An alternative leukocyte homotypic adhesion mechanism, LFA-1/ICAM-1-independent, triggered through the human VLA-4 integrin

The VLA-4 (CD49d/CD29) integrin is the only member of the VLA family expressed by resting lymphoid cells that has been involved in cell-cell adhesive interactions. We here describe the triggering of homotypic cell aggregation of peripheral blood T lymphocytes and myelomonocytic cells by mAbs specific for certain epitopes of the human VLA alpha 4 subunit. This anti-VLA-4-induced cell adhesion is isotype and Fc independent. Similar to phorbol ester-induced homotypic adhesion, cell aggregation triggered through VLA-4 requires the presence of divalent cations, integrity of cytoskeleton and active metabolism. However, both adhesion phenomena differed at their kinetics and temperature requirements. Moreover, cell adhesion triggered through VLA-4 cannot be inhibited by cell preincubation with anti-LFA-1 alpha (CD11a), LFA-1 beta (CD18), or ICAM-1 (CD54) mAb as opposed to that mediated by phorbol esters, indicating that it is a LFA-1/ICAM-1 independent process. Antibodies specific for CD2 or LFA-3 (CD58) did not affect the VLA-4-mediated cell adhesion. The ability to inhibit this aggregation by other anti-VLA-4-specific antibodies recognizing epitopes on either the VLA alpha 4 (CD49d) or beta (CD29) chains suggests that VLA-4 is directly involved in the adhesion process. Furthermore, the simultaneous binding of a pair of aggregation-inducing mAbs specific for distinct antigenic sites on the alpha 4 chain resulted in the abrogation of cell aggregation. These results indicate that VLA-4-mediated aggregation may constitute a novel leukocyte adhesion pathway.

Lipoxin A4 and lipoxin B4 stimulate the release but not the oxygenation of arachidonic acid in human neutrophils: dissociation between lipid remodeling and adhesion

The profiles of actions of lipoxin A4 (LXA4) and lipoxin B4 (LXB4), two lipoxygenase-derived eicosanoids, were examined with human neutrophils. At nanomolar concentrations, LXA4 and LXB4 each stimulated the release of [1-14C]arachidonic acid from esterified sources in neutrophils. Lipoxin-induced release of [1-14C]arachidonic acid was both dose- and time-dependent and was comparable to that induced by the chemotactic peptide f-met-leu-phe. Time-course studies revealed that lipoxin A4 and lipoxin B4 each induced a biphasic release of [1-14C]arachidonic acid, which was evident within seconds (5-15 sec) in its initial phase and minutes (greater than 30 sec) in the second phase. In contrast, the all-trans isomers of LXA4 and LXB4 did not provoke [1-14C]AA release. Lipoxin-induced release of arachidonic acid was inhibited by prior treatment of the cells with pertussis toxin but not by its beta-oligomers, suggesting the involvement of guaninine nucleotide-binding regulatory proteins in this event. Dual radiolabeling of neutrophil phospholipid classes with [1-14C]arachidonic acid and [3H]palmitic acid showed that phosphatidylcholine was a major source of lipoxin-induced release of [1-14C]arachidonic acid. They also demonstrated that lipoxins rapidly stimulate both formation of phosphatidic acid as well as phospholipid remodeling. Although both LXA4 and LXB4 (10(-8)-10(-6) M) stimulated the release of [1-14C]arachidonic acid, neither compound evoked its oxygenation by either the 5- or 15-lipoxygenase pathways (including the formation of LTB4, 20-COOH-LTB4, 5-HETE, or 15-HETE). LXA4 and LXB4 (10(-7) M) each stimulated the elevation of cytosolic Ca2+ as monitored with Fura 2-loaded cells, albeit to a lesser extent than equimolar concentrations of FMLP. Neither lipoxin altered the binding of [3H]LTB4 to its receptor on neutrophils. In addition, they did not stimulate aggregation or induce adhesion of neutrophils to human endothelial cells. Results indicate that both LXA4 and LXB4 stimulate the rapid remodeling of neutrophil phospholipids to release arachidonic acid without provoking either aggregation or the formation of lipoxygenase-derived products within a similar temporal and dose range. Together they indicate that LXA4 and LXB4 display selective actions with human neutrophils and suggest that these eicosanoids possess unique profiles of action which may regulate neutrophil function during inflammation.

