Defensins. Natural peptide antibiotics of human neutrophils

Purification and Characterization of a Proline-Rich Antibacterial Peptide, with Sequence Similarity to Bactenecin-7, from the Haemocytes of the Shore Crab, Carcinus Maenas

Antibacterial peptides are important for non-specific host defence in many animals. They have been extensively characterized from mammals, amphibians, insects and chelicerates but have not so far been found in crustaceans. Here we report the presence of several constitutive antibacterial proteins, active against both gram-positive and gram-negative bacteria, in the haemocytes of the shore crab, Carcinus maenas. These proteins have molecular masses of > 70 kDa, approximately 45 kDa, approximately 14 kDa and 6.5 kDa. The 6.5 kDa peptide has been purified to homogeneity by Sep Pak C18 extraction, gel filtration and reverse-phase HPLC. Partial N-terminal sequence analysis further shows that it is proline rich and shares more than 60% identity in a 28-amino-acid overlap with the mature form of bactenecin 7, an antimicrobial peptide from bovine neutrophils which belongs to the cathelicidin family of mammalian peptide antibiotics.

Intramolecular disulfide bonds enhance the antimicrobial and lytic activities of protegrins at physiological sodium chloride concentrations

Protegrins are 2-kDa antimicrobial peptides that contain 16-18 amino acid residues and two intramolecular disulfide bonds. We studied the contribution of these disulfide bonds to the bactericidal activity of protegrins in physiological concentrations of NaCl by comparing protegrin PG-1 with variants that lacked one or both cysteine disulfides. Whereas the bactericidal and liposome-lytic properties of protegrin PG-1 were enhanced by adding 100 mM NaCl to the phosphate-buffered medium, NaCl addition strongly inhibited the effects of its linearized, disulfide-free variant, [A6, A8, A13, A15]protegrin-1. Whereas protegrin PG-1 manifested beta-sheet structure by CD (circular dichroism) and ATR-FTIR (attenuated-total-reflectance-Fourier-transform-infrared) spectroscopy in buffer or membrane-mimetic environments, [A6, A8, A13, A15]protegrin-1 manifested disordered structure in phosphate buffer and alpha-helical characteristics in membrane-mimetic environments. Both single-disulfide protegrin variants, [A8, A13]protegrin-1 and [A6, A15]protegrin-1, assumed beta-sheet conformations with liposomes that simulated bacterial membranes, and both retained substantial bactericidal activity when 100 mM NaCl was present. These findings demonstrate that the intramolecular disulfide bonds of protegrins are required for their antiparallel beta-sheet conformation in membrane-mimetic environments and for their potent antimicrobial activity in media containing NaCl concentrations comparable to those found in serum and extracellular fluids.

Defensin modulates tissue-type plasminogen activator and plasminogen binding to fibrin and endothelial cells

Defensins are naturally occurring antimicrobial peptides that may participate in host defense against microorganisms. We previously reported that the amino acid sequence of leukocyte defensins resembles the lysine-binding site in the kringles of plasminogen and that defensin inhibits fibrinolysis mediated by tissue-type plasminogen activator (tPA) and plasminogen. In the present paper we analyze the mechanisms of this inhibition. Defensin binds specifically to cultured human umbilical vein endothelial cells (HUVEC) (half-maximal binding = 3 microM) as well as to fibrin. At saturating concentrations (5-10 microM), defensin stimulates the maximum binding of plasminogen to HUVEC and to fibrin approximately 10-fold. However, defensin inhibits plasminogen binding to both surfaces at concentrations >10 microM. Defensin also inhibits tPA and plasminogen-mediated fibrinolysis in a dose-dependent manner at all concentrations tested. Fibrinolysis is almost totally inhibited by 6 microM defensin, a concentration that stimulates the binding of plasminogen to fibrin. Discordance between the enhancement of plasminogen binding and its activation cannot be explained by an inhibitory effect of defensin on tPA binding nor by inhibition of plasmin activity, each of which occur only at higher concentrations. Rather, these results suggest that plasminogen bound to fibrin in the presence of defensin is less susceptible to activation by tPA.

The isolation and characterization of a novel corticostatin/defensin-like peptide from the kidney

We report the isolation and characterization of RK-1, a novel peptide found in the kidney. RK-1 is related to the corticostatin/defensins and has the sequence MPC-SCKKYCDPWEVIDGSCGLFNSKYCCREK but differs from the very cationic corticostatins/defensins in having only one arginine and a calculated charge at pH 7 of +1. Like some myeloid corticostatin/defensins RK-1 inhibits the growth of Escherichia coli. Since corticostatin/defensins effect ion flux in responsive epithelia we used volume changes in villus enterocytes as a model system to study the effects of RK-1 on ion channels in epithelial cells. At concentrations > or = 10(-9) M RK-1 decreased enterocyte volume in a dose-dependent manner through a pathway that requires extracellular calcium and is inhibited by niguldipine, a dihydropyridine-sensitive "L"-type Ca(2+)-channel blocker. In other assay systems for corticostatin-defensins, such as the inhibition of adrenocorticotropin-stimulated steroidogenesis, or cell lysis, RK-1 was inactive or only weakly active. These results demonstrate the existence of a novel system of biologically active peptides in the kidney represented by RK-1 which is antimicrobial and can activate epithelial ion channels in vitro.

