Studies on gonococcus infection. V. Observations on in vitro interactions of gonococci and human neutrophils

Phagocytosis via complement receptor 3 enables microbes to evade killing by neutrophils

CR3 (CD11b/CD18; αmβ2 integrin) is a conserved phagocytic receptor. The active conformation of CR3 binds the iC3b fragment of complement C3 as well as many host and microbial ligands, leading to actin-dependent phagocytosis. There are conflicting reports about how CR3 engagement affects the fate of phagocytosed substrates. Using imaging flow cytometry, we confirmed that binding and internalization of iC3b-opsonized polystyrene beads by primary human neutrophils was CR3-dependent. iC3b-opsonized beads did not stimulate neutrophil reactive oxygen species, and most beads were found in primary granule-negative phagosomes. Similarly, Neisseria gonorrhoeae that does not express phase-variable Opa proteins suppresses neutrophil reactive oxygen species and delays phagolysosome formation. Here, binding and internalization of Opa-deleted (Δopa) N. gonorrhoeae by adherent human neutrophils was inhibited using blocking antibodies against CR3 and by adding neutrophil inhibitory factor, which targets the CD11b I-domain. No detectable C3 was deposited on N. gonorrhoeae in the presence of neutrophils alone. Conversely, overexpressing CD11b in HL-60 promyelocytes enhanced Δopa N. gonorrhoeae phagocytosis, which required the CD11b I-domain. Phagocytosis of N. gonorrhoeae was also inhibited in mouse neutrophils that were CD11b-deficient or treated with anti-CD11b. Phorbol ester treatment upregulated surface CR3 on neutrophils in suspension, enabling CR3-dependent phagocytosis of Δopa N. gonorrhoeae. Neutrophils exposed to Δopa N. gonorrhoeae had limited phosphorylation of Erk1/2, p38, and JNK. Neutrophil phagocytosis of unopsonized Mycobacterium smegmatis, which also resides in immature phagosomes, was CR3-dependent and did not elicit reactive oxygen species. We suggest that CR3-mediated phagocytosis is a silent mode of entry into neutrophils, which is appropriated by diverse pathogens to subvert phagocytic killing.

Human neutrophils ≠ murine neutrophils: Does it matter?

Human and murine neutrophils differ with respect to representation in blood, receptors, nuclear morphology, signaling pathways, granule proteins, NADPH oxidase regulation, magnitude of oxidant and hypochlorous acid production, and their repertoire of secreted molecules. These differences often matter and can undermine extrapolations from murine studies to clinical care, as illustrated by several failed therapeutic interventions based on mouse models. Likewise, coevolution of host and pathogen undercuts fidelity of murine models of neutrophil-predominant human infections. However, murine systems that accurately model the human condition can yield insights into human biology difficult to obtain otherwise. The challenge for investigators who employ murine systems is to distinguish models from pretenders and to know when the mouse provides biologically accurate insights. Testing with human neutrophils observations made in murine systems would provide a safeguard but is not always possible. At a minimum, studies that use exclusively murine neutrophils should have accurate titles supported by data and restrict conclusions to murine neutrophils and not encompass all neutrophils. For now, the integration of evidence from studies of neutrophil biology performed using valid murine models coupled with testing in vitro of human neutrophils combines the best of both approaches to elucidate the mysteries of human neutrophil biology.

Variable Expression of Opa Proteins by Neisseria gonorrhoeae Influences Bacterial Association and Phagocytic Killing by Human Neutrophils

Neisseria gonorrhoeae infection is characterized by local and abundant recruitment of neutrophils. Despite neutrophils' antimicrobial activities, viable N. gonorrhoeae is recovered from infected individuals, leading to the question of how N. gonorrhoeae survives neutrophil attack. One feature impacting N. gonorrhoeae-neutrophil interactions is the phase-variable opacity-associated (Opa) proteins. Most Opa proteins engage human carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) to facilitate bacterial binding and invasion. Neutrophils express two transmembrane CEACAMs, CEACAM1 and the granulocyte-specific CEACAM3. While N. gonorrhoeae isolated from infected individuals is frequently Opa+, expression of OpaD from strain FA1090, which interacts with CEACAMs 1 and 3, is associated with reduced N. gonorrhoeae survival after exposure to human neutrophils. In this study, we hypothesized that the receptor-binding capability of individual Opa proteins impacts bacterial survival in the presence of neutrophils. To test this hypothesis, we introduced opa genes that are constitutively expressed into a derivative of strain FA1090 with all 11 opa genes deleted. The engineered genes encode Opa proteins that bind CEACAM1 and -3, CEACAM1 but not CEACAM3, or neither CEACAM1 nor -3. N. gonorrhoeae expressing CEACAM3-binding Opa proteins survived significantly less well than bacteria expressing other Opa proteins when exposed to primary human neutrophils. The CEACAM3-binding N. gonorrhoeae had significantly greater association with and internalization by neutrophils. However, once internalized, bacteria were similarly killed inside neutrophils, regardless of Opa expression. Furthermore, Opa expression did not significantly impact neutrophil granule mobilization. Our findings indicate that the extent to which Opa proteins mediate nonopsonic binding is the predominant determinant of bacterial survival from neutrophils. IMPORTANCE Neisseria gonorrhoeae, the cause of gonorrhea, is an urgent-threat pathogen due to increasing numbers of infections and increased antibiotic resistance. Many surface components of N. gonorrhoeae are phase variable, including the Opa protein family of adhesins and invasins. While Opa protein expression is selected for in vivo, bacteria expressing some Opa proteins are readily killed by neutrophils, which are recruited to sites of infection. The reason for this discrepancy has remained unresolved. Our work shows that Opa-dependent differences in bacterial survival after exposure to primary human neutrophils correlates with Opa-dependent bacterial binding and phagocytosis. These findings underscore how the ability of N. gonorrhoeae to change Opa expression through phase variation contributes to bacterial resistance to neutrophil clearance.

