Inhibition Of Cell Aggregation Research Articles

Antimalarial, cytotoxic, and antifungal alkaloids from Duguetia hadrantha.

Bioassay-guided isolation of Duguetia hadrantha yielded two new 4,5-dioxo-1-azaaporphinoids, hadranthine A (1) and hadranthine B (2), together with the known alkaloids imbiline-1 (3), sampangine (4), and 3-methoxysampangine (5), whose structures were determined primarily from 2D-NMR 1H-13C HMBC, and 1H-15N HMBC experiments. This is the first report of the co-occurrence of the copyrine alkaloids 4 and 5, as well as the first report of either copyrine or imbiline type alkaloids from a Duguetia species. Compounds 1, 4, and 5 demonstrated in vitro antimalarial activity against Plasmodium falciparum (W-2 clone), while 2 was inactive. Instead, 2 showed in vitro cytotoxicity to selected human cancer cell lines (IC50 = 3-6 microg/mL against SK-MEL, KB, BT-549, and SK-OV-3), and 4 was also cytotoxic to human malignant melanoma (IC50 = 0.37 microg/mL). Sampangine (4) also inhibited cell aggregation with a MIC value of <0.15 microg/mL, while 3-methoxysampangine (5) was only weakly active.

Oligomeric State of the Colon Carcinoma-associated Glycoprotein GA733-2 (Ep-CAM/EGP40) and Its Role in GA733-mediated Homotypic Cell-Cell Adhesion

The GA733-2 antigen (GA733) is a homotypic calcium-independent cell adhesion molecule (CAM) present in most normal human epithelial cells and gastrointestinal carcinomas. Because oligomerization of some CAMs regulates cell adhesion and signal transduction, the correlation between GA733 oligomeric state and cell-cell adhesion was investigated. Sedimentation equilibrium studies showed that full-length (-FL) GA733 exists as dimers and tetramers in solution, whereas the GA733 extracellular domain (-EC) is a monomer. The Kd of GA733-FL is less than 10 nm for the monomer-dimer association, whereas the dimer-tetramer association is about 1000-fold weaker (Kd approximately 10 microm). Chemical cross-linking of purified GA733-FL in solution resulted in a major product corresponding to GA733 dimers, and minor amounts of trimers and tetramers. However, GA733-EC cross-linked under the same conditions was consistently a monomer. Chemical cross-linking of dissociated colon carcinoma cells produced predominantly GA733 dimers, whereas cross-linking of cells in monolayers yielded some tetramers as well. GA733-FL retained its cell-cell adhesion function as shown by inhibition of cell aggregation, whereas monomeric GA733-EC was inactive. These data show that GA733 exists predominantly as high affinity noncovalent cis-dimers in solution and on dissociated colon carcinoma cells. The lower affinity association of dimers to form tetramers is most likely the head-to-head interaction between GA733 cis-dimers on opposing cells that represents its cell-cell adhesion activity.

Identification of clusterin sequences mediating renal tubular cell interactions.

Expression of the glycoprotein clusterin is markedly increased following tissue injury. One function of clusterin is to promote cell interactions which are perturbed in these pathologic settings. Clusterin causes cell aggregation and adhesion in vitro yet the molecular mechanism for this effect is not known. In order to identify the active site(s) of clusterin, 34 peptides, each 15 amino acid residues in length, were synthesized from hydrophilic regions of human clusterin. When studied individually, none of the peptides caused aggregation of LLC-PK1 cells, a porcine renal epithelial cell line. However, two out of the 34 peptides inhibited clusterin-induced cell aggregation in a dose-dependent manner. Scrambled versions of these two 'active' peptides did not inhibit cell aggregation. Seven peptides promoted cell adhesion. In conclusion, these findings provide evidence for novel amino acid sequences mediating clusterin-induced renal cell interactions.

Predominant inhibition of ganodermic acid S on the thromboxane A 2-dependent pathway in human platelets response to collagen

Ganodermic acid S (GAS), a membrane acting agent, exerts multiple effects on human platelet function (C.N. Wang et al. (1991) Biochem. J. 277, 189–197). The study reported how GAS affected the response of human gel-filtered platelets (GFP) to collagen. The agent inhibited cell aggregation by prolonging lag and shape change periods and decreasing the initial cell aggregation rate. However, the inhibitory efficiency was less than its inhibition on GFP response to U46619, a thromboxane (TX) A 2 mimetic. In the agent-effect on biochemical events, GAS effectively inhibited Ca 2+ mobilization, phosphorylation of myosin light chain, dense granule secretion and TXB 2 generation. The inhibitions might originate from blocking Ca 2+ mobilization of the TXA 2-dependent pathway. GAS partially decreased the phosphorylation of most phosphotyrosine proteins from early activation to the integrin α IIbβ 3-regulated steps. The agent did not affect the phosphorylation of three proteins at the steps regulated by integrin α IIbβ 3. The results suggest that GAS inhibits the collagen response predominantly on the TXA 2-dependent signaling, and the tyrosine kinase-dependent pathway in collagen response plays a major role in aggregation.

