Polypeptides on human B lymphocytes associated with cell activation

Expression and Functional Role of CD54/Intercellular Adhesion Molecule-1 (ICAM-1) on Human Blood Cells

CD54/Intercellular Adhesion Molecule-1 (ICAM-1) is a cell adhesion molecule largely distributed among normal and neoplastic tissues. Through the binding to its ligand(s) CD54 plays a key role in cell to cell interactions leading to the immune response. Recently, CD54 expression has been investigated on hematopoietic cells: the antigen is predominantly expressed in the early stages of normal hematopoiesis and during the activation of blood cells. As regards to hematological malignancies, CD54 is strongly expressed on neoplastic cells from "stem cell derived" neoplasms. In AML, CD54 expression is related with other differentiation-linked molecules such as CD34 and HLA-DR and is significantly correlated with FAB morphological classification. In lymphoproliferative disorders, a high CD54 expression is associated with germinal centre lymphomas. This review summarizes our current understanding of CD54 with emphasis on recent advances and reference to unresolved issues such as its prognostic role in the clinical outcome of oncohematological diseases.

Response to sublethal heat treatment of prostatic tumor cells and of prostatic tumor infiltrating T-cells

BACKGROUND

To investigate the possibilities offered by high intensity focused ultrasound (HIFU) in the field of tumor vaccination, we analyzed how prostatic cancer (CaP) cells react towards heat treatment and whether increased access to CaP cells by the immune system would be the result.

METHODS

Heat/stress response of CaP cells in situ and of CaP cell lines was analyzed by immunohistochemistry, Western blotting, and Atlas array. A heat-induced change in immune recognition was analyzed functionally using human T-helper (Th)1 and Th2-cytokine release with tumor infiltrating T-lymphocytes (TIL) as responder and autologous CaP cells either heated or untreated as stimulator cells.

RESULTS

Transcription of 68 out of 500 genes was upregulated by sublethal heat in LNCaP and PC3 cells. Significantly upregulated stress protein (SP) expression (HSP-72, -73, GRP-75, -78) was seen at the border zone of HIFU treatment. Remarkably, even untreated benign prostatic hyperplasia (BPH) specimens revealed relative overexpression of heat shock protein (HSP)-72, -73 and glucose regulated protein (GRP)-75, -78. Heated CaP cells increased Th1-cytokine (IL-2, IFN-gamma, TNF-alpha) release but decreased Th2-cytokine (IL-4, -5, -10) release of TIL.

CONCLUSIONS

HIFU treatment may alter the presentation of prostate tissue and tumor antigens and this presentation is most likely stimulatory. HSP-72/73 overexpression in untreated BPH may suggest a mechanism by which BPH can incite inflammation.

Characterization of human inducible costimulator ligand expression and function

The inducible costimulator (ICOS) is the newest member of the CD28/CD152 receptor family involved in regulating T cell activation. We constructed a soluble-Ig fusion protein of the extracellular domain of human ICOS and used it as a probe to characterize expression patterns of the ICOS ligand (ICOSL). ICOSIg did not bind to CD80- or CD86-transfected Chinese hamster ovary cell lines, demonstrating that ICOSL is distinct from those ligands identified for CD28/CD152. ICOSIg showed selective binding to monocytic and B cell lines, whereas binding was undetectable on unstimulated monocytes and peripheral blood T and B cells. Expression of ICOSL was induced on monocytes after integrin-dependent plastic adhesion. Pretreatment of monocytes with mAb to the beta2-integrin subunit CD18 decreased adhesion and abolished ICOSL up-regulation but had no effect on CD80/86 (CD152 ligand (CD152L)) expression. Both ICOSL and CD152L were up-regulated on monocytes by IFN-gamma but by distinct signaling pathways. Unlike CD152L expression, ICOSL expression did not change when monocytes were differentiated into dendritic cells (DCs) or after DCs were induced to mature by LPS, TNF-alpha, or CD40 ligation. Addition of ICOSIg to allogeneic MLRs between DCs and T cells reduced T cell proliferative responses but did so less efficiently than CTLA4Ig (CD152Ig) did. Similarly, ICOSIg also blocked Ag-specific T cell proliferation to tetanus toxoid. Thus, ICOSL, like CD80/86, is expressed on activated monocytes and dendritic cells but is regulated differently and delivers distinct signals to T cells that can be specifically inhibited by ICOSIg.

Effect of intravenous cyclophosphamide in systemic lupus erythematosus: relation to lymphocyte subsets and activation markers

Since the mechanism mediating the beneficial effect of intravenous cyclophosphamide (IVCY) in systemic lupus erythematosus (SLE) is unknown, we investigated lymphocyte subsets and markers of activated lymphocytes in patients received IVCY, and compared the results with the effect of steroid pulse. In 55 patients with SLE, 34 patients receiving IVCY [21 cases (61.8%) were responsive] and 25 patients received steroid pulse [21 cases (84.0%) were responsive] (four patients who were resistant to steroid pulse therapy were transferred to IVCY). When the lymphocyte subsets and markers of activated lymphocytes were compared in the responsive and unresponsive group of IVCY, soluble CD4 levels and the ratio of HLA-DP-positive T cells were significantly higher in the unresponsive group. Further, the changes of these markers and costimulatory molecules [LFA-1 (CD11a), ICAM-1 (CD54), CD40 and CD40-ligand (CD154)] were also examined in the responsive patients. The ratio of HLA-DP-positive T cells did not change in the IVCY-responsive group, while it decreased in the steroid pulse therapy-responsive group. The ratio of CD11a on T cells increased and CD54 on B cells decreased in the IVCY-responsive group. The ratio of CD154 on T cells increased in the steroid pulse-responsive group, while it decreased in the IVCY-responsive group. These results suggest that the effect of IVCY is different to that of steroid pulse therapy and mainly related to B cell activation, and that these markers may contribute to predict the responsiveness of IVCY.

p38 MAPK Is Required for CD40-Induced Gene Expression and Proliferation in B Lymphocytes

We have investigated the activation of the p38 MAPK pathway in response to CD40 engagement in multiple B cell lines and in human tonsillar B cells to define the role of p38 MAPK in proliferation, NF-κB activation and gene expression. Cross-linking CD40 rapidly stimulates both p38 MAPK and its downstream effector, MAPKAPK-2. Inhibition of p38 MAPK activity in vivo with the specific cell-permeable inhibitor, SB203580, under conditions that completely prevented MAPKAPK-2 activation, strongly perturbed CD40-induced tonsillar B cell proliferation while potentiating the B cell receptor (BCR)-driven proliferative response. SB203580 also significantly reduced expression of a reporter gene driven by a minimal promoter containing four NF-κB elements, indicating a requirement for the p38 MAPK pathway in CD40-induced NF-κB activation. However, CD40-mediated NF-κB binding was not affected by SB203580, suggesting that NF-κB may not be a direct target for the CD40-induced p38 MAPK pathway. In addition, SB203580 selectively reduced CD40-induced CD54/ICAM-1 expression, whereas CD40-dependent expression of CD40 and CD95/Fas and four newly defined CD40-responsive genes cIAP2, TRAF1, TRAF4/CART and DR3 were unaffected. Our observations show that the p38 MAPK pathway is required for CD40-induced proliferation and that CD40 induces gene expression via both p38 MAPK-dependent and -independent pathways.