Delineation of an active fragment and poly(L-proline) II conformation for candidacidal activity of bactenecin 5

Bactenecin 5 and its fragments [BN22 (1-22), BN16 (7-22), and BC24 (20-43)] were synthesized by solid-phase methods. Their antifungal activities on Candida albicans have been studied and compared with those of the native bactenecin 5. The conformational preferences of these peptides in aqueous and nonaqueous solutions and in lipid vesicles were examined by circular dichroism. The highly active N-terminal fragment (BN16) was examined in aqueous solution using 500 MHz two-dimensional NMR. Bactenecin 5 and its fragments are potent candidacidal agents against C. albicans. The N-terminal fragments (BN22 and BN16) of bactenecin 5 are relatively more active than the C-terminal fragment BC24, especially at lower concentrations. The N-terminal region (7-22) which retains the activity of the whole molecule appears to be the functional domain for candidacidal activity. The CD spectra of bactenecin 5 and its fragments are reminiscent of the CD spectrum of poly(L-proline) type II structure in aqueous and nonaqueous solutions and also in lipid vesicles. The temperature dependence of NH chemical shifts and 1H/2H exchange effect on amide resonances suggest the absence of intramolecularly hydrogen-bonded NH groups. The coupling constant (JNH-CalphaH) values, conformational restriction offered by the Pro residues (phi = -60 degrees +/- 15 degrees), the set of medium- and short-range nuclear Overhauser effects observed for the active N-terminal fragment (BN16), and the restrained structure calculation using DIANA suggest that poly(L-proline) type II conformers of the peptide molecules could be significantly populated in aqueous solution. The ability of bactenecin peptides to induce disruption of lipid vesicles correlates well with their activity. Our results suggest that poly(L-proline) type II structure may, indeed, be the biologically active conformation for candidacidal activity of bactenecin peptides.

Intramolecular inhibition of human defensin HNP-1 by its propiece

We examined mechanisms that protect host defense cells from their cytotoxic effector molecules. Human neutrophil peptides (HNP) 1-3 are microbicidal and cytotoxic defensins, initially synthesized as 94-amino acid preproHNP(1-94), cotranslationally proteolyzed to proHNP(20-94), then converted by removal of the anionic propiece to mature HNP(65-94)(HNP-1 and -3) and HNP(66-94) (HNP-2). We hypothesized that during synthesis and subcellular sorting the anionic propiece inhibits the cytotoxicity of the cationic defensin. We expressed preproHNP-1 cDNA in recombinant baculovirus-infected insect cells that secreted the normally transient proHNP-1(20-94) into the medium. Cyanogen bromide cleaved proHNP-1(20-94) at the fortuitously located Met64 to yield mature recombinant HNP-1(65-94) and unlinked propiece. Recombinant and native HNP-1 purified from PMN were identical as judged by mass spectrometry, retention time in reverse-phase high performance liquid chromatography, migration on acid-urea polyacrylamide gels, and reaction with a conformation-specific antibody. Recombinant and native HNP-1 had comparable microbicidal activity towards Listeria monocytogenes and were similarly potent in permeabilizing K562 leukemia cells, but proHNP-1(20-94) was virtually inactive in both assays. Addition of unlinked propiece (proHNP-1(20-64) with Met64-->homoserine) inhibited the bactericidal and cell-permeabilizing activity of mature HNP-1 in a dose-dependent manner. Linked, and to a lesser extent unlinked, propiece interfered with the binding of HNP-1 to target cells. The propiece thus acts as an efficient intramolecular inhibitor of defensin HNP-1 cytotoxicity.

In vitro activity of the antimicrobial peptides human and rabbit defensins and porcine leukocyte protegrin against Mycobacterium tuberculosis

Three independent assay methods were used to investigate the activities of antimicrobial peptides (human and rabbit defensins and protegrin from porcine leukocytes) against Mycobacterium tuberculosis in vitro. M. tuberculosis H37Ra was cultured in the presence of human neutrophil peptide 1, synthetic rabbit neutrophil peptide 1, or porcine protegrin 1 at 37 degrees C for 6 to 48 h, and antimycobacterial activity was measured by CFU assay. These peptides at a concentration of 50 microg/ml showed significant antibacterial effects on M. tuberculosis after 24 and 48 h of incubation (85.9 to 97.5% at 24 h and 91.6 to 99.4% at 48 h). A radiometric method and a radial diffusion assay confirmed these observations. Antibacterial activity against M. tuberculosis was independent of calcium (1.0 mM) or magnesium (1.0 mM) and not inhibited by sodium chloride (100 mM). The optimal pH for antibacterial activity against M. tuberculosis was greater than 4.0. Three clinical isolates of M. tuberculosis were also studied, and these peptides showed 86.3 to 99.0% reduction in CFU of these organisms. Morphological studies using scanning electron microscopy showed that defensins caused lesions on the surface of H37Ra. These observations suggest that antimicrobial peptides such as defensins and protegrins may represent an important component of the host defense mechanism against M. tuberculosis and offer a potential new approach to therapy.

Intracellular survival of Burkholderia pseudomallei

Burkholderia pseudomallei is the causative agent of melioidosis, a disease being increasingly recognized as an important cause of morbidity and mortality in many regions of the world. Several features of melioidosis suggest that B. pseudomallei is a facultative intracellular pathogen. This study was designed to assess the ability of B. pseudomallei to invade and survive in eukaryotic cells. We have shown that B. pseudomallei has the capacity to invade cultured cell lines, including HeLa, CHO, A549, and Vero cells. We have demonstrated intracellular survival of B. pseudomallei in professional phagocytic cells, including rat alveolar macrophages. B pseudomallei was localized inside vacuoles in human monocyte-like U937 cells, a histiocytic lymphoma cell line with phagocytic properties. Additionally, electron microscopic visualization of B. pseudomallei-infected HeLa cells and polymorphonuclear leukocytes confirmed the presence of intracellular bacteria within membrane-bound vacuoles. B. pseudomallei was found to be resistant to the cationic peptide protamine and to purified human defensin HNP-1.

Neutrophil-mediated suppression of virus replication after herpes simplex virus type 1 infection of the murine cornea

Herpes simplex virus type 1 (HSV-1) infection of the murine cornea induces the rapid infiltration of neutrophils. We investigated whether these cells could influence virus replication. BALB/c mice treated with monoclonal antibody (MAb) RB6-8C5 experienced a profound depletion of neutrophils in the bloodstream, spleen, and cornea. In these animals, virus titers in the eye were significantly higher than those in the immunoglobulin G-treated controls at 3 days postinfection. By day 9, virus was no longer detectable in the controls, whereas titers of 10(3) to 10(6) PFU were still present in the neutrophil-depleted hosts. Furthermore, virus spread more readily to the skin and brains of MAb RB6-8C5-treated animals, rendering them significantly more susceptible to HSV-1-induced blepharitis and encephalitis. Only 25% of the treated animals survived, whereas all of the controls lived. Although MAb RB6-8C5 treatment did not alter the CD4+ T-cell, B-cell, natural killer cell, or macrophage populations, the CD8+ T-cell population was partially reduced. Therefore, the experiments were repeated in severe combined immunodeficiency mice, which lack CD8+ T cells. Again virus growth was found to be significantly elevated in the eyes, trigeminal ganglia, and brains of the MAb RB6-8C5-treated hosts. These results strongly indicate that in both immunocompetent and immunodeficient mice, neutrophils play a significant role in helping to control the replication and spread of HSV-1 after corneal infection.

