Isolation of plasma membrane from human neutrophils and determination of cytochrome b and quinone content.

Analyses of plasma membrane and other subcellular fractions indicate that the primary location of cytochrome b in human neutrophils is not the plasma membrane. The procedure developed for the purification of plasma membrane from fresh human neutrophils yielded a 14-fold enrichment in the marker enzyme 5'-nucleotidase and a 10-fold enrichment in ouabain-sensitive ATPase. On sucrose density gradients, the peak density of 5'-nucleotidase activity was 1.12 g/ml, and was shifted after digitonin addition to 1.15 g/ml. Protein in the plasma membrane equalled approximately 8 percent of the whole cell protein. A b-type cytochrome was found to be present in the plasma membrane fraction at a concentration of 205 pmol/mg of protein, which is three times greater than that in the neutrophil overall. Although this cytochrome has been reported previously in the neutrophil, this is the first determination for purified plasma membrane and may indicate that b-type cytochrome has a dual localization in the human neutrophil. Differential centrifugation results suggest that the primary location is in the granules, probably specific granules. Quinone content in the plasma membrane was found to be 740 pmol/mg of protein, a concentration two times greater than in the whole cell. Such a small enhancement of quinone indicates that quinone also is not primarily located in the plasma membrane.

Structural heterogeneity of the C3b/C4b receptor (Cr 1) on human peripheral blood cells.

In these studies CR 1 polymorphism previously demonstrated on erythrocytes (E) was also found on CR 1-bearing peripheral blood leukocytes including polymorphonuclear (PMN), eosinophils, monocytes, and B lymphocytes. However several cell-specific differences in CR1 were found: (a) an approximately 5,000-dalton increase in CR 1 on PMN and eosinophils, (b) unequal band intensity among heterozygotes suggests that there is preferential expression of 220,000- or 225,000-dalton receptors on leukocytes compared to E, and (c) "minor" bands, approximately 15,000 daltons larger than the major receptor molecule, were found on E but not on leukocytes. These observations constitute a unique example of heterogeneity of an integral membrane receptor.

Lactoferrin, an iron-binding protein in neutrophilic leukocytes.

Lactoferrin, an iron-binding protein previously shown to occur in many external secretions, is identified as one of the major proteins present in human and guinea pig neutrophilic polymorphonuclear leukocytes. The identification of this protein in leukocyte extracts was based upon a comparison of its electrophoretic, antigenic, and iron-combining properties with the corresponding properties of the same protein isolated from human and guinea pig milk. Immunochemical quantitations showed that lactoferrin occurs in human neutrophilic leukocytes at the concentration of 3 microg per 10(6) cells. Tissue cultures from guinea pig bone marrow and spleen actively synthesized the protein, as shown both by net production of lactoferrin and incorporation of labeled amino acids into the protein. Immunohistochemical data indicate that lactoferrin first appears in myeloid cells at the stage of the promyelocyte.

Subcellular location and properties of bactericidal factors from human neutrophils.

We examined the subcellular location of bactericidal factors (BF) in human neutrophils, using an efficient fractionation scheme. Nitrogen bomb cavitates of DIFP-treated PMN were centrifuged through discontinuous Percoll gradients, each fraction extracted with 0.05 M glycine, pH 2.0, and tested for the killing of Escherichia coli. greater than 90% of BF coisolated with the azurophil granules. After lysis of azurophils, 98% of azurophil-derived BF (ADBF) sedimented with the membrane. ADBF activity was solubilized from azurophil membrane with either acid or nonionic detergent (Triton X-100, Triton X-114). Bactericidal activity was linear with respect to protein concentration over the range 0.3-30 micrograms/ml. 0.1-0.3 microgram/ml ADBF killed 10(5) E. coli within 30 min at 37 degrees C. At 1.4 micrograms/ml, 50% of 2 X 10(5) bacteria were killed within 5 min. ADBF was effective between pH 5-8, with peak activity at pH 5.5. Glucose (20 mM), EDTA (1-25 mM), and physiologic concentrations of NaCl or KCl had little or no inhibitory effect on ADBF. ADBF killed both Gram-positive and Gram-negative virulent clinical isolates, including listeria, staphylococci, beta-hemolytic streptococci, and Pseudomonas aeruginosa. Thus, under these conditions of cell disruption, fractionation, extraction, and assay, almost all BF in human PMN appeared to be localized to the membrane of azurophilic granules as a highly potent, broad-spectrum, rapidly acting protein(s) effective in physiologic medium. Some of these properties appear to distinguish ADBF from previously described PMN bactericidal proteins.