The BB1 Monoclonal Antibody Recognizes Both Cell Surface CD74 (MHC Class II-Associated Invariant Chain) as Well as B7-1 (CD80), Resolving the Question Regarding a Third CD28/CTLA-4 Counterreceptor

The identification of all CD28/CTLA-4 counterreceptors is critical to our understanding of this pivotal pathway of T cell activation. Clouding our understanding has been the reported discrepancies in expression and function of the B7-1 (CD80) molecule based upon the use of the BB1 vs other anti-B7-1 mAbs. To resolve this issue, we have cloned a BB1-binding molecule from the BB1+B7-1− NALM-6 pre-B cell line. Here, we demonstrate that this BB1-binding molecule is identical to the cell surface form of CD74 (MHC class II-associated invariant chain). CD74-transfected cells bound the BB1 mAb but not other anti-CD80 mAbs, CD28-Ig, or CTLA4Ig. Absorption and blocking experiments confirmed the reactivity of BB1 mAb with CD74. A region of weak homology was identified between CD74 and the region of B7-1 encoding the BB1 epitope. Therefore, the BB1 mAb binds to a protein distinct from B7-1, and this epitope is also present on the B7-1 protein. Many of the puzzling observations in the literature concerning the expression of human B7-1 are resolved by an understanding that BB1 staining is the summation of CD74 plus B7-1 expression. This observation requires the field to reconsider studies using BB1 mAb in the analysis of CD80 expression and function.

Regulation of platelet-derived growth factor receptor expression by cell context overrides regulation by cytokines

Immunocytochemical data has indicated that platelet-derived growth factor receptor beta-subunit (PDGFR beta) expression by connective tissue cells is up-regulated in many disease states. To investigate potential causes of this up-regulation, we have evaluated conditions that regulate PDGF receptor transcript levels in cultured diploid human fibroblast model systems. We found combinations of soluble mediators and cell "context," which can regulate receptor transcripts (and receptor protein) over a 50-fold range, with cell context factors being far more potent regulators than soluble mediators. For cells grown under standard monolayer conditions on plastic, levels of both PDGFR beta and PDGFR alpha increase 10-fold as culture density increases. Cells grown in suspension or in three-dimensional gels express 10- to 20-fold higher transcript levels than cells plated on plastic at comparable density and serum concentration. The soluble mediators tested, including 14 cytokines and conditioned medium from activated lymphocytes, have only modest effects on transcript levels. Lymph decreases PDGFR beta transcript expression 4-fold, suggesting that a component of interstitial fluid contributes to maintenance of the low basal level of expression in normal tissues. The mitogenic responsiveness of cells cultured at different densities parallels the level of PDGFR beta expression. Blocking anti-PDGF receptor antibodies decrease receptor availability and mitogenic responsiveness in parallel. In both cases, the striking overlap between the PDGF-BB binding and mitogenesis dose-response curves suggests that the level of PDGF receptor expression can limit responsiveness to PDGF. Overall, these results suggest that the up-regulation of PDGF receptor expression seen under pathological conditions may be due to disruption of the cell's normal environment/context/cell shape/cell attachment and that this could serve to ensure that a proliferative response to PDGF would occur only under conditions in which there had been significant tissue damage.

Interferon-gamma and tumor necrosis factor-alpha treatment of ex vivo human carcinoma cells potentiates their interaction with allogeneic lymphocytes

Short-term exposure of ex vivo carcinoma and sarcoma cells to IFN-gamma and TNF-alpha induced or elevated to detectable levels the surface expression of MHC class I, class II, and ICAM-1 (CD54), but only rarely the B7 (CD80) molecules. The cytokine-treated tumor cells interacted more efficiently with allogeneic blood lymphocytes collected from healthy donors compared with untreated cells. This was demonstrated (1) by the induction of DNA synthesis and generation of cytotoxic activity in mixed cultures and (2) by the elevated susceptibility to the cytotoxic effectors. Although the cytokine-induced increase in MHC and ICAM-1 on the low-expressor tumors were probably important to the interaction with lymphocytes, it is likely that other properties were also induced that contributed to the phenomenon. This was indicated by the results obtained with several tumors that expressed indigenously high levels of these molecules but reacted with the allogeneic lymphocytes only or more efficiently after treatment with IFN-gamma and TNF-alpha. In these experiments B7 expression did not influence the efficiency of interactions between lymphocyte and tumor cells. The results also showed that, under the conditions used, the untreated tumor cells that did not activate allogeneic lymphocytes were sensitive to appropriately activated effectors. Thus the afferent and efferent arms of lymphocyte-tumor cell interactions appeared to have different requirements.

Intercellular adhesion molecule-1

The intercellular adhesion molecule (ICAM) 1 is an Ig-like cell adhesion molecule expressed by several cell types, including leukocytes and endothelial cells. It can be induced in a cell-specific manner by several cytokines, for example, tumor necrosis factor-alpha, interleukin-1, and interferon-gamma, and inhibited by glucocorticoids. Its ligands are the membrane-bound integrin receptors LFA-1 and Mac-1 on leukocytes, CD43, the soluble molecule fibrinogen, the matrix factor hyaluronan, rhinoviruses, and Plasmodium falciparum malaria-infected erythrocytes. ICAM-1 expression is predominantly transcriptionally regulated. The ICAM-1 promoter contains several enhancer elements, among them a novel kappa B element which mediates effects of 12-O-tetradecanoylphorbol-13-acetate, interleukin-1, lipopolysaccharide, tumor necrosis factor-alpha, and glucocorticoids. Expression regulation is cell specific and depends on the availability of cytokine/hormone receptors, signal transduction pathways, transcription factors, and posttranscriptional modification. ICAM-1 plays a role in inflammatory processes and in the T-cell mediated host defense system. It functions as a costimulatory molecule on antigen-presenting cells to activate MHC class II restricted T-cells, and on other cell types in association with MHC class I to activate cytotoxic T-cells. ICAM-1 on endothelium plays an important role in migration of (activated) leukocytes to sites of inflammation. ICAM-1 is shed by the cell and detected in plasma as sICAM-1. Regulation and significance of sICAM-1 are as yet unclear, but sICAM-1 is increased in many pathological conditions. ICAM-1 may play a pathogenetic role in rhinovirus infections. Derangement of ICAM-1 expression probably contributes to the clinical manifestations of a variety of diseases, predominantly by interfering with normal immune function. Among these are malignancies (e.g., melanoma and lymphomas), many inflammatory disorders (e.g., asthma and autoimmune disorders), atherosclerosis, ischemia, certain neurological disorders, and allogeneic organ transplantation. Interference with ICAM-1 leukocyte interaction using mAbs, soluble ICAM-1, antisense ICAM-1 RNA, and in the case of melanoma mAb-coupled immunotoxin, may offer therapeutic possibilities in the future. Integration of knowledge concerning membrane-bound and soluble ICAM-1 into a single functional system is likely to contribute to elucidating the immunoregulatory function of ICAM-1 and its pathophysiological significance in various disease entities.

Immunogenicity and immunosensitivity of ex vivo human carcinomas: interferon gamma and tumour necrosis factor alpha treatment of tumour cells potentiates their interaction with autologous blood lymphocytes

Human carcinoma cells vary appreciably in the expression of MHC class I, class II, ICAM-1 (CD54) and B7 (CD80) molecules. Short-term in vitro exposure of ex vivo carcinoma cells to interferon gamma and tumour necrosis factor alpha elevated/induced the surface expression of MHC class I, class II and ICAM-1, but only rarely of B7. We found that cytokine treatment elevated the cytotoxic susceptibility and the stimulatory potential of ex vivo tumour cells. This was demonstrated (a) by the increased frequency and elevated level of auto-tumour lysis and (b) by induction of DNA synthesis and generation of cytotoxic lymphocytes in autologous mixed lymphocyte/tumour cell culture (MLTC). The MHC class I and ICAM-1 molecules on the tumour cells were required for interaction with the lymphocytes as indicated by the inhibitory effect of specific mAb both in the stimulation and in the cytotoxic tests. While the cytokine-induced increases in MHC and ICAM-1 on the low-expression tumours were probably important for the modification of functional interaction with the autologous lymphocytes, it is likely that alterations in other properties of tumour cells were also induced which contributed to the phenomenon. This was indicated by the results obtained with several tumours, which expressed indigenously high levels of these molecules but activated the autologous lymphocytes only after cytokine treatment. In several experiments the untreated targets that did not activate the lymphocytes were sensitive to the cytotoxicity of the effectors activated in MLTC. The results show that the afferent and efferent arms of the immune response have different requirements for functional interactions between lymphocytes and tumour cells.

