Characterization of gonococcal antigens responsible for induction of bactericidal antibody in disseminated infection

Neisseria gonorrhoeae lipooligosaccharide glycan epitopes recognized by bactericidal IgG antibodies elicited by the meningococcal group B-directed vaccine, MenB-4C

Introduction

Outer membrane vesicles (OMVs) of Neisseria meningitidis in the group B-directed vaccine MenB-4C (BexseroR) protect against infections with Neisseria gonorrhoeae. The immunological basis for protection remains unclear. N. meningitidis OMV vaccines generate human antibodies to N. meningitidis and N. gonorrhoeae lipooligosaccharide (LOS/endotoxin), but the structural specificity of these LOS antibodies is not defined.

Methods

Ten paired human sera obtained pre- and post-MenB-4C immunization were used in Western blots to probe N. meningitidis and N. gonorrhoeae LOS. Post-MenB-4C sera (7v5, 19v5, and 17v5), representing individual human variability in LOS recognition, were then used to interrogate structurally defined LOSs of N. meningitidis and N. gonorrhoeae strains and mutants and studied in bactericidal assays.

Results and discussion

Post-MenB-4C sera recognized both N. meningitidis and N. gonorrhoeae LOS species, ~10% of total IgG to gonococcal OMV antigens. N. meningitidis and N. gonorrhoeae LOSs were broadly recognized by post-IgG antibodies, but with individual variability for LOS structures. Deep truncation of LOS, specifically a rfaK mutant without α-, β-, or γ-chain glycosylation, eliminated LOS recognition by all post-vaccine sera. Serum 7v5 IgG antibodies recognized the unsialyated L1 α-chain, and a 3-PEA-HepII or 6-PEA-HepII was part of the conformational epitope. Replacing the 3-PEA on HepII with a 3-Glc blocked 7v5 IgG antibody recognition of N. meningitidis and N. gonorrhoeae LOSs. Serum 19v5 recognized lactoneotetrose (LNT) or L1 LOS-expressing N. meningitidis or N. gonorrhoeae with a minimal α-chain structure of Gal-Glc-HepI (L8), a 3-PEA-HepII or 6-PEA-HepII was again part of the conformational epitope and a 3-Glc-HepII blocked 19v5 antibody binding. Serum 17v5 LOS antibodies recognized LNT or L1 α-chains with a minimal HepI structure of three sugars and no requirement for HepII modifications. These LOS antibodies contributed to the serum bactericidal activity against N. gonorrhoeae. The MenB-4C vaccination elicits bactericidal IgG antibodies to N. gonorrhoeae conformational epitopes involving HepI and HepII glycosylated LOS structures shared between N. meningitidis and N. gonorrhoeae. LOS structures should be considered in next-generation gonococcal vaccine design.

Antibody-Dependent Enhancement of Bacterial Disease: Prevalence, Mechanisms, and Treatment

Antibody-dependent enhancement (ADE) of viral disease has been demonstrated for infections caused by flaviviruses and influenza viruses; however, antibodies that enhance bacterial disease are relatively unknown. In recent years, a few studies have directly linked antibodies with exacerbation of bacterial disease. This ADE of bacterial disease has been observed in mouse models and human patients with bacterial infections. This antibody-mediated enhancement of bacterial infection is driven by various mechanisms that are disparate from those found in viral ADE. This review aims to highlight and discuss historic evidence, potential molecular mechanisms, and current therapies for ADE of bacterial infection. Based on specific case studies, we report how plasmapheresis has been successfully used in patients to ameliorate infection-related symptomatology associated with bacterial ADE. A greater understanding and appreciation of bacterial ADE of infection and disease could lead to better management of infections and inform current vaccine development efforts.

Gonorrhea - an evolving disease of the new millennium

Etiology, transmission and protection: Neisseria gonorrhoeae (the gonococcus) is the etiological agent for the strictly human sexually transmitted disease gonorrhea. Infections lead to limited immunity, therefore individuals can become repeatedly infected. Pathology/symptomatology: Gonorrhea is generally a non-complicated mucosal infection with a pustular discharge. More severe sequellae include salpingitis and pelvic inflammatory disease which may lead to sterility and/or ectopic pregnancy. Occasionally, the organism can disseminate as a bloodstream infection. Epidemiology, incidence and prevalence: Gonorrhea is a global disease infecting approximately 60 million people annually. In the United States there are approximately 300, 000 cases each year, with an incidence of approximately 100 cases per 100,000 population. Treatment and curability: Gonorrhea is susceptible to an array of antibiotics. Antibiotic resistance is becoming a major problem and there are fears that the gonococcus will become the next "superbug" as the antibiotic arsenal diminishes. Currently, third generation extended-spectrum cephalosporins are being prescribed. Molecular mechanisms of infection: Gonococci elaborate numerous strategies to thwart the immune system. The organism engages in extensive phase (on/off switching) and antigenic variation of several surface antigens. The organism expresses IgA protease which cleaves mucosal antibody. The organism can become serum resistant due to its ability to sialylate lipooligosaccharide in conjunction with its ability to subvert complement activation. The gonococcus can survive within neutrophils as well as in several other lymphocytic cells. The organism manipulates the immune response such that no immune memory is generated which leads to a lack of protective immunity.

Neisseria gonorrhoeae strain PID2 simultaneously expresses six chemically related lipooligosaccharide structures

Neisseria gonorrhoeae strain PID2 was isolated from a woman suffering from pelvic inflammatory disease. When LOS expressed by this strain is analyzed on SDS-PAGE gels, at least six different lipooligosaccharide (LOS) components are visualized. We characterized the LOSs made by this strain by exoglycosidase digestion, sugar composition analysis, mass spectrometry, and analysis of the genes needed for its synthesis. DNA sequence analysis showed that the lgt gene cluster in this strain has undergone a rearrangement and that it possesses two copies of lgtA, one copy of lgtB and lgtC, and a hybrid gene containing sequences from lgtB and lgtE. We determined that the hybrid lgtB/E gene retained the lgtE gene function. DNA sequence analysis of the gene organization suggested that an intramolecular recombination between lgtA and lgtD and lgtB and lgtE had occurred via homologous recombination between similar sequences. Our studies demonstrated that fluorophore-assisted carbohydrate electrophoresis can be utilized to rapidly determine the composition of LOS. By combining exoglycosidase digestion, in combination with mass spectrometry analysis and compositional analysis, the data indicate that all of the LOS components produced by PID2 extend off of the alpha chain. The longest alpha chain oligosaccharide structure is Gal-GlcNAc-Gal-GlcNAc-Gal-Glc-Heptose I, and the six LOS components are built up by sequentially adding sugars onto the first heptose. PID2 LOS is the first Neisserial LOS to be shown to be devoid of phosphoethanolamine modifications. Because PID2 can surface express its LOS, it indicates that the addition of phosphoethanolamine is not required for LOS surface expression.

Strategies for mimicking Neisserial saccharide epitopes as vaccines

Monoclonal antibody (mAb) 2C7 recognizes a conserved and widely expressed oligosaccharide (OS) epitope on Neisseria gonorrhoeae. This OS epitope evokes a significant bactericidal and opsonic immune response after natural infection and vaccination. The OS epitope structure represents an excellent target for a potential protective gonococcal vaccine. Because carbohydrate antigens are T-cell independent, inducing weak antibody responses, OS molecules are not useful immunogens. We developed and examined two different strategies to mimic the 2C7 OS epitope: (i) an anti-idiotope (mAb CA1); and (ii) a peptide (PEP-1). These surrogate immunogens elicited antibody responses in mice (CA1 and PEP-1) and rabbits (CA1) that were bactericidal in vitro against gonococci. Both CA1 and PEP-1 are true immunologic mimics of OS and may form a basis for the development of vaccine candidates for human immunization against N. gonorrhoeae.

