A contractile protein from leucocytes. Its extraction and some of its properties

The damaging potential of leukocyte activation in the microcirculation

Traditionally leukocytes have been regarded as beneficial cells, owing to their immunologic and antimicrobial activity. Recent evidence suggests, however, an additional role of granulocytes and monocytes as mediators of cardiovascular complications, such as ischemia, reperfusion, diabetes, physiologic shock, venous ulceration, and other conditions. Granulocytes and monocytes have a large volume, and stiff cytoplasm; they have the ability to adhere to endothelium and to other substrates; and they exert several forms of cytotoxicity. Granulocytes and monocytes may be trapped in the microcirculation, may obstruct capillaries and thereby induce a no-reflow phenomenon, and may initiate organ dysfunction via oxygen free radical production and proteolytic cleavage. Few organs seem to be spared from the potential destructive actions of these cells, and novel approaches are required to interfere with leukocyte accumulation in local regions of the peripheral circulation.

Leukocyte biophysics. An invited review

The biophysical properties of leukocytes in the passive and active state are discussed. In the passive unstressed state, leukocytes are spherical with numerous membrane folds. Passive leukocytes exhibit viscoelastic properties, and the stress is carried largely by the cell cytoplasm and the nucleus. The membrane is highly deformable in shearing and bending, but resists area expansion. Membrane tension can usually be neglected but plays a role in cases of large deformation when the membrane becomes unfolded. The constant membrane area constraint is a determinant of phagocytic capacity, spreading of cells, and passage through narrow pores. In the active state, leukocytes undergo large internal cytoplasmic deformation, pseudopod projection, and granule redistribution. Several different measurements for assessment of biophysical properties and the internal cytoplasmic deformation in form of strain and strain rate tensors are presented. The current theoretical models for active cytoplasmic motion in leukocytes are discussed in terms of specific macromolecular reactions.

Cytoplasmic strains and strain rates in motile polymorphonuclear leukocytes

A new method is presented to measure local cytoplasmic deformation and rate of deformation in motile active neutrophils. The deformation is expressed in terms of biomechanical strains and strain rates. For this purpose small phagocytosed latex microspheres were used as intracellular markers. Planar Lagrangian and Eulerian strains and the rate of strain were estimated from the positions of a triad of internalized markers. Principal strains, stretch ratios, and principal directions were computed. The intracellular strains were found to be large relative to the overall cell shape change. Principal cytoplasmic stretch ratios showed large extension in the direction of pseudopod formation and cell locomotion and contraction in perpendicular directions. Regional strain analysis showed contractile strains to predominate in the vicinity of the pseudopod or leading edge of motion. The transitional region between the pseudopod and the main cell body exhibited large shear strains. The posterior region, where the uropod is located, also revealed large extensions but small contractile strains. The rate of strains are relatively small, nonuniform in time, and largely independent of the strain. The method we propose to measure cytoplasmic strain can be applied to a variety of problems in cell mechanics.

Effects of leukocyte inhibitory factor (LIF) on human neutrophil function

The effects of the lymphokine, leukocyte inhibitory factor (LIF), on human neutrophil function were studied. This soluble mediator, which is defined by its specific inhibition of neutrophil locomotion, does not interfere with chemotactic factor binding and does not affect basal or stimulated superoxide generation by neutrophils. In contrast, phagocytosis of opsonized Staphylococcus aureus is markedly inhibited by LIF, and degranulation is stimulated by this lymphokine. The possible mechanisms of LIF action on neutrophils are discussed.

Ecto-protein kinase activity in rabbit peritoneal polymorphonuclear leucocytes

An ectoprotein kinase activity has been identified on intact rabbit peritoneal polymorphonuclear leucocytes and the time course of phosphate incorporation into proteins has been followed at different ATP levels. Saturation is reached at around 3 mM ATP and the activity is inhibited by p-chloromercuribenzoate. The possibility that the observed protein phosphorylation arises through the action of a membrane ATPase liberating phosphate for transfer into the cell, incorporation into ATP and its utilisation by endogenous kinases, has been excluded by studying both enzymes concomitantly and measuring the rate of [32P]orthophosphate uptake. Lactate dehydrogenase measurements in the extracellular media also exclude the possibility of kinase liberation from lysed cells. Moreover, the pattern of 32P-labelling of polypeptides when intact cells are exposed to [32P]ATP is quite different from that when homogenates are incubated with [32P]ATP or intact cells with [32P]-orthophosphate. We have been unable to demonstrate any cAMP dependency for this ectokinase activity.