Cytoplasmic pH of Dictyostelium discoideum amebae during early development: identification of two cell subpopulations before the aggregation stage

Development of the cellular slime mold Dictyostelium discoideum is initiated by the removal of nutrients, and results in formation of a mature fruiting body composed of two cell types, the stalk and spore cells. A considerable body of evidence supports the hypothesis that cytoplasmic pH may be an essential regulator of the choice to differentiate in either the prestalk or prespore pathway. We have devised methods for measurement and analysis of intracellular pH in developing Dictyostelium amebae in order to assess directly the potential role of cytoplasmic pH in regulating the pathway of differentiation. The intracellular pH of single D. discoideum amebae during development and in intact slugs has been measured using the pH-sensitive indicator pyranine in a low light level microspectrofluorometer. We have used the ATP-mediated loading method to introduce pyranine into these cells. Cells loaded by the ATP method appear healthy, have no detectable defects in development, and exhibit a similar population distribution of intracellular pH to those loaded by sonication. The intracellular pH of populations comprised of single amebae was found to undergo a transient acidification during development resulting in a bimodal distribution of intracellular pH. The subpopulations were characterized by fitting two gaussian distributions to the data. The number of cells in the acidic intracellular pH subpopulation reached a maximum 4 h after initiation of development, and had returned to a low level by 7 h of development. In addition, a random sample of single amebae within a slug had a median intracellular pH of 7.2, nearly identical to the median pH (7.19) of similarly treated vegetative cells. No gradient of intracellular pH along the anterior to posterior axis of the slug was detected. Our data demonstrate the existence of two distinct subpopulations of cells before the aggregation stage of development in Dictyostelium, and offers support for the hypothesis that changes in intracellular pH contribute to development in D. discoideum.

Comparative studies of microscopically determined aggregation, degranulation, and light transmission after chemotactic activation of adult and newborn neutrophils

Changes in the light transmission of suspensions of activated neutrophils are widely used to measure the dynamics of neutrophil aggregation. Such studies have suggested, for example, that aggregation is irreversible for human newborn neutrophils but fully reversible for adult cells. We have evaluated aggregation directly by microscopic particle counting and compared it with changes in light transmission (delta T) and with release from three granule subsets for neutrophils activated with N-formyl-methionyl-leucyl-phenylalanine (FMLP). Maximal increases in %T in response to 0.5 micromol/L FMLP were approximately 25% larger for newborn than for adult neutrophils, and were only partially reversible by 8 minutes, while %T increases for adult neutrophils were fully reversible. However, measurements of neutrophil aggregation using light microscopy showed that both newborn and adult neutrophils fully deaggregated. A further independence of delta T from aggregation was found by pretreating adult neutrophils with cytochalasin B (5 micrograms/mL) in the presence of 0.5% gelatin, a pretreatment that blocked FMLP-induced neutrophil aggregation while allowing large increases in %T and degranulation. In response to FMLP, newborn neutrophils released more enzyme from each granule subset than did adult neutrophils. Our results suggest that cellular events associated with neutrophil activation (other than aggregation) are implicated in light transmission responses and that these differ for adults and newborns. These results also suggest that reports of neutrophil aggregation should be based on direct particle counting methods rather than on %T responses.

Drosophila fasciclin I is a novel homophilic adhesion molecule that along with fasciclin III can mediate cell sorting

Fasciclin I is a membrane-associated glycoprotein that is regionally expressed on a subset of fasciculating axons during neuronal development in insects; it is expressed on apposing cell surfaces, suggesting a role in specific cell adhesion. In this paper we show that Drosophila fasciclin I is a novel homophilic cell adhesion molecule. When the nonadhesive Drosophila S2 cells are transfected with the fasciclin I cDNA, they form aggregates that are blocked by antisera against fasciclin I. When cells expressing fasciclin I are mixed with cells expressing fasciclin III, another Drosophila homophilic adhesion molecule, the mixture sorts into aggregates homogeneous for either fasciclin I- or fasciclin III-expressing cells. The ability of these two novel adhesion molecules to mediate cell sorting in vitro suggests that they might play a similar role during neuronal development.

Attraction, deformation and contact of membranes induced by low frequency electric fields

The force of attraction between erythrocyte ghosts induced by low frequency electric fields (60 Hz) was measured as a function of the intermembrane separation. It varied from 10(-14) N for separation of the order of the cell diameter to 10(-12) N for close approach and contact in 20 mM sodium phosphate buffers (conductivity 260 mS/m, pH 8.5). For large separations the interaction force followed a dependence on separation as predicted for dipole-dipole interactions. For small separation an empirical formula was obtained. The membranes deformed at close approach (less than 1 microns) before making contact. The contact area increased with time until reaching the final equilibrium state. The ghosts separated reversibly after switching off the electric field. The membrane tension induced by the ghost interaction at contact was estimated to be of the order of 0.1 mN/m. These first quantitative measurements of the force/separation dependence for intermembrane interactions induced by low frequency electric fields indicate that attractive forces, membrane deformation and contact area of cells depend strongly on intermembrane separation and field strength. The quantitative relationship between them are important for measuring membrane surface and mechanical properties, intermembrane forces and understanding mechanisms of membrane adhesion, instability and fusion in electric fields and in general.