Identification and characterization of specific receptors for monocyte-derived neutrophil chemotactic factor (MDNCF) on human neutrophils.

Specific receptors for a recently purified and cloned monocyte-derived neutrophil chemotactic factor (MDNCF) have been identified on the surface of normal human peripheral blood neutrophils using 125I-labeled recombinant human MDNCF (125I-MDNCF). Competitive binding of 125I-MDNCF to human neutrophils reached a maximal level at 1-3 h at 4 degrees C. The Scatchard analysis showed that there are approximately 20,000 receptors per cell with a single type of high affinity binding (Kd, 8 x 10(-10) M). The receptors for MDNCF are clearly distinct from the receptors for other cytokines and chemotactic agents, e.g., IL-1 alpha, TNF-alpha, and FMLP, C5a, leukotriene B4, and platelet activating factor. Based on the SDS-PAGE analysis of chemically crosslinked 125I-MDNCF receptor complex, there are two polypeptides that bind MDNCF; the molecular weight of these two MDNCF receptors were estimated to be 67,000 and 59,000. Treatment of a promyelocytic cell line, HL60, with 1.25% DMSO for 5 d in vitro increased the number of receptors up to 7,000 receptors/cell with a Kd of 1.2 x 10(-9) M.

Studies on the pathogenesis of fever. XIX. Localization of pyrogen in granulocytes.

Only intact exudate granulocytes from rabbits generated large amounts of endogenous pyrogen when incubated in 0.15 M NaCl. No matter how whole-cell lysates or combinations of subcellular fractions were incubated, their yields of pyrogen never approached those of whole cells; at most, only minimal amounts of pyrogen were formed, once the integrity of the cells had been destroyed. Some pyrogen could be extracted from disrupted cells, but never more than a fraction (<25%) of that released from incubated whole cells. The yield could be slightly improved by lowering the pH (to 3.5) and by increasing the volume of extraction fluid. Virtually all of the preformed pyrogen that could be extracted from sucroselysed cells was found in their cytoplasmic fraction. Contrary to the results of Herion et al. (3), none could be detected in the granular (or lysosomal) fraction. Likewise, all efforts to recover pyrogen from the membrane-nuclear fraction were unsuccessful. In keeping with the finding that preformed pyrogen is contained in the cytoplasmic fraction were the observations that practically all of the aldolase, a cytoplasmic enzyme, and very little of the acid phosphatase, a granular enzyme, were lost from the cells during the release of pyrogen. Lysozyme, an enzyme stored in both the granules and the cytoplasm, was partially released from the cells under the same circumstances. Neither the release of pyrogen nor its slight intracellular buildup that precedes release (4) were affected by concentrations of puromycin that block protein synthesis in the cells and prevent their activation. Hence, it is concluded that the release process, which also involves the formation of active pyrogen (4), does not require protein synthesis, whereas activation of the cells, which may involve the synthesis of an inactive precursor (2), does.

Isolation and characterization of permeability factors from rabbit neutrophils.

