Binding of IgG containing immune complexes to human neutrophil Fc gamma RII and Fc gamma RIII induces actin polymerization by a pertussis toxin-insensitive transduction pathway

The ability of a phagocytic stimulus, rabbit IgG anti-BSA/BSA immune complexes, to increase the F-actin content of human polymorphonuclear leukocytes was quantitated by flow cytometry following staining with nitrobenzoxadiazole-phallacidin. A significant rise in F-actin assembly was induced by addition of 5 micrograms/ml immune complex. Concentrations of immune complex of more than 200 micrograms/ml caused a maximal (approximately twofold) increase in F-actin content. After a delay of 5 s, the F-actin levels rose and reached maximum levels by 60 s after adding immune complexes. The twofold elevation in F-actin persisted for up to 60 min. Both anti-Fc gamma RII and anti-Fc gamma RIII mAb blocked immune complex stimulated actin polymerization. Exposure to pertussis toxin failed to affect the rate or extent of immune complex-induced actin polymerization. Cells incubated with immune complexes and then lysed with Triton had an increased number of sites able to nucleate actin polymerization. These findings suggest that immune complex binding to both polymorphonuclear leukocytes Fc gamma RII and Fc gamma RIII is required for actin filament assembly and that the induction of assembly occurs via transduction pathways that differ from those used by chemoattractants. As with adhesion this phagocytic stimulus induces actin assembly by a pertussis toxin insensitive pathway and produces a rise in actin filament content that persists for prolonged periods of time.

Binding of IgG containing immune complexes to human neutrophil Fc gamma RII and Fc gamma RIII induces actin polymerization by a pertussis toxin-insensitive transduction pathway

The ability of a phagocytic stimulus, rabbit IgG anti-BSA/BSA immune complexes, to increase the F-actin content of human polymorphonuclear leukocytes was quantitated by flow cytometry following staining with nitrobenzoxadiazole-phallacidin. A significant rise in F-actin assembly was induced by addition of 5 micrograms/ml immune complex. Concentrations of immune complex of more than 200 micrograms/ml caused a maximal (approximately twofold) increase in F-actin content. After a delay of 5 s, the F-actin levels rose and reached maximum levels by 60 s after adding immune complexes. The twofold elevation in F-actin persisted for up to 60 min. Both anti-Fc gamma RII and anti-Fc gamma RIII mAb blocked immune complex stimulated actin polymerization. Exposure to pertussis toxin failed to affect the rate or extent of immune complex-induced actin polymerization. Cells incubated with immune complexes and then lysed with Triton had an increased number of sites able to nucleate actin polymerization. These findings suggest that immune complex binding to both polymorphonuclear leukocytes Fc gamma RII and Fc gamma RIII is required for actin filament assembly and that the induction of assembly occurs via transduction pathways that differ from those used by chemoattractants. As with adhesion this phagocytic stimulus induces actin assembly by a pertussis toxin insensitive pathway and produces a rise in actin filament content that persists for prolonged periods of time.

Chemoattractant stimulation of polymorphonuclear leucocyte locomotion

Chemoattractants stimulate both cell locomotion and the orientation of this locomotion (chemotaxis) in polymorphonuclear leukocytes. Cell locomotion is a complex process which includes the coordinated protrusion of cell processes, formation of attachments to the substrate and contraction of the rear of the cell. To understand how chemoattractants regulate this process, it is helpful to dissect the process into components that can be examined separately. Comparison of these components in cells before and after stimulation with chemoattractant provides information about their regulation. In this review we focus on three components: how chemoattractants induce the development of cell polarity; how chemoattractants modulate cytoskeletal components (especially actin) to cause pseudopod protrusion; and how chemoattractant modulation of cell adhesions might contribute to cell locomotion. Spatial and temporal coordination of these and other components of locomotion result in efficient and directed cell movement. Our treatment of these questions is speculative and not comprehensive. We propose simple hypothetical models which can provide the reader with a conceptual framework that integrates the information available.