Association of 75/80-kDa phosphoproteins and the tyrosine kinases Lyn, Fyn, and Lck with the B cell molecule CD20. Evidence against involvement of the cytoplasmic regions of CD20

CD20, a non-glycosylated cell-surface protein expressed exclusively on B lymphocytes, is one of a family of 4-pass transmembrane molecules that also includes the beta chain of the high affinity receptor for IgE. The precise function of CD20 is unknown, although in vitro effects of CD20-specific antibodies on resting B cells indicate that it is able to transduce an extracellular signal affecting the G0/G1 cell cycle transition. Previous studies have demonstrated that CD20-initiated intracellular signals involve tyrosine kinase activation and that CD20 is tightly associated with both serine and tyrosine kinases. Here, analysis of CD20-associated molecules has revealed that CD20 is associated with the Src family tyrosine kinases p56/53lyn, p56lck, and p59fyn and with 75/80-kDa proteins phosphorylated in vivo on tyrosine residues. Mutagenesis of CD20 was performed to define regions of CD20 involved in intermolecular interactions. Mutants were analyzed in the human T lymphoblastoid cell line Molt-4, in which ectopically expressed wild-type CD20 associated with p59fyn, p56lck, and 75/80-kDa phosphoproteins. Deletion of major portions of the cytoplasmic regions of CD20 did not abolish its association with either p75/80 or tyrosine kinases. The interaction between CD20 and the Src-related kinases is therefore likely to be independent of CD20 cytoplasmic domains and may occur indirectly. The interaction may be mediated by the p75/80 phosphoproteins, which were found to be tightly associated with the Src family kinases isolated from the CD20 complex.

A CD44 monoclonal antibody differentially regulates CD11a/CD18 binding to intercellular adhesion molecules CD54, CD102 and CD50

We have made a monoclonal anti-CD44 antibody which is able to activate the leukocyte integrin CD11a/CD18. Activated T cells strongly aggregated, and the aggregation was shown to be intercellular adhesion molecule (ICAM)-1 (CD54) and ICAM-2 (CD102) dependent. Using purified ICAM coated on plastic, only binding to ICAM-1 was increased by the CD44 antibody, whereas activation by phorbol ester increased binding to both ICAM-1 and ICAM-3. The binding to ICAM-2 was not affected by either treatment. These findings show that the CD11a/CD18 integrin can be activated in a ligand-specific manner by engagement of CD44.

Regulation of interleukin 2 gene expression by CD28 costimulation in mouse T-cell clones: both nuclear and cytoplasmic RNAs are regulated with complex kinetics

T-cell receptor (TCR) signalling is required to induce expression of the interleukin 2 (IL-2) gene in mouse T cells. Additional costimulation through CD28 augments IL-2 production by 30- to 100-fold. Using IL-2 RNA accumulation and transcription reporter assays, we have addressed potential mechanisms of CD28 regulation at various time points of stimulation. The kinetic regulation of IL-2 mRNA by TCR and CD28 signals is complex: (i) at the earliest detectable time point, CD28 signalling causes a 20-fold increase compared with TCR signalling alone; (ii) both groups rapidly accumulate mRNA for the first 4 h; (iii) IL-2 mRNA then disappears from cells stimulated through the TCR alone but plateaus or increases slightly in cells costimulated through CD28; and (iv) after 8 h, the mRNA disappears in cultures with the anti-CD28 antibody. Transcription reporter assays did not show a specific effect of CD28 signalling on IL-2 enhancer driven transcription. This was true for either a 353- or a 1.9-kb enhancer, over a broad range of kinetics and TCR occupancy, and with several TCR signal mimics. The early component of CD28 costimulation is nuclear, however, since the initial enhancement of mRNA is also found in unspliced IL-2 RNA. Between 2 and 6 h, there is a marked difference in the rates of decay of IL-2 mRNA in the presence and absence of the CD28 signalling. Rapid decay of IL-2 mRNA commences after 8 h even in the presence of CD28 signals, although the decay occurs at a rate slower than that seen after 4 h of anti-TCR stimulation alone. This complexity suggests the existence of two interesting molecular mechanisms by which CD28 costimulates lymphokine gene expression.

A peptide derived from the intercellular adhesion molecule-2 regulates the avidity of the leukocyte integrins CD11b/CD18 and CD11c/CD18

beta 2 integrin (CD11a,b,c/CD18)-mediated cell adhesion is required for many leukocyte functions. Under normal circumstances, the integrins are nonadhesive, and become adhesive for their cell surface ligands, the intercellular adhesion molecules (ICAMs), or soluble ligands such as fibrinogen and iC3b, when leukocytes are activated. Recently, we defined a peptide derived from ICAM-2, which specifically binds to purified CD11a/CD18. Furthermore, this peptide strongly induces T cell aggregation mainly mediated by CD11a/CD18-ICAM-1 interaction, and natural killer cell cytotoxicity. In the present study, we show that the same ICAM-2 peptide also avidly binds to purified CD11b/CD18, but not to CD11c/CD18. This binding can be blocked by the CD11b antibody OKM10. The peptide strongly stimulates CD11b/CD18-ICAM-1-mediated cell aggregations of the monocytic cell lines THP-1 and U937. The aggregations are energy and divalent cation-dependent. The ICAM-2 peptide also induces CD11b/CD18 and CD11c/CD18-mediated binding of THP-1 cells to fibrinogen and iC3b coated on plastic. These findings indicate that in addition to induction of CD11a/CD18-mediated cell adhesion, the ICAM-2 peptide may also serve as a "trigger" for high avidity ligand binding of other beta 2 integrins.

Expression of adhesion molecules CD11/CD18 (Leu-CAMs, beta 2-integrins), CD54 (ICAM-1) and CD58 (LFA-3) in B-chronic lymphocytic leukemia

Cell adhesion molecules (CAMs) are cell surface proteins with unique specificities that allow intercellular adhesion. The importance of CAMs for normal lymphocyte growth and differentiation is underscored by the association between neoplastic disease states and abnormal CAM expression. In the present study we analysed the cell surface expression of several CAMs on peripheral blood lymphocytes from patients with progressive chronic lymphocytic leukemia of B-cell type (B-CLL) (n = 21) and stable monoclonal B-lymphocytosis of undetermined significance (B-MLUS) (n = 20). The CAM expression was analysed on the B-cell clone and on normal T- and NK-cell populations separately using monoclonal antibodies (MAbs). A phorbol ester-induced lymphocyte aggregation assay and blocking MAbs were also used. The B-cell clone in B-CLL expressed ICAM-1 (CD54) more frequently and at a higher density than in B-MLUS. The brightest CD54 expression was noted in patients with prominent lymphadenopathy and/or splenomegaly. The beta 2 integrin CD11a (Leu-CAMa, LFA-1) was detected on some B-cell clones and seemed to relate to tissue localization of the disease. T and NK cells showed a low expression of CD11a in B-CLL patients, while in B-MLUS a high proportion of non-clonal cells coexpressed CD11a with a high staining intensity. The relative numbers of both CD18+ as well as CD2+ cells showed a positive correlation with phorbol ester induced cell aggregation in B-MLUS patients (p < 0.05). The aggregation was blocked by adding MAbs against CD18 in most cases but to a greater extent in B-CLL. These results extend and corroborate our earlier findings on surface phenotypic characteristics of clonal and non-clonal lymphocytes in different clinical subtypes of B-CLL. CAM expression on the monoclonal lymphocytes may play a role in their interaction with regulatory immune cells and their tissue localization.