Some biochemical responses of buffalo PMN cells to various stimuli

In view of great species differences in biology of polymorphonuclear cells, and non-availability of basic data on buffalo PMN cells for assessing their functional activity, the present work on the immuno-defence system involving protein synthesis and O2- production was undertaken to highlight the immunomodulatory role of thyroxine. Digitonin, LPS and Con-A activation generated superoxide, which was monitored by NBT reduction. The study suggested that concanvalin A (Con-A) and T4 were able to synergetically increase the production of superoxide and H2O2. The likely involvement of thyroxine in activation was studied by [125I]thyroxine incorporation, which was significantly increased due to activation. In contrast, aflatoxin B1 together with Con-A caused a significant decrease (P < 0.05) in incorporation of [125I]T4. Optimum time dependence in [14C]leucine incorporation by buffalo PMN cells was found to be 30 min and the factors like T4 (7.7 ng/ml) and glutathione (400 micrograms/ml) significantly enhanced the incorporation. In contrast, antiinflammatory agent, indomethacin (40 micrograms/ml) inhibited protein synthesis in PMN cells; while puramycin also significantly lowered the [14C]leucine incorporation. Total [14C]leucine incorporation in acid extractable cationic proteins and peptides, known for their antibacterial properties was found to be 30-40% when separated on AU-PAGE. The studies revealed the in vitro immunomodulatory role of T4 in O2-, H2O2 production and cationic protein synthesis by the activated PMN cells of buffalos.

Inheritance of unequal numbers of the genes encoding the human neutrophil defensins HP-1 and HP-3

It is unclear whether the six known human defensin peptides are all encoded by separate genes or whether some of them are allelic. Three of the peptides, HP-1, HP-2, and HP-3, differ by only one amino acid, and it is thought that HP-2 may represent a proteolytic product of HP-1 and/or HP-3. To help determine the relationship of these three proteins, we isolated a nearly full-length cDNA encoding HP-1 with a sequence very similar to, but different from, the previously isolated HP-1 and -3 cDNAs. Gene copy number experiments established that there were at least two but fewer than five defensin genes with a high level of similarity to the HP-1 cDNA (HP-1/3-like). Three genomic clones were isolated that contained two different configurations of the HP-1/3-like sequences. Sequencing established that one encoded the HP-1 peptide, whereas the other encoded HP-3. Analysis of DNAs obtained from 18 unrelated individuals by Southern blot analysis revealed the expected fragments as well as additional fragments that were not present in the genomic clones. This suggested the possibility of alleles; however, when DNAs from families were examined, these fragments did not segregate in an obvious Mendelian fashion. The HP-1/3-like defensin genes are on human chromosome 8. Surprisingly, somatic cell hybrid mapping showed that the number of HP-1/3-like genes on isolated copies of chromosome 8 was variable. We conclude that individuals can inherit versions of chromosome 8 harboring either two or three copies of the genes that encode the HP-1, HP-2, and/or HP-3 peptides.

Neutrophilic defensins penetrate the blood-brain barrier

Defensins are small, cationic, cyclic peptides that are abundantly stored in granules of neutrophils. Defensins non-specifically interact with membranes by forming weakly ion-selective pores. Here we demonstrate immunolocalization of defensin-secreting cells in human brain. Defensins, secreted by activated granulocytes, apparently are not prevented by the blood-brain barrier (BBB) from diffusing across cerebral endothelium to penetrate the neuropil for a considerable distance from the granulocyte. This is in contrast to other neutrophil proteins like the granule-associated enzyme elastase or the cytosolic protein MRP-14, which are strictly localized to the cytoplasm or granules of neutrophils. Thus, defensins, known chemokinetic and chemotactic molecules, display a unique distribution at BBB sites.

Dynamic reorganization of the alkaline phosphatase-containing compartment during chemotactic peptide stimulation of human neutrophils imaged by backscattered electrons

Scanning electron microscopy (EM) and cytochemical techniques were used to examine the alkaline phosphatase-containing compartment in human neutrophils after stimulation with nanomolar concentrations of N-formylmethionyl-leucyl-phenylalanine (10(-8) M fMLP). Alkaline phosphatase (AlkPase) activity was demonstrated with a lead-based metal capture cytochemical method. The reaction product was visualized with the backscattered electron imaging mode of scanning EM, and analyzed by electron probe X-ray microanalysis. Alkaline phosphatase activity was detected only in fMLP-stimulated neutrophils; unstimulated neutrophils displayed no activity. Stimulation of human neutrophils with 10(-8) M fMLP induced a time-dependent intracellular redistribution of irregular round or tubular granules containing alkaline phosphatase activity, as seen by backscattering. The intracellular redistribution of alkaline phosphatase activity was accompanied by increased cytochemical activity on the cell surface. The reaction product was localized preferentially on ridges and folds of polar neutrophils. Reorganization of the AlkPase-containing compartment correlated with changes induced by fMLP in cell shape, ie, membrane ruffling and front-tail polarity, as observed with the secondary electron image mode of scanning EM. These findings demonstrate the intracellular reorganization, increase, and asymmetric distribution of alkaline phosphatase activity on the plasma membrane of human neutrophils after stimulation by chemotactic peptides.