Defining the roles of human carcinoembryonic antigen-related cellular adhesion molecules during neutrophil responses to Neisseria gonorrhoeae

Symptomatic infection of humans with Neisseria gonorrhoeae is characterized by a neutrophil-rich cervical or urethral exudate, suggesting that neutrophils are important both for the clearance of these bacteria and for the pathogenesis of gonorrhea. Neisseria interacts with neutrophils through ligation of human carcinoembryonic antigen related-cellular adhesion molecules (CEACAMs) by their surface-expressed Opa proteins, resulting in bacterial binding, engulfment, and neutrophil activation. Multiple CEACAMs are expressed by human neutrophils, and yet their coexpression has precluded understanding of the relative contribution of each CEACAM to functional responses of neutrophils during neisserial infection. In this work, we directly address the role of each CEACAM during infection by introducing individual human CEACAMs into a differentiated murine MPRO cell line-derived neutrophil model. Murine neutrophils cannot bind the human-restricted Neisseria; however, we show that introducing any of the Opa-binding CEACAMs of human neutrophils (CEACAM1, CEACAM3, and CEACAM6) allows binding and entry of Neisseria into murine neutrophils. While CEACAM1- and CEACAM6-expressing neutrophils bind more bacteria, neisserial uptake via these two receptors unexpectedly proceeds without appreciable neutrophil activation. In stark contrast, neisserial engulfment via CEACAM3 recapitulates the oxidative burst and intracellular granule release seen during human neutrophil infection. Finally, by coexpressing multiple CEACAMs in our model, we show that the expression of CEACAM1 and CEACAM6 potentiate, rather than hinder, CEACAM3-dependent responses of neutrophils, exposing a cooperative role for this family of proteins during neisserial infection of neutrophils. These observations illustrate a divergence in function of CEACAMs in neutrophils and implicate the human-restricted CEACAM3 in the neutrophil innate response to neisserial infection.

Pathogenic Neisseria hitchhike on the uropod of human neutrophils

Polymorphonuclear neutrophils (PMNs) are important components of the human innate immune system and are rapidly recruited at the site of bacterial infection. Despite the effective phagocytic activity of PMNs, Neisseria gonorrhoeae infections are characterized by high survival within PMNs. We reveal a novel type IV pilus-mediated adherence of pathogenic Neisseria to the uropod (the rear) of polarized PMNs. The direct pilus-uropod interaction was visualized by scanning electron microscopy and total internal reflection fluorescence (TIRF) microscopy. We showed that N. meningitidis adhesion to the PMN uropod depended on both pilus-associated proteins PilC1 and PilC2, while N. gonorrhoeae adhesion did not. Bacterial adhesion elicited accumulation of the complement regulator CD46, but not I-domain-containing integrins, beneath the adherent bacterial microcolony. Electrographs and live-cell imaging of PMNs suggested that bacterial adherence to the uropod is followed by internalization into PMNs via the uropod. We also present data showing that pathogenic Neisseria can hitchhike on PMNs to hide from their phagocytic activity as well as to facilitate the spread of the pathogen through the epithelial cell layer.

Retinoic acid treated HL60 cells express CEACAM1 (CD66a) and phagocytose Neisseria gonorrhoeae

Neisseria gonorrhoeae (gonococci, GC) are phagocytosed by neutrophils through the interaction between opacity proteins (Opa) and the CEA (CD66) family of antigens. In order to study this interaction, we used the human myeloid leukemia HL60 cell line, which differentiates into granulocyte-like cells upon treatment with dimethylsulfoxide (DMSO) or retinoic acid (RA). We found that RA-, but not DMSO- or untreated-HL60 cells, can phagocytose OpaI-expressing gonococci as well as Escherichia coli. The interaction of OpaI E. coli with RA-treated HL60 cells was inhibited by antibodies against CEACAM1. Phagocytosis of OpaI E. coli was found to be a result of the expression of CEACAM1 in RA-treated HL60 cells. Our results indicate that the level of expression of CEACAM1 in HL60 cells can be regulated by treatment with RA in a differentiation-dependent manner, and that this is important for phagocytosis of OpaI-expressing gonococci or E. coli.

Comparative genomics identifies the genetic islands that distinguish Neisseria meningitidis, the agent of cerebrospinal meningitis, from other Neisseria species

Neisseria meningitidis colonizes the nasopharynx and, unlike commensal Neisseria species, is capable of entering the bloodstream, crossing the blood-brain barrier, and invading the meninges. The other pathogenic Neisseria species, Neisseria gonorrhoeae, generally causes an infection which is localized to the genitourinary tract. In order to investigate the genetic basis of this difference in disease profiles, we used a strategy of genomic comparison. We used DNA arrays to compare the genome of N. meningitidis with those of N. gonorrhoeae and Neisseria lactamica, a commensal of the nasopharynx. We thus identified sequences conserved among a representative set of virulent strains which are either specific to N. meningitidis or shared with N. gonorrhoeae but absent from N. lactamica. Though these bacteria express dramatically different pathogenicities, these meningococcal sequences were limited and, in contrast to what has been found in other pathogenic bacterial species, they are not organized in large chromosomal islands.

Role of glycosylation at Ser63 in production of soluble pilin in pathogenic Neisseria

Pilus-mediated adhesion is essential in the pathogenesis of Neisseria meningitidis (MC) and Neisseria gonorrhoeae (GC). Pili are assembled from a protein subunit called pilin. Pilin is a glycoprotein, and pilin antigenic variation has been shown to be responsible for intrastrain variability with respect to the degree of adhesion in both MC and GC. In MC, high-adhesion pilins are responsible for the formation of bundles of pili which bind bacteria and cause them to grow as colonies on infected monolayers. In this work, we selected MC and GC pilin variants responsible for high and low adhesiveness and introduced them into the other species. Our results demonstrated that a given pilin variant expressed an identical phenotype in either GC or MC with respect to bundling and adhesiveness to epithelial cells. However, the production of truncated soluble pilin (S pilin) was consistently more abundant in GC than in MC. In the latter species, the glycosylation of pilin at Ser63 was shown to be required for the production of a truncated monomer of S pilin. In order to determine whether the same was true for GC, we engineered various pilin derivatives with an altered Ser63 glycosylation site. The results of these experiments demonstrated that the production of S pilin in GC was indeed more abundant when pilin was posttranslationally modified at Ser63. However, nonglycosylated variants remained capable of producing large amounts of S pilin. These data demonstrated that for GC, unlike for MC, glycosylation at Ser63 is not required for S-pilin production, suggesting that the mechanisms leading to the production of S pilin in GC and MC are different.