Inhibition of adhesion and induction of epithelial cell invasion by HAV-containing E-cadherin-specific peptides.

The E-cadherin/catenin complex, an organizer of epithelial structure and function, is disturbed in invasive cancer. The HAV (histidine alanine valine) sequence in the first extracellular domain of E-cadherin is crucial for homophilic interactions between cadherins. We report that specific peptides containing an HAV sequence interfere with the functions of the E-cadherin/catenin complex. Cells either expressing specific cadherins or not were challenged with both cadherin and noncadherin peptides comprising a central HAV sequence. Specific E-cadherin peptides inhibited cell aggregation, disturbed the epithelial morphotype and were able to stimulate invasion of cells expressing E-cadherins. Conditioned medium, containing E-cadherin fragments, also stimulated invasion in contrast to conditioned medium from which the E-cadherin fragments were removed. Our studies show that E-cadherin functions are inhibited by homologous proteolytic HAV-containing fragments that are released in an autocrine manner and subsequently inhibit the E-cadherin/catenin complex. In this way such cadherin fragments may induce and support cancer invasion.

Homotypic adhesion through carcinoembryonic antigen plays a role in hepatic metastasis development.

We established a cell line with high metastatic potential to the liver (LS‐LM4) after four successive repetitions of splenic injection of liver‐metastatic cells in SCID mice. This cell line strongly expressed CEA and showed increased homotypic adhesion as compared with the parent cell line (LS174T). To examine the role of CEA in the increased homotypic adhesion, LS‐LM4 cells were treated with anti‐CEA antibody and subjected to an in vitro adhesion and aggregation assay. Further, to study the role of CEA in the hepatic metastasis of cells with high metastatic potential, LS‐LM4 cells were treated with anti‐CEA antibody, and the inhibition of hepatic metastasis after splenic injection in vivo was examined. There was a 62% decrease in the homotypic adhesion of anti‐CEA antibody‐treated (100 μg/ml) LS‐LM4 cells under a Ca2+‐free condition as compared with the control (P<0.01). Anti‐CEA antibody (100 μg/ml) inhibited cell aggregation under a Ca2+‐free condition (P<0.05). Treatment with anti‐E‐cadherin antibody (60 μ/ml) plus anti‐CEA antibody (100 μg/ml) inhibited cell aggregation more potently than anti‐E‐cadherin antibody treatment alone in the presence of Ca2+. In vivo, there was a 75% decrease in the number of hepatic metastatic nodules in the G125 anti‐CEA antibody‐treated group as compared with the control group (P<0.01). Similarly, there was a 40% decrease in the diameter of metastatic nodules and there was a 90% decrease in total tumor volume of hepatic metastasis in the G125 anti‐CEA antibody‐treated group as compared with the control (P<0.01). These results suggest that increased metastatic potential to the liver is at least partly due to increased homotypic binding mediated by CEA.

Nitric oxide, an endogenous regulator of Dictyostelium discoideum differentiation.

We have previously demonstrated that nitric oxide (NO)-generating compounds inhibit D. discoideum differentiation by preventing the initiation of cAMP pulses (Tao, Y., Howlett, A. and Klein, C. (1996) Cell. Signal. 8, 37-43). In the present study, we demonstrate that cells produce NO at a relatively constant rate during the initial phase of their developmental cycle. The addition of oxyhemoglobin, an NO scavenger, stimulates cell aggregation, suggesting that NO has a negative effect on the development of aggregation competence. Starvation of cells in the presence of glucose, which has been shown to prevent the initiation of cAMP pulses (Darmon, M. and Klein, C. (1978) Dev. Biol. 63, 377-389), results in an increased production of NO. The inhibition of cell aggregation by glucose treatment can be reversed by oxyhemoglobin. These findings indicate that NO is a signaling molecule for D. discoideum cells and that physiological or environmental conditions that enhance external NO levels will delay the initiation of cAMP pulses, which are essential for cell differentiation.