Morphology of defensin-treated Staphylococcus aureus

Defensins are a family of broad-spectrum antimicrobial peptides found abundantly in the cytoplasmic granules of mammalian neutrophils and Paneth cells of the small intestine. Defensins are known to form ion channels on the membranes of target cells. These channel formations and the cytotoxicity of defensins are intimately linked. We showed the morphological effects of defensins on the cytoplasmic membranes of Staphylococcus aureus by transmission electron microscopy. S. aureus exposed to defensins developed characteristic mesosome-like structures but did not show remarkable changes in cell walls. Defensins induced such structural changes not only at high concentration but also at low concentrations that were not bactericidal. We also showed that increasing the concentration of NaCl in the reaction mixture completely inhibited the occurrence of membranous changes of target cells exposed to defensins. These findings are, to our knowledge, the first report of morphological changes in gram-positive bacteria treated with defensins. Our results indicate that the first effect of defensins in S. aureus is to damage cytoplasmic membranes directly; they also support previous reports that the cell membrane is the principal target of defensins.

Reactive oxygen species in the killing of Pseudomonas aeruginosa by human leukocytes

Pseudomonas aeruginosa (PA) infects hosts with compromised host defenses. An important defense mechanism is the generation of reactive oxygen species (ROS) by white blood cells (WBCs). What roles do ROS play in host defense against PA? Human WBCs killed PA in vitro, and they generated a respiratory burst as measured by the production of H2O2. ROS efficiently killed PA; in acellular assays, less than 10 mM of H2O2 or OCl- eliminated all bacteria in 90 min. However, WBCs with suppressed production of ROS (caused by hypoxia) killed PA normally. In addition, none of the antioxidants vitamin C, N-acetylcysteine, superoxide dismutase, or catalase affected PA killing by WBCs. Thus, PA stimulates WBCs to produce ROS, which can kill the bacteria, but disturbances of WBC ROS production do not interfere with the killing of PA. WBCs have robust, redundant mechanisms for PA elimination.

Cutaneous defenses against dermatophytes and yeasts

Predispositions to the superficial mycoses include warmth and moisture, natural or iatrogenic immunosuppression, and perhaps some degree of inherited susceptibility. Some of these infections elicit a greater inflammatory response than others, and the noninflammatory ones are generally more chronic. The immune system is involved in the defense against these infections, and cell-mediated immunity appears to be particularly important. The mechanisms involved in generating immunologic reactions in the skin are complex, with epidermal Langerhans cells, other dendritic cells, lymphocytes, microvascular endothelial cells, and the keratinocytes themselves all participating in one way or another. A variety of defects in the immunologic response to the superficial mycoses have been described. In some cases the defect may be preexistent, whereas in others the infection itself may interfere with protective cell-mediated immune responses against the organisms. A number of different mechanisms may underlie these immunologic defects and lead to the development of chronic superficial fungal infection in individual patients. Although the immunologic defects appear to be involved in the chronicity of certain types of cutaneous fungal infections, treatment of these defects remains experimental at the present time.

Defensins

Defensins are a family of small cationic, antibiotic peptides that contain six cysteines in disulfide linkage. The peptides are abundant in phagocytes and small intestinal mucosa of humans and other mammals and in the hemolymph of insects. They contribute to host defense against microbes and may participate in tissue inflammation and endocrine regulation during infection. Bioengineered defensins are potentially useful as prophylactic and therapeutic agents in infections.

Effect of a chemical or proteolytic modification on the biological activity of guinea-pig cationic peptide

Guinea-pig neutrophil cationic peptides (GNCPs) are single polypeptides containing 31 amino acid residues and three intramolecular disulfide bonds, which show both antibacterial and histamine-releasing activities. Reduction and alkylation of the disulfide bonds of GNCP did not reduce both biological activities. When pyridylethylated GNCP was digested with trypsin, the biological activities were almost lost, whereas the chymotryptic digest retained the biological activities. Chymotrypsin digested fragments were purified by RP-HPLC, and three active peptide fragments containing two Arg residues at the N-terminal sequence were isolated. When the biological activities were examined using synthetic peptides containing various numbers of Arg residue at the N-terminus, the omission of the Arg residues was found to reduce remarkably the antibacterial and histamine-releasing activities. Together these observations indicate that the primary structures containing Arg residues at the N-terminus but not the intramolecular disulfide cross-linking are important for the expression of the biological activities of GNCP.

Antibacterial proteins from porcine polymorphonuclear neutrophils

Antibacterial peptides were purified from porcine neutrophil granules collected from healthy pigs. Granule proteins, extracted with 0.2 mol/L sodium acetate were subjected to ion-exchange chromatography and five peaks (designated A to E) were detected. Individual porcine neutrophil granule proteins were shown to inhibit the growth of target organisms Escherichia coli and Staphylococcus aureus. The antimicrobial activity was shown to be concentration and time dependent. Peak D showed strong antimicrobial activity against S. aureus and peak C (with a greater number of eluted proteins) was shown to be active against both S. aureus and E. coli. One of the peptides was purified further by reverse-phase HPLC from peak fraction C. The MW of this peptide was approximately 5500 Da as determined by SDS-PAGE and mass spectral analysis and was active against both E. coli and S. aureus in vitro sustaining a > 90% decrease, respectively, in CFU after a 2 h exposure with 50 micrograms of this peptide. Amino acid analysis showed the peptide was rich in aspartate/aspartic acid, glutamine/glutamic acid, proline, arginine and threonine. The antimicrobial activity of this peptide and other novel proteins in porcine neutrophilic granules demonstrates the probable role of these proteins and peptides in host defence of porcine neutrophils against bacterial infection.

Identification of CG-1, a natural peptide antibiotic derived from human neutrophil cathepsin G

Cathepsin G is a neutral serine protease of the granzyme B family which is found in human PMN, cells known to be important in the defense of the periodontium against periodontal bacteria. We propose that cathepsin G serves as a "pro-antibiotic" containing peptide domains which express selective antibiotic properties. In this study, we used HPLC to separate the low-molecular-weight peptides derived from the ultrafiltrate of a granule extract from unstimulated PMN. One of the peptides exhibited intense bactericidal activity as determined by radial diffusion overlay assay (against Escherichia coli ML-35P), an amino-terminal sequence "RVSSFLPWIR...", and a 3.1-kDa molecular mass determined by electrospray ionization-mass spectrometry. The sequence and mass are consistent with the C-terminus of cathepsin G deduced by cDNA analysis. These findings support the hypothesis that antibiotic peptides derived from cathepsin G occur naturally in human PMN. Since this is the first naturally occurring antibiotic peptide derived from cathepsin G, we designate it "CG-1".

