ T cells combined with 10(5) epidermal cells harvested from keratome biopsies of normal skin of an individual allogeneic to the T-cell donor. Addition of 50 micrograms anti-ICAM-3 to the co-culture resulted in a consistent (50%) reduction in degree of alloantigen presentation by Langerhans cells to T cells. Inhibition was 77% of that produced by the addition of anti-LFA-1. These data indicate that ICAM-3 is constitutively expressed by Langerhans cells and is a major ligand for LFA-1 on CD4+ T cells during their response to Langerhans cells. Because fresh Langerhans cells constitutively express little ICAM-1, whereas ICAM-3 is constitutively expressed at high levels, it would appear that ICAM-3 is the dominant functional ICAM on in situ Langerhans cells in the normal epidermis.

Intercellular adhesion molecule-3 is the predominant co-stimulatory ligand for leukocyte function antigen-1 on human blood dendritic cells

Dendritic cells (DC) are potent stimulators of primary T lymphocyte responses to foreign antigen. The initial DC-T lymphocyte interaction involves the binding of the adhesion molecule leukocyte function antigen-1 (LFA-1; CD11a/CD18) on the T lymphocyte to an intercellular adhesion molecule (ICAM) on the DC. Although blood and tonsil DC express ICAM-1 (CD54) and ICAM-2 (CD102) on their surface, anti-ICAM-1 and anti-ICAM-2 monoclonal antibodies (mAb) have little inhibitory activity on the DC-stimulated mixed leukocyte reaction (MLR). We therefore examined the expression of the more recently identified LFA-1 ligand, ICAM-3 (CD50), in comparison to ICAM-1 and ICAM-2 on blood DC and sought a functional role for ICAM-3 in DC-mediated T lymphocyte responses. Resting blood DC expressed significantly more ICAM-3 than ICAM-1 or ICAM-2 as assessed by flow cytometry. Treatment of resting DC with interferon-gamma led to increased expression of ICAM-1; however, ICAM-2 and ICAM-3 levels remained relatively constant. Solid-phase recombinant chimeric molecules ICAM-1-, ICAM-2- and ICAM-3-Fc were able to co-stimulate CD4+ T lymphocyte proliferation in conjunction with suboptimal solid-phase CD3 mAb 64.1. However, the anti-ICAM-3 mAb CAL 3.10 inhibited a DC-stimulated MLR to a greater extent than anti-ICAM-1 or anti-ICAM-2 reagents and appeared to act by blocking the DC ICAM-3- T lymphocyte LFA-1 interaction. As ICAM-3 is the predominant LFA-1 ligand on resting blood DC, we postulate that DC may utilize ICAM-3 for initial DC- T lymphocyte interactions, and that ICAM-1, which is up-regulated upon DC activation, and/or ICAM-2, may contribute to DC migration or later phases of the T lymphocyte activation process.

CD50 (intercellular adhesion molecule-3) is expressed at higher levels on memory than on naive human T cells but induces a similar calcium mobilization on both subsets