Chemoattractant-stimulated polymorphonuclear leukocytes contain two populations of actin filaments that differ in their spatial distributions and relative stabilities

Chemoattractants stimulate actin polymerization in lamellipodia of polymorphonuclear leukocytes. We find that removal of chemoattractant results in rapid (within 10 s at 37 degrees C) and selective depolymerization of the F-actin located in lamellipodia. Addition of 10 microM cytochalasin B, in the presence of chemoattractant, also resulted in rapid and selective depolymerization of lamellar F-actin. The elevated F-actin level induced by chemoattractant rapidly returns to the level present in unstimulated cells after (a) a 10-fold decrease in chemoattractant concentration; (b) the addition of 10 microM cytochalasin B; or (c) cooling to 4 degrees C. The F-actin levels of unstimulated cells are only slightly affected by these treatments. Based on the similar effects of cytochalasin addition and chemoattractant dilution, it is likely that both treatments result in actin depolymerization from the pointed ends of filaments. Based on our results we propose that chemoattractant-stimulated polymorphonuclear leukocytes contain two distinct populations of actin filaments. The actin filaments within the lamellipodia are highly labile and in the continued presence of chemoattractant these filaments are rapidly turning over, continually polymerizing at their plus (barbed) ends, and depolymerizing at their minus ends. In contrast, the cortical F-actin filaments of both stimulated and unstimulated cells are differentially stable.

Polymorphonuclear leukocyte adherence induces actin polymerization by a transduction pathway which differs from that used by chemoattractants

Nitrobenzoxadiazole-phallacidin in combination with quantitative fluorescent microscopy have been used to measure F-actin concentrations in human polymorphonuclear leukocytes (PMN) as they adhere to a plastic surface. Like stimulation with chemoattractants, adherence is associated with a twofold rise in F-actin content. However unlike the rapid rise in F-actin induced by chemoattractants which peaks within 30 s, actin assembly induced by adherence is slower, maximum F-actin values not being observed until 10 min. Furthermore the rise in F-actin induced by adherence is persistent, remaining constant over 60 min while F-actin returns to near basal levels after 20 min exposure to chemoattractant. The combination of adherence (5 min) followed by chemoattractant (FMLP 5 x 10(-8) M for 40 s) resulted in an additive rise in F-actin content to greater than threefold over unstimulated values. Unlike chemoattractant induced actin assembly, adherence-associated PMN actin polymerization was not inhibited by pertussis toxin, but was markedly reduced by lowering extracellular Ca2+. Fluorescent micrographs of adherent PMN stained with nitrobenzoxadiazole-phallacidin revealed F-actin in the lamellipodia and in small foci on the adherent surface. These findings suggest that the transduction mechanisms by which adherence induces PMN actin polymerization differ from those used by chemoattractant receptors.

Measurement of leukocyte motility and chemotaxis parameters with the Millipore filter assay

Although in vitro assays have been widely used to study leukocyte chemotactic migration, finding the best way to quantitate these assays has proven to be an elusive goal. Investigators have usually resorted to reporting quantities such as the leading front distance, total migrating cells or number of cells past a given distance from their starting point. While these measures may often provide a valid comparison of cell migration under specific assay conditions, they also reflect physical characteristics of the assay that are irrelevant to the basic phenomenon of interest; thus, typical quantities measured in the assay are not useful for comparison between different systems or for correlation with in vivo performance. Recently, however, Tranquillo et al. (1988) demonstrated the utility of an analysis of the under-agarose assay in which the density profile of migrating cells is characterized in terms of two parameters: the random motility coefficient, mu, and the chemotaxis coefficient, chi. These parameters do reflect intrinsic cell movement independently of extraneous physical conditions. The analysis relies primarily on matching theoretical cell density profiles, calculated from a mathematical model in which mu and chi appear, to cell density profiles measured experimentally in the assay. In this paper, we extend the work of Tranquillo et al. to show that the same model can be applied successfully to the Millipore filter assay. In addition, we present measured values of mu and chi for rabbit polymorphonuclear leukocytes (PMNs) in response to, and as a function of the concentration of, the peptide attractant formyl-norleucyl-leucyl-phenylalanine (FNLLP). We also examine the relationship between results obtained for the filter assay and the under-agarose assay and consider the mechanistic basis of the parameters mu and chi.

