RESUMEN

We tested the hypothesis that chemical modifications used to produce stable, oxygen-carrying, Hb-based blood substitutes can induce cytotoxicity in endothelial cells in culture because of altered redox activity. We examined the interaction of hydrogen peroxide with nonmodified hemoglobin (HbA0) and two chemically modified hemoglobins, alpha-cross-linked hemoglobin (alpha-DBBF) and its polymerized form (poly-alpha-DBBF). Hydrogen peroxide-induced cell death (as assessed by lactate dehydrogenase release) in bovine aortic endothelial cells (BAEC) was completely inhibited by all three hemoglobin preparations, consistent with their known pseudoperoxidase activity [hemoglobin consumes peroxide as it cycles between ferric (Fe3+) and ferryl (Fe4+) hemes]. However, reaction of the modified hemoglobins, but not HbA0, with hydrogen peroxide induced apoptotic cell death (as assessed by morphological changes and DNA fragmentation) that correlated with the formation of a long-lived ferrylhemoglobin. A preparation of ferryl-alpha-DBBF free of residual peroxide rapidly induced morphological changes and DNA fragmentation in BAEC, indicative of apoptotic cell death. Redox cycling of chemically modified hemoglobins by peroxide yielded a persistent ferryl iron that was cytotoxic to endothelial cells.

Asunto(s)

RESUMEN

Attempts to evaluate the role of kinins in airway inflammation in humans using the bradykinin receptor antagonist [DArg0-Hyp3-DPhe7]-bradykinin (NPC 567) were unsuccessful, possibly because of the low potency and poor stability of this compound. Recently, [DArg0-Hyp3-Thi5-DTic7-Oic8]-bradykinin (Hoe 140), a novel antagonist that seems to overcome these weaknesses, has been developed. The present study was performed to compare the potency and efficacy of Hoe 140 to those of NPC 567 and another antagonist, [DArg0-Hyp3-DPhe7-Ile8]-bradykinin (B7418), on kinin receptors on guinea pig tracheal epithelial cells. Radioligand binding studies showed the presence of two types of B2 kinin receptors on guinea pig tracheal epithelial cells: a high-affinity site with a Kd of 0.44 nM and Bmax of 12.1 fmol/10(6) cells (4000 sites/cell), and a lower affinity site with a Kd of 10 nM and Bmax of 16 fmol/10(6) cells (9600 sites/cell). Bradykinin-induced prostaglandin E2 production seemed to be associated primarily with the lower affinity site. All three B2 receptor antagonists displaced labeled bradykinin from both classes of binding sites and inhibited bradykinin-induced prostaglandin E2 production, but Hoe 140 was up to 40-fold more potent than NPC 567 and showed an affinity comparable to that of bradykinin for both binding sites. This higher potency of Hoe 140, and its stability against peptidases, suggests that this compound will be useful in evaluating the role of bradykinin in inflammatory diseases of the airways.

Asunto(s)

RESUMEN

The course of pregnancy in patients with systemic lupus erythematosus is not known. The Hopkins Lupus Pregnancy Center has followed 64 patients (74 pregnancies) prospectively since 1987. Patients are seen monthly and clinical and pregnancy-related data collected, with particular emphasis on the occurrence of lupus flare. Flare rate during pregnancy was 1.63 per person-year, compared to 0.64-0.65 after delivery or in non-pregnant patients. Flare did not influence pregnancy outcome. Low serum C3 or C4 and high anticardiolipin antibody predicted pregnancy loss, and prednisone dose, aspirin use, diastolic second trimester blood pressure, C3 at first visit, and race predicted preterm birth. Maternal flare and preterm birth are important risks in lupus pregnancy. The latter can be predicted from maternal pregnancy data.

Asunto(s)