Four basic proteins that increase vascular permeability have been isolated in purified form from rabbit neutrophilic granules. These proteins are termed band 1, 2, 3, and 4 protein according to their electrophoretic migration in acrylamide gel. Molecular weights of band 1 and 2 protein derived from amino acid composition were 4800 and 5300, respectively. These values are in good agreement with those obtained for these proteins by gel diffusion techniques. The molecular weight of band 3 protein was also in the range of 5000 by the latter technique. The molecular weight of band 4 protein determined by ultracentrifugal analysis and amino acid composition was 12,000. Although all four proteins had the capacity to induce immediate increase in vascular permeability, only band 2 protein was found to release histamine from isolated rat peritoneal mast cells. Furthermore, it has been shown that the permeability-inducing activity of band 2 protein can be inhibited by pretreating rabbits with antihistamine. Band 2 protein did not release histamine from rabbit platelets and depletion of rabbit platelets from the circulation had no influence on the permeability-inducing activity of this protein. Band 1, 3, and 4 proteins did not release histamine from isolated rat peritoneal mast cells and their capacity to increase vascular permeability remained unaffected by treatment of rabbits with antihistamine. These investigations suggest that the histamine-releasing activity of band 2 protein is a specific phenomenon and is associated with particular amino acid grouping or spacial configuration of the molecules. By the same token, the increase in vascular permeability induced by the nonhistamine-releasing band 1, 3, and 4 proteins represents a specific phenomenon (or phenomena) not particularly related to the over-all charge of these molecules.

Chemotoxis of mononuclear cells.

Chemotaxis of rabbit mononuclear cells was studied by the micropore-filter technique. Mononuclear cells obtained from mineral oil-induced peritoneal exudates respond chemotactically to rabbit serum treated with immune complexes or with streptokinase and plasminogen, to soluble factors produced by bacteria, and to lysates obtained from rabbit neutrophils. The first chemotactic factor requires heat-labile factors in serum for its generation, but, once formed, the chemotactic factor is relatively heat stable. This factor has been compared with the complement-associated factor in serum, C'(5, 6, 7)a, that is chemotactic for neutrophils. The ability to generate the mononuclear cell chemotactic factor in serum that has been treated with potassium thiocyanate suggests that complement is not required. The position of the chemotactic factor in preparative electrophoresis and density-gradient ultracentrifugation indicates that on the basis of physical-chemical criteria, this factor is not C'(5, 6, 7)a. The mononuclear cell chemotactic factor present in lysates of neutrophils sediments slowly in the ultracentrifuge and may be related, at least in part, to cationic peptides of lysosomal granules. A study in the time course of the chemotactic response of mononuclear cells reveals that the response begins to level off after 4 or 5 hr. This is in sharp contrast to the time course for the chemotactic response of neutrophils, in which the reaction is complete within 1.5 hr. Rabbit mononuclear cells obtained from a starch-induced peritoneal exudate respond to serum treated with plasminogen and streptokinase and to the soluble factor produced by bacteria, but no chemotactic response is elicited to serum treated with immune complexes. This indicates a functional difference between two populations of mononuclear cells. Rabbit alveolar macrophages respond poorly to all agents tested, although a weak chemotactic response to bacterial factors was found. The requirement of a serine esterase in the mononuclear cell for the cell to respond chemotactically was defined by the use of organophosphorus inhibitors. Pretreatment of mononuclear cells with several series of phosphonates renders them unresponsive in the chemotactic system. The effect is similar for mononuclear cells responding chemotactically to activated serum and to the bacterial chemotactic factor. Several points of contrast with inhibition profiles obtained in the chemotactic system of the neutrophil suggest that, while the mononuclear cell requires a serine esterase for chemotactic responsiveness, this enzyme is different from the one previously defined in the neutrophil.

Downregulation of tumor necrosis factor receptors on macrophages and endothelial cells by microtubule depolymerizing agents.

Exposure of murine and human macrophages and human umbilical vein endothelial cells to micromolar concentrations of five microtubule (MT)-depolymerizing agents (colchicine, nocodazole, podophyllotoxin, vincristine, and vinblastine) resulted in a loss of binding sites for iodinated TNF-alpha. The reduction amounted to 40-60% by 1 h and approximately 75% by 2-4 h. In 1 h, specific binding was reduced 50% by 0.1-5 microM of these drugs at 37 degrees C, but not at 4 degrees C. Inactive isomers of colchicine were ineffective, as were microfilament-destabilizing cytochalasins. The active agents did not compete with TNF-alpha R for binding. Antiserum against TNF-alpha did not neutralize the effect of colchicine and nocodazole. PGE1 and dibutyryl-cAMP could not mimic, and cyclooxygenase inhibitors could not prevent the drug effects. All the binding sites were regenerated within 3 h after removal of nocodazole, which binds tubulin reversibly, whereas little recovery was found even 18 h after the removal of colchicine, which binds tubulin irreversibly. These findings suggested that MT disassembly was responsible for the observed downregulation of TNF-alpha R. The protein synthesis inhibitor cycloheximide inhibited binding of TNF-alpha to a similar extent and with a similar time course as colchicine in the absence of added ligand. Neither drug affected binding of IFN-gamma to macrophages, nor binding of TNF-alpha to human polymorphonuclear leukocytes. Thus, an intact MT network appears to be important in maintenance of the steady state of TNF-alpha R on those cells in which TNF-alpha R turns over rapidly in the absence of ligand. The antiinflammatory actions of MT-depolymerizing agents may result in part from their interference with the ability of such cells to respond to TNF-alpha.

