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The identification of human inflammatory cells that express inducible nitric oxide synthase and the clarification of the role of inducible nitric oxide synthase in human infectious or inflammatory processes have been elusive. In neutrophil-enriched fractions from urine, we demonstrate a 43-fold increase in nitric oxide synthase activity in patients with urinary tract infections compared with that in neutrophil-enriched fractions from noninfected controls. Partially purified inducible nitric oxide synthase is primarily membrane associated, calcium independent, and inhibited by arginine analogues with a rank order consistent with that of purified human inducible nitric oxide synthase. Molecular, biochemical, and immunocytochemical evidence unequivocally identifies inducible nitric oxide synthase as the major nitric oxide synthase isoform found in neutrophils isolated from urine during urinary tract infections. Elevated inducible nitric oxide synthase activity and elevated nitric oxide synthase protein measured in patients with urinary tract infections and treated with antibiotics does not decrease until 6-10 d of antibiotic treatment. The extended elevation of neutrophil inducible nitric oxide synthase during urinary tract infections may have both antimicrobial and proinflammatory functions.

The formation of nitric oxide by human phagocytes as measured by nitrite production is controversial. We report here that nitrite production by phorbol myristate acetate (PMA)-stimulated human polymorphonuclear leukocytes (PMN) is considerably increased by the addition of azide and a further increase occurs when catalase also is added. Nitrite production by the PMN-PMA-azide-catalase system is unaffected by superoxide dismutase or monomethylarginine but is markedly reduced by the substitution of chronic granulomatous disease for normal neutrophils. The stimulated neutrophils could be replaced by the H2O2-generating enzyme system glucose-glucose oxidase. These findings suggest that nitrite production does not, in this instance, reflect nitric oxide synthase activity by human neutrophils but rather the catalase-catalyzed conversion of azide to nitrite in the presence of H2O2 generated by the stimulated PMN.

The distribution of type I (p55) and type II (p75) tumor necrosis factor receptors (TNF-Rs) in human polymorphonuclear neutrophils (PMNs) was analyzed by Western blotting of subcellular fractions obtained by centrifugation of PMN cavitates on Percoll density gradients. In resting PMNs, the p55 receptor was associated with both gamma and beta fractions, enriched in plasma membranes and specific granules, respectively, whereas the p75 TNF-R was located only in the gamma fraction. Intracellular p55 TNF-R bound 125I-labeled TNF in a ligand blot assay and migrated as a diffuse band of 46-60 kd, similar to the plasma membrane receptor. Activation of PMNs with the chemoattractant N-formyl-methionyl-leucyl-phenylalanine (fMLP), in conditions that induced the selective release of the tertiary granule marker gelatinase, caused the shedding of most of membrane p55 TNF-R as a 28-kd soluble form but had little effect on the distribution of the receptors in beta fractions. By contrast, when specific granule secretion was induced in the presence of cytochalasin B, a marked decrease in reactivity of beta fractions with anti-p55 TNF-R antibody was observed. At the same time, the amount of soluble 28-kd fragment found in the supernatant was increased. Thus, the intracellular pool of p55 TNF-R is associated with functional secretory granules and is redistributed in response to PMN activation.

To localize the protease(s) involved in shedding of tumor necrosis factor receptors (TNF-R) from activated neutrophils (PMN) (Porteu, F., and C. Nathan (1990) J. Exp. Med. 172, 599-607), we tested subcellular fractions from PMN for their ability to cause loss of TNF-R from intact cells. Exposure of PMN to sonicated azurophil granules at 37 degrees C resulted in inhibition of 125I-TNF binding; 50% inhibition ensued when PMN were treated for approximately 1 min with azurophil granules equivalent to 2-3 PMN per indicator cell. The TNF-R-degrading activity in azurophil granules were identified as elastase by its sensitivity to diisopropyl fluorophosphate (DFP), alpha 1-antitrypsin and N-methoxysuccinyl-Ala-Ala-Pro-Val chloromethyl ketone (MSAAPV-CK), and by the ability of purified elastase to reproduce the effect of azurophil granules. Elastase preferentially acted on the 75-kDa TNF-R, reducing by 85-96% the binding of 125I-TNF to mononuclear cells expressing predominantly this receptor, while having no effect on endothelial cells expressing almost exclusively the 55-kDa TNF-R. Elastase-treated PMN released a 32-kDa soluble fragment of p75 TNF-R that bound TNF and reacted with anti-TNF-R monoclonal antibodies. In contrast, fMet-Leu-Phe-activated PMN shed a 42-kDa fragment from p75 TNF-R, along with similar amounts of a 28-kDa fragment from p55 TNF-R. Shedding of both TNF-Rs by intact activated PMN was more extensive than shedding caused by elastase and was completely resistant to DFP and MSAAPV-CK. Thus, the TNF-R-releasing activity of azurophil granules is distinct from that operative in intact stimulated PMN and could provide an additional mechanism for the control of cellular responses to TNF at sites of inflammation.