Dynamic expression patterns of tenascin, proteoglycans, and cell adhesion molecules during human hair follicle morphogenesis

The development of skin appendages such as hair, feathers, and teeth is brought about by reciprocal interactions between epidermal and mesenchymal tissues and is thought to be influenced in part by cell adhesion molecules and components of the extracellular matrix. The developmental distributions of tenascin, neural cell adhesion molecule (NCAM), E-cadherin, intercellular adhesion molecule 1 (ICAM-1), chondroitin sulfate proteoglycan (CSPG), and the heparan sulfate proteoglycan perlecan were studied in relation to hair follicle morphogenesis in fetal human skin. Tenascin first appeared in developing skin in focal concentrations at the epidermal-mesenchymal interface, just prior to, and presumably correlated with, hair follicle initiation. Tenascin immunostaining remained prominent in the basement membrane zone and extracellular matrix of the follicle sheath during subsequent morphogenetic stages. Two forms of tenascin (M(r) 250 x 10(3) and 280-300 x 10(3)), were revealed by Western blots of skin extracts. NCAM immunolabeling was initially present throughout the dermis, and became progressively restricted to the dermal condensation and the follicle sheath. Western blot analysis revealed an isoform of NCAM (M(r) 160 x 10(3)) which lacked polysialic acid. At all stages, E-cadherin staining was diminished on follicle cells situated adjacent to the basement membrane, relative to cells in the follicle interior. Follicle-specific immunostaining for ICAM-1 was transient, appearing only at the pre-germ and hair germ stages of development. Antibodies to three distinct CSPG determinants revealed unique immunolabeling patterns following follicle initiation: One CSPG epitope co-distributed with tenascin in the follicle basement membrane and follicle sheath extracellular matrix; one CSPG epitope was similarly expressed, and was also found on follicle epithelial cells; and the third CSPG determinant was noticeably absent from the follicle sheath during elongation of the developing appendage. Perlecan was concentrated in the dermal papilla, in addition to its distribution in all skin basement membranes. A model for how these diverse molecules may interact to influence human hair follicle morphogenesis is presented.

ICAM-3 interacts with LFA-1 and regulates the LFA-1/ICAM-1 cell adhesion pathway

The interaction of lymphocyte function-associated antigen-1 (LFA-1) with its ligands mediates multiple cell adhesion processes of capital importance during immune responses. We have obtained three anti-ICAM-3 mAbs which recognize two different epitopes (A and B) on the intercellular adhesion molecule-3 (ICAM-3) as demonstrated by sequential immunoprecipitation and cross-competitive mAb-binding experiments. Immunoaffinity purified ICAM-3-coated surfaces were able to support T lymphoblast attachment upon cell stimulation with both phorbol esters and cross-linked CD3, as well as by mAb engagement of the LFA-1 molecule with the activating anti-LFA-1 NKI-L16 mAb. T cell adhesion to purified ICAM-3 was completely inhibited by cell pretreatment with mAbs to the LFA-1 alpha (CD11a) or the LFA-beta (CD18) integrin chains. Anti-ICAM-3 mAbs specific for epitope A, but not those specific for epitope B, were able to trigger T lymphoblast homotypic aggregation. ICAM-3-mediated cell aggregation was dependent on the LFA-1/ICAM-1 pathway as demonstrated by blocking experiments with mAbs specific for the LFA-1 and ICAM-1 molecules. Furthermore, immunofluorescence studies on ICAM-3-induced cell aggregates revealed that both LFA-1 and ICAM-1 were mainly located at intercellular boundaries. ICAM-3 was located at cellular uropods, which in small aggregates appeared to be implicated in cell-cell contacts, whereas in large aggregates it appeared to be excluded from cell-cell contact areas. Experiments of T cell adhesion to a chimeric ICAM-1-Fc molecule revealed that the proaggregatory anti-ICAM-3 HP2/19 mAb was able to increase T lymphoblast attachment to ICAM-1, suggesting that T cell aggregation induced by this mAb could be mediated by increasing the avidity of LFA-1 for ICAM-1. Moreover, the HP2/19 mAb was costimulatory with anti-CD3 mAb for T lymphocyte proliferation, indicating that enhancement of T cell activation could be involved in ICAM-3-mediated adhesive phenomena. Altogether, our results indicate that ICAM-3 has a regulatory role on the LFA-1/ICAM-1 pathway of intercellular adhesion.

Fibrinogen mediates leukocyte adhesion to vascular endothelium through an ICAM-1-dependent pathway

Leukocyte traffic in immune-inflammatory responses requires regulated adhesion of leukocyte subsets to vascular endothelium. We show that fibrinogen or normal human plasma enhances by 2- to 5-fold the adhesion of cells of myeloid and lymphoid lineage to endothelium. This mechanism is mediated by fibrinogen binding to complementary membrane receptors on leukocytes and endothelial cells. Using an affinity chromatography purification strategy, genetically engineered transfectants, and direct binding studies to the isolated recombinant protein, we identified a novel hematopoietic fibrinogen receptor participating in this adhesion pathway as intercellular adhesion molecule 1 (ICAM-1). Accordingly, a new model can be proposed, in which fibrinogen binding to a variety of vascular cell receptors mediates a specific pathway of cell to cell adhesion by bridging together leukocytes and endothelial cells.

Molecular regulation of the IL-2 gene: rheostatic control of the immune system

The delivery of costimulation and the effects of the anergic state impinge on IL-2 production via different molecular mechanisms. The strongest experimental support at this stage suggests that CD28 signaling effects mRNA stability of several lymphokine genes including IL-2. While there may also be transcriptional effects of CD28 signals in human cells, controversy surrounding relevant TCR mimics must be addressed. In the case of clonal anergy, however, transcriptional non-responsiveness is evident when anergic cells are restimulated with TCR and costimulatory signals. This repression affects predominantly AP-1 activity. So far, the nature of the repression has not been identified.

The CD2 and CD28 adhesion molecules induce long-term autocrine proliferation of CD4+ T cells

In vitro human T lymphocyte activation requires two-signal triggering delivered by lectins, phorbol esters or antibodies directed against surface molecules. Stimulation of adhesion molecules by CD2 and/or CD28 antibodies defines alternative activation pathways. Activation by CD2 + CD28 monoclonal antibodies induces high-level, long-lasting and monocyte-independent proliferation of highly purified T cells. Limiting dilution cultures showed that CD28 in association with CD2 or CD3, without addition of exogenous cytokines, induced single-cell proliferation. CD2 + CD28 stimulation induced long-term interleukin (IL)-2-dependent autocrine proliferation of CD4+ T cell clones. We tried to elucidate this long-term proliferation by evaluating cytokine secretion and cytokine dependency. CD28 associated to CD3 or CD2 induced high levels of IL-2, tumor necrosis factor (TNF) and IL-4 secretion for 10 days, in contrast to CD3 alone which induced only TNF secretion. Cytokines of the monocytic lineage were also secreted, such as colony-stimulating factor-1, granulocyte-macrophage colony-stimulating factor or IL-1, the latter being more specific of CD2 + CD28 activation. Blocking antibodies confirmed the crucial role of IL-2 in CD2 + CD28 activation. Anti-IL-4, anti-IL-7 receptor or anti-TNF antibodies had no effect on proliferation. Stimulation with CD2 + CD28 induced long-term autocrine (at least for IL-2) proliferation for CD4+ T cells, with no evidence for the implication of another cytokine among those tested other than IL-2. This represents a model for long-term autocrine growth for non-leukemic cells.

Cloning and characterization of a new intercellular adhesion molecule ICAM-R

The human intercellular adhesion molecules ICAM-1, ICAM-2 and their counter-receptors, the beta 2 or leukointegrins, mediate a variety of homotypic and heterotypic leukocyte and endothelial cell-cell adhesions central to immunocompetence. It has been found that cell-cell adhesion which is dependent on expression of the leukocyte function-associated antigen LFA-1 is not always blocked completely by antibodies raised against ICAM-1 and ICAM-2. Other leukointegrin ligands therefore probably exist, such as a glycoprotein of M(r) 124K that binds LFA-1 and has been designated ICAM-3 on the basis of this function. We have molecularly cloned a new member of the ICAM family, ICAM-R, which is related to ICAM-1 and ICAM-2. The complementary DNA encoding ICAM-R is 1,781 base pairs long and the protein has five extracellular immunoglobulin-family type domains. The mature cell-surface form of the ICAM-R protein has an M(r) which varies from 116 to 140K in a cell type-specific fashion. Overall identities in protein sequence with ICAM-1 and ICAM-2 are 48% and 31% respectively, with the degree of similarity varying between individual domains. The high level of expression of ICAM-R on resting leukocytes of all lineages and its lack of expression on either resting or cytokine-activated endothelial cells indicates a pattern of expression distinct from ICAM-1 and ICAM-2. In common with ICAM-1 and ICAM-2, ICAM-R is a ligand for the beta 2-integrin CD11a/LFA-1 (CD18).