Structural and immunochemical characterization of the lipooligosaccharides expressed by Neisseria subflava 44

Neisserial lipooligosaccharides (LOSs) are a family of complex cell surface glycolipids. We used mass spectrometry techniques (electrospray ionization, collision-induced dissociation, and multiple step), combined with fluorophore-assisted carbohydrate electrophoresis monosaccharide composition analysis, to determine the structure of the two low-molecular-mass LOS molecules (LOSI and LOSII) expressed by Neisseria subflava 44. We determined that LOSI contains one glucose on both the alpha and beta chains. LOSII is structurally related to LOSI and differs from it by the addition of a hexose (either glucose or galactose) on the alpha chain. LOSI and LOSII were able to bind monoclonal antibody (MAb) 25-1-LC1 when analyzed by Western blotting experiments. We used a set of genetically defined Neisseria gonorrhoeae mutants that expressed single defined LOS epitopes and a group of Neisseria meningitidis strains that expresses chemically defined LOS components to determine the structures recognized by MAb 25-1-LC1. We found that extensions onto the beta-chain glucose of LOSI block the recognition by this MAb, as does further elongation from the LOSII alpha chain. The LOSI structure was determined to be the minimum structure that is recognized by MAb 25-1-LC1.

Haemophilus ducreyi produces a novel sialyltransferase. Identification of the sialyltransferase gene and construction of mutants deficient in the production of the sialic acid-containing glycoform of the lipooligosaccharide

Haemophilus ducreyi, the cause of the sexually transmitted disease chancroid produces a lipooligosaccharide (LOS) containing a terminal sialyl N-acetyllactosamine trisaccharide. Previously, we reported the identification and characterization of the N-acetylneuraminic acid cytidylsynthetase gene (neuA). Forty-nine base pairs downstream of the synthetase gene is an open reading frame (ORF) encoding a protein with a predicted molecular weight of 34,646. This protein has weak homology to the polysialyltransferase of Escherichia coli K92. Downstream of this ORF is the gene encoding the H. ducreyi homologue of the Salmonella typhimurium rmlB gene. Mutations were constructed in the neuA gene and the gene encoding the second ORF by insertion of an Omega kanamycin cassette, and isogenic strains were constructed. LOS was isolated from each strain and characterized by SDS-polyacrylamide gel electrophoresis, carbohydrate, and mass spectrometric analysis. LOS isolated from strains containing a mutation in neuA or in the second ORF, designated lst, lacked the sialic acid-containing glycoform. Complementation studies were performed. The neuA gene and the lst gene were each cloned into the shuttle vector pLS88 after polymerase chain reaction amplification. Complementation of the mutation in the lst gene was observed, but we were unable to complement the neuA mutation. Since it is possible that transcription of the neuA gene and the lst gene were coupled, we constructed a nonpolar mutation in the neuA gene. In this construct, the neuA mutation was complemented, suggesting transcriptional coupling of the neuA gene and the lst gene. Sialyltransferase activity was detected by incorporation of 14C-labeled NeuAc from CMP-NeuAc into trichloroacetic acid-precipitable material when the lst gene was overexpressed in the nonpolar neuA mutant. We conclude that the lst gene encodes the H. ducreyi sialyltransferase. Since the lst gene product has little, if any, structural relationship to other sialyltransferases, this protein represents a new class of sialyltransferase.

A novel sialic acid binding site on factor H mediates serum resistance of sialylated Neisseria gonorrhoeae

Factor H (fH), a key alternative complement pathway regulator, is a cofactor for factor I-mediated cleavage of C3b. fH consists of 20 short consensus repeat (SCR) domains. Sialic acid binding domains have previously been localized to fH SCRs 6-10 and 13. To examine fH binding on a sialylated microbial surface, we grew Neisseria gonorrhoeae in the presence of 5'-cytidinemonophospho-N-acetylneuraminic acid, which sialylates lipooligosaccharide and converts to serum resistance gonococci previously sensitive to nonimmune serum killing. fH domains necessary for binding sialylated gonococci were determined by incubating organisms with recombinant human fH (rH) and nine mutant rH molecules (deletions spanning the entire fH molecule). rH and all mutant rH molecules that contained SCRs 16-20 bound to the sialylated strain; no mutant molecule bound to serum-sensitive nonsialylated organisms. Sialic acid was demonstrated to be the fH target by flow cytometry that showed a fourfold increase in fH binding that was reversed by neuraminidase-mediated cleavage of sialic acid off gonococci. Functional specificity of fH was confirmed by decreased total C3 binding and almost complete conversion to iC3b on sialylated gonococci. Sialic acid can therefore bind fH uniquely through SCRs 16-20. This blocks complement pathway activation for N. gonorrhoeae at the level of C3.

Heparin protects Opa+ Neisseria gonorrhoeae from the bactericidal action of normal human serum

The pathobiological significance of lipooligosaccharide (LOS) and outer membrane opacity protein (Opa) changes in gonorrheal disease are poorly understood. We assessed variants of strain MS11mk with different LOS and Opa phenotypes for their liability to killing by normal human sera. LOS differences correlated with strikingly disparate susceptibilities to serum killing; LOSa variants were serum resistant, LOSb variants were serum sensitive, and sialylation of LOSb variants enhanced their survival (as reported previously). Opa phenotype had little influence on the killing of serum-sensitive LOSb cells that were incubated directly in normal human sera, but preincubation of Opa+ LOSb variants in heparin increased their serum resistance whereas Opa- LOSb variants showed no change. Some Opa proteins conferred slightly higher resistance than others, but heparin preincubation increased serum resistance for variants expressing each of seven Opa proteins. These in vitro phenomena may relate to conditions within the male urethra where sulfate-containing proteoglycans are abundant and where antibody and complement may transude from blood plasma. The results suggest that the selective advantage for Opa+ Neisseria gonorrhoeae bacteria observed in vivo may reflect their ability to utilize host cell components to resist killing by host defenses.

Serum resistance of Neisseria gonorrhoeae. Does it thwart the inflammatory response and facilitate the transmission of infection?

N. gonorrhoeae differentially subvert the effectiveness of complement (C) and alter the inflammatory responses elicited in human infection. Disseminated (DGI) isolates typically resist killing by normal serum (are serum-resistant), inactivate more C3b (to iC3b preferentially bound via amide linkages), generate less C5a, and result in less inflammation at local sites. Pelvic inflammatory disease isolates are serum-sensitive, inactivate less C3b (while maintaining active C3b via stable amide linkages), generate more C5a, and result in more inflammation at local sites. Sialylation of SS gonococci, presumed to occur in vivo, converts them to serum-resistant, but it does not change the patterns of C3b inactivation and therefore may not affect local inflammation. IgG antibody directed against gonococcal reduction modifiable protein (Rmp) blocks C-mediated killing of N. gonorrhoeae. Anti-Rmp blocking antibodies may harbor specificity for OmpA sequences shared with other neisserial species or Enterobacteriaceae or may be directed against unique Rmp upstream cysteine loop specific sequences, or both. Preexisting antibodies directed against Rmp facilitate transmission of gonococcal infection to exposed women; exclusion of highly immunogenic Rmp antigens from vaccine candidates may be important.