Bacterial stimulators of macrophages

Our current understanding of the interaction between bacteria and macrophages, cells of the immune system that play a major role in the defense against infection, is summarized. Cell-surface structures of Gram-negative and Gram-positive bacteria that account for these interactions are described in detail. Besides surface structures, soluble bacterial molecules, toxins that are derived from pathogenic bacteria, are also shown to modulate macrophage functions. In order to affect macrophage functions, bacterial surface structures have to be recognized by the macrophage and toxins have to be taken up. Subsequently, signal transduction mechanisms are initiated that enable the macrophage to respond to the invading bacteria. To destroy bacteria, macrophages employ many strategies, among which antigen processing and presentation to T cells, phagocytosis, chemotaxis, and different bactericidal mechanisms are considered to be the main weapons.

Identification of defensin binding to C1 complement

In human serum we found strong defensin binding to the complexes of activated C1 complement (C1) and C1 inhibitor (C1i). Purified C1q, activated C1 tetramer (r2s2) and C1i did not bind defensin. When r2s2 was dissociated by EDTA, only the activated C1s (C1s) bound defensin. Binding of defensins to C1 complement represents a newly recognized bridge between the complement- and phagocyte-mediated host defenses, and a potential mechanism for protecting infected tissue from cytotoxic injury by defensin.

Killing of Giardia lamblia by cryptdins and cationic neutrophil peptides

Antimicrobial polypeptides such as the defensins kill a wide range of organisms, including bacteria, fungi, viruses, and tumor cells. Because of the recent finding that intestinal defensins, also known as cryptdins, are synthesized by the Paneth cells of the small intestinal crypts and released into the lumen, we asked whether defensins and other small cationic antimicrobial peptides could kill the trophozoites of Giardia lamblia, which colonize the small intestine. Four mouse cryptdins, two neutrophil defensins (HNP-1 [human] and NP-2 [rabbit]), and the unique tryptophan-rich bovine neutrophil polypeptide indolicidin each had some antigiardial activity against trophozoites in vitro. Cryptdins 2 and 3, indolicidin, and NP-2 each reduced viability by more than 3 log units in 2 h, and killing by all peptides was dose and time dependent. Exposure of trophozoites to peptides frequently resulted in cell aggregation and dramatic changes in morphology. The mechanism of binding and lysis appeared to involve charge interactions, since 150 mM NaCl as well as millimolar levels of Ca2+ and Mg2+ inhibited killing by most of the peptides. Our studies show that G. lamblia is sensitive to defensins and indolicidin and suggest that these small polypeptides could play a role in nonimmune host defenses.

In vitro activity of naturally occurring peptides (defensins) against Listeria monocytogenes

Autoclaved distilled water samples were inoculated with L. monocytogenes strain V7 and strain VPH-1, and incubated aerobically, at 30 C for 48 hours. Each strain was tested individually, and growth curves were determined at 1, 2, 3, 4, 5, 21, 24, and 48 hours. The growth or survival of L. monocytogenes was similar for both strains, with survivors at 24 hour-incubation. The microbicidal activity of one synthetic cationic peptide (NP-2) was examined against L. monocytogenes strain V7, in a water system. Antibacterial activity of NP-2 (1, 5, and 10 g/ml) was best expressed at 60 minute-incubation, with 10 g/ml of peptide, at 30 C.

Role of cationic proteins in the airway. Hyperresponsiveness due to airway inflammation

Major basic protein (MBP) is a highly cationic protein found in the granules of eosinophils. It has been postulated that MBP may participate in the pathogenesis of airway hyperresponsiveness exhibited by asthmatic patients. Accordingly, we have employed a rat system to investigate the effect of human MBP instillation on airway responsiveness and the possible role of cationic charge in the determination of this effect. Major basic protein caused a significant increase in airway responsiveness to inhaled methacholine. Two polycations, poly-L-arginine and poly-L-lysine, also increased airway responsiveness to inhaled methacholine. Moreover, two other very different cationic proteins, platelet factor 4 (PF4) and cathepsin G were also capable of inducing airway hyperresponsiveness. These effects were dependent on their positive charge, since the charge--and, hence the effect--of these proteins was neutralized with low molecular weight heparin. In addition, other polyanions, such as low molecular weight heparin, albumin, or dextran sulfate, were also effective. We investigated whether two synthetic cationic proteins, poly-L-arginine and poly-L-lysine, could modify epithelial-dependent responses using a perfused guinea pig tracheal tube preparation. With an intact epithelium, methacholine was some 150 times less potent when applied intraluminally than when applied extraluminally. Perfusion of the luminal surface with cationic proteins increased the potency of intraluminally applied methacholine without modifying the responses to extraluminally applied methacholine. Cationic proteins also attenuated the relaxant effects of intraluminally applied KCl. These effects occurred in the absence of any overt epithelial cell damage. Our data demonstrates that cationic proteins can modify epithelial-dependent responses in the airways.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytokines in the treatment of fungal infections

The incidence of invasive fungal infections in the immunocompromized host has increased during the past decade. Even the recently developed antifungal drugs are unable to cure these infections in patients with severely impaired host defense mechanisms. Cytokines have great potential to augment host resistance and as adjunctive therapy of invasive mycoses. We discuss the mechanisms of host defense against invasive candidiasis, aspergillosis, and cryptococcosis, and review the use of cytokines and growth factors in this setting. Interleukin-1 has been shown effective in an animal model of disseminated candidiasis, even during severe granulocytopenia. Interferon-gamma has been very effective as a modulator of resistance against a variety of fungal infections in vitro. The effect of interferon-gamma against disseminated candidiasis has been demonstrated in a mouse model. Activation of neutrophils is the main mechanism by which interferon-gamma enhances the elimination of Candida, and consequently the agent is not effective in severely granulocytopenic animals. Data on the role of colony-stimulating factors against fungal pathogens are accumulating, and trials with these agents for hematologic patients with invasive fungal infections are now being performed.