Inhibitory effects of tunicamycin on cell-cell adhesion and cell reaggregation of the cellular slime mold,Polysphondylium pallidum

To assess the role in cell-cell adhesion of gp64, a putative cell-cell adhesion molecule ofPolysphondylium pallidum, we treated the cells with tunicamycin (TM), a known inhibitor of the synthesis of the N-linked oligosaccharide precursor, and examined TM's effect on cell-cell adhesion. The vegetative growth ofPolysphondylium cells was inhibited with TM in a dose-dependent manner. When cells were treated with TM (2.0 μg/ml) during only the first 4 hr of starvation and further starved for 8 hr without TM, the cells dissociated considerably, although even the growth phase cells ofPolysphondylium normally show EDTA-resistant (Ca2+-independent) cell adhesions. In parallel with the above effects, the amounts of intact gp64 decreased considerably in time with the lengths of incubation (0 hr>4 hr >8 hr). When TM-treated cells were washed free of TM, and shaken for a further 12 hr, the cells began to aggregate again, accompanied by an increase of gp64. In conclusion, TM affected cell-cell adhesion ofPolysphondylium cells, but we were not able to distinguish whether the inhibition of cell aggregation was due to defects in glycosylation on glycoproteins and/or due to reduced levels of glycoproteins themselves.

Influences of silicates and carnitine-silicate mixtures on the inhibition of aggregation of erythrocytes elicited by the presence of fibrinogen.

Carnitine and acylcarnitine derivatives have been reported to inhibit cell aggregation (Fritz and Burdzy, 1989, J. Cell. Physiol., 140:18-28). A follow-up of these observations showed that whereas the previously described effects of long-chain acylcarnitines were well replicated, those of carnitine on erythrocytes showed marked variability. The latter phenomenon was traced to the presence of silicates in carnitine solutions derived from the use of sodium hydroxide solutions stored in glass containers for the neutralization of carnitine. The present experiments have led to the discovery that oligomeric forms of silicates are powerful inhibitors of red blood cell aggregation which otherwise occurs in the presence of fibrinogen alone. The active form(s) of silicates in this assay, which appear to be generated by polymerization of silicates in metasilicate solutions on neutralization, are unstable and therefore transient under usual conditions. We estimate that the active oligomeric forms contain between 4 to 18 silicon atoms per molecule. When maintained at -18 degrees C in the presence of carnitine, but not in its absence, the active forms of oligomeric silicates remained stable for months, judging from their ability to inhibit cell aggregation. We conclude that carnitine stabilized the oligomeric form(s) of silicate, or that the species stabilized is an oligomeric silicate-carnitine complex. Comparable concentrations of choline, deoxycarnitine, or gamma-aminobutyrate were less effective in stabilizing the active silicate oligomers. The active forms of the silicate oligomers had Ki values of about 10 microM, calculated as the monomeric form, in inhibiting red blood cell aggregation. The data indicate that free carnitine does not directly inhibit erythrocyte inhibition, as previously interpreted, whereas long-chain acylcarnitine derivatives are active in the absence of silicates. Possible mechanism of actions of silicate oligomers on membranes are discussed.

A novel class of adhesion acidic glycans in sea urchin embryos. Isolation, characterization and immunological studies during early embryonal development.

Total glycans were isolated and purified from Lytechinus pictus embryos at early developmental stages by gel-filtration chromatography after pronase and DNase digestion, and alkali-borohydride treatment. Fractionation by Superose 6 and HPLC gel-filtration chromatography revealed three major glycan fractions of 580, 150 and 2 kDa consistently throughout development up to the stage of end gastrula. The 580-kDa and the 150-kDa glycan fractions isolated from fertilized eggs up to the stage of end gastrula are highly acidic, whereas the 2-kDa glycan fractions have no detectable uronic acid residues and charged groups. Chemical analysis of the glycan fractions showed that their content of neutral hexoses, uronic acid, GlcNAc, GalNAc and sulphate changes during development. The resistance of the 580-kDa and the 150-kDa glycan fractions to glycosaminoglycan-degrading enzymes indicates a structure which is different from the glycosaminoglycans. The incorporation of [3H]glucosamine into the 580-kDa, the 150-kDa and the 2-kDa glycan fractions showed that glycan synthesis increases in a linear fashion from the stage of early blastulation to end of gastrulation. Maximal incorporation of the radioligand occurs in the 2-kDa glycan fractions, with the highest rate observed between the stages of mesenchyme blastula and early gastrulation. Immunological studies, using a monoclonal antibody which inhibits cell aggregation, showed that the total glycans isolated from morula, early blastulation, early gastrulation and the end of gastrulation carry cell-adhesion epitopes. The number of these epitopes, as indicated by the intensity of the immunostaining, increases from morula formation to end-gastrulation stages and correlates with the increased rate of morphogenetic movements. These results suggest that controlled expression of the cell-adhesion glycan epitopes play an important role in sea urchin gastrulation.