Lipo-oligosaccharides (LOS) of mucosal pathogens: molecular mimicry and host-modification of LOS

Immunochemical studies of the lipo-oligosaccharides (LOS) of the Gram-negative bacteria Neisseria gonorrhoeae and Neisseria meningitidis have revealed some interesting structural characteristics of these LOS that might relate to their roles during pathogenesis. The carbohydrate moieties of the LOS of pathogenic Neisseria mimic carbohydrates present in glycosphingolipids of human cells. Firstly, an LOS component present among a number of Neisseria species is antigenically and/or chemically identical to lactoneoseries glycosphingolipids present in human cells. The lactoneoseries LOS becomes sialylated on Neisseria gonorrhoeae when they are grown in the presence of cytidine 5'-monophospho-N-acetyl-neuraminic acid (CMP-NANA), the nucleotide sugar for sialic acid. Examination of gonococci present in exudates from males with natural infection indicates that sialylation also occurs in vivo. The mechanism for this process apparently involves a bacterial sialyltransferase scavenging available host CMP-NANA ("host-modification" of LOS) and transferring the sialic acid to the lactoneoserieslike LOS. Strains of N. meningitidis and Haemophilus influenzae also express similarly sialylated LOS suggesting that this is a common mechanism of pathogenesis among these bacteria. Additional examples of LOS that mimic other glycosphingolipid series have been identified also and the fact that multiple series can be expressed in a single population of gonococci suggests that a diverse set of LOS can be presented to the host during infection. It is possible that this diverse set of LOS serve different functions for the bacteria in various hosts and/or environments during infection.

Structural analysis of lipooligosaccharide produced by Neisseria gonorrhoeae, strain MS11mk (variant A): a precursor for a gonococcal lipooligosaccharide associated with virulence

We studied the structure of the lipooligosaccharide (LOS) that is produced by a variant A of strain MS11mk. This variant produces a single LOS that is recognized by monoclonal antibody (MAb) 2-1-L8. In a recent study of the pathogenesis of Neisseria gonorrhoeae in male volunteers, variant A gave rise to other phase variants that produce higher molecular weight LOSs, and these LOS were associated with virulence. Definition of the structure of the variant A LOS is important to understand the biosynthesis of LOS and its expression in vivo. The dephosphorylated oligosaccharide (OS) structure derived from the variant A LOS was analyzed by two-dimensional NMR and methylation analysis. The OS structure was found to be a truncated form of the LOS produced by strain F62 [Yamasaki et al. (1991) Biochemistry 30, 10566-10575]; the variant A OS is a hexamer, a beta-lactosyl residue linked to a tetrasaccharide: Gal beta 1-->4Glc beta 1-->4[GlcNAc alpha 1-->2Hep alpha 1-->3]Hep alpha 1-->KDO. We determined that the variant A LOS is a precursor for the synthesis of higher MW LOS. We also studied expression of the MAb 2-1-L8-defined epitope present on the variant A LOS. Our data indicate that the MAb-defined epitope is not a linear beta-lactosyl residue but its specificity is directed toward the phosphorylated GlcNAc-Hep-Hep residue. Since this MAb binds to gonococci, at least part of the phosphorylated diheptose area is exposed on the gonococcal surface.

Infectious diseases associated with complement deficiencies

The complement system consists of both plasma and membrane proteins. The former influence the inflammatory response, immune modulation, and host defense. The latter are complement receptors, which mediate the cellular effects of complement activation, and regulatory proteins, which protect host cells from complement-mediated injury. Complement activation occurs via either the classical or the alternative pathway, which converge at the level of C3 and share a sequence of terminal components. Four aspects of the complement cascade are critical to its function and regulation: (i) activation of the classical pathway, (ii) activation of the alternative pathway, (iii) C3 convertase formation and C3 deposition, and (iv) membrane attack complex assembly and insertion. In general, mechanisms evolved by pathogenic microbes to resist the effects of complement are targeted to these four steps. Because individual complement proteins subserve unique functional activities and are activated in a sequential manner, complement deficiency states are associated with predictable defects in complement-dependent functions. These deficiency states can be grouped by which of the above four mechanisms they disrupt. They are distinguished by unique epidemiologic, clinical, and microbiologic features and are most prevalent in patients with certain rheumatologic and infectious diseases. Ethnic background and the incidence of infection are important cofactors determining this prevalence. Although complement undoubtedly plays a role in host defense against many microbial pathogens, it appears most important in protection against encapsulated bacteria, especially Neisseria meningitidis but also Streptococcus pneumoniae, Haemophilus influenzae, and, to a lesser extent, Neisseria gonorrhoeae. The availability of effective polysaccharide vaccines and antibiotics provides an immunologic and chemotherapeutic rationale for preventing and treating infection in patients with these deficiencies.

Complement binding on serum-sensitive and serum-resistant transformants of Neisseria gonorrhoeae: effect of presensitization with a non-bactericidal monoclonal antibody

The binding of C3 and C9 on serum sensitive (FA635) and serum resistant (FA638) transformants of serum sensitive Neisseria gonorrhoeae strain F62 was examined. Previous studies showed that these transformants have Protein IAs which are minimally different by proteinase K cleavage and primary structural and peptide mapping and bear LPS which vary slightly on SDS-PAGE. Binding of C3 and C9 on FA635 exceeded binding on FA638 in NHS and in adsorbed NHS. Monoclonal antibody 4G5, which binds to PI on FA638 but not FA635, increases C9 binding on FA638 to levels 3-3.5 fold greater than on FA635 but does not result in killing. The majority of additional 125IC9 deposited on FA638 following presensitization with 4G5 is released from the bacterial surface by trypsin. These results extend our earlier results with N. gonorrhoeae by showing that, although PI monoclonals can lead to substantial deposition of non-bactericidal C5b-9, this C5b-9 is not fully inserted into the gonococcal outer membrane.

Neisseria lactamica and Neisseria meningitidis share lipooligosaccharide epitopes but lack common capsular and class 1, 2, and 3 protein epitopes

Neisseria lactamica, a common human pharyngeal commensal, contributes to acquired immunity to Neisseria meningitidis. To define the surface antigens shared between these two species, we used monoclonal antibodies (MAbs) to study 35 N. lactamica strains isolated in various parts of the world for cross-reactivity with meningococcal capsules, outer membrane proteins, and lipooligosaccharides (LOS). No N. lactamica strain reacted significantly with MAbs specific for capsular group A, B, C, Y, or W, and we were unable to extract capsular polysaccharide from them. Only 2 of 33 strains reacted weakly with MAbs against class 2 serotype proteins P2b and P2c. None reacted with MAbs specific for meningococcal class 1 protein P1.2 or P1.16 or class 2/3 serotype protein P2a or P15. Most N. lactamica strains (30 of 35) bound one or more of seven LOS-specific MAbs. Two LOS epitopes, defined by MAbs O6B4 and 3F11, that are commonly found on pathogenic Neisseria species were found on 25 of 35 N. lactamica. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting showed that the LOS of N. lactamica are composed of multiple components that are physically and antigenically similar to the LOS of pathogenic Neisseria species. Among four other commensal neisserial species, only Neisseria cinerea shared LOS epitopes defined by MAbs O6B4 and 3F11. Previous studies have shown that pharyngeal colonization with N. lactamica induces bactericidal antibodies against the meningococcus. We postulate that shared N. lactamica and meningococcal LOS epitopes may play an important role in the development of natural immunity to the meningococcus.