Fate of surface proteins of rabbit polymorphonuclear leukocytes during phagocytosis. I. Identification of surface proteins.

To study the fate of external membrane proteins during phagocytosis, rabbit peritoneal neutrophils were labeled by enzymatic iodination. Iodine was incorporated into at least 13 proteins ranging in size from approximately 250,000 to 18,000 daltons as judged from autoradiography of gels after SDS-polyacrylamide gel electrophoresis of labeled cells. The major contractile proteins of neutrophils, actin and myosin, were not labeled when intact cells were iodinated but were labeled when homogenates of these cells were iodinated. Nine of the iodinated proteins were released by mild protease treatment of intact cells. A plasma membrane-rich fraction was isolated by density centrifugation. This fraction was enriched at least 10-fold for lactoperoxidase-labeled acid-insoluble proteins. It was enriched to the same extent for the presence of iodinated wheat germ agglutinin that had been bound to intact cells at 4 degrees C before homogenization. Analysis of SDS-polyacrylamide gel electrophoresis revealed that the proteins of this fraction were predominantly of high molecular weight. However, only 8 of the 13 proteins iodinated on intact cells were found in this fraction. The remaining five were enriched in a dense fraction containing nuclei, intact cells, and membranous vesicles, and may represent a specialized segment of the neutrophil cell surface.

Apparent anomalies in nuclear feulgen-DNA contents. Role of systematic microdensitometric errors.

The Feulgen-DNA contents of human leukocytes, sperm, and oral squames were investigated by scanning and integrating microdensitometry, both with and without correction for residual distribution error and glare. Maximally stained sperm had absorbances which at lambdamax exceeded the measuring range of the Vickers M86 microdensitometer; this potential source of error could be avoided either by using shorter hydrolysis times or by measuring at an off-peak wavelength. Small but statistically significant apparent differences between leukocyte types were found in uncorrected but not fully corrected measurements, and some apparent differences disappeared when only one of the residual instrumental errors was eliminated. In uncorrected measurements, the apparent Feulgen-DNA content of maximally stained polymorphs measured at lambdamax was significantly lower than that of squames, while in all experimental series uncorrected measurements showed apparent diploid:haploid ratios significantly greater than two. In fully corrected measurements no significant differences were found between leukocytes and squames, and in four independent estimations the lowest diploid:haploid ratio found was 1.99 +/- 0.05, and the highest 2.03 +/- 0.05. Discrepancies found in uncorrected measurements could be correlated with morphology of the nuclei concerned. Glare particularly affected measurements of relatively compact nuclei such as those of sperm, polymorphs and lymphocytes, while residual distribution error was especially marked with nuclei having a high perimeter:area ratio (e.g. sperm and polymorphs). Uncorrected instrumental errors, especially residual distribution error and glare, probably account for at least some of the previously reported apparent differences between the Feulgen-DNA contents of different cell types. On the basis of our experimental evidence, and a consideration of the published work of others, it appears that within the rather narrow limits of random experimental error there seems little or no reason to postulate either genuine differences in the amounts of DNA present in the cells studied, or nonstoichiometry of a correctly performed Feulgen reaction.

Lateral segregation of neutrophil chemotactic receptors into actin- and fodrin-rich plasma membrane microdomains depleted in guanyl nucleotide regulatory proteins.