CD50, the intercellular adhesion molecule-3 (ICAM-3), is expressed almost exclusively on hematopoietic cells. T lymphocytes display a bimodal distribution on CD50 expression levels. It was observed that CD45RO+ cells expressed higher levels of CD50 than CD45RA+ T lymphocytes. A similar situation was observed when CD4 and CD8 subpopulations were analyzed, with CD8+ cells expressing higher levels of CD50 than CD4+ cells. When adult T lymphocytes were analyzed by three-color flow cytometry in CD8+CD45RA+ cells both CD50low and CD50high expressing cells were detected, in accordance with several memory markers on T lymphocytes, whereas only cells with a low level of CD50 were observed in CD4+CD45RA+. The different level of CD50 expression was confirmed by analyzing purified CD45RA+ and CD45RO+ T cells. Moreover, after the comparison of CD50 expression level in thymocytes, cord blood and adult T lymphocytes, a progressive increase was observed. When T cells were sorted by their intensity of CD50 expression, only CD50high cells proliferated in response to tetanus toxoid. Therefore, the phenotypic and functional analysis of adult and cord blood T lymphocytes as well as thymocytes indicates that CD50 expression increases during the maturation process of T lymphocytes: from the lowest CD50 levels present on CD1+ thymocytes, to the highest levels of CD50 on human memory T cells. In addition, we have observed that after CD50 cross-linking on human T lymphocytes, a transient increase in intracellular calcium concentration ([Ca2+]i) is produced. When CD45RA+ and CD45RO+ T cells were analyzed, in spite of the level of CD50 expression, the stimulation through CD50 induced a similar level of Ca2+ mobilization in both subpopulations, contrasting with the higher rise in [Ca2+]i induced by CD3 stimulation on CD45RA+ versus CD45RO+. These data suggest that the signal transduction pathways activated after CD50 cross-linking are, at least partially, independent of those involved after CD3 stimulation.

Epitope mapping and functional properties of anti-intercellular adhesion molecule-3 (CD50) monoclonal antibodies

Intercellular adhesion molecule-3 (ICAM-3, CD50), a member of the immunoglobulin gene superfamily, is a major ligand for the lymphocyte function-associated antigen 1 (LFA-1, CD18/CD11a) in the resting immune system and plays a role as a signaling and costimulatory molecule on T lymphocytes. In this study we have generated a large panel of anti-ICAM-3 monoclonal antibodies (mAb) and show that the biological effects of these antibodies are critically dependent on the epitope recognized. By using an adhesion assay employing COS cells expressing LFA-1 binding to recombinant chimeric ICAM-3-Fc proteins (which overcomes the confounding effects of interleukocyte LFA-1/ICAM binding events), we have been able to examine the effects of these antibodies in blocking LFA-1/ICAM-3 adhesion. Our data suggests that only a small minority of ICAM-3 mAb, recognizing a distinct epitope, are able to mimic the effects of LFA-1 binding to ICAM-3. Moreover these antibodies are functionally distinct as defined by their costimulatory activity and ability to elicit interleukin-2 production and cell proliferation in T lymphocytes.

Expression of ICAM-3 on human epidermal dendritic cells

Three counter-receptors for LFA-1 of the immunoglobulin family have been discovered: ICAM-1, ICAM-2, and ICAM-3. Despite their homologies, their patterns of expression suggest specialized roles. The finding that ICAM-3 is much better expressed than other LFA-1 ligands on monocytes and resting T cells, and that this discovery may be important in the initiation of immune responses prompted us to search for the expression of ICAM-3 by human epidermal Langerhans cells (LC). Six out of eight different ICAM-3 monoclonal antibodies were found to be reactive with epidermal LC. Immunoelectron-microscopy staining revealed that 100% of freshly-isolated, typical Birbeck granules containing LC expressed ICAM-3. After one day and three days of culture, 100% of LC still expressed ICAM-3, but the staining intensity was decreased by 58% and 76% respectively. Immunoprecipitation of 125I surface-labeled LC with anti-ICAM-3 antibodies revealed a polypeptide with apparent M(r) of 122,000-125,000. To determine whether ICAM-3 was involved in LC function, mixed epidermal cell-lymphocyte reactions were performed with freshly isolated LC in the presence of various concentrations of different anti-ICAM-3 antibodies. Among the different antibodies tested, HP2/19 and CBR-IC3/1 were found to partially block the reaction in a dose-dependent manner, suggesting that ICAM-3 represents a new molecule involved in the initiation of the immune response driven by epidermal LC.