Epitope expression of gonococcal lipooligosaccharide (LOS). Importance of the lipoidal moiety for expression of an epitope that exists in the oligosaccharide moiety of LOS

Antigenic expression of lipooligosaccharide (LOS) of strain F62 of Neisseria gonorrhoeae, was investigated with mouse monoclonal IgM antibody 3F11. F62 LOS was modified in various ways in order to understand structural requirements for expression of the 3F11-defined epitope. When the LOS was partially deacylated by treating it with 50 mM NaOH at 80 degrees C for 20 min or with anhydrous hydrazine at 80 degrees C for 20 min, the binding of 3F11 to those deacylated LOS samples decreased significantly. Removal of phosphate groups by treatment of the LOS with HF (4 days at 4 degrees C) did not affect the antigenicity at all. Neither did reduction of carboxyl groups in the LOS molecule (by activation of carboxyl groups with a carbodiimide followed by treatment with NaBH4) alter epitope expression. On oxidation with NaIO4, the LOS lost its antigenicity completely. The presence of Mg2+ did not change the circular dichroism (CD) behavior of F62 LOS. However, the partially deacylated LOS samples showed significantly different CD patterns in the 190-200 nm region compared with F62 LOS, which suggests conformational changes of F62 LOS due to the loss of fatty acids in the lipoidal moiety. Oligosaccharide (OS) and lipoidal components obtained after hydrolysis of F62 LOS with 1% acetic acid, were not recognized by the antibody. The antigenicity of OS was not retained by non-stereospecific acylation of OS with decanoyl chloride. We conclude the following: (1) 3F11-defined epitope exists in the OS moiety of F62 LOS; however, for it to be expressed, the carbohydrate moiety must be in a certain conformation that is defined by an overall structure of the LOS molecule. This structure is significantly influenced by some of the fatty acids in the lipoidal moiety of the LOS molecule; (2) the presence of phosphate or 3-deoxy-manno-2-octulosonic acid (dOclA) is not essential for expression of the 3F11-defined epitope; (3) the presence of divalent cations does not affect epitope expression.

Use of transformation to construct Neisseria gonorrhoeae strains with altered lipooligosaccharides

DNA isolated from a nalidixic acid- and rifampin-resistant derivative of Neisseria gonorrhoeae serum-resistant strain 302 (MUG116), a strain that reacts with monoclonal antibody (MAb) 2-1-L8, was used to transform N. gonorrhoeae DOV, a serum-sensitive strain, to antibiotic resistance and/or reactivity with the MAb. MAb 2-1-L8 binds to a 3.6-kilodalton lipooligosaccharide (LOS). Reactivity with MAb 2-1-L8 transformed as a single marker and was unlinked to either of the antibiotic resistance markers. Immunoblot analysis of LOSs separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that new LOSs were synthesized in the transformed cells and that these LOSs corresponded to those of the DNA donor. Although multiple LOS components were made by the transformants, the MAb recognized only one. All transformants that were selected for on the basis of strong reactivity with MAb 2-1-L8 were serum resistant; however, the level of resistance correlated with the apparent loss of recipient LOS components. MAb 2-1-L8-reactive transformants that still produced DOV LOS components remained serum sensitive.

Human immunoglobulin G antibody response to the major gonococcal iron-regulated protein

In humans, gonococcal infection occurs in environments limited with respect to free iron. Neisseria gonorrhoeae produces increased quantities of iron-regulated membrane proteins when grown under in vitro conditions which restrict the availability of free iron. Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot (immunoblot) techniques, we studied the reactivity of specific antibodies to the 37-kilodalton (kDa) major iron-regulated protein (MIRP) of gonococci grown under iron-limiting conditions. Antibodies reactive with the 37-kDa MIRP were distinguished from those reactive with protein I by using purified 37-kDa MIRP or gonococcal protein preparations. Acute-phase sera from patients with disseminated gonococcal infection (DGI) reacted strongly to both the 37-kDa MIRP and protein I. Acute sera from nine patients with uncomplicated gonorrhea did not exhibit strong reactivity with the 37-kDa MIRP and were indistinguishable from five control sera. When compared with acute-phase sera, convalescent-phase sera from patients with DGI failed to demonstrate increased reactivity, whereas convalescent-phase sera from one of nine patients with uncomplicated gonorrhea developed reactivity to the 37-kDa MIRP. These data indicate that (i) the 37-kDa MIRP is expressed and antigenic in vivo and (ii) humans with DGI consistently develop a systemic antibody response to the 37-kDa MIRP.

The immunochemistry of neisserial LOS

The outer membrane glycolipids of Neisseria lack long polysaccharides and are properly termed lipooligosaccharides (LOS). A Neisseria strain makes from two to six LOS of Mr 3150-7100. Different species commonly make LOS of identical Mr and epitope content. Oligosaccharide (OS) differences account for physical heterogeneity. OS consist of a conserved triantenary basal oligosaccharide, two linear segments of (n) hexose residues that determine OS mass, and terminal sequences similar to those of glycosphyngolipids. Epitope expression is linked to physical heterogeneity and conditioned by the molecular environment of the outer membrane. Serotype epitopes are expressed on Mr-restricted LOS. LOS regulate complement activation onto the bacterial surface and, hence, immune lysis.

Physical heterogeneity of neisserial lipooligosaccharides reflects oligosaccharides that differ in apparent molecular weight, chemical composition, and antigenic expression

We studied the oligosaccharides (OS) of outer membrane lipooligosaccharides (LOS) of Neisseria gonorrhoeae and Neisseria meningitidis. OS from the LOS of an individual neisserial strain always eluted from Sephadex G-50S as multiple peaks; the polyacrylamide gel elution profiles were nearly identical to the polyacrylamide gel electrophoresis profiles of the sodium dodecyl sulfate-disaggregated native LOS from which the OS were derived. Neisserial OS coeluted with Dex14 to Dex27 dextran oligomers (Mr, 2,210 to 4,320). Monosaccharide composition varied among the several OS released from the LOS of a single strain. The two OS of a gonococcal strain sensitive to normal human serum (NHS) bacteriolysis (sers) varied in their ability to inhibit the binding of NHS immunoglobulin M to their parental LOS. The OS that was rich in hexosamines inhibited NHS immune lysis of its parent strain; the OS that was poor in hexosamines did not. We conclude that structural differences in their OS account for the Mr heterogeneity of the LOS of a strain.