Increased expression of ICAM-1, E-selectin, and VCAM-1 by cultured human endothelial cells upon exposure to haptens

Contact allergens induce several accessory signals which promote the activation of antigen-specific T cells. One of these signals is the increased expression of adhesion molecules on antigen-presenting cells and endothelial cells. Epicutaneous application of non-toxic doses of 2,4-dinitrofluorobenzene (DNFB) onto the skin of non-sensitized individuals elicited progressive staining for ICAM-1 on dermal microvascular endothelial cells. To elucidate the question of whether contact allergens can act directly on endothelial cells to elevate their expression of surface structures that bind leukocytes, confluent monolayers of human umbilical vein endothelial cells were incubated with the contact allergens NiSO4, CoSO4 or DNFB. The ICAM-1, E-selectin and HLA-DR expression were quantified by immunofluorescence flow cytometric analysis. Furthermore VCAM-1, E-selectin and ICAM-1 transcription were demonstrated by Northern blot hybridization. Constitutive ICAM-1 expression on HUVEC increased similarly to that obtained after LPS (20 micrograms/ml) stimulation after 4 and 24 hours of incubation with 1 or 2 mM NiSO4 or CoSO4, respectively. Pulse-stimulation with 100 or 500 nM DNFB resulted in a modest but significant increase of ICAM-1-positive cells. E-selectin and VCAM-1 were not expressed on untreated HUVEC; 4 to 6 hours exposure to nickel sulfate and LPS resulted in a potent induction of E-selectin and VCAM-1 expression. DNFB and PMA had no significant influence on VCAM-1 expression. None of the tested contact allergens was capable of inducing HLA-DR expression on EC at 48 to 72 hours. Enhanced expression of adhesion molecules may be an important early unspecific mechanism for induction and elicitation of a contact dermatitis.

Expression of ICAM-1 (CD54) on normal and leukaemic B cells: implication for the mixed lymphocyte reaction

Peripheral blood normal B lymphocytes were found to be poor stimulators in the mixed lymphocyte reaction (MLR), in contrast to normal activated B cells which were strong stimulators. This increased capacity to stimulate a strong MLR correlated with an increased expression of the ICAM-1 (CD54) molecule on the surface of these cells. Similarly, the capacity of leukaemic B cells to induce an allogenic stimulation in the MLR was limited to the ICAM-1 (CD54) positive leukaemic cells. The ability of normal activated or leukaemic B cells to induce an MLR was blocked by antibodies directed against ICAM-1.

Relationships between the degree of cross-linking of surface immunoglobulin and the associated inositol 1,4,5-trisphosphate and Ca2+ signals in human B cells

Cross-linking of surface immunoglobulin (Ig) receptors on human B cells leads to the activation of a tyrosine kinase. The activated tyrosine kinase subsequently phosphorylates a number of substrates, including phospholipase C-gamma. This enzyme breaks down phosphoinositol bisphosphate to form two intracellular messengers, diacylglycerol and inositol 1,4,5-trisphosphate, leading to the activation of protein kinase C and the release of intracellular Ca2+ respectively. We have used h.p.l.c. and flow cytometry to measure accurately the inositol phosphate turnover and Ca2+ release in anti-Ig-stimulated human B cells. In particular, we have examined the effect of dose of the cross-linking antibody on the two responses. The identity of putative messenger inositol phosphates has been verified by structural analysis, and the amounts of both inositol phosphates and Ca2+ present have been quantified. In the Ramos Burkitt lymphoma, which is very sensitive to stimulus through its Ig receptors, both inositol phosphate production and Ca2+ release were found to be related to the dose of anti-Ig antibody applied. This suggests that phospholipase C-mediated signal transduction in human B cells converts the degree of cross-linking of the immunoglobulin receptor quantitatively into intracellular signals.

Multiple ICAM-1 (CD54) epitopes are involved in homotypic B-cell adhesion

Two monoclonal antibodies (MoAbs), F10.2 and F10.3, were selected for their ability to interfere in homotypic adhesion of human B cells. Precipitation studies and binding to intercellular adhesion molecule 1 (ICAM-1, CD54) cDNA transfected COS cells revealed that both MoAbs are directed against ICAM-1. The binding of MoAb F10.2 was inhibited by LB-2, a MoAb recognizing the NH2-terminal immunoglobulin-like domain of ICAM-1. This suggests that the epitope recognized by F10.2 is located on the first domain of the ICAM-1 molecule. Binding of the other MoAb, F10.3, was not inhibited by F10.2 nor by two other MoAbs mapping to the first domain of the ICAM-1 molecule. The ability of F10.3 to bind to ICAM-1 is influenced by glycosylation, suggesting that this epitope is located on one of the domains carrying possible glycosylation sites, i.e. domain 2, 3 or 4. The ICAM-1 epitopes recognized by F10.3 and LB-2 or F10.2 co-operated in homotypic adhesion of cells from the EBV cell line ML1. These results suggest that in addition to an epitope located on domain 1 of the ICAM-1 molecule, another epitope whose exposure can be regulated by glycosylation is involved in homotypic B-cell adhesion of cell line ML1.

Genomic organization and chromosomal location of the human gene encoding the B-lymphocyte activation antigen B7

The human B lymphocyte activation antigen B7 provides regulatory signals for T lymphocytes as a consequence of binding to its ligands CD28 and CTLA-4. The cDNA for B7 has previously been isolated and predicted to encode a type I membrane protein. The predicted polypeptide has a secretory signal peptide followed by two contiguous Ig-like domains, a hydrophobic transmembrane region and a short cytoplasmic tail. Here we report the exon-intron genomic organization of human B7 and the chromosomal location. The gene has six exons that span approximately 32 kilobases of DNA. Exon 1 is not translated and the second exon contains the initiation ATG codon and encodes a predicted signal peptide. This gene structure is characteristic for several eukaryotic genes with tissue-specific expression. The third and fourth exons correspond to two Ig-like domains whereas the fifth and sixth exons encode respectively the trans-membrane portion and the cytoplasmic tail. This close relationship between exons and functional domains is a characteristic feature of genes of the Ig superfamily. Cell surface expression of the B7 gene product has previously been mapped to human chromosome 12 by antibody reactivity with the B7-specific monoclonal antibody BB-1. We here demonstrate that the B7 gene is located to the q21-qter region of chromosome 3 by DNA blot analysis of human x rodent somatic cell hybrids.

CD43, a molecule defective in Wiskott-Aldrich syndrome, binds ICAM-1

THE protein CD43 (also known as sialophorin, leukosialin, large sialoglycoprotein or gp115) is expressed on the surface of T lymphocytes, monocytes, neutrophils, platelets and some B lymphocytes. Expression of CD43 is deficient and/or defective in the X-chromosome-linked immunodeficiency disorder Wiscott-Aldrich syndrome, suggesting that CD43 might have a role in T-cell activation. We have shown that expression of human CD43 in an HLA-DR-specific murine T-cell hybridoma enhances the antigen-specific response to stimulation by the human lymphoblastoid cell line Daudi, and that Daudi cells bind specifically to purified immobilized CD43. These data indicate that the specific interaction of CD43 with a ligand on the surface of Daudi cells might contribute to T-cell activation. Here we report evidence that intercellular adhesion molecule-1 (ICAM-1, or CD54), is a ligand for CD43.

The expression of human intercellular adhesion molecule-2 is refractory to inflammatory cytokines

The beta 2-integrin CD11a/CD18 binds to the intercellular adhesion molecules (ICAM)-1 (CD54) and ICAM-2. ICAM-1 has a wide distribution, and its expression is up-regulated by various cytokines. In contrast, ICAM-2 has a more restricted distribution, and is mainly expressed on endothelial cells. In the present study we show that it is not induced by inflammatory cytokines or other treatments on any of several cells studied. Moreover, antibodies to the intercellular adhesion ligands were not able to block all CD11a/CD18-dependent adhesion, indicating the presence of additional CD11a/CD18 ligands.