CD50 (intercellular adhesion molecule 3) stimulation induces calcium mobilization and tyrosine phosphorylation through p59fyn and p56lck in Jurkat T cell line

The leukocyte differentiation antigen, CD50, has been recently identified as the intercellular adhesion molecule 3 (ICAM-3), the third counter-receptor of leukocyte function-associated antigen 1 (LFA-1). This molecule seems to be specially involved in the adhesion events of the initial phases of the immune response. To characterize the role of CD50 in leukocyte interactions, the different molecular events induced after cross-linking of CD50 on T cell-derived Jurkat cell line have been analyzed. When cells were incubated with anti-CD50 mAbs and cross-linked with polyclonal goat anti-mouse immunoglobulins, a rise in intracellular calcium concentration ([Ca2+]i) was observed. This increase in [Ca2+]i was mainly due to the uptake of extracellular Ca2+. This Ca2+ flux involved tyrosine phosphorylations and was further increased by CD3 costimulation. These data, together with those obtained by phosphotyrosine (P-Tyr) immunoprecipitation and in vitro kinase assays, suggested the involvement of protein-tyrosine kinases (PTK) in CD50 transduction pathways. By using specific antisera, the presence of p56lck and p59fyn protein tyrosine kinases (PTK) was clearly demonstrated in the CD50 immunoprecipitates. These findings suggest that the interaction of CD50 with its natural ligand (LFA-1) may result in T lymphocyte activation events, in which CD50 could play a very active role after antigen triggering.

Signaling through CD50 (ICAM-3) stimulates T lymphocyte binding to human umbilical vein endothelial cells and extracellular matrix proteins via an increase in beta 1 and beta 2 integrin function

Regulated adhesion of T lymphocytes to antigen-presenting cells, endothelial cells and extracellular matrix proteins is crucial in T lymphocyte activation and migration to the sites of injury. In this study, we show that three monoclonal antibodies (mAb) recognizing different epitopes on the CD50 (ICAM-3) molecule increase T lymphocyte adhesion to tumor necrosis factor (TNF)-stimulated human umbilical vein endothelial cells and extracellular matrix proteins. These phenomena are mediated by an increase in beta 1 and beta 2 integrin avidity since (a) CD50-induced adhesion to endothelial cells was abrogated by simultaneous blocking of beta 1- and beta 2-mediated adhesion pathways but not by interfering with either one individually, (b) CD50 mAb increased beta 1 integrin-mediated adhesion to extracellular matrix proteins and to fibronectin-derived synthetic peptides, (c) CD50 mAb enhanced T lymphocyte binding to ICAM-1 transfectants, and (d) CD50 mAb did not modify surface expression patterns of beta 1 or beta 2 integrins on T lymphocytes. Our data suggest that constitutively expressed CD50 (ICAM-3) can play a pivotal role in initiating a cascade of adhesion events which may be crucial in immune activation and in the development of inflammatory lesions.

Characterization of the function of intercellular adhesion molecule (ICAM)-3 and comparison with ICAM-1 and ICAM-2 in immune responses

We have characterized the immunobiology of the interaction of intercellular adhesion molecule 3 (ICAM-3; CD50) with its counter-receptor, leukocyte function-associated antigen 1 (LFA-1; CD11a/CD18). Purified ICAM-3 supported LFA-1-dependent adhesion in a temperature- and cation-dependent manner. Activation of cells bearing LFA-1 increased adhesiveness for ICAM-3 in parallel to adhesiveness for ICAM-1. Although CBR-IC3/1 monoclonal antibody (mAb) blocked adhesion of cells to purified LFA-1, when tested alone, neither CBR-IC3/1 nor five novel ICAM-3 mAbs characterized here blocked adhesion of cells to purified ICAM-3 or homotypic adhesion. Two ICAM-3 mAbs, CBR-IC3/1 and CBR-IC3/2, were required to block LFA-1-dependent adhesion to purified ICAM-3- or LFA-1-dependent, ICAM-1-, ICAM-2-independent homotypic adhesion of lymphoid cell lines. Two ICAM-3 mAbs, CBR-IC3/1 and CBR-IC3/6, induced LFA-1-independent aggregation that was temperature and divalent cation dependent and was completely inhibited by ICAM-3 mAb, CBR-IC3/2, recognizing a distinct epitope. Purified ICAM-3 provided a costimulatory signal for proliferation of resting T lymphocytes. mAb to ICAM-3, together with mAbs to ICAM-1 and ICAM-2, inhibited peripheral blood lymphocyte proliferation in response to phytohemagglutinin, allogeneic stimulator cells, and specific antigen. Inhibition was almost complete and to the same level as with mAb to LFA-1, suggesting the most functionally important, and possibly all, of the ligands for LFA-1 have been defined.