Phenotypic variants of meningococci and their potential in phagocytic interactions: the influence of opacity proteins, pili, PilC and surface sialic acids

In previous studies we have examined the roles of meningococcal surface structures (capsule, lipopolysaccharides, pili and opacity proteins: Opa and Opc) in bacterial interactions with human epithelial, endothelial and mononuclear phagocytic cells. In the current investigations, using defined derivatives of a serogroup A strain C751 and a serogroup B strain MC58, we studied the roles of these structures with human polymorphonuclear phagocytes (PMN). In addition, we examined the potential influence of the pilus-associated protein, PilC, previously known to affect epithelial cell interactions. The data show, that, as with monocytes, opacity proteins affect bacterial interactions with PMN and require surface sialic acids (on capsule and LPS) to be down-modulated in order to function. Also, in contrast to their role in human epithelial and endothelial adherence, neither pili nor PilC expression had any effect on phagocytic cell interactions with respect to induction of chemiluminescence as well as phagocytic killing. Examination of the relative influence of Opa and Opc indicated that Opa proteins are more effective than Opc in PMN interactions whereas the reverse was the case with monocytes. These results suggest that Opa and Opc mediate interactions with phagocytic cells via distinct mechanisms. Observations presented here and reported previously collectively show that the structural requirements of meningococci for interacting with phagocytes, in the absence of opsonins, are present in the phenotype which is often isolated from the nasopharynx (asialylated, piliated, Opa/Opc+) whereas the phenotype prevalent in the blood (sialyted, piliated, Opa/Opc+) retains the ability to adhere to endothelial cells (via pili) but appears to be refractory to interactions with phagocytic cells.

Analysis of the genetic differences between Neisseria meningitidis and Neisseria gonorrhoeae: two closely related bacteria expressing two different pathogenicities

We have investigated genetic differences between the closely related pathogenic Neisseria species, Neisseria meningitidis and Neisseria gonorrhoeae, as a novel approach to the elucidation of the genetic basis for their different pathogenicities. N. meningitidis is a major cause of cerebrospinal meningitis, whereas N. gonorrhoeae is the agent of gonorrhoea. The technique of representational difference analysis was adapted to the search for genes present in the meningococcus but absent from the gonococcus. The libraries achieved are comprehensive and specific in that they contain sequences corresponding to the presently identified meningococcus-specific genes (capsule, frp, rotamase, and opc) but lack genes more or less homologous between the two species, e.g., ppk and pilC1. Of 35 randomly chosen clones specific to N. meningitidis, DNA sequence analysis has confirmed that the large majority have no homology with published neisserial sequences. Mapping of the cloned DNA fragments onto the chromosome of N. meningitidis strain Z2491 has revealed a nonrandom distribution of meningococcus-specific sequences. Most of the genetic differences between the meningococcus and gonococcus appear to be clustered in three distinct regions, one of which (region 1) contains the capsule-related genes. Region 3 was found only in strains of serogroup A, whereas region 2 is present in a variety of meningococci belonging to different serogroups. At a time when bacterial genomes are being sequenced, we believe that this technique is a powerful tool for a rapid and directed analysis of the genetic basis of inter- or intraspecific phenotypic variations.

Novel lipoprotein expressed by Neisseria meningitidis but not by Neisseria gonorrhoeae

The ppk gene, which codes for the enzyme polyphosphate kinase in Neisseria meningitidis strain BNCV, is preceded by an open reading frame coding for a protein with a predicted size of 19.2 kDa with a typical lipoprotein signal sequence of 21 amino acids. The protein has significant homology to the N-terminal portion of an outer membrane protein from Haemophilus somnus (J. Won and R. W. Griffith, Infect. Immun. 61:2813-2821, 1993). Sequencing of the same open reading frame from meningococcus strain M1080 predicted an almost identical protein. Antisera were raised against the lipoprotein, expressed in Escherichia coli as a fusion protein with glutathione S-transferase. The antisera reacted with meningococcal membrane fractions on a Western blot (immunoblot) but did not elicit complement-dependent bactericidal activity. Restriction enzyme digestion demonstrated conservation of this portion of the meningococcal and gonococcal chromosomes. However, antisera raised to the recombinant protein showed that the protein was absent from all strains of gonococcus tested. The sequences of the gene from several strains of Neisseria gonorrhoeae and N. meningitidis were compared and found to be almost identical, except that the coding sequences from all of the gonococcal strains were terminated prematurely as a result of a frameshift mutation. The significance of the remarkable conservation of these gonococcal genes is discussed.

Human neutrophil response to recombinant neisserial Opa proteins

Interactions of human neutrophils with recombinant Escherichia coli expressing gonococcal outer membrane Opa proteins were examined using chemiluminescent and biological assays. Seven opa loci from Neisseria gonorrhoeae MS11 4.8 were expressed as beta-lactamase-Opa fusion proteins that contained all but the mature N-terminal amino acid of the full-length Opa protein fused to three N-terminal amino acids derived from the mature beta-lactamase. The Opa fusion proteins were exported and assembled in the outer membrane of E. coli in a manner similar to that of Opa in N. gonorrhoeae, as evaluated by antibody binding and in situ proteolytic cleavage. All fusion proteins exhibited the characteristic heat-modifiable migration in SDS-polyacrylamide gel electrophoresis that typifies Opa proteins of neisseriae. Opa fusion proteins conferred on E. coli the ability to stimulate a chemiluminescent response from human neutrophils in the absence of antibody or complement. The nature of the response in terms of chemiluminescence, phagocytosis, and killing was in all cases analogous to that seen using N. gonorrhoeae expressing the equivalent Opa protein. Neither E. coli nor gonococci expressing OpaA elicited a response from neutrophils. Use of E. coli expressing Opa fusions should be useful in defining their biological activities and pathogenic roles.