Detection of lymphocyte subsets using three-color/single-laser flow cytometry and the fluorescent dye peridinin chlorophyll-alpha protein

The fluorescent dye, Peridinin chlorophyll A protein (PerCP) derived from dinoflagellate organisms (Glenodinium sp.) can be excited by a 488 nm laser and emits light with a large Stokes shift and no major spectral overlap with commonly used chromophores such as fluorescein isothiocyanate (FITC) and R-phycoerythrin (PE). PerCP was conjugated directly to various mouse monoclonal antibodies (mAb) specific for human leukocyte markers or to avidin for use with biotinylated-mAb, and used to perform three color single-laser flow cytometry. The efficacy of this method was demonstrated by analyzing the heterogeneity of thymus T lineage subsets and B lymphocyte subsets in blood. CD4-CD8-, CD4+CD8+ and CD4+CD8- or CD4-CD8+ subsets differ in their expression of cell-cell interaction markers including CD18, CD28, CD44 and Leu 8, and activation/subset markers CD45RO, CD45RA and CD26. Some CD5+ peripheral blood B cells, unlike CD5-B cells, expressed CD45RO or high levels of CD54 (ICAM-1) suggesting the CD5+ B cell population contains activated lymphocytes. The availability of such an accessible method for three color analysis will make it possible to do routine three color monitoring of immunologic diseases such as AIDS, and autoimmune or periodontal diseases.

Viral and cellular gene expression in CD4+ human lymphoid cell lines infected by the simian immunodeficiency virus, SIV/Mne

Our laboratory has undertaken an analysis of cellular and viral gene expression in CD4+ human lymphoid cell lines infected by the human and simian immunodeficiency viruses, HIV-1 and SIV/Mne, respectively. The purpose of the current study was to: (i) examine the effects of SIV/Mne infection on host macromolecular synthesis and compare the results to those in the HIV-1 system; and (ii) investigate the mechanisms responsible for the restriction of SIV/Mne infection in CD4 positive lymphoid cells which are readily infected by HIV-1. First we determined that SIV does not impose selective blocks on host macromolecular synthesis, unlike HIV-1, which induces both the selective inhibition of cellular protein synthesis and the degradation of cellular mRNAs (Agy, M., Wambach, M., Foy, K., and Katze, M. G., 1990, Virology 177, 251-258). No such selective reduction in cellular mRNA stability or protein synthesis was observed in cells infected by SIV/Mne. Additional differences between SIV and HIV-1 were observed using a panel of CD4+ human cell lines. While HIV-1-infected all cell lines. SIV/Mne efficiently infected only the MT-4, C8166, and 174 x CEM cell lines. Repeated efforts to infect CEM or Jurkat cells were unsuccessful as determined by PCR analysis of viral DNA. HUT 78 cells supported a limited infection detectable only by PCR analysis. These data suggest the block in viral replication in the nonsusceptible cell lines is at an early step. Interestingly, all the SIV susceptible cells were virally transformed, C8166 and MT-4 by HTLV-1, and 174 x CEM by Epstein-Barr virus. Furthermore FACS analysis revealed that all susceptible cells expressed two B cell associated markers, B7/BB1 and CD40. These observations taken together highlight differences between the HIV and SIV viruses, and suggest that for efficient replication, SIV/Mne may require an additional cell surface molecule, cofactors provided by transforming viruses, or a complex interplay between the two.

The CD28 ligand B7/BB1 provides costimulatory signal for alloactivation of CD4+ T cells

Activation via the T lymphocyte cell surface molecule CD28 provides a potent amplification signal for interleukin 2 (IL-2) production in several in vitro systems. The B lymphocyte activation antigen, B7/BB1, is a natural ligand for CD28. Here we investigate the role of CD28 and B7/BB1 in primary activation of CD4+ T lymphocytes stimulated with allogeneic B lymphoblastoid cell lines. A subset of peripheral CD4+ T cells that is unresponsive to crosslinking of CD3/T cell receptor (TCR) with CD3 monoclonal antibody (mAb) does proliferate in response to allogeneic B lymphoblasts. TCR binding to allogeneic major histocompatibility complex antigens was an absolute requirement for activation of these cells because mAbs to either CD3 or human histocompatibility leukocyte antigen (HLA) class II completely inhibited activation. CD28 and B7/BB1 antibodies inhibited T cell proliferation 90% and 84%, respectively. Similar results were obtained with the total CD4+ T lymphocyte population. Crosslinking of HLA-DR antigens on small, resting B cells induced rapid expression of B7/BB1, which peaked at 6 h and returned to baseline levels within 18 h. These data demonstrate that CD28-B7/BB1 binding provides an important early second signal for alloactivation of CD4+ T lymphocyte by B lymphoblasts. The results also suggest that T cells interacting with allogeneic resting B cells may induce B7/BB1 expression in the alloantigen-presenting cell as a consequence of interaction between the TCR and class II molecules.

Increased susceptibility of IFN-gamma-treated neuroblastoma cells to lysis by lymphokine-activated killer cells: participation of ICAM-1 induction on target cells

We have investigated the effect of interferon-gamma (IFN-gamma) treatment of neuroblastoma cells on the susceptibility to lysis by lymphokine-activated killer (LAK) cells and examined the participation of cell-adhesion molecules on the target cells in LAK cell lysis. Untreated neuroblastoma cells expressed lymphocyte-function-associated antigen 3 (LFA-3) and neural-cell-adhesion molecule (NCAM), but did not express MHC-class-I, MHC-class-II, or intercellular-adhesion molecule I (ICAM-I). IFN-gamma treatment of neuroblastoma cells induced the expression of MHC-class-I and ICAM-I antigens, but did not affect the expression of MHC-class-II, LFA-3, and NCAM. This was accompanied by an increased susceptibility to lysis by LAK cells. Anti-ICAM-I antibody inhibited partially the increased sensitivity of IFN-gamma-treated neuroblastoma cells to LAK cell lysis, and blocked completely the increase in binding of LAK cells observed after IFN-gamma treatment of the target cells. These results suggest that the increased LAK sensitivity of IFN-gamma-treated neuroblastoma cells is partially attributable to the induction of ICAM-I on neuroblastoma cells and indicate that post-binding events also play a role in the increased sensitivity to LAK cell lysis observed after IFN-gamma treatment.

The human leukocyte-adhesion ligand, intercellular-adhesion molecule 2. Expression and characterization of the protein

The leukocyte cell-adhesion receptors, complexes of the cluster of differentiation antigen 11a with cluster of differentiation antigen 18 (CD11a/CD18), cluster of differentiation antigen 11b with cluster of differentiation antigen 18 (CD11b CD18) and cluster of differentiation antigen 11c with cluster of differentiation antigen 18 (CD11c CD18), are of major importance in several leukocyte functions. Previously a cellular ligand named intercellular-adhesion molecule 1 (ICAM-1) was identified, isolated and extensively characterized. Recently a second similar molecule, intercellular-adhesion molecule 2 (ICAM-2), was found by a functional DNA-cloning method. We have now synthesized the ICAM-2 DNA by the polymerase chain reaction (PCR), sequenced it, and transferred it into mammalian and bacterial expression vectors. A functional leukocyte-binding glycoprotein was obtained by transfection of COS-1 cells. A soluble protein-A - ICAM-2 fusion protein was made in Escherichia coli, purified and used for antiserum production. The antiserum precipitated a cell-surface protein with an apparent molecular mass of 55 kDa from ICAM-2 transfected COS-1 cells, leukocytes and endothelial cells, and inhibited leukocyte binding to transfected COS-1 cells. The bacterial fusion protein, lacking carbohydrate, specifically bound to leukocyte receptors.