Differential, LFA-1-Sensitive Effects of Antibodies to Nectadrin, the Heat-Stable Antigen, on B Lymphoblast Aggregation and Signal Transduction

Nectadrin, the heat-stable antigen (HSA), is a highly glycosylated GPI-linked glycoprotein that can undergo homophilic and heterophilic binding. In the present work we have examined short-term effects of nectadrin antibodies on splenic B lymphoblast aggregation and signal transduction. Monoclonal antibody 79 inhibited cell aggregation and induced an intracellular Ca ++ signal in the absence of cross-linking. Both these effects were perturbed in the presence of LFA-1 antibodies. Nectadrin antibody M1/69 and polyclonal nectadrin antibodies stimulated cell aggregation, did not induce a Ca ++ signal, and their effects were functionally independent of LFA-1. These results suggest that nectadrin may concomitantly mediate primary and activate secondary adhesion mechanisms whereby each of these processes may be related to a different signal transduction pathway.

Glycopeptide of P0 protein inhibits homophilic cell adhesion Competition assay with transformants and peptides

Expression of major myelin glycoprotein P0 by PO cDNA transfection into C6 glioma cells promoted homophilic cell adhesion of the cells. After the dissociated cells were incubated for various times, the number of particles at each time point was measured. The total number of particles decreased to 24% in 60 min for transformant (C6P0) cells, in contrast to only 68% for control (C6P0′) cells. To confirm the homophilic mechanism of adhesion, mixed-cell aggregation experiments were performed. Among the four synthetic peptides corresponding to a part of the P0 sequence used, only peptide 3 (residues 90–96), which contained a carbohydrate attaching site, caused considerable inhibition of cell aggregation (approximately 50%). In addition, the glycopeptide (residues 91–95) obtained from bovine P0 markedly inhibited cell aggregation (by approximately 85%).

Inhibition of lipopolysaccharide synthesis in Agrobacterium tumefaciens and Aeromonas salmonicida.

Lipopolysaccharide (LPS) synthesis was inhibited, new lipid A metabolites accumulated, and growth ceased, when the plant pathogen Agrobacterium tumefaciens and the fish pathogen Aeromonas salmonicida were treated with an antibacterial agent which specifically inhibits CTP:CMP-3-deoxy-manno-octulosonate cytidylyltransferase (CMP-KDO synthase). The new lipid A metabolites were purified by chromatography on DEAE-cellulose and chemically analysed. Metabolites isolated from both bacterial species contained glucosamine and phosphate in a 1:1 molar ratio, and 3-OH-C14:0 was the major fatty acid present (1 mol and 1.4 mol per mol glucosamine for A. tumefaciens and A. salmonicida, respectively). Inhibition of LPS synthesis by CMP-KDO synthase inhibitor had no effect on the initial kinetics of A. tumefaciens attachment to cultured carrot cells, but did inhibit cell aggregation normally induced by bacterial cellulose synthesis. Bacteria treated with inhibitor remained viable and able to synthesize protein at 15% the rate of control cells, indicating that the lack of cellulose-induced aggregation was not due to the inability of bacteria to make protein, but rather the inability to respond normally to the bacterial-plant cell interaction.

Cultural conditions affecting Azospirillum brasilense cell aggregation and adsorption to maize roots

Sugars. EDTA and trypsin were tested for their effect in preventing aggregation of Azospirillum brasilense Cd cell suspension grown on malate as a C-source. d-Fructose (25–30 mM) strongly inhibited cell aggregation at various pH levels (5.0–8.4). Treatment of malate-grown cells with 20 mM d-fructose for 7.5 min. or with maize root extracts, significantly promoted the subsequent adsorption of Azospirillum cells to maize roots. No enhancement of adsorption could be observed when roots had been treated with d-fructose. The highest cell adsorption to roots was obtained with Azospirillum grown on d-fructose as C-source in combination with cells that had been exposed to root extract.