RESUMEN

Bradykinin has been implicated in the pathogenesis of inflammatory arthritis by virtue of its potent proinflammatory properties. We have previously shown bradykinin to be a potent stimulus for the release of prostanoids from interleukin-1 (IL-1)-treated, but not untreated, human synovial cells. We hypothesize that one mechanism by which IL-1 induces responsiveness to bradykinin is by upregulation of number or affinity of kinin receptors on human synovial cells. We performed [3H]bradykinin binding studies in intact human synovial tissue and in cultured human synovial cells. Specific, saturable [3H]bradykinin binding sites in intact synovia were identified by autoradiographic localization and were present in much higher density in rheumatoid, than in osteoarthritis, synovia. In untreated human synovial cells in culture, a single (B2) class of kinin binding sites with a Kd of 2.3 nM and Bmax of 58 +/- 9 fmol/10(6) cells was demonstrated. In matched experiments, IL-1 treatment enhanced specific [3H]bradykinin binding 1.5- to 2.0-fold above that observed in untreated cells. This enhancement was attributable to an increase in Bmax (53 +/- 4 vs. 105 +/- 24 fmol/10(6) cells in untreated and IL-1-treated cells, respectively), rather than an alteration in Kd (1.7 and 1.4 nM, respectively). The potencies of a series of kinin analogs and antagonists and unrelated peptides in displacing [3H]bradykinin from IL-1-treated cells correlated well with their abilities to induce prostanoid release. These studies provide novel information regarding the nature of kinin receptors in intact human synovia and in cultured human synovial cells, their regulation by IL-1 and their role in IL-1-treated cells in kinin-mediated prostaglandin E2 production.

Asunto(s)

RESUMEN

Bradykinin (BK) is a weak stimulus for prostaglandin E2 (PGE2) release in untreated human synovial cells, but a potent stimulus in interleukin-1 (IL-1) pretreated cells. The mechanism(s) by which IL-1 induces responsiveness of synovial cells to BK appears to be multifactorial. IL-1 not only upregulates the number of kinin receptors on these cells, but may also upregulate a calcium-dependent process involved in the synthesis of prostaglandins.

Asunto(s)

RESUMEN

The synthesis of large quantities of 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (1-acyl-2-acetyl-GPC) relative to 1-alkyl-2-acetyl-GPC (PAF; platelet-activating factor) has been demonstrated in several inflammatory cells. The present study has examined agonist and antagonist activities of 1-acyl-2-acetyl-GPC in the human neutrophil. 1-Acyl-2-acetyl-GPC induced a rapid increase in cytosolic calcium in the neutrophil; this effect was detected at 2 x 10(-9) M and was maximal at 10(-6) M. The peak response induced by 1-acyl-2-acetyl-GPC was similar to that induced by PAF although the potency of 1-acyl-2-acetyl-GPC was 300-fold lower than that of PAF. The dose response curves for both 1-acyl-2-acetyl-GPC and PAF were shifted in a parallel fashion by L-652,731 (10(-6) M), a PAF receptor antagonist, suggesting that both 1-acyl-2-acetyl-GPC and PAF act on the same receptor. High concentrations of 1-acyl-2-acetyl-GPC (10(-5) M) induced the release of beta-glucuronidase and lysozyme from the human neutrophil. The percent release of lysozyme induced by 1-acyl-2-acetyl-GPC was consistently higher than that of beta-glucuronidase. Prior stimulation of neutrophils with 1-acyl-2-acetyl-GPC dose-dependently inhibited the increase in cytosolic calcium induced by a subsequent challenge with an optimal concentration of PAF. Similarly, preincubation of neutrophils with 1-acyl-2-acetyl-GPC dose-dependently inhibited beta-glucuronidase and lysozyme release induced by a subsequent stimulation with PAF. The inhibitory effect on degranulation could not be surmounted even by concentrations of PAF 10-fold higher than that of 1-acyl-2-acetyl-GPC. The inhibition appeared to be selective for PAF since 1-acyl-2-acetyl-GPC did not affect f-met peptide-induced degranulation. This study suggests that 1-acyl-2-acetyl-GPC may act as a naturally-occurring specific inhibitor of PAF-induced activation of the human neutrophil.

Asunto(s)

RESUMEN

A radiolabeled N-(3-aminopropyl)-leukotriene B4 amide ([3H]LTB4-APA) analog of the potent leukocyte chemotactic factor leukotriene B4 (LTB4) binds to receptors for LTB4 in plasma membrane-enriched preparations from human blood polymorphonuclear leukocytes (PMNL) and intact PMNL with respective mean dissociation constants of 2.3 nM and 69 nM at 4 degrees C. The [3H]LTB4-APA bound to plasma membrane-enriched preparations from PMNL was covalently cross-linked to membrane proteins with disuccinimidyl suberate. Solubilization and resolution by SDS-PAGE of proteins from [3H]LTB4-APA-labeled PMNL membranes revealed predominant labeling of a 60-kDa protein. Labeling of the PMNL membrane protein was inhibited by LTB4 and its analogs at concentrations similar to those inhibiting the binding of [3H]LTB4 to its receptor, with an identical rank order of potency of LTB4 greater than 20-hydroxy-LTB4 greater than LTB4-APA = 5(S),12(R)-dihydroxy-eicosa-14-cis-6,8,10-trans-tetraenoic acid much greater than LTD4 = LTC4. GTP suppressed the labeling of the 60-kDa PMNL membrane protein to an extent consistent with the decrease in receptor affinity for LTB4 induced by GTP. The stereospecificity of the affinity cross-linking reaction and the regulation by GTP support the identification of an approximately 60-kDa protein as the binding component of the PMNL receptor for LTB4.