Specificity of antibodies against Neisseria gonorrhoeae that stimulate neutrophil chemotaxis. Role of antibodies directed against lipooligosaccharides

Five strains each of Neisseria gonorrhoeae sensitive or resistant to complement (C) dependent killing by normal human serum (NHS) were examined for their ability to stimulate chemotaxis of polymorphonuclear leukocytes (PMNs) after preincubation with NHS; or IgM or IgG derived from NHS. Serum-sensitive N. gonorrhoeae stimulated C-dependent chemotaxis when opsonized with IgM, but not IgG, however, serum-resistant strains, taken as a whole, failed to promote chemotaxis when opsonized with either isotype. IgM titers in NHS against lipooligosaccharide (LOS) antigens from individual serum-sensitive, but not serum-resistant strains, correlated with the magnitude of chemotaxis generated by the corresponding opsonized strains (r = 0.99). Western blots demonstrated that IgM and IgG from NHS recognized different antigenic determinants on LOS from serum-sensitive gonococci. IgM from NHS immunopurified against serum-sensitive LOS accounted for two-thirds of the chemotaxis promoting activity present in whole serum. IgG titers in NHS against LOS antigens from individual serum-resistant strains also correlated with magnitude of chemotaxis generated by the corresponding opsonized strains (r = 0.87), although most opsonized serum-resistant strains did not generate significantly higher magnitudes of chemotaxis than controls. In contrast, a serum-resistant isolate from a patient with disseminated gonococcal infection (DGI) stimulated chemotaxis when opsonized with IgG obtained from the patient's convalescent serum. By Western blot, convalescent IgG antibody recognized an additional determinant on serum-resistant LOS not seen by normal IgG.

Immunoglobulin G antibodies directed against protein III block killing of serum-resistant Neisseria gonorrhoeae by immune serum

Neisseria gonorrhoeae that resist complement-dependent killing by normal human serum (NHS) are sometimes killed by immune convalescent serum from patients recovering from disseminated gonococcal infection (DGI). In these studies, killing by immune serum was prevented or blocked by IgG isolated from NHS. Purified human IgG antibodies directed against gonococcal protein III, an antigenically conserved outer membrane protein, contained most of the blocking activity in IgG. Antibodies specific for gonococcal porin (protein I), the major outer membrane protein, displayed no blocking function. In separate experiments, immune convalescent DGI serum which did not exhibit bactericidal activity was restored to killing by selective depletion of protein III antibodies by immunoabsorption. These studies indicate that protein III antibodies in normal and immune human serum play a role in serum resistance of N. gonorrhoeae.

Identification of a 16,600-dalton outer membrane protein on nontypeable Haemophilus influenzae as a target for human serum bactericidal antibody

A 16,600-D outer membrane protein is present in all strains of Haemophilus influenzae and antibodies to this protein are present in human serum. This study was designed to assess the role of this outer membrane protein (P6) in nontypeable H. influenzae as a target for human serum bactericidal antibody. P6 was isolated and coupled to an affinity column. Depleting normal human serum of antibodies to P6 by affinity chromatography resulted in reduced bactericidal activity of that serum for nontypeable H. influenzae. Immunopurified antibodies to P6 from human serum were bactericidal. Finally, preincubation of bacteria with a monoclonal antibody that recognizes a surface epitope on P6, inhibited human serum bactericidal killing. Taken together, these experiments establish that P6 is a target for human bactericidal antibodies. This observation provides evidence that P6 plays a potentially important role in human immunity to infection by nontypeable H. influenzae.

Protection by serum antibodies in experimental nontypable Haemophilus influenzae otitis media

The chinchilla experimental model of otitis media was used to examine the importance of serum antibodies in protection against disease caused by nontypable Haemophilus influenzae. An immune serum pool was prepared by immunizing chinchillas with killed bacterial cells of nontypable H. influenzae 3245. Pooled preimmune or immune serum from these immunized animals was administered intravenously to a group of nonimmune chinchillas 1 day before intrabullar challenge with strain 3245. Of 5 animals receiving preimmune serum, 5 developed otitis media compared with 0 of 10 animals receiving immune serum (P = 0.008). The immune serum pool contained antibodies directed against both surface-exposed outer membrane proteins and lipopolysaccharide (LPS). The 39-kilodalton major outer membrane protein was the immunodominant surface protein. Anti-LPS antibodies were removed from the immune serum pool by affinity chromatography, and affinity-purified anti-LPS antibodies were recovered. Immune serum, immune serum absorbed of LPS antibodies, or affinity-purified LPS antibodies were then administered to another group of experimental animals 1 day before bacterial challenge. Of four animals that received the affinity-purified LPS antibodies, four developed otitis compared with zero of four animals that received the immune serum or zero of four animals that received the LPS-absorbed immune serum (P = 0.028). These studies indicate that passive immunization with immune serum is protective in experimental nontypable H. influenzae otitis media and that bacterial outer membrane proteins may be the principal targets of protective antibody.

Mechanism of action of blocking immunoglobulin G for Neisseria gonorrhoeae

Blocking immunoglobulin G (IgG) inhibits complement-mediated killing of serum-resistant Neisseria gonorrhoeae (GC) in immune human serum. We examined the mechanism of action of blocking IgG. Presensitization of GC with increasing concentrations of blocking IgG or F(ab')2 before incubation with bactericidal antibody and absorbed pooled normal human serum increased consumption and deposition of the third component of human complement (C3) and the ninth component of human complement (C9) but inhibited killing in dose-related fashion. We next showed that blocking IgG or F(ab')2 partially inhibited binding of bactericidal IgG to GC. Also, binding of a monoclonal antibody recognizing GC outer membrane protein PIII was almost completely inhibited by blocking F(ab')2, confirming other work (Rice, P. A., M. R. Tam, and M. S. Blake, manuscript submitted for publication) showing that PIII is a target for blocking antibody. Studies of the C3 deposition site showed that one quarter of the C3 deposited on GC in the presence of blocking IgG bound covalently to the antibody molecule. Finally, 125I-GC constituents with covalently bound C3 were affinity purified on Sepharose bearing antibodies to C3 and identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis. C3 deposition on a 40,000-mol wt surface protein was enhanced six- to ninefold by blocking IgG, which indicates that the site of complement deposition was altered by blocking antibody. These studies show that blocking IgG competes with bactericidal antibody for binding to GC, but enhances rather than blocks complement activation, and leads to complement deposition at new sites that do not result in serum killing.

Role of lipopolysaccharide and complement in susceptibility of Haemophilus ducreyi to human serum

The role of lipopolysaccharide (LPS) in the susceptibility of Haemophilus ducreyi to human serum and the mechanism of complement activation by serum-susceptible (Sers) strains were investigated. Serum treated with 2 mM Mg2+ and 20 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid was nonbactericidal, but inulin-treated serum remained bactericidal. Absorption of serum with heat-killed whole cells of an Sers strain removed its bactericidal activity against the absorbing strain and also against other Sers strains. LPS obtained from Sers strains inhibited the bactericidal activity of serum against all Sers strains, whereas LPS from serum-resistant (Serr) strains and an Serr isogenic strain did not. However, high concentrations of LPS from the Serr strain inhibited the bactericidal activity of serum, an indication that part of the structural site involved in serum susceptibility is retained in the LPS of this strain. The LPS of Sers strains exhibited higher anticomplement activity than the LPS of Serr strains. These findings suggest that the classical pathway of complement activation is involved in the serum killing of H. ducreyi and that LPS composition may contribute to their susceptibility to complement-mediated serum bactericidal activity.