Growth of Neisseria gonorrhoeae in CMP-N-acetylneuraminic acid inhibits nonopsonic (opacity-associated outer membrane protein-mediated) interactions with human neutrophils

Gonococci possessing certain opacity-associated (Opa) outer membrane proteins adhere to and are phagocytosed by human neutrophils in the absence of serum. Recently, it has been shown that serum-sensitive strains of Neisseria gonorrhoeae possessing the appropriate lipooligosaccharide phenotype become serum resistant when grown in the presence of CMP-N-acetylneuraminic acid (CMP-NANA) because of sialylation of their lipooligosaccharide. We investigated whether such sialylation affects nonopsonic (antibody- and complement-independent) interactions of gonococci with human neutrophils in vitro. We grew Opa+ gonococci in the presence of up to 50 micrograms of CMP-NANA per ml, incubated them with neutrophils in vitro, and measured their abilities to adhere to neutrophils, stimulate neutrophil luminol-dependent chemiluminescence (LDCL), and be phagocytically killed by neutrophils. Growth in CMP-NANA dramatically inhibited (in a dose-dependent manner) the ability of Opa+ gonococci to adhere to neutrophils and stimulate neutrophil LDCL. Growth of Opa+ gonococci in 50 micrograms of CMP-NANA per ml appeared to delay, but did not inhibit, their killing by neutrophils. Sialidase treatment of sialylated Opa+ gonococci, i.e., gonococci grown with CMP-NANA, totally restored their abilities to adhere to neutrophils and stimulate neutrophil LDCL. Opa- gonococci grown in the presence of 50 micrograms of CMP-NANA per ml and opsonized with fresh human serum bound to neutrophils only about 30% less efficiently than did Opa- gonococci grown without CMP-NANA and opsonized. The results of our studies show that sialylated Opa+ gonococci have dramatically reduced nonopsonic interactions with neutrophils. Some gonococcal strains may resist killing by human neutrophils in vivo by such a mechanism.

Stimulation of human neutrophil oxidative metabolism by nonopsonized Neisseria gonorrhoeae

Nonopsonized gonococci possessing opacity-associated (Opa; previously PII) outer membrane proteins stimulate neutrophils to undergo a vigorous oxidative response when measured by luminol-dependent chemiluminescence (LDCL). In these studies, we characterized the mechanism of this stimulation. No gonococci that we tested induced measurable release of neutrophil superoxide anion (O2-) or hydrogen peroxide (H2O2) as measured by reduction of cytochrome c or the oxidation of scopoletin, respectively. Neutrophils pretreated with gonococci and then exposed to phorbol myristate acetate, the chemotactic peptide formylmethionylleucylphenylalanine, or opsonized zymosan released levels of neutrophil O2- and H2O2 comparable to controls, indicating that gonococci were not preventing or inhibiting neutrophil O2- or H2O2 release. To ascertain a possible explanation for these seemingly contradictory observations (i.e., induction of LDCL, but no release of O2- or H2O2), we further characterized the ability of Opa+ gonococci to stimulate LDCL. By using 1 mM azide and 4 U of horseradish peroxidase to monitor extracellular LDCL selectively and 2,000 U of catalase to monitor intracellular LDCL selectively, we determined that greater than 80% of total gonococcus-induced neutrophil LDCL occurred intracellularly. In addition, neutrophils stimulated with Opa+ gonococci showed a marked increase in O2 uptake and hexose monophosphate shunt activity. We conclude that Neisseria gonorrhoeae induces neutrophil oxidative metabolism without causing release of detectable amounts of reactive oxygen intermediates into the surrounding milieu. The gonococcus apparently directs oxidase assembly and activity to the phagolysosomal membrane. This could be a mechanism by which extracellular gonococci persist for extended periods in vivo in the presence of high concentrations of neutrophils.

Interactions of Neisseria gonorrhoeae with human neutrophils: studies with purified PII (Opa) outer membrane proteins and synthetic Opa peptides

We investigated the role of gonococcal outer membrane protein PII (also called Opa protein) in nonopsonic adherence to human neutrophils. Gonococcal outer membranes, purified Opa in detergent (Opa), purified Opa in liposomes (Opa+ lips), and peptides composing the second hypervariable (HV2) region of OpaB (strain FA1090) in liposomes (pepHV2 lips) were tested for their abilities to inhibit subsequent gonococcal adherence to human neutrophils. Outer membranes from gonococci possessing adherent Opa, liposomes containing adherent Opa, purified adherent Opa, and two of three liposome preparations (pepHV2 lips) containing peptides from the HV2 region of an adherent Opa inhibited subsequent adherence to neutrophils of homologous Opa+ gonococci. On the other hand, outer membranes from Opa- gonococci, outer membranes containing a nonadherent Opa (OpaA from strain FA1090), purified OpaA, and OpaA lips had little or no inhibitory effect. Outer membranes containing adherent Opas, purified adherent Opas, and liposomes containing such Opas all bound to neutrophils, whereas preparations containing OpaA or no Opa protein did not. The results indicate that (i) Opa proteins can bind to neutrophils in a partially purified or purified form and (ii) the HV2 region of Opa appears to at least partially mediate Opa's biological role.

Gonococci possessing only certain P.II outer membrane proteins interact with human neutrophils

We investigated the role of the protein II (P.II) family of gonococcal outer membrane proteins in the interaction of seven single P.II variants of Neisseria gonorrhoeae FA1090 with human neutrophils in vitro. The abilities of nonpiliated gonococci to adhere to and be killed by neutrophils and to stimulate luminol-dependent chemiluminescence (CL) depended on the possession of at least one P.II. Gonococci lacking P.II (i.e., P.II-) adhered poorly to and were not killed by neutrophils and induced only minimal CL. Although most P.II-containing (i.e., P.II+) variants adhered to, stimulated, and were readily killed by neutrophils, one variant, containing P.IIa, possessed none of these characteristics; it acted just like a P.II- variant. No correlation was found between the colony opacity phenotype and the interaction of gonococci with neutrophils. Data from CL experiments suggest that the stimulatory effect of P.II was dominant over that of pili; i.e., piliated P.II+ gonococci were much more stimulatory than piliated P.II- gonococci. The results indicate that most but not all P.II proteins mediate, in part or in full, the interaction of N. gonorrhoeae with human neutrophils, including adherence, stimulation of the neutrophil respiratory burst, and phagocytic killing.