Asunto(s)

RESUMEN

The effects of histamine on lung macrophages have been studied by both biologic and radioligand experiments. After overnight adherence, lung macrophages spontaneously released beta-glucuronidase (beta-G) at a rate of approximately 7 nmol of hydrolyzed substrate/h/million cells. Histamine at low concentrations (10(-9) to 10(-8) M) resulted in a consistent potentiation of this release. The concentration-effect curve of histamine was bell-shaped, reaching an optimum at 10(-9) M, with concentrations greater than 10(-8) M having no significant effect. At a maximally effective concentration (10(-9) M), histamine evoked a 135 +/- 9.6% (mean +/- SE; n = 8, P less than 0.001) potentiation in the total amount of beta-G released during the first 60 min of incubation. This increase in beta-G release represented both a slight increase in beta-G synthesis as well as an increase in the percentage of beta-G released. When the secreted beta-G is expressed as a percentage of total content, histamine (10(-9) M) evoked a 125 +/- 3.2% (mean +/- SE; n = 27, P less than 0.0005) enhancement. The potentiation of beta-G release by histamine was evident after 45 min of incubation and persisted for up to 6 h. The potentiation of beta-G by histamine was sensitive to inhibition by pyrilamine (10(-7) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Asunto(s)

RESUMEN

Rat hepatocyte homogenates converted 5-hydroperoxyeicosatetraenoic acid into leukotriene B4 (LTB4). The reaction was dependent on time and protein and substrate concentration, did not require NADPH or oxygen, and was not supported by heat-inactivated hepatocyte homogenates. The authenticity of the biologically generated LTB4 that eluted at the position of synthetic LTB4 during high performance liquid chromatography was established by UV spectrophotometry, mass spectral analysis, radioimmunoassay, and a LTB4 receptor displacement assay. In addition, a leukotriene bioassay is described in which transient increases in cytosolic Ca2+ within human neutrophils are measured by means of fura-2 fluorescence. Biologically generated LTB4 was 40, 40, and 33% as active as synthetic LTB4 in the radioimmunoassay, receptor displacement assay, and cytosolic calcium bioassay, respectively. This activity is consistent with the biologically derived LTB4 being an epimeric mixture of (5S),(12R)-LTB4 and the much less active (5S),(12S)-LTB4. The formation of LTB4 was inhibited by 5,8,11,14-eicosatetraynoic acid (1 mM), 5,6-dehydro-arachidonic acid (50 microM), propanethiol (1 mM), and O2 (100%) to the extent of 53, 42, 48, and 66%, respectively. No inhibition was observed in the presence of diethylcarbamazine (1 mM) and desferal (1 mM). A possible contribution towards LTB4 formation by contaminating Kupffer cells was excluded (less than 0.2%). These results suggest that hepatocytes can convert lipid peroxides into potent chemoattractants that may alter the homeostasis of immunomediators within the liver.

Asunto(s)

Asunto(s)

Asunto(s)

RESUMEN

During a 2-min incubation of leukotriene A4 (LTA4) with human liver microsomes, 1.7 mol% was converted into leukotriene B4 (LTB4). The reaction was dependent on protein concentration, time, and substrate concentration, was not supported by heat-inactivated microsomes, and did not require NADPH. Kinetic analysis of the reaction revealed apparent Michaelis-Menten type behavior (app Km approximately 20 microM). Production rates varied widely among three patients examined. Piperonyl butoxide, propanethiol, and cyclohexene oxide (1 mM) inhibited LTB4 formation by microsomal LTA4-hydrolase by 52, 40, and 60%, respectively. The latter two compounds were shown not to inhibit cytosolic LTA4-hydrolase activity. The activity of microsomal and cytosolic LTA4-hydrolase was decreased in the presence of 100% O2 by 45 and 64%, respectively. Direct chemical ionization mass spectrometry was used to obtain a mass spectrum of 50 ng of underivatized synthetic LTB4 free acid and show that this spectrum is identical with that of 10 ng of the product isolated from LTA4 hydrolysis by human liver microsomes. The authenticity of the biologically generated LTB4 was confirmed by functional characterization in a receptor displacement assay. Displacement of [3H]LTB4 from the high affinity receptors of LTB4 on human neutrophils revealed KD50 values of 8.2 and 5.1 nM for human liver microsome derived and synthetic LTB4, respectively. The nearly two-fold higher KD50 of the microsomally generated LTB4 is suggested to result from an epimeric mixture of the active 5(S),12(R)- and the less active 5(S),12(S)-dihydroxy-6,14-cis-8,10-trans-eicosatetraenoic acid.