T lymphocyte aggregation with immobilized anti-TCR-antibodies is dependent upon energy and microfilament assembly

An assay has been developed to quantitate the binding of beads coated with anti-T cell receptor (TCR) monoclonal antibodies (MoAb) to T lymphocytes. The Ab used were a hamster MoAb, 145.2C11 (2C11), directed against the epsilon chain of the CD3 complex of the murine TCR, and a murine MoAb, F23.1, directed against the V beta 8-encoded determinant of the alpha/beta heterodimer of the TCR. Ab were adsorbed onto polystyrene beads and the beads labeled with [125I]bovine serum albumin [( 125I]BSA). The labeled, Ab-coated beads were mixed at 4 degrees C with murine, cloned T-helper (Th) cells and contact between beads and cells was promoted by centrifugation. The mixtures were incubated at 37 degrees C for 10-20 min, and unbound beads were separated from cell-bound beads by Percoll gradient centrifugation. Beads coated with anti-TCR Ab formed stable conjugates with Th cells; an average of 6-10 2C11 Ab-coated beads/cell, or 10-15 F23.1 Ab-coated beads/cell was measured under optimal conditions. Beads coated with control Ab (hamster or mouse IgG) did not appreciably bind to the cells. Conjugation with 2C11 Ab-coated beads could be prevented by coating the cells with soluble 2C11 Ab, but not with soluble F23.1 Ab. Blocking the CD3 epsilon chain with soluble 2C11 Ab also reduced conjugate formation with F23.1 Ab-coated beads, suggesting a steric hindrance phenomenon. The extent of conjugation depended on the density of immobilized Ab. Maximum conjugation was observed when 100 micrograms of 2C11 Ab was used to coat 10(6) beads; higher Ab amounts did not further increase binding. Increasing the bead to cell ratio in the mixture increased binding, reaching optimal binding at 300:1, irrespectively of the amount of Ab adsorbed onto the beads. Stable binding of anti-TCR Ab-coated beads to T cells was temperature and energy dependent. It was prevented when glucose was removed from the medium and the glycolysis inhibitor, 2-deoxy-D-glucose was added, or when cells were treated with sodium azide. Conjugate formation was prevented by pretreatment of the cells with cytochalasins, indicating that microfilament assembly was essential. Microtubules were not involved, as vinca alkaloids were without effect. This novel assay system provides a simple means of studying aspects of TCR function including its physical and metabolic regulation.

Bone conditioned medium enhances cell aggregation, cell proliferation and alkaline phosphatase activity in serum-deprived medium

The effect of medium conditioned by whole bone was examined on the activity of a heterogeneous population of rat calvarial cells grown under serum-deprived conditions. Conditioned medium (CM) had pronounced effects on the appearance of cultures within 24-48 hours of addition. This was characterized by the breakdown of the cell monolayer, rounding of cells and formation of alkaline phosphatase-positive aggregates. Cellular alkaline phosphatase activity was increased compared to controls while acid phosphatase levels were reduced. These aggregates grown in the presence of 10 mM beta-glycerophosphate did not show evidence of mineralization. These results show that soluble factors derived from calvarial bone are responsible for cell aggregation, cell proliferation and increase in alkaline phosphatase activity.

State of leukocyte adhesiveness/aggregation in the peripheral blood of pemphigus and psoriatic patients

The purpose of this study was to assess the role of leukocyte adherence in the pathogenesis of the psoriatic lesion. Use was made of the fact that psoriasis and pemphigus differ considerably as to the presence of leukocytes in the respective lesions: abundance in psoriasis, and absence in pemphigus. The state of leukocyte adhesiveness/aggregation (LAA) was determined in the peripheral blood of 56 patients with psoriasis and 31 patients with pemphigus. Both classes of patients were subdivided into two categories according to the severity of the disease. It was found that in both diseases elevated values of LAA were obtained in the severe cases, whereas the mild cases did not differ significantly from normal controls. Thus, in psoriasis mean LAA values of 9.5% +/- 8% were recorded in the severe patients and 5.5% +/- 4.2% in the mild cases (p = 0.01), while in pemphigus the values were 15% +/- 9.6% and 6.6% +/- 3.7% respectively (p = 0.03). It is concluded that LAA per se does not play a primary role in causing the psoriatic lesion.

A novel assay for neutrophil clustering activity of human sera: relation to disease activity and neutropenia in systemic lupus erythematosus

A simple and reproducible method for the measurement of serum neutrophil clustering activity was developed. High clustering activity was found in 19/30 patients with active systemic lupus erythematosus (SLE), and 14/20 of those with severe disease flares. In contrast, 0/10 patients with quiescent SLE and 2/20 patients with rheumatoid arthritis had high neutrophil clustering activity. Particularly high clustering activity was found in patients with SLE with lupus glomerulonephritis and in certain patients with central nervous system disease. An inverse correlation was found between neutrophil clustering activity and peripheral blood neutrophil count in patients with SLE not treated with glucocorticoids, and clustering activity was high in all patients with low neutrophil counts in this group. A moderate correlation was found between neutrophil clustering activity and C1q binding circulating immune complexes. Non-steroidal anti-inflammatory drugs and glucocorticoids had little direct effect on neutrophil clustering activity.