Localization of human neutrophil peptide (HNP) and its messenger RNA in neutrophil series

Human neutrophil peptides (HNPs) 1,2 and 3, also called defensins, have high antimicrobial activity and are cytotoxic to both normal and transformed human cells. The localization of HNPs 1-3 and their mRNAs in cells of normal human bone marrow and peripheral blood was investigated. Immunoreactivity for HNPs 1-3 appeared in the promyelocyte stage and increased with the maturation of the neutrophil series. HNPs 1-3 were absent from such mononuclear phagocyte systems as peripheral monocytes, alveolar macrophages, and Kupffer cells in the liver. HNP 1-3 mRNAs were detected in bone marrow cells by Northern blot analysis and in peripheral leukocytes by the reverse transcription-polymerase chain reaction (RT-PCR). HNPs 1-3 are restricted to cells of neutrophil lineage and seem to function as microbicidal agents in the neutrophil-mediated defense system.

Lactoferricin, a new antimicrobial peptide

Lactoferricin B (LF-B) is a peptide derived from acid-pepsin digestion of bovine lactoferrin, which has antimicrobial properties. In order to assess the antimicrobial spectrum of LF-B and its possible in vivo uses, the minimum inhibitory and microbicidal concentrations of pure lactoferricin B were determined for a range of bacterial species and under varying conditions of growth including growth phase and size of the inoculum, pH and ionic strength of the medium. Lactoferricin B was bactericidal against a wide range of bacteria and Candida albicans. Proteus spp., Pseudomonas cepacia and Serratia spp. were resistant. The bactericidal activity of LF-B was inhibited by increasing ionic strength and bacterial inoculum and at acid pH. The activity of lactoferricin B was completely inhibited by the addition of 5% whole cow's milk and was reduced in the presence of increasing concentrations of mucin. These results indicate the potential of LF-B to reduce the numbers of organisms in a simple medium, but raise doubts about its role in vivo because of its sensitivity to changes in physical variables. It may be that lactoferricin exerts a transient antimicrobial effect at mucosal surfaces.

Comparison of the sensitivities of Salmonella typhimurium oxyR and katG mutants to killing by human neutrophils

The respiratory burst of neutrophils is believed to kill bacteria by generating oxidative species, such as superoxide anion, hydrogen peroxide, and oxidized halogen species. The oxyR gene of Salmonella typhimurium controls a regulon induced by oxidative stress, such as exposure to hydrogen peroxide. Some researchers have suggested that oxyR may play a key role in bacterial survival following phagocytosis. We have tested this possibility by comparing the survival, following exposure to human neutrophils, of isogenic strains bearing different oxyR alleles. Neither inactivation of the oxyR gene nor constitutive overexpression of the oxyR-regulated proteins (oxyR1 allele) greatly alters bacterial resistance to neutrophils. The katG gene, encoding the oxyR-regulated enzyme hydroperoxidase I, was also without effect on survival following exposure to neutrophils. We conclude that the oxyR response does not play a significant role in the resistance of S. typhimurium to phagocytic killing in vitro.

Inhibition of intracellular Histoplasma capsulatum replication by murine macrophages that produce human defensin

Although purified defensins are effective microbicides in vitro, their operation within intact phagocytes has not been established. To address this question, we inserted cDNA encoding human defensin HNP-1 into a pBabe/neo retroviral vector and transduced it into RAW 264.7 cells, a murine macrophage line that lacks endogenous defensins. We isolated five independent clones of HNP-1-transduced cells, all of which secreted prodefensin and contained small amounts of fully processed HNP-1. The two clones that produced the largest amounts of defensin (clones 5 and 14), together with wild-type RAW cells and pBabe/neo-transduced RAW cells (control), were used for the present study. All cells were grown in Dulbecco's modified Eagle's medium-F12 medium that contained 10% heat-inactivated fetal bovine serum and gentamicin. The medium used for the transduced cells contained aminoglycoside G418 in lieu of gentamicin. Both wild-type and transduced cells were placed in antibiotic-free medium 96 h prior to challenge with a yeast-phase strain of Histoplasma capsulatum. Phagocytosis of yeast cells was allowed to proceed for 90 min and was followed by washing and further incubation for 18.5 h. Whereas the phagocytic index did not differ significantly among the four cell populations under study, the mean level of intracellular growth of H. capsulatum in the defensin-transduced RAW cells was significantly lower than those observed for any other cell types (P < 0.05). These findings constitute the first instance of xenogeneic expression of an antimicrobial peptide by phagocytes and suggest that macrophages can be armed with defensins to enhance their ability to restrict certain intracellular pathogens.

Lidocaine hydrochloride and acetylsalicylate kill bacteria by disrupting the bacterial membrane potential in different ways

Lidocaine hydrochloride (LH), a local anesthetic, and acetylsalicylate (AcSAL), show antibacterial activity for both gram-negative and gram-positive bacteria. Kinetic studies indicated that antibacterial activity of LH was different from that of AcSAL. A subinhibitory concentration of LH and AcSAL enhanced the sensitivity of Escherichia coli, Salmonella typhimurium, and Pseudomonas aeruginosa to novobiocin and nalidixic acid. The synergistic effect of AcSAL with novobiocin and nalidixic acid was higher than that of LH. The effect of both drugs on the membrane potential of inner membrane was also studied using inverted membrane vesicles of bacteria. Both LH and AcSAL depolarized the membrane potential after the vesicles were energized with nicotinamide adenine dinucleotide. However, unlike AcSAL, pre-treatment of vesicles with LH had no effect on the generation of membrane potential. These results suggest that depolarization of the cytoplasmic membrane, preceded by the permeabilization of the outer membrane for gram-negative bacteria, is associated with antibacterial activity of LH and AcSAL. The difference in actions of LH and AcSAL was discussed.

