Nature and Heterogeneity of the Antigens of Neisseria gonorrhoeae Involved in the Serum Bactericidal Reaction

Re-visiting humoral constitutive antibacterial heterogeneity in bloodstream infections

Although cellular immunity has garnered much attention in the era of single-cell technologies, humoral innate immunity has receded in priority due to its presumed limited roles. Hence, despite the long-recognised bactericidal activity of serum-a functional characteristic of constitutive humoral immunity-much remains unclear regarding mechanisms underlying its inter-individual heterogeneity and clinical implications in bloodstream infections. Recent work suggests that the immediate antimicrobial effect of humoral innate immunity contributes to suppression of the excessive inflammatory responses to infection by reducing the amount of pathogen-associated molecular patterns. In this Personal View, we propose the need to re-explore factors underlying the inter-individual heterogeneity in serum antibacterial competence as a new approach to better understand humoral innate immunity and revisit the clinical use of measuring serum antibacterial activity in the management of bacterial bloodstream infections. Given the current emphasis on subtyping sepsis, a serum bactericidal assay might prove useful in defining a distinct sepsis endotype, to enable more personalised management.

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.

Diversion of complement-mediated killing by Bordetella

The complement cascade participates in protection against bacterial infections, and pathogens, including Bordetella pertussis, have developed complement-evading strategies. Here we discuss current knowledge on B. pertussis complement evasion strategies and the role of antibody-dependent complement-mediated killing in protection against B. pertussis infection pointing out important knowledge gaps for further research to improve current pertussis vaccines.

Desialylation of Neisseria gonorrhoeae Lipooligosaccharide by Cervicovaginal Microbiome Sialidases: The Potential for Enhancing Infectivity in Men

Previous studies have demonstrated that Neisseria gonorrhoeae sialylates the terminal N-acetyllactosamine present on its lipooligosaccharide (LOS) by acquiring CMP-N-acetyl-5-neuraminic acid upon entering human cells during infection. This renders the organism resistant to killing by complement in normal human serum. N-acetyllactosamine residues on LOS must be free of N-acetyl-5-neuraminc acid (Neu5Ac; also known as "sialic acid") in order for organisms to bind to and enter urethral epithelial cells during infection in men. This raises the question of how the gonococcus infects men if N-acetyllactosamine residues are substituted by Neu5Ac during infection in women. Here, we demonstrate that women with gonococcal infections have levels of sialidases present in cervicovaginal secretions that can result in desialylation of (sialylated) gonococcal LOS. The principle sialidases responsible for this desialylation appear to be bacterial in origin. These studies suggest that members of the cervicovaginal microbiome can modify N. gonorrhoeae, which will enhance successful transmission to men.

Kinetics of conversion of Neisseria gonorrhoeae to resistance to complement by cytidine 5'-monophospho-N-acetyl neuraminic acid

Freshly isolated gonococci upon subculture are readily lysed by normal human serum although a few strains remain inherently resistant to the complement activity. The sensitive gonococci can be converted to serum resistance by incubation with a host derived factor referred to as cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-NANA). These gonococci resist complement mediated killing due to their sialylation of an epitope structure on a component of lipo-oligosaccharide (LOS). In the present study, the kinetics of conversion to serum resistance by the action of sialyltransferase (STase) in Neisseria gonorrhoeae was followed with very low concentrations of CMP-NANA. This conversion could not be perceived at 2 x 10(-3) nmol.ml-1 but was fully attainable from 8 x 10(-3) to 2 x 10(-2) nmol.ml-1 CMP-NANA. When pretreated up to 100 min in presence of the very low concentration of 2 x 10(-3) nmol.ml-1, a potentiating effect on the conversion of gonococci by 2 x 10(-2) nmol.ml-1 was observed in relation to the time of preincubation. This action was abolished after exposure to a subinhibitory concentration of chloramphenicol (0.5 microgram.ml-1). The gonococci recovered their ability to convert to serum resistance following adequate washing. The potential for increase in STase activity should be of interest for understanding the conversion from a serum sensitive to a serum resistance state.