Pathways of mononuclear cell infiltration in rheumatoid synovitis

The mononuclear cell infiltration which characterizes the chronic inflammatory reaction results from the migration of lymphocytes and monocytes through the endothelium of the postcapillary venule. The initial step in the emigration of these cells in their binding to the vascular endothelium. The binding capacity of the endothelial cell (EC) for lymphocytes and monocytes is increased by IFN-gamma, IL-1, TNF alpha, and TNF beta. Production of these cytokines by chronic inflammatory cells may be expected to amplify the chronic inflammatory reaction. Initiation of the chronic synovitis of rheumatoid and other chronic synovitides probably results from the interaction of antigen with sensitized T cells in the sublining region of the synovium. This interaction is facilitated by the presence of substantial numbers of DR + macrophage + accessory cells in the synovial interstitial space. It is likely that these accessory cells are bone marrow derived monocytes migrating to the synovial lining layer in response to chemotactic factors released by the hyperplastic synovial lining cells. Lymphocytes differ in their binding affinity for ECs, and more strongly binding lymphocytes may be preferentially bound. Since binding is the first step in lymphocyte emigration, this event may lead to the selection of more strongly binding lymphocytes in the perivascular infiltrate. The T cells present in the mononuclear cell infiltrates of rheumatoid arthritis, other chronic synovitides, and multiple sclerosis have been shown to be composed largely of the CDw29 + CD4+, helper-inducer, memory cell subset. The predominance of this T-cell subset may result from its demonstrated greater binding affinity for ECs.(ABSTRACT TRUNCATED AT 250 WORDS)

Is cortisol involved in upper-body obesity?

Obesity is a major health problem that can be defined as an excess of body fat, associated with hypertension, diabetes and coronary heart disease. Several groups have evaluated the clinical significance of variations in fat cell distribution on these complications. A frequently used index of fat cell distribution is the waist to hips ratio (W/H). A high W/H ratio is said to reflect upper body fat cell distribution while a low waist to hips ratio reflects a lower body type fat cell distribution. Studies have shown that those whose W/H ratio indicate upper body fat cell distribution had a higher prevalence of diabetes and hypertension than those with the lower type. Over the years cortisol has attracted considerable interest as a possible factor in the development and maintenance of obesity. The clinical findings associated with upper body type of obesity are in many ways similar to those of the hypercortisol state. Our hypothesis is that upper body obesity forms a unique subgroup of the obese population and their regional fat distribution is associated with mild cortisol excess. In humans, studies have reported that some obese subjects hypersecrete cortisol and have an increase in the cortisol production rate. Although recent studies would tend to discount any influence of cortisol in human obesity, several factors should be taken into consideration. It is difficult to measure cortisol economy in obese subjects because among other things the measurements are less than precise; and cortisol secretion changes during the day and in response to outside stimuli. Further, obesity is a heterogeneous disorder and not all obese subjects may have the same disorder.(ABSTRACT TRUNCATED AT 250 WORDS)

Stepwise aggregation, compaction, and differentiation of uncompacted F9 cells

To study the relationship between compaction and differentiation in aggregates of F9 embryonal carcinoma cells, a subline was developed which grows mostly uncompacted in monolayer culture in medium containing a low concentration of calcium (about 0.05 mM). When these cells were trysinized and cultured in suspension in the same medium, they formed loose, open aggregates, which failed to differentiate into embryoid bodies after exposure to 10 nM retinoic acid, confirming the requirement of compaction for differentiation. If, after culture for 3 days, the uncompacted F9 aggregates were exposed to additional calcium (4 nM), all compacted within an hour. The number of days necessary for aggregates to acquire this ability to compact rapidly was reduced if the monolayer of cells from which the aggregates were derived had been exposed to additional calcium to cause compaction for several days prior to trypsinization and aggregation. Next, treatment of the compacted F9 aggregates with 10 nM retinoic acid was followed by differentiation into embryoid bodies. The number of days required for this was also reduced if the aggregates were formed from previously compacted cells, presumably because compaction of the aggregates occurred sooner. The acceleration in compaction and differentiation in aggregates formed from previously compacted cells suggests that some of the proteins important for compaction, which are synthesized in a monolayer of compacted cells, persist through trypsinization and are carried over from monolayer to aggregates. Alternatively, an inhibitor of compaction is decreased in the compacted monolayer.(ABSTRACT TRUNCATED AT 250 WORDS)