Subcellular fractions were prepared from human neutrophils desensitized at 15 degrees C with stimulatory doses of the photoaffinity derivative F-Met-Leu-Phe-N epsilon-(2-(rho-azido[125I]salicylamido)ethyl-1,3'- dithio-propionyl)-Lys. The covalently labeled receptors were found in a membrane fraction of higher density than those from cells preexposed to ligand at 4 degrees C but not desensitized. The denser fraction (rho approximately equal to 1.155 g/cc) was the cellular locus of the membrane associated cytoskeletal proteins, actin, and fodrin, as detected immunologically on western blots. The light fraction (rho approximately equal to 1.135), cosedimented with neutrophil plasma membrane markers, plasma membrane guanyl nucleotide regulatory proteins, and several characteristic polypeptides identified by SDS-PAGE, including a major 72-kD species. The photoaffinity-labeled species in either case showed the same mobility on SDS-PAGE (Mr = 50,000-70,000) corresponding to previously reported values for N-formyl chemotactic receptors. These labeled receptors were sensitive to proteolysis after exposure of the intact photoaffinity-labeled cells to papain at 4 degrees C. We conclude that (a) the fractions isolated are probably derived from different lateral microdomains of the surface of human neutrophils; (b) the higher density fraction contains occupied N-formyl-chemotactic receptors previously shown to have been converted, to a high affinity, slowly dissociating form coisolating with neutrophil cytoskeleton and implicated in the termination of formyl peptide-induced neutrophil activation; and (c) the translocation of receptors to these microdomains may serve to compartmentalize receptors and perhaps regulate the interaction of the receptor/G-protein transduction pair.

Transmembrane linkage between surface glycoproteins and components of the cytoplasm in neutrophil leukocytes.

An experimental approach is described that enables the analysis of interactions between exogenous surface ligands and components of the cytoplasm in neutrophil leukocytes. Neutrophils treated with the nonionic detergent Lubrol PX, under controlled conditions, yield intact detergent-insoluble ghosts. Morphological analysis of neutrophil ghosts shows that they retain the original dimensions of the cell and consist almost entirely of a peripheral filamentous network, representing the submembranous cortical web, concentric to nuclear remnants. All intracellular membrane-bounded organelles, plasma membrane, and background cytoplasmic electron density are absent. Biochemical analysis of the ghosts shows that less than 10% of enzyme markers for the soluble and granule fractions remain, and that greater than 90% of total cell phospholipid is removed during detergent extraction. The major proteins remaining in the ghosts comigrate, on polyacrylamide gels in the presence of SDS, with chicken gizzard actin, myosin, filamin, and a 110-kdalton protein. Patches and caps induced on neutrophils with either fluorescein isothiocyanate-concanavalin A or ferritin-concanavalin A retain their original location and morphology on ghosts after lysis, as determined by both fluorescence and electron microscopy. In similar experiments, but using 125I-labeled lectins, 37% of total cell bound concanavalin A (Con A) and 25% succinylated Con A remain attached to the ghosts. A major 125I-labeled membrane glycoprotein (80 kdaltons) is associated with ghosts prepared from intact neutrophils iodinated in the presence of exogenous lactoperoxidase. Further 125I-labeled membrane glycoproteins (217, 170, and 147 kdaltons) become associated with ghosts prepared from iodinated cells treated before lysis with Con A, but not with succinylated Con A. These data taken together suggest that linkages exist in neutrophils between proteins exposed on the outer surface of the plasma membrane and the peripheral filamentous network independent of the presence of lipid bilayer. The implications of these findings for surface motile phenomena will be discussed.

An analogue of the erythroid membrane skeletal protein 4.1 in nonerythroid cells.