Anaerobic growth and cytidine 5'-monophospho-N-acetylneuraminic acid act synergistically to induce high-level serum resistance in Neisseria gonorrhoeae

In vivo, gonococci encounter a myriad of conditions not present in vitro. At some stages of infection and disease, gonococci may grow anaerobically, probably by using sodium nitrite as a terminal electron acceptor. Also, gonococci sialylate their lipooligosaccharide (LOS) in vivo, by using low concentrations of cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-NANA) present in host tissue. This sialylation is responsible for the acquired resistance of gonococci to both normal and immune human serum. Given that gonococci grown in the absence of oxygen or in the presence of CMP-NANA probably more closely resemble gonococci grown inside a human host, we studied the serum resistance of gonococci cultivated under these conditions. In the absence of CMP-NANA, anaerobically grown (anaerobic) gonococci were somewhat less sensitive to serum killing than were aerobically grown (aerobic) gonococci. However, anaerobic gonococci grown with 6 micrograms of CMP-NANA per ml exhibited almost complete serum resistance, while aerobic gonococci required 16-fold-higher CMP-NANA concentrations to achieve significant serum resistance. Anaerobic gonococci incubated in CMP-NANA converted to serum resistance two to three times faster than did similarly treated aerobic gonococci and incorporated up to six times as much sialic acid into their LOS. Gonococci can express several different LOS molecules. Anaerobic gonococci expressed the LOS molecule that acts as an acceptor for sialic acid from CMP-NANA in greater quantity than aerobic gonococci did. Finally, Triton X-100 extracts of anaerobic gonococci contained about four times more sialyltransferase activity than did extracts of aerobic gonococci. Sialyltransferase activity in these extracts was not inhibited by oxygen or enhanced by anaerobiosis. These data indicate that anaerobic conditions lead to altered LOS biosynthesis and to induction of sialyltransferase activity in gonococci. In vivo, where decreased oxygen levels and relevant concentrations of CMP-NANA are found, gonococci could readily become resistant to killing by normal and immune human serum.

The interaction of naturally elaborated blebs from serum-susceptible and serum-resistant strains of Neisseria gonorrhoeae with normal human serum

We studied the interaction of normal human serum immunoglobulins with outer-membrane bleb antigens of Neisseria gonorrhoeae. Gonococcal 68,000 Dalton and Lip (H.8 antigen) outer-membrane proteins were recognized by normal human serum immunoglobulins in blebs from serum-resistant strains, but not in blebs from serum-susceptible strains. The addition of blebs from a serum-resistant strain to bactericidal assays resulted in significantly greater inhibition of serum killing than the addition of blebs from a serum-susceptible strain. Our results indicate that blebs from two serum-resistant gonococcal strains have an enhanced ability to bind and remove cell-targeted bactericidal factors, and that outer-membrane blebbing may contribute to serum resistance.

Sialylation of lipopolysaccharide and loss of absorption of bactericidal antibody during conversion of gonococci to serum resistance by cytidine 5'-monophospho-N-acetyl neuraminic acid

Changes in lipopolysaccharide (LPS) which occur when serum susceptible gonococci are converted to resistance by incubation with cytidine 5'-monophospho-N-acetyl neuraminic acid (CMP-NANA) have been investigated. Transfer of radioactivity to bacterial LPS from CMP-NANA labelled with 14C in the NANA moiety was detected by fluorography following lysis, proteinase K digestion and SDS-PAGE. Incorporation of radioactivity was inhibited by cytidine 5'-monophosphate (CMP). Both the radioactivity of the LPS and the resistance of gonococci to fresh human serum were largely lost after incubation with neuraminidase. No evidence was obtained to suggest that CMP-NANA is an inducer of new protein synthesis as well as a substrate for the sialylation of LPS. Little radioactivity was incorporated into components other than LPS. Sialylated, serum resistant gonococci were less able than serum susceptible gonococci to absorb the bactericidal activity of fresh human serum. Hence, we conclude that serum resistance conferred on gonococci by CMP-NANA is due to transfer of sialyl groups to surface LPS sites and this inhibits their reaction with bactericidal antibody in human serum.