Two 29-kD polypeptides, azurocidin and p29b, were purified to homogeneity from human neutrophils by acid extraction of azurophil granule membrane-associated material followed by gel filtration and reverse-phase chromatography. Azurocidin and p29b share NH2-terminal sequence homology with each other as well as with elastase, cathepsin G, and other serine proteases. p29b bound [3H]diisopropyl fluorophosphate and hydrolyzed elastin, casein, and hemoglobin. A peptide substrate for p29b could not be identified. Azurocidin neither bound [3H]diisopropyl fluorophosphate nor hydrolyzed any of the proteins, peptides, or esters tested. In microbicidal assays, purified azurocidin was comparable to p29b in activity against Escherichia coli, Streptococcus faecalis, and Candida albicans. The antimicrobial activity of azurocidin was enhanced under mildly acidic conditions, but was inhibited in a dose-dependent manner by NaCl, CaCl2, or serum. Immunoblot analysis with monospecific antibodies localized greater than 90% of the azurocidin and greater than 75% of the p29b to azurophil granule-rich fractions of PMN lysates. Immunoelectron microscopy confirmed the localization of azurocidin to the azurophil granules. Azurocidin associated with the azurophil granule membrane, but did not appear to be an integral membrane protein. Thus, azurocidin and p29b are members of a family of serine protease homologs stored in azurophil granules and may play a role in inflammatory and antimicrobial processes involving PMN.

Recombinant tumor necrosis factor alpha (rTNF alpha) and beta (rTNF beta) did not trigger H2O2 release from PMN in suspension. However, when PMN were plated on polystyrene surfaces coated with serum, fibronectin, vitronectin, laminin, or human umbilical vein endothelial cells (HUVEC), rTNFs induced a massive, prolonged secretory response, similar to that elicited by phorbol myristate acetate (PMA) or bacteria. On serum-coated plates, the maximum sustained rate of H2O2 release in response to rTNF alpha was 2.6 +/- 0.2 nmol/min per 10(6) PMN, the same as that with PMA; release continued for 73 +/- 4 min. On laminin-coated surfaces or HUVEC, release of H2O2 in response to rTNFs was slower, but lasted approximately 3.5 h, reaching the same total (greater than 100 nmol/10(6) PMN). Not only was this response far longer and larger than for other soluble stimuli of the respiratory burst studied with PMN in suspension, but the concentration necessary to elicit a half-maximal response (EC50) for rTNF alpha was orders of magnitude lower (55 pM). Responses were similar with FMLP, but ranged from zero to small with recombinant IFN alpha, recombinant IFN beta, recombinant IFN gamma, platelet-derived growth factor, recombinant IL-1 beta, or bacterial lipopolysaccharide. Adherent monocytes did not secrete H2O2 in response to rTNFs. H2O2 secretion by adherent PMN was first detectable 15-90 min after addition of rTNFs or FMLP. This lag period was unaffected by prior exposure of PMN to rTNF alpha in suspension, by allowing PMN to adhere before adding rTNF alpha, or by incubating adherent PMN in medium conditioned by rTNF alpha-treated PMN. Cytochalasins abolished H2O2 secretion in response to rTNFs, but not FMLP, if added during, but not after, the lag period. Thus, H2O2 secretion from rTNF alpha-treated PMN appears to be a direct but delayed response that requires assembly of microfilaments during exposure to the cytokine. These results suggest that PMN adherent to intra- or extravascular surfaces may undergo a massive, prolonged respiratory burst at the command of macrophages and lymphocytes reacting to microbial products and antigens.