Protein 4.1 is a crucial component of the erythrocyte membrane skeleton. Responsible for the amplification of the spectrin-actin interaction, its presence is required for the maintenance of erythrocyte integrity. We have demonstrated a 4.1-like protein in nonerythroid cells. An antibody was raised to erythrocyte protein 4.1 purified by KCl extraction (Tyler, J. M., W. R. Hargreaves, and D. Branton, 1979, Proc. Natl. Acad. Sci. USA, 76:5192-5196), and used to identify a serologically cross-reactive protein in polymorphonuclear leukocytes, platelets, and lymphoid cells. The cross-reactive protein(s) were localized to various regions of the cells by immunofluorescence microscopy. Quantitative adsorption studies indicated that at least 30-60% of the anti-4.1 antibodies reacted with this protein, demonstrating significant homology between the erythroid and nonerythroid species. A homologous peptide doublet was observed on immunopeptide maps, although there was not complete identity between the two proteins. When compared with erythrocyte protein 4.1, the nonerythroid protein(s) displayed a lower molecular weight--68,000 as compared with 78,000-and did not bind spectrin or the nonerythroid actin-binding protein filamin. There was no detectable cross-reactivity between human acumentin or human tropomyosin-binding protein, which are similarly sized actin-associated proteins, and erythrocyte protein 4.1. The possible origin and significance of 4.1-related protein(s) in nonerythroid cells are discussed.

Protein and glycoprotein electrophoretic patterns of enriched fractions of primary and secondary granules from guinea pig polymorphonuclear leukocytes.

The postnuclear supernatant fraction of sucrose homogenates of guinea pig polymorphonuclear leukocytes (PMNL) was subjected to differential centrifugation to obtain a total particulate fraction, a particle-free supernatant fraction, highly enriched fractions of primary and secondary granules, and a membrane-rich fraction. The various fractions were solubilized in buffer containing sodium dodecyl sulfate (SDS) and analyzed for protein and glycoproteincomponents by SDS -polyacrylamide gel electrophoresis. The major glycoprotein components of the postnuclear supernatant fraction were found mainly associated with the enriched fraction of secondary granules and, to a lesser extent, with the membrane-rich fraction. No major glycoprotein components were visible in the polypeptide electrophoretic patterns of the primary granule fraction or of the particle-free supernate. Attempts at separation of guinea pig granules by zonal sucrose density gradient centrifugation were only partially successful. Data supporting a species difference in this regard between rabbit and guinea pig PMNL granules are presented.

Specific and azurophilic granules from rabbit polymorphonuclear leukocytes. I. Isolation and characterization of membrane and content subfractions.

The specific and azurophilic granules of rabbit polymorphonuclear heterophils (PMNs) have been isolated and fractionated into membrane and extractable subfractions. Analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) revealed several features of the protein composition of the two granules: (a) Whereas each type of granule had 40-60 proteins separable on one-dimensional gradient gels, few of the proteins were common to both granules. (b) The proteins of the extractable fractions (which comprised approximately 98% of the total granule protein) of each granule were distinct from the proteins of the membrane fractions (which comprised approximately 2% of the total granule protein). (c) The extractable proteins co-migrated with those collected from the medium of ionophore-treated, degranulating PMNs and therefore were defined as content proteins. These results were confirmed by radiolabeling studies. Lactoperoxidase-catalyzed iodination of intact granules did not label the content proteins but did label proteins that co-migrated with major granule membrane proteins. Moreover, disruption of the granules before iodination led to labeling of both content and membrane proteins. We conclude that the membranes of specific and azurophilic granules, which arise from different faces of the Golgi complex, are composed of unique sets of membrane proteins some of which are exposed on the cytoplasmic face of the granules.

Specific and azurophilic granules from rabbit polymorphonuclear leukocytes. II. Cell surface localization of granule membrane and content proteins before and after degranulation.

The compositional relationship between the cell surface of rabbit polymorphonuclear leukocytes (PMNs) and the membranes of PMN cytoplasmic granules has been investigated. Heterophilic PMNs obtained from peritoneal exudates contained 13 cell surface polypeptides ranging in molecular weight from 220,000 to 12,000 daltons as determined by lactoperoxidase-catalyzed protein iodination and gel electrophoresis. Of these, four polypeptides co-migrated with proteins identified as the major constituents of specific (SpG) and azurophilic (AzG) granule membranes. The most notable of these were cell surface proteins of 145,000 and 96,000 daltons that co-migrated with proteins identified as granule content proteins released from PMNs during exocytosis. Extensive washing did not remove these proteins from the cell surface. Iodination of PMNs after the release of SpG and AzG contents by calcium ionophore- induced exocytosis revealed that there was not a dramatic quantitative change in the proteins on the cell surface. Instead, there were large, quantitative increases in the relative amounts of (125)I that were incorporated into several pre-existing cell surface proteins; all of these cell surface proteins co-migrated as a set with those polypeptides identified as either granule membrane or content proteins. Although nearly all of the major polypeptides of SpG and AzG had counterparts on the cell surface of freshly isolated peritoneal exudates PMNs, there were several polypeptides that were unique to the cell surface. Thus, the PMN has at least three membrane compartments with strikingly different protein compositions.