Neisseria gonorrhoeae survive intraleukocytic oxygen-independent antimicrobial capacities of anaerobic and aerobic granulocytes in the presence of pyocin lethal for extracellular gonococci

The resistance of a piliated, transparent variant of Neisseria gonorrhoeae FA19 to intraleukocytic killing by human polymorphonuclear neutrophils (PMN) was examined. In both aerobic and anaerobic PMN monolayers, approximately 2% of the intracellular gonococci survived for as long as 165 min. Anaerobic PMN were as effective as aerobic PMN in the intracellular killing of gonococci. Hence, O2-independent antimicrobial systems of PMN performed a significant role in the intraleukocytic killing of gonococci were intracellular was supported by the elimination of extracellular bacteria by the addition of pyocin 103 and confirmed by the fluorescent antibody staining of intact gonococci after the PMN were permeabilized to antibody with a Formalin-acetone treatment of PMN monolayers. Our data indicate that while the majority of ingested gonococci are killed by O2-independent antimicrobial systems, a small number (about 2%), survive even when care is taken to eliminate extracellular bacteria.

Stimulation of human leukocytes by protein II+ gonococci is mediated by lectin-like gonococcal components

We investigated the ability of carbohydrates, glycosidases, and concanavalin A to inhibit the stimulation of the human leukocyte oxidative burst by gonococci in the absence of serum. The gonococci used in this study contained protein II (P.II) outer membrane proteins, and neutrophil oxidative burst was measured by luminol-enhanced chemiluminescence (CL). The following carbohydrates inhibited CL induced by nonpiliated P.II+ gonococci: beta-D-glucosamine greater than N-acetylneuraminic acid (sialic acid) greater than mannose greater than alpha-methylmannoside greater than N-acetyl-beta-D-glucosamine greater than or equal to glucose greater than or equal to lactose. Fucose, galactose, or beta-D-galactosamine (all 100 mM) did not inhibit or slightly increased CL, indicating a specificity for the observed effects. Mannose and alpha-methylmannoside also inhibited induction of monocyte CL by P.II+ gonococci. Incubation of neutrophils with concanavalin A inhibited subsequent gonococcus-induced CL but not phorbol myristate acetate-induced CL. Treatment of neutrophils with alpha-mannosidase reduced subsequent gonococcus-induced CL greater than 99%, whereas such treatment of gonococci had no effect on their ability to induce neutrophil CL. Incubation of a P.IIb-containing variant of Neisseria gonorrhoeae FA1090 with anti-P.IIb monoclonal antibody inhibited subsequent stimulation of neutrophil CL in a dose-responsive manner, indicating a specific role for P.IIb in the stimulatory process. The data suggest that one or more lectin-like components on the surface of P.II+ gonococci mediate their ability to stimulate the oxidative burst of human phagocytes.

Anaerobiosis increases resistance of Neisseria gonorrhoeae to O2-independent antimicrobial proteins from human polymorphonuclear granulocytes

We investigated the in vitro resistance of Neisseria gonorrhoeae FA19 to the O2-independent antimicrobial systems of human polymorphonuclear leukocytes. Acid extracts of polymorphonuclear leukocyte granules (crude granule extracts) and a purified granule protein (57 kilodaltons) were, at low concentrations, bactericidal for gonococci under aerobic conditions that permitted growth. However, they were less effective under anaerobic conditions that imposed bacteriostasis. We found that adding sodium nitrite to reduced growth media permitted the growth of strain FA19 in an anaerobic environment. Under these conditions with nitrite, anaerobic cultures of strain FA19 were no more resistant to the crude granule extract and the 57-kilodalton protein than aerobic cultures. In contrast, Salmonella typhimurium SL-1004, a facultative anaerobe, was readily killed by both the crude granule extract and the 57-kilodalton antimicrobial protein regardless of the presence or absence of free molecular oxygen. This is the first demonstration that an isolated antimicrobial protein from polymorphonuclear leukocyte granules is active against bacteria under anaerobic conditions. Our results also indicated that the efficacy of human polymorphonuclear leukocyte O2-independent killing of N. gonorrhoeae may, in part, be inhibited by bacteriostatic conditions imposed by hypoxia.

Chlorine-induced damage to surface adhesions during sublethal injury of enterotoxigenic Escherichia coli

A comparison of the adhesive ability of noninjured and chlorine-injured enterotoxigenic Escherichia coli was made by in vitro attachment to human peripheral leukocytes. Chlorination selected for noninjured cells with greater capabilities for colonizing the small intestine. Injured populations exhibited reduced association with leukocytes. Maximum reduction was seen in populations with greater than 80% injury. These cells demonstrated less adhesive ability than nonpiliated populations. Electron micrographs suggested that reduced adhesive ability was due to the loss of surface structures as a consequence of sublethal chlorination. The data imply a reduced ability among chlorine-injured pathogens to colonize the small intestine and initiate disease.

Gonococci-human polymorphonuclear leukocyte interactions: metabolic studies associated with attachment and ingestion

Utilizing monolayers of human polymorphonuclear leukocytes, optimal conditions for attachment and ingestion of Neisseria gonorrhoeae were determined. Both attachment and ingestion were optimal at 36 degrees C when a bacteria-leukocyte ratio of 100:1 was employed. After 30 min of incubation, log-phase viable type 2 gonococci were attached to 90% of leukocytes, whereas log-phase viable type 4 gonococci were ingested by 80 to 90% of cells. Respiratory inhibitors had no effect on attachment or ingestion, whereas glycolytic inhibitors blocked ingestion but did not affect attachment of gonocci to the leukocyte surface. Inhibition was dose dependent and partially reversible. The oxidative metabolism of leukocytes with gonococci attached or ingested was also examined. Attachment of log-phase type 2 gonococci stimulated a minimal increase in glucose oxidation and oxygen consumption by leukocytes in contrast to marked increases by leukocytes that had ingested viable type 4 or heat-killed typed 2 organisms. These results demonstrate that attachment of log-phase type 2 gonococci to the surface membrane does not stimulate significant leukocyte oxidative metabolism nor initiate the phagocytic process.