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.

Characterization of the susceptibility of Pseudomonas aeruginosa to complement-mediated killing: role of antibodies to the rough lipopolysaccharide on serum-sensitive strains

The mechanism of complement-mediated killing of seven serum-sensitive Pseudomonas aeruginosa strains was examined. All seven strains were sensitive to the bactericidal activity of 20% pooled normal human serum (PNHS) containing magnesium EGTA, which blocks the classical complement pathway (CCP), or 20% PNHS preheated to 50 degrees C for 20 min, which inactivates the alternative complement pathway, suggesting that either pathway was effective against these strains. However, for four of these strains, optimal killing required the function of both pathways. Preabsorption of PNHS with serum-sensitive strains dramatically reduced the killing activity of serum for the homologous strains when a concentration of 10% serum was used, implying a role for antibody in the activation of complement via the CCP. Affinity purification of antibodies to the rough lipopolysaccharide (LPS) on strain 144M resulted in a pool of antibodies which could restore all of the bactericidal activity and most of the C3 activation-deposition activity of serum which had been lost by preabsorption with 144M. Confirmation that the LPS was the target for these bactericidal antibodies was provided by demonstrating that exogenously added 144M LPS inhibited the killing activity of PNHS. These anti-144M LPS-specific antibodies were also bactericidal for the six other serum-sensitive strains examined, suggesting that all seven strains shared an antigenic determinant recognized by these anti-144M LPS-specific antibodies. Results from cross-absorption studies imply that there are bactericidal antibodies in PNHS directed to additional bacterial targets. These studies suggest that part of the bactericidal activity of PNHS is due to binding of antibodies to the rough LPS on serum-sensitive strains, initiating activation of the CCP, and that all seven strains examined shared this bactericidal antibody-binding site.

A rapid micro-method for the study of antibody-mediated killing of bacteria, with specific application to infection of sheep with Pasteurella haemolytica

A micro-titration plate bactericidal assay was developed to measure complement-dependent antibody-mediated killing of Pasteurella haemolytica. Sera and lung washings from specific pathogen-free (SPF) lambs convalescent from a challenge with live, virulent P. haemolytica were bactericidal in the presence of complement. Similar samples from naive SPF lambs had no such activity. Purified IgG derived from a convalescent lamb serum was as bactericidal as the whole serum. Absorption of convalescent serum with lipopolysaccharide from P. haemolytica abolished bactericidal activity, suggesting that this antigen may be a target for antibody in the bactericidal complex.

Role of lipopolysaccharide and complement in susceptibility of Klebsiella pneumoniae to nonimmune serum

The role of lipopolysaccharide (LPS) in the susceptibility of Klebsiella pneumoniae to serum and the mechanism of complement activation by serum-susceptible (SerS) strains were investigated. The classical and alternative complement pathways are involved in serum killing of susceptible K. pneumoniae strains. The LPS composition seems to play a very important role in the serum bactericidal reaction, while capsular polysaccharide from this bacterium does not play any role. High-molecular-weight LPS from serum-resistant (Serr) K. pneumoniae strains was able to inhibit completely the serum bactericidal activity. LPS from SerS K. pneumoniae strains was not able to inhibit completely the serum bactericidal activity; low-molecular-weight LPS from Serr K. pneumoniae strains could not either. All these findings suggested that LPS composition, especially the O-antigen polysaccharide chains, contributes to the susceptibility of K. pneumoniae strains to complement-mediated serum bactericidal activity.

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.

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.