ICAM-1 (CD54): a counter-receptor for Mac-1 (CD11b/CD18)

While the leukocyte integrin lymphocyte function-associated antigen (LFA)-1 has been demonstrated to bind intercellular adhesion molecule (ICAM)-1, results with the related Mac-1 molecule have been controversial. We have used multiple cell binding assays, purified Mac-1 and ICAM-1, and cell lines transfected with Mac-1 and ICAM-1 cDNAs to examine the interaction of ICAM-1 with Mac-1. Stimulated human umbilical vein endothelial cells (HUVECs), which express a high surface density of ICAM-1, bind to immunoaffinity-purified Mac-1 adsorbed to artificial substrates in a manner that is inhibited by mAbs to Mac-1 and ICAM-1. Transfected murine L cells or monkey COS cells expressing human ICAM-1 bind to purified Mac-1 in a specific and dose-dependent manner; the attachment to Mac-1 is more temperature sensitive, lower in avidity, and blocked by a different series of ICAM-1 mAbs when compared to LFA-1. In a reciprocal assay, COS cells cotransfected with the alpha and beta chain cDNAs of Mac-1 or LFA-1 attach to immunoaffinity-purified ICAM-1 substrates; this adhesion is blocked by mAbs to ICAM-1 and Mac-1 or LFA-1. Two color fluorescence cell conjugate experiments show that neutrophils stimulated with fMLP bind to HUVEC stimulated with lipopolysaccharide for 24 h in an ICAM-1-, Mac-1-, and LFA-1-dependent fashion. Because cellular and purified Mac-1 interact with cellular and purified ICAM-1, we conclude that ICAM-1 is a counter receptor for Mac-1 and that this receptor pair is responsible, in part, for the adhesion between stimulated neutrophils and stimulated endothelial cells.

Functional characteristics of the intercellular adhesion molecule-1 (CD54) expressed on cytotoxic human blood lymphocytes

We have shown that intercellular adhesion molecule-1 (ICAM-1) (CD54) positive cells are mainly responsible for the natural cytotoxic function of human blood lymphocytes. The evidences were the inhibition of cytotoxicity by anti-ICAM-1 (LB-2) monoclonal antibodies (mAb) and the loss of lytic activity after removal of the ICAM-1+ cells. In addition, the cytotoxic potential of the separated ICAM-1- lymphocyte population after activation appeared in parallel with the expression of this molecule. The ICAM-1+ lymphocytes lysed both LFA-1 (CD11a/CD18 or Leu-CAMa) positive and negative cell lines, and pretreatment of the effectors with the LB-2 mAb also inhibited the lysis of LFA-1- targets. The results point to a yet unrecognized role of ICAM-1 on the lymphocytes. Kinetics experiments suggested that pretreatment of lymphocytes with alpha-ICAM-1 (LB-2) mAb did not inhibit the promptly established lytic interactions but influenced later events, recycling and/or recruitment of effectors. It is possible that the cytotoxic potential is regulated by contacts between the members of the lymphocyte population and that these events occur via their ICAM-1 and LFA-1. Exposure of lymphocytes to NK-sensitive targets for 16 hr elevated their cytotoxic potential. The function of activated lymphocytes was not inhibited by the LB-2 mAb.

Activation of lymphocytes after platelet allotransfusion possessing only class I MHC product

After platelet allotransfusion, we found a characteristic increase in the expression of interleukin-2 receptor, dipeptydilpeptidase IV (CD26), activation-inducer molecule (AIM, CD69) and transferrin receptors (CD71) on day 3 indicating that important functional molecules expressed on the activation of lymphocytes by allogeneic platelets. At the same time, no consistent increase of other activation molecules such as Ki-l (CD30), intercellular adhesion molecule (ICAM-1, CD54) and Ki-24 (CDw70) antigen expression was detected, probably as a result of the selective activation of some lymphocyte subsets. In order to obtain further evidence for the in vivo activation triggered by allogeneic platelets, subsequent step of T cell activation towards differentiation was investigated with monoclonal antibodies to leucocyte common antigens. A sharp expression of the UCHL1, coupled with a decrease of the CD45R molecule was detected on day 7 or 14, suggesting a T cell priming.

ICAM-1-dependent fibroblast-lymphocyte adhesion: discordance between surface expression and function of ICAM-1

We have previously reported that stimulation of human fibroblasts (FB) with interferon-gamma (IFN-gamma) leads to their increased adhesiveness for resting peripheral blood T lymphocytes. With the use of blocking monoclonal antibodies, we determined that intercellular adhesion molecule-1 (ICAM-1) and its T cell ligand, lymphocyte function-associated antigen-1 (LFA-1) are the major, if not only ligands involved in this system. Using an ELISA, we have confirmed earlier reported observations that IFN-gamma induces an increase of ICAM-1 expression on the surface of FB suggesting that this increase mediates lymphocyte adhesion. However, we show that treatment of FB with IL-1, while leading to comparable increases in ICAM-1 synthesis and expression, failed to induce increased adhesion. In contrast, treatment of fibroblasts with the phorbol ester, TPA, stimulated ICAM-1-dependent adhesion without an increase in ICAM-1 surface expression. This suggested that the detection of ICAM-1 by monoclonal antibody techniques may not always correlate with its functional capabilities. The contrasting effects of IFN-gamma and IL-1 on ICAM-1-dependent FB adhesion suggest that qualitative as well as quantitative alterations of the ICAM-1 molecule may regulate ligand interaction.

Participation of CD11a-c/CD18 and RGD-recognizing adhesion molecules in the binding of LGL to fibroblasts. Evidence for the role of CD11a in the fibroblast-mediated inactivation of NK cells

We have previously shown that large granular lymphocytes (LGL) are inactivated by contact with natural killer (NK) resistant monolayer target cells. In this work we have analysed which adhesion molecules are involved in the binding of LGL to such targets, as exemplified by fibroblasts, and in the subsequent inhibition of their NK activity. The results indicate that antibodies against CD54 (intercellular adhesion molecule 1, ICAM-1), CD11a (leucocyte function antigen 1, LFA-1, alpha chain), and CD18 (common beta chain of the beta 2-integrin family) significantly (by 50%) reduce the binding of LGL onto inhibitory target cells. The matrix protein-based synthetic peptide RGD and anti-CD29 (the common beta chain of the beta 2-integrin family) antibodies also diminish the binding (by 35%). The effects of the antiadhesion molecule antibodies and the peptide are additive, the combination of both leading to an almost complete block of adhesion. It may be hypothesized that some of the binding-relevant adhesion molecules of the RGD-binding domain on LGL (CD29) may be involved in the delivery of the inactivating signal to the effector cell. Indeed, incubation of LGL with anti-CD11a antibodies, but neither with antibodies against other binding-relevant epitopes nor with RGD, significantly reduced their NK activity. The mechanism of the inactivation was similar to that induced by intact NK-resistant target cells. On the basis of the present results we suggest that the CD11a molecule is involved in the down-regulation of the NK activity of peripheral blood lymphocytes.

T-cell antigen CD28 mediates adhesion with B cells by interacting with activation antigen B7/BB-1

Studies using monoclonal antibodies (mAbs) have implicated the homodimeric glycoprotein CD28 as an important regulator of human T-cell activation, in part by posttranscriptional control of cytokine mRNA levels. Although the CD28 antigen has functional and structural characteristics of a receptor, a natural ligand for this molecule has not been identified. Here we show that the CD28 antigen, expressed in Chinese hamster ovary (CHO) cells, mediated specific intercellular adhesion with human lymphoblastoid and leukemic B-cell lines and with activated primary murine B cells. CD28-mediated adhesion was not dependent upon divalent cations. Several mAbs were identified that inhibited CD28-mediated adhesion, including mAb BB-1 against the B-cell activation antigen B7/BB-1 and some mAbs against major histocompatibility complex class I antigens. B7/BB-1 expression correlated closely with CD28-mediated adhesion, but class I expression did not. Transfected COS cells expressing the B7/BB-1 antigen adhered to CD28+ CHO cells; this adhesion was blocked by mAbs to CD28 and B7/BB-1. The specific recognition by CD28 of the B-cell activation antigen B7/BB-1 represents a heterophilic interaction between members of the immunoglobulin superfamily that may serve to regulate T-cell cytokine levels at sites of B-cell activation.