Chemoattractant-stimulated GTPase activity is decreased on membranes from polymorphonuclear leukocytes incubated in chemoattractant

Polymorphonuclear leukocytes, PMNs, incubated in a chemoattractant undergo a time-dependent decrease in responsiveness to the chemoattractant; i.e. they desensitize or adapt. We have examined the role of ligand-induced changes at early steps in signal transduction for adaptation of PMNs to chemoattractants. The chemoattractant stimulation of a pertussis toxin-sensitive GTPase activity on PMN membranes was used as an assay of signal transduction. We find a decreased basal GTPase activity and a decrease in the ability of N-formylnorleucylleucylphenylalanine (FN-LLP) to stimulate this activity on membranes prepared from PMNs incubated with the chemotactic peptide FNLLP. The basal GTPase activity is decreased by up to 70% and the peptide-stimulated GTPase activity by up to 95% on membranes from PMNs incubated for 20 min at 37 degrees C in 10(-7) M FNLLP. The decrease in peptide-stimulated GTPase activity cannot be accounted for by the decreased number of FNLLP receptors on the membranes. Rather, receptors that remain available for binding stimulate the GTPase activity with a decreased efficiency. The ligand-induced change in GTPase activity is not stimulus specific. GTPase activity stimulated by both C5a and LTB4 was decreased on membranes from PMNs incubated in FNLLP. The decrease in chemoattractant-stimulated GTPase activity is partially reversed if cells are subsequently incubated at 37 degrees C in the absence of peptide prior to membrane preparation. We detected no quantitative or qualitative change in either pertussis toxin substrates or immunoreactive G proteins when membranes from control and FNLLP-treated cells were compared.

A stochastic model for leukocyte random motility and chemotaxis based on receptor binding fluctuations

Two central features of polymorphonuclear leukocyte chemosensory movement behavior demand fundamental theoretical understanding. In uniform concentrations of chemoattractant, these cells exhibit a persistent random walk, with a characteristic "persistence time" between significant changes in direction. In chemoattractant concentration gradients, they demonstrate a biased random walk, with an "orientation bias" characterizing the fraction of cells moving up the gradient. A coherent picture of cell movement responses to chemoattractant requires that both the persistence time and the orientation bias be explained within a unifying framework. In this paper, we offer the possibility that "noise" in the cellular signal perception/response mechanism can simultaneously account for these two key phenomena. In particular, we develop a stochastic mathematical model for cell locomotion based on kinetic fluctuations in chemoattractant/receptor binding. This model can simulate cell paths similar to those observed experimentally, under conditions of uniform chemoattractant concentrations as well as chemoattractant concentration gradients. Furthermore, this model can quantitatively predict both cell persistence time and dependence of orientation bias on gradient size. Thus, the concept of signal "noise" can quantitatively unify the major characteristics of leukocyte random motility and chemotaxis. The same level of noise large enough to account for the observed frequency of turning in uniform environments is simultaneously small enough to allow for the observed degree of directional bias in gradients.

Polymorphonuclear leukocyte locomotion is insensitive to lowered cytoplasmic calcium levels

Chemotactic factors stimulate the rate of locomotion of polymorphonuclear leukocytes (PMNs). To investigate the importance of cytoplasmic calcium we have examined the ability of the chemotactic peptide N-formylnorleucyl eucylphenalanine (FNLLP) to stimulate the locomotion of PMNs whose cytoplasmic calcium levels were reduced by incubation in EGTA or in EGTA plus the calcium ionophores, ionomycin or A23187. Locomotion was assayed by migration through micropore filters and by time-lapse videomicroscopy. Cells in EGTA exhibited similar or slightly reduced rates of locomotion compared to cells in Hanks' balanced salt solution (HBSS). The peptide dose dependence for the stimulation of locomotion was similar in medium containing calcium or EGTA. The presence of 1 microM ionophore plus EGTA had no effect on the stimulation of locomotion by peptide. The presence of ionophores (1 microM) plus external calcium inhibited locomotion.

Measurement of the chemotaxis coefficient for human neutrophils in the under-agarose migration assay