Mannose-sensitive interaction of Escherichia coli with human peripheral leukocytes in vitro

The ability of Escherichia coli which possess or lack mannose-sensitive adherence factors (adhesins) to associate with human peripheral leukocytes in vitro in the absence of serum was studied. E. coli 19+, which have mannose-sensitive adhesins, were derived from E. coli strain 19 by culturing in static Trypticase soy broth at 37 degrees C. E. coli 19-, which lack mannose-sensitive adhesins, were derived from E. coli 19 by culturing in agitated Trypticase soy broth at 30 degrees C. E. coli 19+ attached to leukocytes and stimulated the release of lysozyme but not beta-glucuronidase or lactate dehydrogenase. In contrast, E. coli 19- showed poor attachment to the leukocytes and failed to stimulate lysosomal enzyme release. During a 60-min incubation with the leukocytes, the number of viable 19+ organisms decreased, whereas the number of viable 19- remained constant. Purified type 1 pili from E. coli 19+ agglutinated the leukocytes but did not stimulate lysosomal enzyme release. Pretreatment of leukocytes with type 1 pili failed to prevent the adherence of E. coli 19+. The association of 19+ with leukocytes and subsequent release of lysozyme could be blocked by alpha-methyl-D-mannoside but not by equivalent concentrations of dextrose and sucrose. These results show that mannose-sensitive adhesins on E. coli mediate association of the organisms with leukocytes in the absence of serum components. The identity of the adhesins involved in leukocyte association has yet to be determined.

Killing of Neisseria gonorrhoeae by human polymorphonuclear neutrophil granule extracts

Neisseria gonorrhoeae was grown in vitro (on agar and in broth) and in vivo (in 10-day chicken embryos) and tested for its sensitivity to the bactericidal action of human neutrophil granule extracts. Under all conditions studied, type 1 and type 4 N. gonorrhoeae were killed equally well by dialyzed extracts of neutrophil granules (containing both azurophil and specific granule contents) and by the myeloperoxidase-Cl- - H2O2 bactericidal system. However, sensitivity to the bactericidal activity of granule extracts depended upon growth conditions and growth phase. Log-phase, egg-grown gonococci were the most sensitive; they were killed 100% by 250 to 300 micrograms of granule extract (60 min, 37 degrees C) per ml. N. gonorrhoeae grown on agar for 20 h (to stationary phase) were the least sensitive, being killed only 80 to 90% with 500 micrograms of granule extract per ml. Thus, susceptibility to granule extract of gonococci grown under the four conditions studied in this report decreased in the order: log phase, egg grown; log phase, broth grown; stationary phase, egg grown; and stationary phase, agar grown. Killing was time and temperature dependent; little killing occurred when incubations were done at 10 degrees C. Boiled granule extract had only minimal effects on N. gonorrhoeae viability. Addition of catalase (500 U/ml) to the granule extract bactericidal system did not protect; however, the same concentration of catalase completely inhibited the bactericidal activity of the myeloperoxidase-Cl- - H2O2 system.

Pili of Neisseria meningitidis: effect of media on maintenance of piliation, characteristics of Pili, and colonial morphology

In contrast to information in the literature which indicates that meningococci rapidly lose pili upon cultivation in vitro, we found that piliation of meningococci could be maintained in vitro for 15 or more passages. Pili were present on all eight isolates tested, whether from asymptomatic carriers or from subjects with meningococcal disease. Complete loss of piliation occurred in the same two strains on two of the three media tested. On one medium (Thayer-Martin medium with supplement B), there was partial or complete loss of pili by all strains. The optimal medium for maintaining pili was chocolate agar with 1% IsoVitaleX; 95% or more of the microorganisms of six of the eight strains tested were piliated after 15 passages in vitro, and more than 60% of the microorganisms of the other two strains were piliated. Meningococci passed on this medium generally maintained their initial density of piliation (3 to 34 pili per diplococcus). The ability to predictably cultivate piliated meningococci in vitro and to select piliated and nonpiliated clones of the same strain should allow investigation of the biochemical and immunological properties of meningococcal pili as well as their possible role in the pathogenicity of Neisseria meningitidis.

The biology of the gonococcus

Gonorrhea has been known since antiquity. Today, this disease is the most commonly reported infectious disease in the U.S. The natural environment of the etiological agent, Neisseria gonorrhoeae, is man. In this host, the organism usually parasitizes mucosal surfaces populated by columnar epithelial cells. Under certain conditions, the gonococcus may disseminate or spread to adjacent organs. The gonococcus is well adapted to its environment and is a successful parasite. Until recently, gonococci were uniformly sensitive to penicilin. However, a plasmid encoding beta-lactamase has been identified in some isolates. Most strains exhibit specific requirements for various amino acids, vitamins, purines, and pyrimidines. Only glucose, pyruvate, and lactate are utilized as sources of energy. Glucose is dissimilated by a combination of the Entner-Doudoroff and pentose phosphate pathways. A tricarboxylic acid cycle is also present and active under certain conditions. Structurally, the cell envelope of the gonococcus resembles that of a typical Gram-negative bacterium. Gonococci are highly autolytic, especially in older cultures or after depletion of the energy source. Autolysis is not due solely to peptidoglycan hydrolysis, but appears to involve a destabilization of the outer membrane as well. Cell surface components such as pili, lipopolysaccharide, outer membrane proteins, and a capsule are associated with the virulence and pathogenicity of this organism.