Signaling through CD19, Fc receptors or transforming growth factor-beta: each inhibits the activation of resting human B cells differently

To understand further the roles that negative regulatory signals may play in B cell immune responses, we compared three inhibitors of B cell proliferation: cross-linking CD19 with monoclonal antibody (mAb), signaling through Fc receptors by intact anti-mu mAb, and transforming growth factor-beta (TGF-beta). Each agent was tested for its ability to block proliferation and specific activation events induced in human tonsilar B cells activated by either cross-linking surface immunoglobulin, signaling through CD20, or direct activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate. We found that each inhibitor was functionally distinct. Both anti-CD19 mAb and anti-mu mAb inhibited anti-immunoglobulin activated cells and anti-CD20-activated cells, but neither inhibited cells activated by phorbol 12-myristate 13-acetate. TGF-beta, on the other hand, inhibited equally profoundly cells activated by each of the three regimens. These results suggest that TGF-beta blocks B cell activation at a step following the activation of PKC, whereas both signaling through CD19 and Fc receptor block early steps in the PKC activation pathway. Signaling through anti-CD19 mAb was unique in that proliferation of anti-immunoglobulin-activated cells was reduced on day 3 and then augmented subsequently. With all other inhibitory combinations the block was permanent. We conclude that each of these three inhibitors has unique important functions and therefore suggest that the effectiveness of negative signaling in B cell immune regulation will depend on the combinations of specific inhibitors modulating a specific activation program.

The arrangement of the immunoglobulin-like domains of ICAM-1 and the binding sites for LFA-1 and rhinovirus

Intercellular adhesion molecule 1 (ICAM-1, CD54) binds to the integrin LFA-1 (CD11a/CD18), promoting cell adhesion in immune and inflammatory reactions. ICAM-1 is also subverted as a receptor by the major group of rhinoviruses. Electron micrographs show that ICAM-1 is a bent rod, 18.7 nm long, suggesting a model in which the five immunoglobulin-like domains are oriented head to tail at a small angle to the rod axis. ICAM-1 sequences important to binding LFA-1, rhinovirus, and four monoclonal antibodies were identified through the characterization of chimeric ICAM-1 molecules and mutants. The amino-terminal two immunoglobulin-like domains of ICAM-1 appear to interact conformationally. Domain 1 of ICAM-1 contains the primary site of contact for both LFA-1 and rhinovirus; the presence of domains 3-5 markedly affects the accessibility of the binding site for rhinovirus and less so for LFA-1. The binding sites appear to be distinct but overlapping; rhinovirus binding also differs from LFA-1 binding in its lack of divalent cation dependence. Our analysis suggests that rhinoviruses mimic LFA-1 in binding to the most membrane-distal, and thus most accessible, site of ICAM-1.

Leukocyte-cell adhesion: a molecular process fundamental in leukocyte physiology

Leukocyte-cell adhesion is a form of physical contact characterized by fast (firm) stickiness between the cells. To analyze the biology and molecular basis of this process, an adhesion-specific assay was developed: the phorbol ester-induced aggregation of human lymphocytes. This rapid and antigen-independent intercellular adhesion requires cellular metabolism, an intact cytoskeleton and extracellular divalent cations, and is mediated by preformed cell-surface proteins referred to as CAMs. Phorbol ester also induces aggregation of monocytes and granulocytes, as well as adhesion of T lymphocytes to either B cells or monocytes and of the leukocytes to vascular endothelial cells. By using the adhesion-specific assay and blocking monoclonal antibodies, several CAMs have been identified, namely the Leu-CAM family (CD11a-c/CD18) and ICAM-1 (CD54). The Leu-CAM family is composed of Leu-CAMa (CD11a/CD18), Leu-CAMb (CD11b/CD18) and Leu-CAMc (CD11c/CD18), three glycoprotein heterodimers made of a common beta-chain and distinct alpha-chains. ICAM-1 is an adhesive ligand for Leu-CAMa. Expression and use of the various CAMs is selective in different types of leukocytes. The Leu-CAMs have been purified and partially characterized. CD18, whose gene is on human chromosome 21, contains 5-6 N-linked complex-type oligosaccharides, and CD11 binds Ca++. Another adhesion pathway is mediated by CD2 and CD58. CD2, a glycoprotein selectively expressed by T cells, is a receptor for CD58, a cell-surface adhesive ligand with broad tissue distribution. Antibodies to the latter CAMs do not block the phorbol ester-induced lymphocyte aggregation. Adhesion is involved in a large variety of leukocyte functions. Anti-Leu-CAM antibodies block induction of IL-2 production and lymphocyte proliferation. Lymphocyte-mediated cytotoxicity is also inhibited. Endogenous NK and LAK cells use Leu-CAMs, ICAM-1 and CD2, and sometimes RGD receptors, to bind and kill tumor cells. Endogenous compounds such as H2O2 and LTB4 also induce Leu-CAM-dependent adhesion in monocytoid cells and granulocytes, respectively, and degranulation of the latter cells is enhanced by the adhesion process. Homologous CAMs have been identified in rabbit and mouse. In in vivo studies in the former species, anti-Leu-CAM antibodies block adhesion of leukocytes to vascular endothelium and thereby their migration into extravascular tissues. The antibodies thus inhibit granulocyte accumulation and plasma leakage in inflammatory lesions, and induce lympho- and granulocytosis, indicating that cell-adhesion contributes to the distribution of leukocytes in the body.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of the adhesion molecule ICAM-1 and major histocompatibility complex class I antigens on human tumor cells is required for their interaction with autologous lymphocytes in vitro

In a group of 30 human tumors, comprising 12 lung, 14 ovarian, 2 breast carcinomas, 1 hypernephroma and 1 mid-gut carcinoid, the expression of major histocompatibility complex (MHC) class I molecules and the intercellular adhesion molecule 1 (CAM-1, CD54) was found to vary independently. Some tumors expressed both or neither of these molecules. Among 9/13 ICAM-1+ tumors, in which greater than 50% cells reacted with the anti-ICAM-1 monoclonal antibody (mAb) (LB-2), the class I antigen was also detected on greater than 50% of the cells. Only 2 ICAM-1+ tumors were class-I-. In 5/17 cases the tumors were MHC-class-I+ and ICAM-1-. Lymphocytes collected from the blood or from the tumor site were assayed for recognition on the tumor cells in the auto-tumor cytotoxicity test and in mixed lymphocyte tumor cell culture (MLTC). Positive results were obtained only with the MHC-class-I+/ICAM-1+ tumors. In vitro treatment of the tumor cell suspensions with interferon gamma and tumor necrosis factor alpha (TNF alpha) induced or enhanced the ICAM-1 and/or class I antigen expression in 8/12 cases. Of the tumor samples treatged, 8/9 acquired stimulatory capacity and 3/10 became susceptible to lysis by the lymphocytes. In 6/6 MLTC performed with the cytokine-treated tumor cells, cytotoxicity against the autologous tumor was generated. Three of these MLTC lymphocytes also lysed the untreated targets. mAb directed to class I antigens or to ICAM-1 inhibited both the stimulation by and the lysis of tumor cells when confronted with fresh lymphocytes. The cytotoxicity generated in the MLTC was also inhibited. If, however, the cytotoxic function was induced in MTLC containing interleukin-2 (5 U/ml), inhibition was obtained only by pretreatment of the targets with mAb against ICAM-1. The results show thus (a) that the lymphocytes react in vitro with tumor cells only if these express both MHC class I molecules and ICAM-1; (b) that expression of these molecules can be induced by interferon alpha and TNF alpha; (c) that cytotoxic effectors generated in the MLTC with cytokine-treated tumors can also act on the untreated tumor cells. The requirement of the two surface moieties for the interaction with lymphocytes was also substantiated by blockade with relevant mAb.