The in vitro effect of human polymorphonuclear leukocyte azurophil granule components on natural killer cell cytotoxicity

We previously demonstrated that human polymorphonuclear leukocyte (PMN) secretions are capable of activating and inhibiting natural killer cell (NK) cytotoxicity depending on the eliciting PMN stimulus. Serum-opsonized zymosan induced PMN to secrete substances that enhanced NK activity in vitro. Serum-opsonized zymosan stimulates the release of PMN azurophil granules, which contain both human neutrophil peptides (HNPs) and neutral serine proteases (NSPs). When HNPs and NSPs were tested for their ability to activate NK cells in peripheral blood lymphocytes, all but cathepsin G consistently enhanced cytotoxicity above control values. HNP-induced cytotoxicity was significantly enhanced within 12 h, peaking at approximately 24 h. Of the HNPs, HNP-1 was the most potent activator, enhancing NK activity at 1.25 micrograms/ml. Interleukin-2 and interferon-gamma were not involved in this activational process, as antibodies to interleukin-2 and interferon-gamma did not block activation by HNPs and NSPs, and interleukin-2 receptor expression was unaltered after 24 h of incubation. Enzymatically inactivated elastase and cathepsin G produced equivalent activational effects to their active counterparts. Antisera to elastase and cathepsin G decreased but did not eliminate NK activation over untreated peripheral blood lymphocytes. These data suggest that certain PMN azurophil granule components, including HNPs and NSPs directly increase the cytotoxic activity of NK cells.

Bactericidal action of tachyplesin I against oral streptococci

Tachyplesin I, a polycationic antimicrobial peptide isolated from hemocytes of horseshoe crabs, kills bacteria by disrupting the membrane potential of the cytoplasmic membrane. The present study shows that, among 36 oral streptococcal strains, 12 of 21 Streptococcus sanguis, 3 Streptococcus mutans, 9 Streptococcus salivarius and 3 Streptococcus milleri strains were susceptible to tachyplesin I, whereas 9 S. sanguis strains were resistant. Interestingly, these resistant strains include the clinical isolates from both Kawasaki disease and Behçet patients. According to the time-kill study, tachyplesin I inhibited irreversibly the growth of S. sanguis, S. mutans and S. salivarius strains within 20 min and an S. milleri strain within 80 min. Although it has been suggested that Escherichia coli cultured in rich media were more susceptible to tachyplesin I, the present results show that only 3 S. milleri strains were more sensitized to tachyplesin I in a glucose-supplemented medium, and other tested strains were not. Similarly, only 4 strains were more resistant to tachyplesin I in saline than these were in a rich medium.

Bactenecin, a leukocytic antimicrobial peptide, is cytotoxic to neuronal and glial cells

Small antimicrobial peptides are abundantly produced by leukocytes. These peptides are active against a broad range of pathogens, notably bacteria, fungi, and enveloped viruses, but hardly anything is known about their physiological and pathophysiological relevance. We observed that bactenecin, a dodecapeptide, is strongly cytotoxic to rat embryonic neurons, fetal rat astrocytes and human glioblastoma cells. This neurotoxicity is unique to bactenecin, as a panel of antibacterial peptides from vertebrates and invertebrates, like defensins, corticostatin, indolicidin, cecropin P1, tachyplesin I, the magainins, or apidaecins did not impair neuronal viability.

Fungicidal properties of defensin NP-1 and activity against Cryptococcus neoformans in vitro

Defensin NP-1, derived from the neutrophils of rabbits, was tested for its fungistatic and fungicidal activity against strains of Cryptococcus neoformans. The MICs for the encapsulated strains tested ranged from 3.75 to 15.0 micrograms of NP-1 per ml. The minimum fungicidal concentrations for these strains were similar to the MICs. An acapsular strain, however, had a lower MIC of 0.93 and minimum fungicidal concentration of 1.88 micrograms/ml. NP-1 demonstrated time-dependent and concentration-dependent killing of C. neoformans. Killing occurred rapidly in the first 20 min of exposure to NP-1 and was maximum at 90 to 120 min. Killing of C. neoformans by NP-1 was concentration dependent with 31% +/- 9% survival at 25 micrograms/ml, 13% +/- 4% survival at 50 micrograms/ml, 9% +/- 5% survival at 75 micrograms/ml, and 5% +/- 3% survival at 100 micrograms/ml. NP-1's fungicidal effect on C. neoformans was also inoculum dependent, with increased activity observed at 10(4) versus 10(5) or 10(6) cells per ml. In addition, stationary-phase C. neoformans was less susceptible to NP-1 killing than yeast cells in the logarithmic phase. Subinhibitory concentrations of both NP-1 (0.25 x MIC) and fluconazole (0.25 x MIC) acted synergistically in inhibiting growth of C. neoformans. Similar combinations of NP-1 and amphotericin B, however, did not yield synergy.

Human neutrophil granules and secretory vesicles

The traditional classification of neutrophil granules as peroxidase-positive (azurophil, or primary) and peroxidase-negative (specific or secondary) has proven to be too simple to explain the differential exocytosis of granule proteins and incorporation of granule membrane into the plasma membrane which is an important aspect of neutrophil activation. Combined subcellular fractionation and immunoelectron microscopy has revealed heterogeneity among both peroxidase-positive and peroxidase-negative granules with regard to their content, mobilization and time of formation. Peroxidase-negative granules may be classified according to their content of lactoferrin and gelatinase: 15% of peroxidase-negative granules contain lactoferrin, but no gelatinase. 60% contain both lactoferrin and gelatinase. The term specific or secondary granule should be reserved for these two subsets. In addition, 25% of peroxidase-negative granules contain gelatinase but no lactoferrin. These should be termed gelatinase granules or tertiary granules. Gelatinase granules are formed later than specific granules and mobilized more readily. In addition, a distinct, highly mobilizable intracellular compartment, the secretory vesicle, has now been recognized as an important store of surface membrane-bound receptors. This compartment is formed in band cells and segmented cells by endocytosis. This heterogeneity among the neutrophil granules is of functional significance, and may also be reflected in the dysmaturation which is an important feature of myeloproliferative and myelodysplastic disorders.