The actin released from profilin--actin complexes is insufficient to account for the increase in F-actin in chemoattractant-stimulated polymorphonuclear leukocytes.

Chemoattractant stimulation of polymorphonuclear leukocytes is associated with a nearly two-fold rise in actin filament content. We examined the role of the actin monomer sequestering protein, profilin, in the regulation of PMN actin filament assembly during chemoattractant stimulation using a Triton extraction method. Poly-L-proline-conjugated Sepharose beads were used to assess the relative concentration of actin bound to profilin with high enough affinity to withstand dilution (profilin-actin complex) and DNase I-conjugated beads to measure the relative concentration of actin in the Triton-soluble fraction not bound to profilin. Actin associated with the Triton-insoluble fraction (F-actin) was also measured. In unstimulated PMN, the relative concentration of actin bound to profilin was maximum. After FMLP stimulation, profilin released actin monomers within 10 s, with the profilin-actin complex concentration reaching a nadir by 40 s and remaining low as long as the cells were exposed to chemoattractant (up to 30 min). If FMLP was dissociated from PMN membrane receptors using t-BOC, actin reassociated with profilin within 20 s. Quantitative analysis of these reactions, however, revealed that profilin release of and rebinding to actin could account for only a small percentage of the total change in F-actin content. Determination of the total profilin and actin concentrations in PMN revealed that the molar ratio of profilin to actin was 1 to 5.2. When purified actin was polymerized in PMN Triton extract containing EGTA, removal of profilin from the extract minimally affected (12% reduction) the high apparent critical concentration at which actin began to assemble. Although profilin released actin at the appropriate time to stimulate actin assembly during exposure to chemoattractants, the concentration of profilin in PMN was insufficient to explain the high unpolymerized actin content in unstimulated PMN and the quantity of actin released from profilin too small to account for the large shifts from unpolymerized to polymerized actin associated with maximal chemoattractant stimulation.

Biochemical and morphological characterization of azurophil and specific granules of human neutrophilic polymorphonuclear leukocytes.

Postnuclear supernates from homogenates of purified neutrophil polymorphonuclear leukocytes (PMNs) from human blood were fractionated by zonal sedimentation and isopycnic equilibration in sucrose gradients. The fractions were characterized biochemically by measuring protein content and the activities of eight enzymes. Selected fractions were further analyzed by electron microscopy. In both centrifugation systems, azurophil and specific granules could be resolved almost completely. Azurophil granules sediment three to four times faster than the specifics and have an average density of 1.23. They contain all the peroxidase of the cells, large portions of four lysosomal hydrolases, and about half of the total lysozyme, and therefore appear to be, in biochemical terms, very similar to the azurophil granules of rabbit PMNs. The specific granules, which have an average density of 1.19, contain the remaining half of the lysozyme but appear to be free of the other components of the azurophil granules, and of alkaline phosphatase. Isopycnic equilibration disclosed a minor lysosomal population, which strongly overlaps the specific granules, and made possible the identification of a membrane-fraction which is characterized by the presence of the thiol-sensitive acid 4-nitrophenyl phosphatase and of alkaline phosphatase.

A Salmonella locus that controls resistance to microbicidal proteins from phagocytic cells.

Facultative intracellular pathogens pose an important health problem because they circumvent a primary defense mechanism of the host: killing and degradation by professional phagocytic cells. A gene of the intracellular pathogen Salmonella typhimurium that is required for virulence and intracellular survival was identified and shown to have a role in resistance to defensins and possibly to other microbicidal mechanisms of the phagocyte. This gene may prove to be a regulatory element in the expression of virulence functions.