Clinical and scientific investigations of leukocyte chemotaxis will be greatly aided by an ability to measure quantitative parameters characterizing the intrinsic random motility, chemokinetic, and chemotactic properties of cell populations responding to a given attractant. Quantities typically used at present, such as leading front distances, migrating cell numbers, etc., are unsatisfactory in this regard because their values are affected by many aspects of the assay system unrelated to cell behavioral properties. In this paper we demonstrate the measurement of cell migration parameters that do, in fact, characterize the intrinsic cell chemosensory movement responses using cell density profiles obtained in the linear under-agarose assay. These parameters are the random motility coefficient, mu, and the chemotaxis coefficient, chi, which appear in a theoretical expression for cell population migration. We propose a priori the dependence of chi on attractant concentration, based on an independent experimental correlation of individual cell orientation bias in an attractant gradient with a spatial difference in receptor occupancy. Our under-agarose population migration results are consistent with this proposition, allowing chemotaxis to be reliably characterized by a chemotactic sensitivity constant, chi 0, to which chi is directly proportional. Further, chi 0 has fundamental significance; it represents the reciprocal of the difference in number of bound receptors across cell dimensions required for directional orientation bias. In particular, for the system of human peripheral blood polymorphonuclear neutrophil leukocytes responding to FNLLP, we find that the chemotaxis coefficient is a function of attractant concentration, a following the expression: chi = chi 0NT0 f(a) S(a) Kd/(Kd + a)2 where Kd is the FNLLP-receptor equilibrium dissociation constant and NT0 is the total number of cell surface receptors for FNLLP. f(a) is the fraction of surface receptors remaining after down-regulation, and S(a) is the cell movement speed, both known functions of FNLLP concentration. We find that chi 0NT0 = 0.2 cm; according to a theoretical argument outlined in the Appendix this means that these cells exhibit 75% orientation toward higher attractant concentration when the absolute spatial difference in bound receptors is 0.0025NT0 over 10 micron. (For example, if NT0 = 50,000 this would correspond to a spatial difference of 125 bound receptors over 10 micron.) This result can be compared with estimates obtained from visual studies of individual neutrophils.

An actin-nucleating activity in polymorphonuclear leukocytes is modulated by chemotactic peptides

We examined the actin-nucleating activity in polymorphonuclear leukocyte lysates prepared at various times after chemotactic peptide addition. The actin nucleation increases two- to threefold within 15 s after peptide addition, decays to basal levels within 90 s, and is largely independent of cytoplasmic calcium fluxes. The peptide-induced nucleation sites behave as free barbed ends and therefore may increase the level of polymerized actin in vivo. The new nucleation sites may also determine the cellular sites of actin polymerization. This localization of actin polymerization could be important for the directional extension of lamellipodia during chemotaxis.

Chemotactic peptide binding by rabbit polymorphonuclear leukocytes. Presence of two compartments having similar affinities but different kinetics

N-Formylnorleucylleucylphenylalanine (f-Nle-LeuPhe) bound to rabbit peritoneal polymorphonuclear leukocytes at 4 degrees C exists in at least two compartments that can be differentiated by their off rates. The off rate of one compartment is similar to that of the receptor characterized previously, about 0.4 min-1 (Aswanikumar, S., Corcoran, B., Schiffmann, E., Day, A. R., Freer, R. J., Showell, H. J., Becker, E. L., and Pert, C. B. (1977) Biochem. Biophys. Res. Commun. 74, 810-817; Sullivan, S. J., and Zigmond, S. H. (1980) J. Cell Biol. 85, 703-711); the off rate of the second compartment is about 0.005 min-1. Lysis of the cells at 4 degrees C with 1% Triton does not affect the peptide release from either compartment. Accumulation of peptide at 4 degrees C into the fast off-rate compartment is rapid, reaching a plateau in about 5 min, while peptide in the slow off-rate compartment continues to increase for up to 4 h. The rate of accumulation in the slow off-rate compartment is approximately proportional to the amount of peptide bound to the fast off-rate compartment. Cells lysed at 4 degrees C before binding are still able to accumulate peptide into both compartments. Three possible models to explain the data are presented.

Assays of leukocyte chemotaxis

A number of disorders of leukocyte motility and chemotaxis have been reported clinically. In this paper we present a rational approach for testing cell populations for a defect in leukocyte migration and for defining the cellular basis of any abnormality observed. The principles and difficulties of individual and population-type assays are discussed.

Inhibition of receptor-mediated but not fluid-phase endocytosis in polymorphonuclear leukocytes

We have found that hypertonic medium inhibited the receptor-mediated uptake of the chemotactic peptide N-formylnorleucylleucylphenylalanine without affecting fluid-phase endocytosis by polymorphonuclear leukocytes (PMNs). Morphological and biochemical evidence demonstrated that cells in hypertonic medium did not accumulate peptide in a receptor-mediated manner. However, the cells continued to form endosomes containing fluid-phase markers. Furthermore, the content of these endosomes was processed normally, i.e., both digested and intact material were released into the medium. The inhibition of receptor-mediated uptake was a function of the tonicity. Partial inhibition occurred in 0.45 and 0.6 osmolar medium and maximal inhibition occurred in 0.75 osmolar medium. The inhibition was independent of the solute used to increase the tonicity: sodium chloride, sucrose, and lactose all inhibited uptake to similar extents. Hypertonic medium had little effect on saturable peptide binding. However, it did prevent the clustering of surface molecules as indicated by the inhibition of capping of fluorescent concanavalin A. In addition, hypertonic medium prevented the peptide-stimulated increase in cytosolic calcium levels as measured by quin 2 fluorescence. The tonicity dependence of the inhibition of quin 2 fluorescence paralleled the inhibition of receptor-mediated uptake.