Antigenic heterogeneity of outer membrane proteins of nontypable Haemophilus influenzae is a basis for a serotyping system

A serotyping system for nontypable Haemophilus influenzae (NTHI) was developed by using isolated outer membrane protein (OMP) preparations and rabbit antisera. OMPs of 23 strains were isolated by molecular sieve chromatography of outer membranes in 1.5% sodium deoxycholate buffer. These OMP preparations were relatively free of lipopolysaccharide as determined by silver staining of sodium dodecyl sulfate gels and by dot assay with a monoclonal antibody which is specific for the lipid A of H. influenzae. Three antisera raised to whole organisms were used to serotype 21 of 23 strains with a kinetic enzyme-linked immunosorbent assay. Digestion of OMP preparations with proteinase K removed greater than 90% of the antigenic reactivity, indicating that the system is based on OMP antigens. Marked antigenic heterogeneity of OMPs exists among strains of NTHI. By determining the pattern of serological reactivity of OMPs with the three antisera, isolates were divided into groups based on antigenic differences. Six serotypes were identified. This OMP serotyping system is based on multiple antigenic determinants. Future studies will focus on identifying serotype-specific epitopes to further refine this serological classification scheme for NTHI.

Antigenic heterogeneity of lipid A of Haemophilus influenzae

The chemical structure and biologic function of the lipid A portion of lipopolysaccharide are not identical among gram-negative bacteria. This study indicates that antigenically heterogeneous lipid A exists among strains of Haemophilus influenzae. An immunoglobulin G3 murine monoclonal antibody, 3D2, produced against a nontypable H. influenzae strain 3524 has specificity for a site on the lipid A portion of the H. influenzae lipopolysaccharide. With the Western blot and immunodot assay, 3D2 recognized this lipid A determinant on 14 of 24 (58%) of strains of nontypable H. influenzae and in 51 of 95 (54%) strains of H. influenzae type b. This lipid A epitope has a high degree of specificity for H. influenzae, since it is not present on the lipid A of 39 gram-negative strains from 14 non-Haemophilus species. In addition, studies of 36 strains of six Haemophilus species other than H. influenzae and 8 strains of 4 species of Actinobacillus did not contain the 3D2 epitope. Enzyme-linked immunosorbent assay analysis with a kinetic assay and enzyme-linked immunosorbent assay inhibition confirmed the antigenic heterogeneity of H. influenzae lipid A. Thin-layer chromatography demonstrated that the 3D2 epitope is associated with a chloroform-soluble lipid moiety in the lipid A. Fluorescent antibody analysis of H. influenzae indicated that the epitope is on the cell surface. The monoclonal antibody was not bactericidal for strain 3524, and it did not inhibit the bactericidal action of normal human serum against the same strain. These studies demonstrate that the lipid As of H. influenzae are antigenically heterogeneous.

Role of anti-pilus antibodies in host defense against gonococcal infection studied with monoclonal anti-pilus antibodies

Several monoclonal antibodies directed against gonococcal pili have been used to investigate the potential contribution of anti-pilus antibodies to host defense against gonococcal infection. Included were two antibodies (SM1 and SM2) which reacted with conserved determinants present on pili from all strains tested and others which exhibited antigenic specificity. Immunoblotting experiments revealed that antibodies SM1 and SM2 recognize epitopes on two different peptides derived by CNBr cleavage of alpha-pili from Neisseria gonorrhoeae P9-2. All antibodies used were capable of activating complement, as shown by their ability to bind Clq, and one type-specific antibody was effective in complement-mediated bactericidal killing. Antibodies directed against at least some pilus epitopes may therefore contribute to bactericidal activity during the course of natural infection. The opsonic effect of type-specific antibodies was demonstrated by their ability to stimulate luminol-dependent chemiluminescence of human polymorphonuclear leukocytes and promote phagocytic killing of variant P9-2. Phagocytic killing in the presence of each monoclonal antibody paralleled the increase in chemiluminescence, suggesting that for this variant killing was an inevitable consequence of the interaction of polymorphonuclear leukocytes with gonococci opsonized with anti-pilus antibodies. Antibody-mediated chemiluminescence of polymorphonuclear leukocytes was enhanced in the presence of human complement, and a weak opsonic effect was detected with one of the cross-reacting antibodies (SM1) when this system was used. Although cross-reacting antibody SM1 and type-specific antibody SM13 showed considerable differences in biological properties, they were of the same isotype and bound to native pili on intact gonococci in similar numbers and with similar avidity.

Characterization of antigens from nontypable Haemophilus influenzae recognized by human bactericidal antibodies. Role of Haemophilus outer membrane proteins

Major outer membrane antigens, proteins, and lipopolysaccharides (LPSs), from nontypable Haemophilus influenzae were characterized and examined as targets for complement-dependent human bactericidal antibodies. Outer membranes from two nontypable H. influenzae isolates that caused otitis media and pneumonia (middle ear and transtracheal aspirates) were prepared by shearing organisms in EDTA. These membranes were compared with membranes prepared independently by spheroplasting and lysozyme treatment of whole cells and found to have: similar sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns of the proteins; identical densities (rho = 1.22 g/cm3); and minimal d-lactose dehydrogenase activity indicating purity from cytoplasmic membranes. Outer membranes were solubilized in an LPS-disaggregating buffer and proteins were separated from LPS by molecular sieve chromatography. The SDS-PAGE patterns of outer membrane proteins (OMPs) from the two strains differed in the major band although other prominent bands appeared similar in molecular weight. LPS prepared by hot phenol water extraction of each of the strains contained 45% (pneumonia isolate) and 60% (otitis isolate) lipid (wt/wt), 49% and 50% carbohydrate (wt/wt), respectively, and less than 1%, 3-deoxy-manno octulosonic acid. Immunoglobulin M (IgM) purified from normal human serum (NHS) plus complement was bactericidal for both strains. Purified immunoglobulin G (IgG) from NHS killed the middle ear isolate and immune convalescent IgM from the serum of the patient with pneumonia killed his isolate. NHS or convalescent serum were absorbed with OMPs and LPS (0.6-110 micrograms) from each of the strains and immune specific inhibition of bactericidal antibody activity by each antigen was determined. OMPs from the pulmonary isolate inhibited bactericidal antibody activity directed against the isolate in both NHS (1.5 microgram of antigen) and immune serum (0.75 microgram of antigen). OMPs (60 micrograms) from the ear isolate also inhibited bactericidal activity in the respective immune serum. LPSs exhibited minimal inhibition (greater than 110 micrograms). Three human sera (two normal, one immune) were selectively depleted of 80% of antibody activity against OMPs (measured by enzyme-linked immunosorbent assay) by affinity chromatography using OMPs from the pulmonary isolate coupled to a solid phase. These OMP antibody-depleted sera also showed an 88% reduction of bactericidal activity against this strain. Immunopurified antibody against OMPs eluted from the solid phase was bactericidal.

Analysis of the antigen specificity of the human serum immunoglobulin G immune response to complicated gonococcal infection

The antigen-specific basis of human serum immunoglobulin G antibody response to complicated gonococcal infection was studied in 13 patients by using the Western blot technique for transfer of proteins from sodium dodecyl sulfate-polyacrylamide gels to nitrocellulose paper. Of 13 patients (8 with disseminated gonococcal infection, 4 with pelvic inflammatory disease, 1 with gonococcal epididymitis), 12 reacted with protein I antigens and 9 with lipopolysaccharide (LPS). Sera from eight patients reacted with both protein I and LPS, whereas sera from four reacted only with protein I, and one sera reacted with LPS alone. One serum with antibody to both protein I and LPS by Western blot analysis was tested for bactericidal activity before and after adsorption of antibody to LPS. Removal of antibody to LPS reduced the bactericidal titer of this serum from 1:100 to 1:50, indicating that antibody to both antigens may be bactericidal for Neisseria gonorrhoeae.