Reactivity of sera from sheep immunised with individual outer membrane proteins of Bacteroides nodosus against heterologous bacterial strains

In order to identify those bacterial antigens which might be involved in immunity against ovine footrot, antisera were raised in sheep to 6 proteins in the outer membrane complex (OMC) of one strain of Bacteroides nodosus. Examination of the specificity of these antisera by Western blotting, crossed immunoelectrophoresis (XIEP) and IEP, revealed that they recognized the homologous OMC protein, but did not precipitate either undenatured pili or OMC, nor could they agglutinate the homologous bacteria. In contrast, anti-OMC and anti-pili sera could precipitate OMC or pili respectively, and agglutinate whole bacteria. Subsequent analysis of these sera against 5 strains of B. nodosus from different serogroups revealed that Proteins 1, 3 and 4 had a similar antigenic structure in all strains examined. The reactivity of anti-pili sera was restricted to homologous bacteria whereas anti-pilin sera (raised against denatured pili) also reacted with pilin from 2 of 3 heterologous strains. However, none of the patterns of staining or absorption of any of these sera matched the spectrum of cross-protection afforded by vaccination of sheep with B. nodosus strain 198 cells. The results question the role of individual OMC proteins in cross-protective immunity and may imply that interactions between several bacterial components are involved in the phenomenon.

Effect of dilution rate on lipopolysaccharide and serum resistance of Neisseria gonorrhoeae grown in continuous culture

Growth of Neisseria gonorrhoeae strain FA171 in continuous culture under glucose-limiting conditions resulted in a growth-rate-dependent change in the lipopolysaccharide (LPS). The evidence for this change is an alteration in the mobility of purified alkali-treated LPS on sodium dodecyl sulfate-polyacrylamide gels and a quantitative difference in the amount of the LPS serotype antigen. The LPS from cells grown at a low dilution rate (0.12 h-1) contained ca. eightfold less serotype antigen than the LPS from cells grown at a high dilution rate (0.56 h-1). The decrease in LPS serotype antigen was associated with an increase in sensitivity to the bactericidal activity of normal human serum and an increase in cell surface hydrophobicity. An increase in the amount of serotype antigen was associated with a reduction in the accessibility of a monoclonal antibody to a core LPS determinant, an increase in resistance to normal human serum, and a decrease in cell surface hydrophobicity. The microheterogeneity of gonococcal LPS with respect to the content of serotype antigen may result from an alteration in the metabolism of glucose.

Bactericidal and bacteriolytic activity of serum against gram-negative bacteria

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A bactericidal microassay for testing serum sensitivity of Neisseria gonorrhoeae

A reproducible gonococcal serum bactericidal microassay is described which has easily determined endpoints and lends itself to large scale tests. The microassay may be used to assess sensitivity to normal human serum among strains of gonococci, and to define the antigens conferring this sensitivity. It may be readily adapted to test for bactericidal activity in hyperimmune antisera and to evaluate antigens which inhibit serum bactericidal 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.

Natural bactericidal activity of human serum against Neisseria meningitidis isolates of different serogroups and serotypes

We used a microtiter assay, standardized with serum-sensitive and serum-resistant strains of Neisseria gonorrhoeae, to determine the serum sensitivity of Neisseria meningitidis isolates of different serogroups and serotypes. Numbers of serum-resistant isolates varied among serogroups: group A = 7/8 (88%), group B = 26/50 (52%), group C = 5/8 (63%), group Y = 4/6 (67%), group W135 = 5/8 (63%), group 29E (Z') = 0/8 (0%), nongroupable isolates = 0/8 (0%). In comparison to group B isolates, group A isolates were more serum resistant (P less than 0.06), and group 29E and nongroupable isolates were more serum sensitive (P less than 0.001). Poor correlation was observed between serum sensitivity results and group-specific levels of bactericidal antibody in the normal human serum of volunteers. The frequency of serum-resistant strains among group B disease isolates (45%) was not significantly different from throat isolates of asymptomatic carriers (52%). Serotype 2 isolates of group B were no more serum resistant than were other serotypes examined. The serum sensitivity of meningococci appears to involve both capsular and noncapsular antigens and varies between serogroups. The increased serum sensitivity of nongroupable and group 29E isolates may account for the low incidence of disease caused by these organisms.