Studies on gonococcus infection. XV. Identification of surface proteins of Neisseria gonorrhoeae correlated with leukocyte association

Neisseria gonorrhoeae which exhibit high levels of leukocyte association have a surface protein which is considerably diminished in isogenic gonococci which exhibit low levels of leukocyte association (LA). The LA protein exhibits strain variation in molecular weight and immunogenicity. Membranes derived from LA+ and LA- organisms show quantitative differences in their adsorption to leukocytes; these differences are analogous to those found for the intact organisms regarding their association with leukocytes.

Quantitative measurement of phagocytosis of Neisseria gonorrhoeae by mouse peritoneal macrophages

The simultaneous labeling of gonococci with [6-3H]uracil and of mouse peritoneal macrophages with L-[U-14C]leucine permits a quantitative assessment of the association of gonococci with macrophages under various experimental conditions. Colony-type T1 (piliated) gonococci associated more than T4 (nonpiliated) organisms at 4 degrees C, but at 37 degrees C the association of T4 gonococci with macrophages exceeded that for the T1 organisms. The association of T1 gonococci with macrophages could be enhanced as much as 70-fold by homologous rabbit antisera prepared against whole, formaldehyde-treated organisms. This immune enhancement represented primarily increased phagocytosis rather than surface attachment, as shown by its inhibition at 4 degrees C or with 2-deoxyglucose. The data further suggested that this enhanced phagocytosis was mediated via the Fc receptor for immunoglobulin G.

Variations in buccal cell adhesion of Neisseria gonorrhoeae

Human buccal cells were found to vary in their day-to-day capacity to support attachment of certain strains of gonococci. Gonococci serially cultured in vitro also differed in their day-to-day ability to attach to buccal cells.

Isolation and characterization of a rough colony type of Neisseria gonorrhoeae

A new colony type of Neisseria gonorrhoeae was detected in the primary cultures from 8 of 180 men with gonococcal urethritis. This colony type contrasts with those previously described by having a rough and irregular surface. In six of the eight cases, the rough form predominated. The distinctive morphology of the rough colony variant could be maintained indefinitely by selective subculture. By electron microscopy, organisms taken from rough colonies of each of the eight isolates were piliated. Antimicrobial susceptibilities of type 1 and rough clones derived from the same patients were identical for ampicillin, penicillin, tetracycline, and spectinomycin. After inoculation of rough colonies into subcutaneous chambers in mice and guinea pigs, type 1 colonies predominated in cultures of material obtained from the chambers. This new piliated colony type of N. gonorrhoeae may provide an opportunity to investigate factors other than pili that contribute to gonococcal virulence.

Ethylenediaminetetraacetic acid-sensitive antiphagocytic activity of Neisseria gonorrhoeae

Colonial types of Neisseria gonorrhoeae were examined for the presence of pilus-independent antiphagocytic activity. Type 3 and depiliated type 1 gonococci had a shearing- and protease-resistant antiphagocytic activity that was eliminated by treatment with ethylenediaminetetraacetic acid (EDTA) and that was not present on type 4 bacteria. Incubation of EDTA-treated bacteria 37 degrees C for 90 min resulted in fas prevented by antibiotics that block the final assembly of cell wall macromolecules that depend on the C55-isoprenoid carrier for export. These include both lipopolysaccharide and peptidoglycan. Restoration was, however, unaffected by drugs that interfere with the synthesis of peptidoglycan, but not that of lipopolysaccharide, and by inhibitors of protein synthesis. These data suggested that gonococci have an antiphagocytic mechanism in addition to the previously described determinant (presumably pili) that was removed by blending or by treatment with proteases. Of the two antiphagocytic activities, type 1 had both, type 3 had only the EDTA-sensitive component, and type 4 had neither.

In vitro interaction of Neisseria gonorrhoeae type 1 and type 4 with tissue culture cells

As a basis for studies of gonococcal pathogenicity, tissue culture cells were infected with type 1 or type 4 Neisseria gonorrhoeae to determine intracellular viability. A simple and objective means of measurement was devised, based on the uptake of tritiated protein and deoxyribonucleic acid precursors by cycloheximide-inhibited cells infected with gonococci. Cycloheximide was found to inhibit protein synthesis by over 97% tissue culture cells at a concentration of 100 microng/ml. In contrast, N, gonorrhoeae was found to be highly resistant to this antibiotic, and protein synthesis was unaffected by concentrations up to 1,000 microng/ml. Extracellular gonococci were eliminated by treatment with high concentrations of penicillin during cycloheximide inhibition and prior to the addition of radioisotope. Levels of protein and deoxyribonucleic acid synthesis by N. gonorrhoeae in the cycloheximide-treated cells were significantly higher in T1-infected cells (RE2, HeLa, or HEp-2) than in the corresponding T4-infected cells. No differences were observed in tissue cell susceptibility to gonococcal infection. Intracytoplasmic localization of N. gonorrhoeae was confirmed by electron microscopy.

Inhibition of adherence of Neisseria gonorrhoeae by human genital secretions

Local genital antibodies to the infecting strains of Neisseria gonorrhoeae were demonstrated by indirect immunofluorescence (binding antibody) and by their ability to inhibit the attachment of gonococci to epithelial cells (functional antibody). Both IgG and IgA classes of immunoglobulin were involved, and the IgA component were primarily of a secreting (11S) nature. The ability of local genital antibody to inhibit attachment appears to persist for at least a short period of time and to be relatively strain specific.

Specificity of inhibition of epithelial cell adhesion of Neisseria gonorrhoeae

Inhibition of epithelial cell adhesion (attachment) for individual strains of Neisseria gonorrhoeae is antigenically distinct.

Attachment of gonococci to sperm. Influence of physical and chemical factors

Neisseria gonorrhoeae of pilated T1 and nonpilated T4 colony types attached themselves to human sperm in greatest numbers and most reproducibly when suspensions of the cells were incubated at 35 degrees C in Ringer's solution, pH 6-8. After incubation for 15 or 30 min. in a water bath shaker, 50 per cent. of human sperm had T1 gonococci attached and 25 per cent. T4. Sperm and both types of gonococci were pre-incubated separately with various chemical agents, selected because the agent is found in genital fluids, or has a known effect on bacterial cell walls or sperm membrane. After treatment, sperm were washed or were not washed, and were then tested for attachment by mixture with untreated gonococci. Treated gonococci were handled in the same manner. Change in the percentage of attachment was defined as deviation from the range expected on the basis of a standard curve. Treatment of sperm with the nucleotides, ATP or cAMP, curtailed attachment by T1 gonococci but had no effect on attachment by T4.