Phosphorylase a activity as an indicator of neutrophil activation by chemotactic peptide

The activity of glycogen phosphorylase, an enzyme that is activated by both cAMP and calcium, was used as an indicator of the state of the cytoplasm after chemotactic stimulation of polymorphonuclear leukocytes (neutrophils). The activity of the enzyme showed a clear dependence on cytoplasmic calcium. Addition of the calcium ionophore A23187 caused a 4-5-fold increase in activity of phosphorylase a. In the absence of external Ca2+, A23187 caused only brief transient activation of phosphorylase; probably reflecting release of sequestered intracellular Ca2+. Addition of the chemotactic peptide N-formylnorleucylleucylphenylalanine (FNLLP) caused a transient 2-3-fold activation of the enzyme. The dose-dependence of activation by FNLLP showed a peak at 10(-8) M, near the Kd of the receptor for FNLLP. The phosphorylase activity peaks by 90 s and then declines, returning to basal levels by 20 min after stimulation with 10(-8) M peptide and by 60 min with 10(-7) M peptide. This finding suggests that the cells do not need to maintain elevated cytoplasmic calcium levels to exhibit stimulated locomotion. Thus, if calcium continues to modulate the motility, there either must be highly localized changes that are not detected in measures of the total cytoplasm, or the sensitivity to calcium must be variable such that basal levels are sufficient to maintain locomotion. Cells loaded with the fluorescence calcium probe quin2 (0.6 mM) in the presence or absence of external Ca2+ had elevated phosphorylase levels before addition of FNLLP. Thus, the presence of quin2 may alter the cytoplasmic Ca2+ level, and it clearly alters some aspects of the neutrophil physiology. Phosphorylase a appears to be a sensitive, nonperturbing indicator of the cytoplasmic calcium levels.

Effects of sodium on chemotactic peptide binding to polymorphonuclear leukocytes

The affinity of binding of the chemotactic peptide N-formylnorleucylleucylphenylalanine to rabbit peritoneal polymorphonuclear leukocytes is increased when sodium ions are removed from the medium. In Hanks' balanced salt solution, the dissociation constant of the binding is about 2 X 10(-8) M, while in Na+-free medium, the dissociation constant is between 3 and 6 X 10(-9) M. Removal of Na+ appears to cause little or no change in receptor number. The change in affinity is rapid and reversible, occurs at 4 degrees C as well as 37 degrees C, and occurs when the Na+ is replaced by K+, choline, or sucrose. The increased binding of low concentrations of peptide is seen on broken as well as whole cells and therefore does not depend on an ion gradient across the membrane. The high affinity receptors are functional in mediating peptide uptake and lysosomal enzyme release. The receptors undergo down-regulation in Na+-free medium, and the dose dependence of the receptor loss is shifted to lower concentrations consistent with the higher affinity of the binding.

Effects of sodium on chemotactic peptide binding to polymorphonuclear leukocytes

The affinity of binding of the chemotactic peptide N-formylnorleucylleucylphenylalanine to rabbit peritoneal polymorphonuclear leukocytes is increased when sodium ions are removed from the medium. In Hanks' balanced salt solution, the dissociation constant of the binding is about 2 X 10(-8) M, while in Na+-free medium, the dissociation constant is between 3 and 6 X 10(-9) M. Removal of Na+ appears to cause little or no change in receptor number. The change in affinity is rapid and reversible, occurs at 4 degrees C as well as 37 degrees C, and occurs when the Na+ is replaced by K+, choline, or sucrose. The increased binding of low concentrations of peptide is seen on broken as well as whole cells and therefore does not depend on an ion gradient across the membrane. The high affinity receptors are functional in mediating peptide uptake and lysosomal enzyme release. The receptors undergo down-regulation in Na+-free medium, and the dose dependence of the receptor loss is shifted to lower concentrations consistent with the higher affinity of the binding.