Pyocin-resistant lipopolysaccharide mutans of Neisseria gonorrhoeae: alterations in sensitivity to normal human serum and polymyxin B

Pyocins from Pseudomonas aeruginosa were used to select several lipopolysaccharide (LPS) mutants of Neisseria gonorrhoeae strain FA19. Three classes of LPS mutans were found in the initial group selected for study. The LPS of one class lacked galactose. That of a second group lacked the typical heptose found in the parental LPS, was reduced in glucose, galactose, and N-acetylglucosamine content, appeared to contain a new unidentified sugar component, and consisted of two species of LPS separable on sodium dodecyl sulfate-polyacrylamide gels. The LPS of a third strain lacked the heptose, glucose, galactose, and N-acetylglucosamine found in the oligosaccharide portion of parental FA19 LPS. The minimal inhibitory concentration for polymyxin B of the mutant strains was 3 to 4 times that of the parental strain. The strains lacking only galactose were as resistant as the parent to the bactericidal action of normal human serum, but cells of the other two classes were quickly killed by serum. Gonococcal LPS thus appears to be important in determining phenotypic properties of the cells.

Optimal strategies in immunology III. The IgM-IgG switch

During a primary immune response generally two classes of antibody are produced, immunoglobulin M (IgM) and immunoglobulin G (IgG). It is currently thought that some lymphocytes which initially produce IgM switch to the production of IgG with the same specificity for antigen. During a secondary immune response IgG is the predominant antibody made throughout the response. In this paper we address the question of why such apparently complicated modes of response should have been adapted by evolution. We construct mathematical models of the immune response to growing antigens which incorporate complement dependent cell lysis. By comparing the times required to eliminate antigen we show that under certain conditions it is advantageous for an animal to switch some of its lymphocytes from IgM to IgG production during a primary response, but yet to secrete only IgG during a secondary response. The sensitivity of such a conclusion to parameter variations is studied and the biological basis and implications of our models are fully discussed.

Strain differentiation of Neisseria gonorrhoeae by reverse passive hemagglutination

A reverse passive hemagglutination test that utilizes human erythrocytes coated with antibody to gonococci was developed to distinguish differences among 11 strains of Neisseria gonorrhoeae. Different rabbits were immunized with each strain of gonococcus. Antibody was purified by passing antiserum over an immunoadsorbent column containing homologous cell walls trapped in a cross-linked polyacrylamide gel. Antibody, after absorption with N. meningitidis, was used for coating 11 individual suspensions of erythrocytes, each with antibody to one gonococcal strain. The panel of coated erythrocytes was added to microtiter trays containing dilutions of homologous bacterial lysate and lysates from 10 heterologous strains. Agglutination titers were highest with homologous lysates, although cross-reactions occurred among some heterologous lysates. Lysates of nongonococcal Neisseria species and of other genera did not agglutinate coated erythrocytes. The reverse passive hemagglutination test can be a useful procedure to distinguish differences among strains of N. gonorrhoeae.

Immunological and serological diversity of Neisseria gonorrhoeae: identification of new immunotypes and highly protective strains

Gonococci, irrespective of serotype or immunotype, varied significantly in their capacity to induce immunity in animal models, and in vitro serological relatedness did not always insure in vivo cross-protection. By using a serum bactericidal assay followed by in vivo cross-protection studies, new immunotypic strains which were highly protective were identified from cultures isolated in different geographical areas and from patients with various clinical manifestations. Beta-lactamase production and gonococcal immunotype did not appear as related characteristics in that certain penicillin-sensitive strains were highly effective in immunizing animals against infection with beta-lactamase producers. The findings of this study emphasize the importance of using appropriate biological tests and strains for the investigation of gonococcal immunity and vaccine development. Immunization with a combination of a few major gonococcal immunotypic immunogens may provide substantial protection against the majority of penicillin-sensitive and beta-lactamase-producing gonococci. Investigation of isolated immunotypic immunogens is in progress.