Leukocytic antimicrobial peptides kill autoimmune T cells

Small antimicrobial peptides are abundantly produced by leukocytes. These peptides are active against a broad range of pathogens, notably bacteria, fungi and enveloped viruses, but hardly anything is known about their physiological and pathophysiological relevance. We observed that indolicidin, and to a lesser extent bactenecin, are strongly cytotoxic to rat and human T lymphocytes, while a variety of other cell lines are not affected by these endogenous antibiotics. The defensins HNP-1, HNP-2 and HNP-3, the structurally related but not bactericidal corticostatin, or cecropin P1 did not affect T lymphocyte viability or proliferation. Thus, indolicidin and bactenecin might function as local regulators inhibiting clonal expansion of T lymphocytes during ongoing immune responses. As immunosuppressive agents in the treatment of autoimmune disease, these peptides appear to be of limited potential, as systemic activity of such peptides is low, and we did not observe significant immunosuppressive effects in experimental autoimmune neuritis or encephalomyelitis.

Defensins promote fusion and lysis of negatively charged membranes

Defensins, a family of cationic peptides isolated from mammalian granulocytes and believed to permeabilize membranes, were tested for their ability to cause fusion and lysis of liposomes. Unlike alpha-helical peptides whose lytic effects have been extensively studied, the defensins consist primarily of beta-sheet. Defensins fuse and lyse negatively charged liposomes but display reduced activity with neutral liposomes. These and other experiments suggest that fusion and lysis is mediated primarily by electrostatic forces and to a lesser extent, by hydrophobic interactions. Circular dichroism and fluorescence spectroscopy of native defensins indicate that the amphiphilic beta-sheet structure is maintained throughout the fusion process. Taken together, these results support the idea that protein-mediated membrane fusion depends not only on hydrophobic and electrostatic forces but also on the spatial arrangement of the amino acid residues to form a three-dimensional amphiphilic structure, which promotes the efficient mixing of the lipids between membranes. A molecular model for membrane fusion by defensins is presented, which takes into account the contributions of electrostatic forces, hydrophobic interactions, and structural amphiphilicity.

Protegrins: leukocyte antimicrobial peptides that combine features of corticostatic defensins and tachyplesins

Porcine leukocytes contained three homologous peptides, PG-1, 2 and 3, that manifested potent microbicidal activity against Escherichia coli, Listeria monocytogenes and Candida albicans in vitro. The peptides ('protegrins') were composed of 16 (PG-2) or 18 amino acid residues, and, like tachyplesins (broad-spectrum antibiotic peptides of horseshoe crab hemocytes), they contained two intramolecular cystine disulfide bonds. Considerably smaller than defensins, protegrins nevertheless showed substantial homology to them, especially to the 'corticostatic' rabbit defensin, NP-3a. The relatively simple structure of protegrins should provide useful prototypes for constructing congeners with selectively enhanced host defense activities.

Selective inhibition of microbial serine proteases by eNAP-2, an antimicrobial peptide from equine neutrophils

Equine neutrophil antimicrobial peptide 2 (eNAP-2), a recently described antimicrobial peptide isolated from equine neutrophils, was found to selectively inactivate microbial serine proteases (subtilisin A and proteinase K) without inhibiting mammalian serine proteases (human neutrophil elastase, human cathepsin G, and bovine pancreatic trypsin). Although the primary structure of eNAP-2 resembled that of several known antiproteases that belong to the 4-disulfide core peptide family, this pattern of selectivity is unique. eNAP-2 formed a noncovalent complex with native subtilisin A or proteinase K but did not associate with these enzymes if they had been treated with phenylmethylsulfonyl fluoride, a serine protease inhibitor. The eNAP-2-microbial protease complex was disrupted by boiling or by exposure to low pH. We suggest that eNAP-2 exerted selective antiproteinase activity by binding tightly but noncovalently to the active site of subtilisin A or proteinase K. Since microbial exoproteases may act as virulence factors, the combined antimicrobial and antiprotease activities of eNAP-2 could allow it to play an important role in neutrophil-mediated antimicrobial defenses.

Defensins are mitogenic for epithelial cells and fibroblasts

Defensins are a family of structurally homologous peptides contained within phagocytic cells. Although these peptides are best known for their broad spectrum antimicrobial properties, they also inhibit ACTH (corticotropin) stimulated corticosterone production, chemoattract monocytes, and lyse mammalian cells. We now report that these peptides are potent mitogens in vitro in the same concentration range that they display potent antimicrobial activity in vitro. These concentrations are in the same range as those expected to be present in vivo during the wound healing process. All defensins tested were stimulatory for epithelial cells and fibroblasts and acted synergistically with insulin. These are the first data to disclose the strong growth-promoting effects of this unique family of peptides and point to another basic mechanism whereby the macrophage and neutrophil may participate in a variety of trophic, physiologic, and pathologic processes.

Evidence for homology of buffalo and goat granular cationic peptides

Due to lack of studies on PMN granular cationic proteins to assess immunostatus of buffaloes, the peripheral PMN leukocytes were subjected to homogenization by sonication and centrifugation cycles in order to obtain pure pellet of granules. Acid extracted granules contained cationic proteins and peptides, which were further separated by exclusion Sephadex G-50 chromatography, the peptides were in the last peak and were found to be active against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. The peptides were conjugated to ovalbumin in order to develop antibodies, which were further tested by Ouchterlony double immunodiffusion and enzyme linked immunosorbent assay. These tests demonstrated the antigenic relationship between buffalo and goats for the PMN cationic peptides as well as the peptide release which was also monitored in activated buffalo PMN leukocytes.

The effect of biotinylation on the antigenic specificity of anti-defensin monoclonal antibodies

We studied the effects of biotinylation on three monoclonal antibodies (Mabs) that were raised against carrier protein conjugates of human defensin HNP-1, and of rabbit defensins NP-2 and NP-5 respectively. Before biotinylation, each Mab specifically bound to its peptide hapten. Biotinylation of these Mabs by the N-hydroxysuccinimide-biotin (NHS-biotin) resulted in crossreactivity of each Mab with the two irrelevant defensin peptides. In contrast, Mab specificity was preserved after biotinylation with biotin hydrazide, which links biotin to the glycan moiety of antibodies. The effects of NHS-biotinylation were in part mimicked by 2,4-dinitrofluorobenzene, another agent that modified primary amine groups of proteins, suggesting that this modification contributed to the change in antibody specificity. When a high degree of antigenic specificity against peptide immunogens is required, biotinylation on the glycan moiety of Mabs may be preferable.