Asunto(s)

RESUMEN

Rabbit anti-idiotypic IgG antibodies to the combining site of a mouse monoclonal IgG2b antibody to leukotriene B4 (LTB4) cross-reacted with human polymorphonuclear (PMN) leukocyte receptors for LTB4. Anti-idiotypic IgG and Fab both inhibited the binding of [3H]LTB4, but not [3H]N-formylmethionyl-leucylphenylalanine (fMLP), to PMN leukocytes with similar concentration-effect relationships, whereas neither nonimmune rabbit IgG nor Fab had any inhibitory activity. At a concentration of anti-idiotypic IgG that inhibited by 50% the binding of [3H] LTB4 to PMN leukocytes, the antibodies preferentially recognized high affinity receptors. Anti-idiotypic IgG and Fab inhibited PMN leukocyte chemotactic responses to LTB4, but not fMLP, with concentration-effect relationships resembling those characteristic of the inhibition of binding of [3H] LTB4, without altering the LTB4-induced release of beta-glucuronidase. Chemotaxis and increases in the cytoplasmic concentration of calcium equal in magnitude to those elicited by optimal concentrations of LTB4 were attained at respective concentrations of anti-idiotypic IgG equal to and 1/25 the level required for inhibition of binding of [3H]LTB4 by approximately 50%. Thus, the anti-idiotypic antibodies bound to PMN leukocyte receptors for LTB4 with a specificity, preference for high affinity sites, and capacity to alter PMN leukocyte functions that were similar to LTB4.

Asunto(s)

Asunto(s)

RESUMEN

The distinctive characteristics of human polymorphonuclear (PMN) leukocyte receptors for leukotriene B4 (LTB4) have been elucidated by studies of binding of [3H]LTB4, the structure of protein constituents of the receptors isolated from plasma membranes, and the effects of antireceptor antibodies. A high-affinity class of 4400 receptors with a KD of 0.4 nM mediates chemotaxis and increased adherence of PMN leukocytes, whereas a low-affinity class of 270,000 receptors with a KD of 61 nM mediates the release of lysosomal enzymes and increases in oxidative metabolism. The low-affinity receptors are composed of a 60,000-dalton protein-binding unit. The high-affinity receptors are composed of the same binding unit in association with a 40,000-dalton guanine nucleotide-binding protein. That antireceptor antibodies as well as LTB4 distinguish the two classes of receptors with different functional consequences suggests the possibility of unique approaches to the regulation of leukocyte function at the receptor level.

Asunto(s)

RESUMEN

Peripheral blood polymorphonuclear leukocytes (PMNL) isolated from rabbits after an i.v. injection of endotoxin exhibited decreased chemotactic migration in response to leukotriene B4 (LTB4) and C5a, but not N-formyl-methionyl-leucyl-phenylalanine (fMLP), after endotoxin treatment. The binding of radiolabeled LTB4, fMLP, and C5a to isolated PMNL was assessed in order to determine whether altered receptor expression could account for the observed functional changes. Control PMNL expressed binding sites for fMLP, LTB4, and C5a similar to those previously characterized from human PMNL. Control PMNL expressed a single class of 14,600 +/- 2700 receptors for fMLP with a mean dissociation constant (Kd) of 2.0 +/- 0.6 nM at 0 degrees C, whereas two subclasses of binding sites were expressed for LTB4: 10,300 +/- 6800 high-affinity and 85,600 +/- 53,000 low-affinity binding sites per PMNL with mean Kd for LTB4 of 0.75 +/- 0.43 nM and 70 +/- 58 nM (mean +/- SD, n = 5), respectively. Control PMNL bound [125I]-C5a in a dose-dependent and saturable manner at 24 degrees C. At saturating concentrations of C5a, PMNL obtained from control rabbits bound 270,000 +/- 50,000 molecules of [125I]-C5a with half-maximal binding occurring at [125I]-C5a concentrations of 5.5 +/- 1.9 nM. The binding of LTB4 and C5a to PMNL obtained 24 hr after an i.v. injection of endotoxin was markedly decreased compared with control PMNL. PMNL from endotoxin-treated rabbits exhibited 68% fewer high-affinity binding sites per PMNL for LTB4 and a 51% decrease in the amount of [125I]-C5a bound at saturating concentrations compared with control PMNL. There was no significant change in the Kd of the high-affinity binding sites for LTB4, no change in the Kd and number of the low-affinity binding sites for LTB4, and a small decrease in the apparent Kd for C5a to 3.3 +/- 1.1 nM. Even though the pretreatment with i.v. endotoxin did not alter chemotactic or degranulation responses elicited by fMLP, the endotoxin pretreatment induced an eightfold increase in the receptor density without altering the Kd for fMLP. Decreased receptor expression could account in large part for the decreased chemotactic responsiveness towards C5a and LTB4 induced by LPS. The finding that a substantial increase in receptors for fMLP need not be accompanied by a comparable functional change suggests that decreased efficiency in receptor coupling to intracellular biochemical events may also result from i.v. endotoxin.