Inherited deficiency of C8 in a patient with recurrent meningococcal infections: further evidence for a dysfunctional C8 molecule and nonlinkage to the HLA system

An adult male with recurrent meningococcal infections is reported whose serum lacked functional C8 activity but possessed antigenic C8. The addition of 1500 U of purified C8/ml of serum restored hemolytic activity to normal. Four to five times more C8 was required to restore bactericidal activity than to restore hemolytic activity. Bactericidal activity could also be restored by mixing the patient's serum with a second C8-deficient serum that lacked detectable antigenic or functional C8. The patient's serum contained bactericidal antibody for groups A, B, C, and Y meningococci and specific antibody to group Y capsular polysaccharide. There was two to three times more bactericidal antibody activity in the serum than in a pool of normal sera for the infecting strain. Family studies disclosed a sibling who was HLA identical to the patient but whose serum contained normal amounts of total hemolytic and C8 functional activity.

Characterization of the immune response in subcutaneous chambers of guinea pigs immunized with a ribosomal preparation from Neisseria gonorrhoeae

Immunization of guinea pigs with ribosomal preparations has been previously shown to be protective against chamber infection with Neisseria gonorrhoeae, and this protection could be correlated with the presence of serum bactericidal antibody. Analysis of the chamber fluids from ribosome-immunized and nonimmunized guinea pigs has demonstrated that the chamber fluid may accurately reflect serum antibody levels and proteins. At least one major population of antiribosomal antibodies is present in both immune serum and chamber fluid as revealed by lines of identity between these components. Antibody- and complement-mediated bactericidal assays revealed that matched chamber fluids and sera from immune animals had comparable bactericidal titers. These results suggest that the antibody-complement-mediated bactericidal activity plays a major role in the protection against N. gonorrhoeae infection. Protection could not be explained on the basis of the cellular components of the inflammatory response since both immune and nonimmune chambers had comparable increases in polymorphonuclear neutrophils, monocytes, and lymphocytes after challenge.

Characterization of serum resistance of Neisseria gonorrhoeae that disseminate. Roles of blocking antibody and gonococcal outer membrane proteins

Neisseria gonorrhoeae isolated from patients with disseminated infection (DGI) often resist complement (C')-dependent killing by normal human serum (NHS) and less commonly by convalescent DGI serum. 7 of 10 NHS specimens completely inhibited killing of serum-resistant (ser(r)) gonococci by convalescent or immune DGI serum. Immunoglobulin G (IgG) purified from NHS was shown to be the blocking agent. In addition, IgM (plus C') purified from NHS was shown to be fivefold more effective (wt/wt) in killing serum-sensitive (ser(s)) gonococci than equivalent amounts of IgM tested in the presence of IgG (whole serum). Although inhibition of NHS killing of ser(s) gonococci required a 640% excess of IgG, only a 40% excess was required to block immune serum killing of ser(r) gonococci. F(ab')(2) prepared from IgG also blocked killing of ser(r) gonococci by immune serum indicating antigenic specificity of blocking IgG.IgG immunoconcentrated against outer membrane protein (OMP) derived from ser(r) gonococci showed 40-fold increased blocking activity over normal IgG (wt/wt) and lacked antibody activity directed against gonococcal lipopolysaccharide by ELISA. Using direct immunoabsorption of IgG with purified gonococcal OMP; ser(r)-OMP was found sixfold more effective than ser(s)-OMP in neutralizing the blocking of immune serum killing of ser(r) gonococci, and 10-fold more effective in systems that used excess blocking IgG, NHS, and ser(s) gonococci. Blocking IgG preabsorbed with whole ser(r) gonococci lost 75% of its ability to block immune serum killing compared with no loss in this system using a similar absorption with ser(s) gonococci. IgG purified from NHS contained fivefold higher titers of antibody against ser(r)-OMP than ser(s)-OMP by ELISA.

Application of a Limulus test device in rapid evaluation of gonococcal and nongonococcal urethritis in males

A test device incorporating Limulus amoebocyte lysate (Mallinckrodt, Inc., St. Louis, Mo.) was developed for the rapid, presumptive diagnosis of gonococcal and nongonococcal disease in males. The device, which was evaluated in 550 men with exudative urethritis, consisted of a specimen collection syringe, a dilution reservoir containing 10 ml of pyrogen-free water, and a Limulus amoebocyte lysate single-test vial. After specimen collection, the syringe was affixed to the dilution reservoir for rapid, accurate dilution of the clinical sample. Contamination of the specimen and potential biohazards to the user were prevented. The diluted sample was then transferred (via the collection syringe) to the lysate test vial for assay of endotoxin. Various incubation times at 37 degrees C were also studied in an additional 301 male patients, and time was reduced from the standard 60 to 30 min while still retaining equivalent predictability of culture results (P less than 0.05). Of the 550 males evaluated with the test device, 366 had positive cultures for Neisseria gonorrhoeae, and 184 were negative. A sensitivity of 99.2% and a specificity of 96.7% were obtained with the test device. Overall ability to predict culture results was 98.4%. Gram-stain sensitivity and specificity were 96.4% and 99.5%, respectively, with an overall accuracy of 97.5%. There were no statistical differences between the Limulus amoebocyte lysate test and Gram stain in predicting cultures (P less than 0.05). Thus, use of the Limulus amoebocyte lysate test device would enable the private physician to make an accurate, presumptive diagnosis of gonococcal and nongonococcal disease in males with exudative urethritis within 30 min without the need of a microscope and to initiate proper therapy during the patient's initial evaluation.

Reactivity of the limulus lysate assay with uterine cervical secretions. A preliminary evaluation

A limulus lysate assay was performed on cervical secretions from 66 women. When secretions were tested at a 1/100 dilution the assay gave a positive result in 15 (62.5%) of 24 patients with gonorrhoea confirmed by Gram-stained smear or culture or both. When secretions from seven of the nine remaining patients who had gonorrhoea but negative results to the limulus lysate test were retested at 1/50 dilution, two gave a positive result, increasing the positivity rate of the test to 17 (70.8%) of 24 infected patients. Material from one patient with a history of contact with gonorrhoea and from three (7.3%) of the other 41 patients without any history of gonorrhoea gave positive reactions.

Antigen-specific serotyping of Neisseria gonorrhoeae: characterization based upon principal outer membrane protein

Principal outer membrane protein (protein I) of Neisseria gonorrhoeae was prepared nearly free of lipopolysaccharide (LPS) and substantially purified from other membrane proteins by chromatography of partially purified gonococcal outer membranes over Sepharose 6B in the presence of deoxycholate at pH 9.0. This protein I of nine separate antigenic types was coated to polystyrene tubes and used in the enzyme-linked immunosorbent assay (ELISA) to measure antibody to protein I or in inhibition tests to quantitate protein I antigen. No significant inhibition of the ELISA test was produced by purified LPS from the strain used to prepare each of the protein I types or by whole gonococci bearing the same LPS but different protein I antigens as the strain used to produce a given protein I antigen. Of 125 strains of gonococci used as whole organisms to inhibit the protein I ELISA, 124 (99%) typed with one or more of the nine protein I types, and 35% of these typed with a single protein I serotype. Sixty-one of 65 (94%) strains from Seattle and Atlanta patients with disseminated gonococcal infection contained protein I serotype 1, and 16 of 24 (64%) strains from Seattle patients with salpingitis bore one or both of protein I serotypes 1 and 2.