CDw50 and ICAM-3: two names for the same molecule

CDw50 differentiation antigen is a molecule broadly expressed on hematopoetic cells but not on other cells. Previous experiments showed that CDw50 monoclonal antibodies (mAb) inhibited primary mixed lymphocyte culture (MLC). To understand the function of CDw50 better, we purified it and obtained peptide sequence. At the same time, intercellular adhesion molecule (ICAM)-3, the third ligand of lymphocyte function-associated molecule 1, was described by mAb and subsequent cDNA cloning. Immunochemical, functional, and protein sequencing studies show that ICAM-3 and CDw50 are the same glycoprotein, a 120-kDa surface molecule with presumably an important role in the immune responses.

Isolation and characterisation of a CDw50 negative Jurkat T-cell line variant (PPL.1)

PPL.1, a Jurkat cell line variant deficient in CDw50 surface expression, has been selected by fluorescence-activated cell sorting and expanded in cell culture. We have studied the expression of several leukocyte surface markers (CD2, CD3, CD4, CD8, CD7, CD26, CD25, CD14, CD18, kCD20, CD43, CD45, CD45R, CD71 and HLA class I and II) and we find no differences in their expression between PPL.1 and its parental Jurkat cell line. Immunoprecipitation analysis of metabolically labelled PPL.1 cells ([35S]-cysteine plus [35S]-methionine) fails to detect the presence of a preformed cytoplasmic pool of CDw50 molecules. The deficient CDw50 expression on PPL.1 cells is stable after several weeks of continuous culture and even after exposure of cells to several lymphocyte activating agents (PGE2, PHA, Con A, calcium ionophore A23187 and human recombinant IFN-gamma). No karyotype changes responsible for such phenotype deficiency are found. PPL.1 cells are as efficient as wild-type Jurkat or K562 cells, when used as targets in cytotoxicity assays with fresh or PHA-stimulated peripheral blood lymphocytes. No blocking effects of CDw50-specific mAb are observed in such assay. These results are consistent with the fact that CDw50 is not involved in alloreactive T-cell-specific cytotoxicity. They also suggest that this antigen is implicated only on a very specialized type of cell-cell interactions.

Effect of protein kinase C activators on the phosphorylation and the surface expression of the CDw50 leukocyte antigen

The CDw50 antigen is a constitutively non-phosphorylated leukocyte surface molecule which becomes highly phosphorylated in all the normal and lymphoblastoid cells analyzed (peripheral blood mononuclear cells, Molt 4, CEM, 8402, Namalwa), after stimulation with tumor promoter agents (phorbol 12-myristate 13-acetate, phorbol 12,13-dibutyrate, mezerein). This phosphorylation is rapid (within 1-5 min), dose-dependent and results in the incorporation of PO(3-)4 groups on serine residues. Furthermore, the level of CDw50 phosphorylation induced by tumor promoter agents is decreased by the protein kinase C inhibitors staurosporine and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine. Activation of peripheral lymphocytes with concanavalin A, phytohemagglutinin and cross-linking of CD3 molecules also induces CDw50 phosphorylation, but the response is delayed and less intense than when tumor promoting agents are used. Treatment with any of the aforementioned agents is not accompanied by quantitative changes in the CDw50 surface expression. We therefore conclude that protein-kinase-C-mediated mechanisms are involved in phosphorylation, but not in regulation of the surface expression of the CDw50 leukocyte antigen.