Asunto(s)

RESUMEN

The incubation of HL-60 human promyelocytic leukemia cells for 7 days with 100 nM 1 alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3] induced differentiation into monocyte-like cells, as assessed by morphologic and biochemical characteristics. Stereospecific receptors for leukotriene B4 (LTB4) developed on the surface of the HL-60 cell-derived monocytes that had the capacity to transduce LTB4 stimulation of a transient increase in the cytosolic concentration of calcium ([Ca+2]in). HL-60 cell-derived monocytes, but not undifferentiated HL-60 cells, expressed a high affinity subset of 6400 +/- 3700 receptors per cell with a dissociation constant (Kd) of 2.3 +/- 1 nM (mean +/- SD, n = 3) and a low affinity subset of approximately 2.2 X 10(6) receptors per cell with an apparent Kd of 680 +/- 410 nM. Derivatives of LTB4 inhibited the binding of [3H]LTB4 to HL-60 cell-derived monocytes with a rank order of potency of LTB4 greater than 20-OH-LTB4 greater than 3-aminopropyl amide-LTB4, which is similar to the order for LTB4 receptors of human blood PMNL. In contrast, leukotrienes C4 and D4 and formyl-methionyl chemotactic peptides did not inhibit the binding of [3H] LTB4, which demonstrates the specificity of these receptors for isomers of 5,12-dihydroxy-eicosatetraenoic acid. LTB4 stimulated an increase in [Ca+2]in in HL-60 cell-derived monocytes which reached 50% of the maximal level at an LTB4 concentration of 0.5 nM (EC50). Preincubation of HL-60 cell-derived monocytes with 10 nM LTB4 resulted in a selective loss of high affinity receptors, as assessed by binding of [3H]LTB4, and a 200-fold increase in the EC50 for stimulation by LTB4 of increases in [Ca+2]in, without alterations in either the low affinity receptors for LTB4 or the responsiveness of [Ca+2]in to formyl-methionyl chemotactic peptides. HL-60 cells that are induced to differentiate into monocytes thus develop stereospecific receptors for LTB4 with binding and transductional characteristics similar to those of human blood PMNL.

Asunto(s)

RESUMEN

Mast cell-dependent late-phase reactions (LPR) occur in rat skin and are characterized histologically by an early (1 to 8 hours) neutrophil-rich infiltrate, which is essential to a later (24 hours) infiltration by mononuclear cells. Although the ability of preformed mast cell-granule constituents alone to elicit LPR is clearly established, the relative pathogenetic contributions of newly generated lipid mediators to rat LPR are unknown. Leukotriene B4 (LTB4) may be generated by stimulated mast cells in a number of species and might potentially contribute to the neutrophil ingress. In order to examine this possibility in a well-characterized animal model of LPR, the capacity of LTB4 to influence rat cutaneous inflammation was studied. LTB4 (0.1 to 100 ng) alone did not induce vasopermeability in rat skin nor potentiate the blueing response to histamine. Intracutaneous LTB4 (0.1 to 100 ng) did not cause significant infiltration of neutrophils 3 to 4, 6 to 8, or 24 hours after injection; increased numbers of mononuclear leukocytes were not appreciated through 24 hours. In the same animals intracutaneous anti-IgE and intact mast cell granules both produced intense biphasic infiltration characteristic of rat LPR. In order to examine if rat polymorphonuclear leukocytes were capable of responding to LTB4, several in vitro studies were performed. Rat peritoneal and peripheral blood neutrophils migrated toward formyl-methionyl-leucyl-phenyl-alanine in vitro but not to purified human or synthetic LTB4. Rat peripheral blood and elicited peritoneal neutrophils bound only 32% and 27%, respectively, of the quantity of [3H]LTB4 bound by human neutrophils.(ABSTRACT TRUNCATED AT 250 WORDS)