Role of outer envelope contamination in protection elicited by ribosomal preparations against Neisseria gonorrhoeae infection

A recent report (Cooper et al., Infect. Immun. 28:92-100, 1980) demonstrated that immunization of guinea pigs with ribosomal preparations was protective (approximately 90%) against chamber infections with Neisseria gonorrhoeae. Similar protection has been demonstrated with other cellular immunogens such as outer membranes (OM) (92%) or purified lipopolysaccharide (LPS) (83%). Protection of LPS (5 to 100 micrograms) was dose dependent (83% with 100 micrograms). Treatment of LPS with pronase reduced the protection by 50%. Ribosomal preparations contained LPS contamination (3.9%) based on dry weight determinations by 2-keto-3-deoxyoctonate analysis. Analysis of ribosomal preparations isolated from cells after lactoperoxidase-mediated 125I labeling indicated a major OM contamination (Protein I). The ribosomal preparation also contained low levels of succinic and lactic dehydrogenase. Passive hemagglutination tests revealed that sera from guinea pigs immunized with ribosomal preparations also demonstrated antibody to OM proteins and LPS. LPS was able to absorb one line of precipitation seen in immunodiffusion reactions as well as the bactericidal activity of such sera. OM preparations were unable to absorb the remaining precipitin line or remove the bactericidal activity. It appears that LPS is the major antigen responsible for the bactericidal activity seen in ribosome-immune sera.

Response of several Limulus amoebocyte lysates to native endotoxin present in gonococcal and nongonococcal urethral exudates from human males

Three Limulus amoebocyte lysate (LAL) preparations obtained from three different suppliers were comparatively evaluated for sensitivity to native endotoxin contained in urethral exudates from 28 men with gonococcal urethritis and 16 men with nongonococcal urethritis. One LAL preparation was not extracted with organic solvents during manufacture, whereas the other two were extracted with chloroform. All three LAL preparations had equivalent sensitivities (0.06 ng/ml) to an established reference endotoxin standard (EC-2), but significant differences in sensitivities were found among the different LAL preparations when testing clinical specimens. Dilution breakpoints of urethral samples for maximum sensitivity and specificity ranged from 1:400 to 1:1,600, depending on the LAL preparation. The nonextracted lysate was significantly more sensitive to the presence of endotoxin in gonococcal exudates than the other two preparations (P less than 0.001) but not significantly different from one LAL preparation (P greater than 0.05) in detecting endotoxin in nongonococcal exudates. An additional 116 men, 61 with culture-proven gonococcal urethritis and 55 with nongonococcal urethritis, were evaluated with three lots of nonextracted lysate with sensitivities ranging from 0.04 to 0.06 ng/ml, reference endotoxin EC-2. At a dilution breakpoint of 1:1,600, the sensitivity of the LAL test was 100%, and the specificity was 96%.

Gonococcal salpingitis is less likely to recur with Neisseria gonorrhoeae of the same principal outer membrane protein antigenic type

If protective immunity were to develop following an episode of gonococcal pelvic inflammatory disease (salpingitis), PID should recur with organisms bearing antigens that do not react with these immune mechanisms. To test this hypothesis, gonococci from 15 women with gonococcal PID, who experienced 19 subsequent episodes of gonococcal infection, were serotyped for their principal outer membrane protein (Protein I) antigens. Of nine cases in which the initial and subsequent infections involved the same Protein I serotype, none was associated with recurrence of PID. Of 10 cases in which the initial and subsequent infections involved different Protein I types, five were associated with recurrent PID (p = 0.02). These data suggest that an episode of gonococcal PID produces some immunity to repeated episodes of salpingitis with the same Protein I serotype, while not preventing reinfection with the same Protein I serotype. The immune response to Protein I antigen may thus provide serotype-specific protection against gonococcal salpingitis.

Rapid presumptive diagnosis of gonococcal cervicitis by the limulus lysate assay

In an evaluation of the limulus lysate assay (LLA) as a method for detecting gonococcal endotoxin in cervical exudates diluted 1:800, positive LLA results were obtained from 17 of 18 patients (94%) with culture-proved gonococcal cervicitis, and negative results were obtained from 22 of 22 patients (100%) with culture-negative specimens. In vitro tests comparing the sensitivity of the LLA for Neisseria gonorrhoeae and other gram-negative organisms showed the LLA to be more sensitive in detecting N. gonorrhoeae (minimum sensitivity, 10(4) organisms per milliliter) than other commonly encountered urogenital gram-negative bacteria (minimum sensitivity, greater than 10(5) organisms per milliliter). Thus, in preliminary studies involving otherwise healthy women, the LLA appeared to correlate with bacteriologic methods for diagnosing gonococcal cervicitis and may aid in identifying nongonococcal cervicitis. In addition, the LLA was easy to perform, with test results available within an hour after the patient's initial examination.

High-molecular-weight antigenic protein complex in the outer membrane of Neisseria gonorrhoeae

The outer membrane of Neisseria gonorrhoeae contains approximately 15 proteins, with 2 or 3 accounting for over 75% of the total protein mass. Samples of outer membrane from strain 2686 T4 analyzed by electrophoresis in 2% polyacrylamide gels revealed a band with an apparent molecular weight of 800,000. The band was protein material, as indicated by trypsin and pronase sensitivity and by L-[3H]proline incorporation. Peptidoglycan, nucleic acids, and carbohydrate were not detected in the band. Dye binding, L-[3H]proline incorporation, and labeling of solubilized outer-membrane proteins with 125I-labeled Bolton-Hunter reagent indicated that the band made up 10 to 13% of the total protein mass of isolated outer membranes. The material in the band was purified by gel filtration and, after reduction and alkylation, quantitatively recovered as subunits with an apparent molecular weight of 76,000. The protein in complex form was exposed at the cell surface, as evidenced by labeling whole cells with 125I by using a lactoperoxidase-catalyzed reaction and with CNBr-activated dextran. Rabbit serum raised against whole 2686 T4 gonococci contained antibody which reacted with the protein complex. The protein complex was detected in all gonococcal strains tested, but its presence could not be demonstrated in several other gram-negative species.

Antigenic heterogeneity of the non-serogroup antigen structure of Neisseria gonorrhoeae lipopolysaccharides

Studies of the antigenic structure of the polysaccharide component of gonococcal lipopolysaccaride (LPS) indicated that the non-serogroup antigen structure is antigenically heterogeneous. Immunodiffusion studies of Gc4 strain 8551 indicated that in addition to the Gc serogroup determinent, this polysaccharide contains two other sets of determinants, one which is shared with the other five Gc serogroups and a second which is shared by the Gc1 and Gc3 serogroups. Enzyme-linked immunosorbent assay (ELISA) studies confirmed the immunodiffusion, documented qualitative differences, and suggested that quantitative differences may exist in the common determinant from serogroup to serogroup. As measured by ELISA inhibition, native LPS showed the same antigenic arrangement as the purified LPS polysaccharides. Studies with LPS-derived polysaccharides from nonprototype strains in immunodiffusion gave results identical to the prototype strains. This antigen variation, although distinct from serogroup specificity, was related to the serogroup determinant.