The extracellular matrix modulates the response of PC12 cells to nerve growth factor: Cell aggregation versus neurite outgrowth on 3-dimensional laminin substrata

PC12 cells attach well to plastic culture dishes coated with laminin, collagen, polylysine or a basement membrane extract (2-dimensional substrata) and, in the presence of NGF, extend short neurites within 1-2 days. However, on gels (3-dimensional substrata) reconstituted from a basement membrane extract (RBM), PC12 cells attach extending short processes transiently and within one day, form networks of small aggregates interconnected by process-bearing cells. By 3 days the network collapses into large aggregates that, in media supplemented with NGF, extended a halo of neurites resembling dorsal root ganglia in culture. Time-lapse video recordings indicate that cell motility on RBM gel is accompanied by extensive blebbing as well as extension of processes that attach to and pull together neighbouring cells. These cellular events may contribute to the disruption of the gel underneath aggregates that is apparent when cultures are stained with Coomasie Blue. Ultrastructural studies indicated that aggregates often have zonula adherens-type junctions where cell bodies and processes come in contact. PC12 cells seeded onto gels of laminin alone behave essentially the same as on RBM gels, whereas on collagen gels they behave as on 2-dimensional substrata and extended neurites rather than aggregate. The extent of aggregation increases with greater cell density and is enhanced significantly by NGF. Antisera to NGF reduce the NGF-enhancement of aggregation but do not block aggregation in the absence of NGF. Dibutyryl cAMP or epidermal growth factor, which stimulate process extension and cell division respectively, do not enhance aggregation. However, 3A3, a monoclonal antibody to a laminin/collagen receptor on PC12 cells and antibodies (Fab fragments) to the neural cell adhesion molecule both inhibit cell aggregation.

Inhibitory effect of salicylate on 2,4-dinitrophenol and diethyl maleate in isolated rat intestinal epithelial cells

Studies on the mechanism of chemically induced intestinal epithelial injury were carried out using isolated, rat small intestinal epithelial cells. Compounds such as 2,4-dinitrophenol (DNP) and diethyl maleate (DEM), caused NADH loss, an increase in cytosolic Ca 2+ concentration and protein thiol loss. Further, these compounds accelerated cell aggregation and decreased cell viability. Calmodulin antagonists inhibited protein thiol loss induced by either of the compound, inhibited cell aggregation and prolonged cell viability, but did not influence NADH loss. It has been reported that the calmodulin-binding protein may regulate cytoskeletal activity. Therefore, the inhibition of protein thiol loss by calmodulin antagonist may be due to a dissociation of calmodulin-binding proteins from cytoskeletal elements. Salicylate also inhibited protein thiol loss induced by DNP and DEM, and inhibited cell aggregation. However, salicylate may have a direct effect in reducing the cytosolic free Ca 2+ concentration by complexation and subsequent facilitated release of Ca 2+ from cells. Further, in the present study, the induction of cell aggregation may be caused by the appearance of specific sites on the cell membrane surface to which arsenazo III could adsorb, since adsorption of arsenazo III to the isolated epithelial cells seemed to correlate with increased cell aggregation.

A monoclonal antibody (NKI-L16) directed against a unique epitope on the alpha-chain of human leukocyte function-associated antigen 1 induces homotypic cell-cell interactions.

In the present study a unique antibody (NKI-L16) reacting with the alpha-chain of the human leukocyte function-associated Ag-1 (LFA-1) is described, which stimulates homotypic cell-cell interactions in a manner very similar to 12-O-tetradecanoyl-phorbol-13-acetate (TPA), in contrast to other anti-LFA-1 mAb which inhibit cell aggregation. The induction of aggregate formation of EBV-transformed B cells (JY) and CTL clones by TPA or NKI-L16 is not accompanied by an increase in the expression of LFA-1. Nevertheless, this cluster formation is LFA-1 dependent, inasmuch as anti-LFA-1 antibodies, other than NKI-L16, completely abrogate aggregation. Simultaneous addition of NKI-L16 and TPA did not result in a further increase of the speed of cluster formation, suggesting that a similar pathway is activated. Immunoprecipitation and enzyme digestion studies revealed that NKI-L16 recognizes a unique epitope on the alpha-chain of LFA-1, most likely situated close to the transmembrane segment of the molecule. It is hypothesized that NKI-L16 or TPA can cause the LFA-1 molecule to convert from an inactive to an active configuration, thereby permitting binding of LFA-1 to its natural ligand.