Asunto(s)

RESUMEN

The uptake of Quin-2 by human polymorphonuclear (PMN) leukocytes permitted accurate fluorimetric quantification of the cytosolic concentration of intracellular calcium [( Ca+2]in), without altering the expression of the two subsets of leukotriene B4 (LTB4) receptors, as assessed by the binding of [3H]LTB4. Chemotactic concentrations of LTB4 elicited a rapid increase in [Ca+2]in, which reached a peak within 0.6 to 1 min and then decayed back to baseline levels by 6 to 10 min. The maximal increase and the half-maximal increase in [Ca+2]in were achieved by LTB4 at mean concentrations of 5 X 10(-10) M and 2 X 10(-10) M, respectively, where the binding of LTB4 to high-affinity receptors predominates. A rank order of potency of LTB4 greater than 5(S),12(S)-6-trans-LTB4 greater than 12(S)-LTB4 was established for the elicitation of increases in [Ca+2]in, which reflects the binding of the isomers to low-affinity receptors. PMN leukocytes were preincubated with 10(-8) M LTB4 to induce chemotactic deactivation, which eliminates the expression of high-affinity receptors without altering the expression of the low-affinity receptors for LTB4. LTB4 elicited an increase in [Ca+2]in in the deactivated PMN leukocytes with an EC50 of 3 X 10(-8) M, which is similar to the Kd for LTB4 binding to the low-affinity receptors. Two lines of cultured human leukemic cells, IM-9 and HL-60, did not bind LTB4 specifically and did not show any change in [Ca+2]in upon the addition of 3 X 10(-8) M LTB4. The HL-60 human promyelocytic leukemia cell line was induced to differentiate in 1% dimethyl sulfoxide to leukocytes with more mature myelocytic characteristics. Differentiated HL-60 cells expressed an average of 54,000 low-affinity receptors for LTB4 per cell with an average dissociation constant of 7.3 X 10(-8) M and concurrently developed the capacity to respond to LTB4 with an increase in [Ca+2]in. The binding of LTB4 to either high-affinity or low-affinity receptors appears to be sufficient to initiate an increase in [Ca+2]in in human PMN leukocytes and differentiated HL-60 cells. The specificity of LTB4 receptors in transducing maximum increases in [Ca+2]in is determined by the subset of receptors that predominate as a result of the concentration of LTB4 and the state of the responding cells.

Asunto(s)

RESUMEN

Chemotactic factors stimulate a rapid increase in the cytosolic concentration of intracellular calcium ions ([Ca2+]in) in human polymorphonuclear leukocytes (PMNL), which may be an event that is critical to the expression of chemotaxis and other PMNL functions. Treatment of PMNL with pertussis toxin catalyzes ADP-ribosylation of a protein similar or identical to the inhibiting regulatory protein of adenylate cyclase, Gi, and suppresses the increase in [Ca2+]in elicited by leukotriene B4(LTB4) and formyl-methionyl-leucyl-phenylalanine. Chemotactic migration and lysosomal enzyme release elicited by chemotactic factors were inhibited by pertussis toxin with a concentration-dependence similar to that for inhibition of the increase in [Ca2+]in, without an effect on lysosomal enzyme release induced by the ionophore A23187 and phorbol myristate acetate. Activated pertussis toxin catalyzed the [32P]ADP-ribosylation of a 41 kD protein in homogenates of PMNL. The extent of [32P]ADP-ribosylation of this protein was reduced 59% by pretreatment of intact PMNL with pertussis toxin. Pertussis toxin selectively decreased the number of high-affinity receptors for LTB4 on PMNL by 60% without altering the number or binding properties of the low-affinity subset of receptors. Pertussis toxin modification of a membrane protein of PMNL analogous to Gi thus simultaneously alters chemotactic receptors and attenuates the changes in cytosolic calcium concentration and PMNL function caused by chemotactic factors.

Asunto(s)