The effect of adenosine on the respiratory burst was investigated using human neutrophils adherent to serum-coated surfaces. Adenosine caused complete suppression of the respiratory burst elicited by TNF-alpha, FMLP, or CSF for granulocytes; partial suppression of the response to CSF for granulocytes/macrophages, Staphylococcus aureus, Escherichia coli, Listeria monocytogenes, or uncoated polystyrene surfaces; and no suppression of the response to PMA. In most experiments, 4.7 x 10(-7) M and 2.5 x 10(-8) M adenosine caused 50% suppression of H2O2 release in response to TNF-alpha and FMLP, respectively, and 10 microM caused 100% suppression. Preexposure of neutrophils to ADP blocked the inhibitory effect of adenosine. With adherent neutrophils, there is a prolonged lag period in the onset of the respiratory burst in response to cytokines. Adenosine was fully suppressive if its addition was delayed past the first third of this lag period, or if it was removed during the last third of the lag period. A 10-min pulse with adenosine was most inhibitory when delivered in the middle third of the lag period. Dihydrocytochalasin B abolished the suppressive effect of adenosine on H2O2 release in response to FMLP. Thus adenosine, at concentrations found in human plasma, is a potent but selective inhibitor of the respiratory burst of adherent human neutrophils in response to physiologic, soluble stimuli, and ADP is a potentially physiologic counter-suppressant. Adenosine appears to exert most of its effect during a discrete interval within the lag period before onset of the respiratory burst, and may affect the coupling of agonist receptors to the cytoskeleton.

Human neutrophils adherent to proteins derived from serum or plasma, or to the basement membrane protein laminin, underwent a delayed but massive respiratory burst in response to recombinant human CSF-GM or CSF-G. No such response was elicited from neutrophils in suspension. On a molar basis, CSF-GM (EC50 approximately 126 pmol/L) and CSF-G (EC50 approximately 585 pmol/L) were about as potent as TNF alpha and TNF beta in their elicitation of H2O2 release and orders of magnitude more potent than previously studied formylated peptides or C5a. CSF-GM and CSF-G prime suspended neutrophils for a respiratory burst in response to soluble agonists, such as formylated peptides. Compared to the CSF-primed respiratory burst of nonadherent neutrophils, the CSF-triggered response of adherent neutrophils is markedly more delayed in onset (73 to 95 minutes), prolonged in duration (150 to 180 minutes), and greater in extent (approximately 60 to 100 nmol H2O2 released/10(6) neutrophils). Neither CSF-M, interleukin-3 (IL-3), nor bacterial lipopolysaccharide triggered the respiratory burst in adherent neutrophils, nor did CSF-GM or CSF-G trigger a respiratory burst in adherent monocytes. Release of CSF-GM and CSF-G in response to antigens, bacterial products, or cytokines may give mononuclear cells control over the respiratory burst of noncirculating neutrophils during inflammatory and immune responses.

Nine polypeptide peaks with antibiotic activity were resolved from human polymorphonuclear leukocyte azurophil granule membranes. All but 1 of the 12 constituent polypeptides were identified by N-terminal sequence analysis. Near quantitative recovery of protein and activity permitted an assessment of the contribution of each species to the overall respiratory-burst-independent antimicrobial capacity of the cell. Three uncharacterized polypeptides were discovered, including two broad-spectrum antibiotics. One of these, a defensin that we have designated human neutrophil antimicrobial peptide 4, was more potent than previously described defensins but represented less than 1% of the total protein. The other, named azurocidin, was abundant and comparable to bactericidal permeability-increasing factor in its contribution to the killing of Escherichia coli.

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.

A cyanide-insensitive b-type cytochrome (cytochrome b559) is involved in the respiratory burst of phagocytes. Spectroscopic measurement of its content in polymorphonuclear leukocytes or macrophages is complicated by signals arising from contaminating Hb or mitochondrial cytochromes upon reduction by dithionite. These interferences can be overcome by reducing the sample with dithionite, aerating it, and reducing it a second time with dithionite, in the presence of 10 microM cyanide. Cyanide suppresses the response of the interfering proteins to the second dithionite reduction. This modified method allows an accurate determination of the content of cytochrome b559 using smaller numbers of cells than previously feasible.