Cytoplasmic and plasma membrane adenosine triphosphatase of polymorphonuclear neutrophils: comparison of their enzymatic properties and attempt for a direct determination of myosin ATPase activity using polymorphonuclear neutrophil extract

Enzymatic properties of the ATPase of the plasma membrane and cytoplasmic myosin B from guinea-pig polymorphonuclear neutrophils were compared. In the plasma membrane, Mg2+- and Ca2+-activated ATPases showed the same dependence pattern on KCl concentration and pH, i.e., both ATPases increased with decreasing KCl concentration and with rising pH until pH 9.0. The maximum activation of Mg2+-ATPase was observed at 1 . 10(-3) M Mg2+. On the other hand, EDTA-activated ATPase activity was so low that no clear dependence curve was obtained. In myosin B, Mg2+-ATPase activity was below one-tenth that of the plasma membrane ATPase with the maximum activation at 1 . 10(-2) M Mg2+ and pH 9.0 EDTA- and Ca2+-activated ATPase exhibited almost the same activity and the same KCl-dependence curve, i.e., both ATPases increased and increasing KCl concentration. With regard to pH-dependence, Ca2+-ATPase showed a U-shaped curve with the minimum at pH 7.0, wherease EDTA-activated ATPase indicated a bell-shaped curve with the maximum at pH 9.0. Based on the findings that the EDTA-activated ATPase activity was hardly detected in the plasma membrane but high in myosin B, the distribution of ATPase activity on subcellular fractions was studied and the results obtained that the myosin-ATPase activity could be directly measured using the polymorphonuclear neutrophil extract if the EDTA-activated ATPase activity was used as an enzymatic marker for myosin.

Phagocytosis: a review

Primitive unicellular organisms depend greatly on internalization of particulate matter for nourishment. In metazoa, this process is further developed to play a major role in mechanisms of defense. This review analyzes, mainly in mammalian systems, the various phenomena surrounding the phagocytic act. Much of the emphasis is placed on experimental work which has recently elucidated some of its features. Both the structural and functional aspects of phagocytosis are considered throughout the review, which is subdivided into an examination of chemotaxis and the various agents inducing it, the mode of recognition of particles to be phagocytized, and the mechanisms of ingestion. The last includes a discussion of the possible means whereby recognition is translated into ingestion, the modes of adhesion of particles onto the surface of phagocytes, the formation and fusion of pseudopodia during engulfment and ingestion, and process and significance of degranulation. In addition, the metabolic changes in phagocytes during the processes of chemotaxis, ingestion, and digestion are described. A discussion of the various ways phagocytes may destroy microorganisms incorporates an appreciation of the importance of the microbicidal action of the acidic environment of the phagosome, the various lysosomal contents, hydrogen peroxide, superoxide, singlet oxygen, and chemiluminescence. The interdependence and interrelationship of the induction and cooperation of these mechanisms are examined.

Smooth muscle-associated contractile protein in human and experimental acute leukaemias

Cells from ten human myeloblastic leukaemias and from spontaneous rat myeloblastic and lymphoblastic leukaemias were examined by indirect immunofluorescence with human serum containing smooth muscle antibody. Strong positive cell outline staining of blast cells was seen in cryostat sections of rat leukaemic lymph nodes, spleen and liver. In cell smears of human and rat leukaemias, cell outline fluorescence was restricted to cells in close contact with each other. Membrane immunofluorescence tests of suspensions of viable leukaemic cells were negative. Specificity of the immunofluorescent staining reaction was established by failure to obtain staining with normal serum, or with smooth muscle antibody serum neutralized by homogenates of smooth muscle or extracts containing actin derived from smooth muscle. These observations suggest that smooth muscle-associated microfilaments are present in leukaemic blast cells and that expression of the antigen is dependent on cell-cell contact. The presence of this antigen may facilitate leukaemic infiltration of tissues.