Serology of Neisseria gonorrhoeae. Demonstration of strain-specific antigens by immunoelectrophoresis, immunofluorescence and co-agglutination techniques

Among a group of four selected strains of Neisseria gonorrhaeae, common and strain-specific antigens were demonstrated by immunoelectrophoresis, indirect immunofluorescence (IFL) and co-agglutination (COA). In preparations of ultrasonically-disrupted organisms, the strain-specific antigens appeared in crossed-line immunoelectrophoresis (C-LIE) with antigen containing intermediate agar gel as a two-peak precipitin line, one peak close to the antigen well, the other towards the anode. A similar pattern was found for each of the four strains studied. These strain-specific precipitin lines were also identified in rocket-line immunoelectrophoresis (R-LIE) tests, which were found useful for comparative studies. Using whole cells, strain-specific antigens were also demonstrated by COA and IFL tests with the use of cross-absorbed antibodies. The results corresponded to those obtained with C-LIE and R-LIE. Immunosorption experiments indicated identity between the strain-specific antigens shown by COA tests and those demonstrated by C-LIE and R-LIE tests.

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.

Comparison of antigenic heterogeneity of Neisseria gonorrhoeae strains by micro-immunofluorescence and serum bactericidal tests

The antigenic heterogeneity of Neisseria gonorrhoeae strains was assessed by the micro-immunofluorescence (micro-IF) and the serum bactericidal tests. The micro-IF test verified the antigenic heterogeneity of nine strains received from the Center for Disease Control and placed them into immunotypes A and B. The serum bactericidal system also detected different antigenic determinants among the strains. Although the micro-IF and bactericidal assays did not correspond in each instance, the overall pattern of similarities and differences among these gonococcal strains was similar. The micro-IF pattern obtained with mouse antisera was identical to the pattern revealed with guinea pig antisera. Different colony type organisms showed similar sensitivity in the bactericidal test. The micro-IF test is a rapid technique for the immunotyping of N. gonorrhoeae and has the additional advantages of reproducibility and simplicity.

Effects of iron and culture filtrates on killing of Neisseria gonorrhoeae by normal human serum

Neisseria gonorrhoeae GC9, both colony types T2 and T4, were killed by normal human serum, although populations of colony type T4 were more susceptible. Ferric ammonium citrate prevented the killing of populations of both T2 and T4 colony types. Other iron compounds tested showed no protective effect, nor did ammonium citrate or the divalent cations magnesium or calcium. A filtrate from cultures of an N. gonorrhoeae strain grown in a liquid defined medium showed a similar protective effect in the serum assay. The filtrate appeared to chelate iron, as measured by decreased ability of iron-free transferin to bind iron in the presence of the filtrate. However, the two effects did not appear to be related. Neither ferric ammonium citrate nor the culture filtrate sufficiently inactivated complement to account for protection.

Serological diagnosis of gonorrhoea by an enzyme-linked immunosorbent assay (Elisa)

IgG antibody to an outer membrane protein extracted from Neisseria gonorrhoeae was measured in patients with gonorrhoea. The level in such patients was significantly higher than in normal controls or in patients with other conditions who were attending the clinic for sexually transmitted diseases. Significantly higher antibody levels were detectable in half the patients within a few days of infection and in a similar proportion of carriers--both male and female. Men with rectal gonorrhoea had particularly high antibody levels. Sixteen per cent of presumptively normal men and 11% of normal women gave positive results but the actual false positive rate could be lower.