Human deficiency of the eighth component of complement. The requirement of C8 for serum Neisseria gonorrhoeae bactericidal activity

The serum of a 23-yr-old woman with prolonged disseminated gonococcal infection syndrome failed to normally promote hemolysis of sensitized sheep red blood cells (RBC). The patient's serum was deficient in the eight component of complement (C8) as determined by functional assays, immunoelectrophoresis, and quantitative immunoprecipitation. Functional titers of each of her other complement components were normal. No serum inhibitors of C8 were detected. The patient's serum supported activation of both the classical and alternate complement pathways. Her fresh serum lacked any bactericidal activity against Neisseria gonorrhoeae, but addition of purified C8 or complement donor serum restored bactericidal activity as well as RBC hemolytic activity. Her serum gave normal opsonization of yeast particles and staphylococci and had normal capacity to coat sensitized RBC with C8 and C4 and to generate chemotactic activity. No defects were observed in the patient's blood coagulation mechanisms. Complement-mediated bacterial lysis may be important in human defense against bacteremic Neisseria infections.

Egestion of degraded meningococci by polymorphonuclear leukocytes

Quantitative studies were carried out on the in vitro phagocytosis of 14C-labeled Neisseria meningitidis by mouse polymorphonuclear leukocytes. Intact, "loaded" leukocytes were found to excrete radioactive bacterial products back into supernatant fluids. Morphological events associated with the exocytosis events revealed a fusion between the phagocytic vacuole and plasma membranes of the leukocyte followed by an emptying of the vacuole contents. Egested materials were free from whole meningococci and consisted mainly of membranous vesicles.

Studies on Gonococcus infection. IX. In vitro decreased assocation of pilated gonococci with mouse peritoneal macrophages

Pili, in addition to enhancing attachment of gonococci to tissue culture cells, appear to reduce association (attachment/ingestion) of Neisseria gonorrhoeae with mouse peritoneal macrophages in vitro.

Studies on Gonococcus infection. X. Pili and leukocyte association factor as mediators of interactions between gonococci and eukaryotic cells in vitro

Two independent gonococcal surface components, pili and leukocyte association factor, appear to mediate in vitro interactions of Neisseria gonorrhoeae with tissue culture cells and human peripheral blood leukocytes, respectively.

Attachment and ingestion of gonococci human neutrophils

Previous studies have indirectly shown that type 1 gonococci are more resistant to phagocytosis by human neutrophils (PMN) than type 3 gonococci. Using phase contrast, fluorescent, and light microscopy, we directly quantitated PMN-gonococcal interaction, with emphasis on separating ingestion from attachment. PMN monolayers were incubated on slides with type 1 or type 3 gonococcal fluorescent antibody (FA). After methanol fixation, the FA-stained gonococci associated with PMN were cointed. Since the live PMN excludes FA, the FA-stained gonococci represent only extracellular gonococci. Methylene blue was then added to the smae slide to stain both ingested and surface attached gonococci. Using these methods, intracellular and extracellular cell-associated gonococci were quantitated under varying conditions. The numbers of methylene blue-stained cell-associated gonococci that were ingested were: with normal serum, 3.7 plus or minus 4.1 per cent for type 1 and 56.2 plus or minus 3.7 percent for type 3 (P smaller than 0.001); with heat-inactivated serum, 1.0 plus or minus 3.0 per cent for type 1 and 52.6 plus or minus 3.7 per cent for type 3 (P smaller than 0.001); with higher-titer anti-gonococcal antibody serum, 4.8 plus or minus 4.3 percent for type 1 and 64.0 plus or minus 1.6 per cent for type 3 (P smaller than 0.001). Thus, most type 3 organisms were ingested, but most type 1 gonococci were bound on the PMN surface.

Studies on gonococcus infection. VIII. 125Iodine labeling of gonococci and studies on their in vitro interactions with eukaryotic cells

Intact gonococci (GC) have been labeled with 125iodine by the lactoperoxidase plus hydrogen peroxide procedure. The specific activities of types 2, 4, and 4 GC have been determined and are found to show small differences as follows: T4 greater than T2 greater than T4. 125I-labeled GC have been studied for their associations with both leukocytes and tissue culture cells. 125I-labeled GCshow the following relative order of association with the leukocytes: T2 equals T4* greater than T4. This contrasts with the relative degree of interaction between the GC and tissue culture cells, which follows the relative order: T2 greater than T4 equals T4*. Trypsin pretreatment of GC markedly reduces the association of all three types (T2, T4 AND T4*) with leukocytes but does not alter the level of attachment of any of the gonococcal types with tissue culture cells.

Studies on gonococcus infection. VII. In vitro killing of gonococci by human leukocytes

The comparative killing of pilated and nonpilated forms of Neisseria gonorrhoeae by human peripheral blood leukocytes was studied in vitro. Some nonpilated gonococci (T2) were killed to a lesser extent than were pilated, T2 organisms, which were killed less readily than another nonpilated (T4*) form of gonococcus. Thus, the relative order of killing of gonococci by human peripheral blood leukocytes appears to be: T4 less than T2 less than T4*. These data suggest that pilation, though correlated with virulence of gonococci, has little influence on the survival or killing of these organisms by human leukocytes.

Studies on gonococcus infection. VI. Electron microscopic study on in vitro phagocytosis of gonococci by human leukocytes

The ingestion of Neisseria gonorrhoeae by isolated human leukocytes in vitro has been studied by electron microscopy. Use of the modified critical-point drying method allows clear visualization of progressive ingestion of both pilated and nonpilated gonococci by leukocytes. Incomplete ingestion of pilated gonococci with protrusion of tangled masses of pili from sites of phagocytosis are also found.