Calcium influx requirement for human neutrophil chemotaxis: inhibition by lanthanum chloride

Calcium fluxes of human neutrophils measured in the presence of chemotactically active serum showed a marked stimulation of calcium-45 uptake from the media. Chemotactically inactive serum did not cause an influx of calcium. The magnitude of the calcium influx due to activated serum is sufficient to trigger contractile systems previously described in muscle cells. Lanthanum chloride inhibited the chemotactic response of human neutrophils to activated serum. Lanthanum in concentrations that suppressed chemotaxis also inhibited the calcium influx caused by activated serum. Lanthanum in concentrations that suppressed chemotaxis also inhibited the calcium influx caused by activated serum. The data support a direct role of calcium influx in chemotaxis of neutrophils.

Leucocyte myosin and its location in the cell

The intracellular location of the binding site of antibody against purified myosin prepared from equine leucocytes was investigated in neutrophils and lymphocytes by electron microscopy using peroxidase-labelled antibody method. The myosin extracted from equine leucocytes could bind skeletal muscle F-actin and the formed complex showed the biophysical and biochemical properties and electron microscopic appearance of actomyosin. On immunodiffusion, the leucocyte myosin formed a single precipitin line with its antibody prepared in rabbits. The antibody also formed single precipitin lines with myosins from lymphocytes and thrombocytes, fusing with each other. The antibody against the leucocyte myosin did not react with myosins from skeletal or arterial smooth muscle. The specificity of the antibody was further established by determination of K+-EDTA-activated ATPase activity remained in the supernate of antigen-antibody mixture. Under electron microscope, the intracellular immunoreactive products of peroxidase labelled antibody were found in cytoplasm of neutrophils and lymphocytes incubated with antibody against leucocyte myosin, but not in neutrophils or lymphocytes treated with IgG from normal rabbits.

The distribution, ultrastructure, and chemistry of microfilaments in cultured chick embryo fibroblasts

The distribution, ultrastructure, and chemistry of microfilaments in cultured chick embryo fibroblasts were studied by thin sectioning of flat-embedded untreated and glycerol-extracted cells, histochemical and immunological electron microscopic procedures, and the negative staining of cells cultured on electron microscopic grids. In these cultured cells, the microfilaments are arranged into thick bundles that are disposed longitudinally and in looser arrangements in the fusiform-shaped cells. In the latter case, they are concentrated along the margins of the flattened cell, on the dorsal surface, and particularly at the ends of the cell and its ventral surface, where contact is made with the plastic dish or with other cells. Extracellular filaments, presumably originating from within the cell, are found at these points of contact. The microfilaments are composed in part of an actin-like protein. These filaments are between 70 and 90 A in diameter, they are stable in 50% glycerol, they have an endogenous ATPase (myosin-like?) associated with them, they bind rabbit muscle heavy meromyosin, and they specifically bind antibody directed against isolated actin-like protein. In the cultured chick embryo fibroblasts, the microfilaments are essential for the establishment and maintenance of form, and they are probably critical elements for adhesion and motility. The microfilaments might also serve as stabilizers of intramembranous particle fluidity.

Cytochalasin B, its interaction with actin and actomyosin from muscle (cell movement-microfilaments-rabbit striated muscle)

Cytochalasin B, an alkaloid that inhibits a wide variety of cellular movements, interacts with actomyosin, the contractile protein complex of striated muscle. This interaction causes a decrease in viscosity of the actomyosin complex and an inhibition of acto-heavy meromyosin ATPase activity of at least 60%. Cytochalasin B does not affect the viscosity of myosin nor the ATPase activity of heavy meromyosin, suggesting that the drug might interact directly with the actin moiety of the actomyosin complex. Indeed, as judged by viscometry, there is a strong interaction of cytochalasin B with actin, at nearly stoichiometric concentrations. Myosin appears to compete with cytochalasin for binding to actin.