Polyamines affect growth of cultured rat cerebellar neurons in different sera

The study examines the effects of polyamines on growth of cultured neurons from 6-day-old rat cerebellar cortex, by means of: (a) irreversible inhibition of ornithine decarboxylase activity with α-difluoromethylornithine, and (b) treatment with the exogenous diamine putrescine and the polyamines spermidine and spermine, in the presence of sera from different sources. Inhibition of ornithine decarboxylase activity starting at plating time led after 24 hr to a partial inhibition of cell aggregation with a drastic (90%) inhibition of neurite formation. However, after 48 hr of enzyme inhibition aggregation and neurite formation increased to approach the 24 hr control values and eventually cultures fully recovered. Polyamines added at plating time in the presence of fetal calf serum led to a permanent dose-dependent inhibition of aggregation and neurite formation, spermine being effective at lower doses (spermine < spermidine ⪡ putrescine). Adhesion of cells to polylysine coated surfaces was not affected by polyamines. Recovery from the cytostatic polyamine effect was observed after washing and addition of fresh medium. Prevention of the effect was achieved in the presence of aminoguanidine, an inhibitor of diamine and polyamine oxidases. The preventive effect of aminoguanidine was dose polyamine-dependent, with higher aminoguanidine concentrations needed to prevent the spermine effect (spermine > spermidine > putrescine). The polyamine effects were observed in the presence of fetal calf, heat-inactivated fetal calf and human sera, but not with rat serum. Addition of polyamines to 24-hr-old cultured neurons, in the presence of fetal calf serum, led 12 hr later to cell death. This lethal effect could be inhibited by aminoguanidine. We conclude: (a) irreversible inhibition of ornithine decarboxylase activity delays but does not prevent neuronal growth in culture; (b) oxidation products of extracellular polyamines inhibit cell aggregation and neurite formation of cultured neuroblasts, and have lethal effects on growing neurons in culture, and (c) different pharmacological effects of polyamines can be expected in different species.

Identification of a Cell‐Surface Glycoprotein Mediating Adhesion in Human Granulocytes

Previous studies have shown that monoclonal antibody 60.3 reacting with a surface antigen common to human leukocytes inhibits phorbol ester-induced adhesion among blood mononuclear cells and precipitates from these cells three surface polypeptides with apparent molecular weights of 90,000, 130,000 and 160,000. Now we report that the same antibody, either as purified IgG or Fab fragments, also inhibits the extensive adhesion among granulocytes induced by phorbol ester. Inhibition of cell aggregation was not observed with monoclonal antibodies to C3b receptor, common leukocyte antigen T200, C3bi receptor, brain granulocyte-T lymphocyte antigen, IgG Fc receptor, class I transplantation antigen, or a granulocyte-specific antigen. Intercellular adhesion induced by either the chemotactic tripeptide N-formylmethionyl-leucyl-phenylalanine (FMLP) or the ionophore A23187 was also inhibited by antibody 60.3. However, this antibody did not affect phorbol ester-induced superoxide (O2-) generation or lysozyme release. Two major surface glycopolypeptides with apparent molecular weights of 92,000 and 155,000 were immunoprecipitated from granulocytes. Dissociation of the protein complexes obtained from blood mononuclear cells and granulocytes indicated the presence of the epitope on the 90,000-92,000 molecular-weight components. It is thus concluded that the smallest glycopolypeptides mediate adhesion in human granulocytes and mononuclear leukocytes.

Identification of a cell surface protein complex mediating phorbol ester-induced adhesion (binding) among human mononuclear leukocytes.

Phorbol esters rapidly induce aggregation of human mononuclear leukocytes in vitro. Previous studies have indicated that cell surface proteins are involved. We report now that the monoclonal antibody 60.3, either as purified IgG or as Fab' fragments, to an antigen common to leukocytes completely inhibited the phorbol ester-induced intercellular adhesion (binding). No inhibition of cell aggregation was observed with monoclonal antibodies to common leukocyte antigen T 200, T-cell-associated antigen, monocyte-granulocyte antigen, brain granulocyte-T-lymphocyte antigen, transferrin receptor, mature T-cell antigens (mol.wt either 67,000 or 19,000/29,000), T helper/inducer cell antigen, sheep erythrocyte receptor, class I or class II antigens, or T cytotoxic/suppressor cell antigen. The antibody 60.3 did not inhibit stimulation of the cells since the characteristic phorbol ester-induced morphological changes and phorbol ester-enhanced cap formation of membrane glycoproteins were readily observed. Two major cell surface polypeptides with apparent molecular weights of 90,000 and 160,000 were immunoprecipitated. We conclude that this protein complex, or at least one of its components, mediates adhesion among mononuclear leukocytes.