Cell-mediated immune response in gonococcal infections

Peripheral blood lymphocyte (PBL) transformation stimulated by gonococcal and meningococcal antigens was studied in 29 men and 21 women with uncomplicated gonorrhoea. The blastogenic responses of PBLs from these men and women were substantially higher than from normal controls. Cross-reactivity between Neisseria gonorrhoeae and Neisseria meningitidis was manifested by the PBL transformation responses in patients with gonorrhoea to non-purified meningococcal antigen (MGC-I). In both male and female patients the PBLs were stimulated by non-purified gonococcal antigen (GC-I) and by non-purified meningococcal antigen. The extent of the blastogenic response in women was much greater than in men. Partial purification of these antigens by gel chromatography resulted in reduced cross-reactive responses to the semi-purified meningococcal antigen (MGC-II). Female patients demonstrated marked stimulation with the semi-purified gonococcal antigen (GC-II), while male patients showed slight stimulation with GC-II. It is possible that cell-mediated immunity may act to limit the spread of gonococcal infection beyond the genital mucous membranes.

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

The role of gonococcal antigens in serum bactericidal activity was determined for an isolate of Neisseria gonorrhoeae from a patient with disseminated gonococcal infection (DGI). Gonococcal outer membranes were purified by differential ultracentrifugation of sheared organisms treated with EDTA. The membranes were solubilized in an endotoxin-disaggregating buffer, and the proteins were separated from the endotoxin by molecular sieve chromatography. Chemical characterization of the endotoxin from the DGI strain revealed the presence of heptose (7.8% of carbohydrate composition) and 2-keto-3-deoxyoctonate (6.1%, wt/wt) in concentrations similar to rough endotoxins of gram-negative enteric bacteria. Dermal Schwartzman reactions were positive for this endotoxin (4 mug) and the corresponding outer membrane (139 mug), but negative for the protein fraction (>500 mug). The patient's whole serum or the IgG fraction, each with complement, reduced the number of the infecting organisms by greater than 1 log(10) in a bactericidal assay. Outer membrane and its protein and endotoxin fractions (0.8-500 mug) from the DGI strain were separately preincubated with the patient's convalescent serum and specific inhibition of bactericidal activity occurred with the endotoxin fraction (25 mug) and the outer membrane (100 mug); the protein (500 mug) exhibited no inhibition. Similar results were obtained by inhibiting the bactericidal activity of rabbit antiserum, prepared by intravenous inoculation of an isolate from a patient with pelvic inflammatory disease, with antigen purified from that strain. That this was specific immune inhibition and not anticomplementary activity was shown by the failure of these antigens to inhibit other complement-dependent bactericidal systems.

Penicillin sensitivity and serum resistance are independent attributes of strains of Neisseria gonorrhoeae causing disseminated gonococcal infection

We have determined that isolates of Neisseria gonorrhoeae from patients with disseminated gonococcal infection (DGI) are different from randomly collected isolates from patients with uncomplicated (local) disease. Our comparison was based on the six phenotypic properties of: sensitivity to penicillin (PenS), erythromycin, and streptomycin; resistance to the bactericidal effects of pooled human sera; requirements for arginine, hypoxanthine, and uracil (AHU-); and sensitivity to toxic agar. Although the marked association among these traits made analysis difficult, several factors independently related to virulence were defined. The DGI isolates were significnatly more PenS and resistant to serum, even when the other variables were held constant. An apparent correlation between AHU- auxotype and virulence was shown to be due to the PenS property of most AHU- isolates. Thus, certain mutations to antibiotic resistance as well as susceptibility to sera, may result in loss of virulence in the gonococcus, perhaps through alteration of cell envelope structure.

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.

Immunological and serological diversity of Neisseria gonorrhoeae: gonococcal serotypes and their relationship with immunotypes

Strains of gonococcus were shown to be immunologically heterologous. Serum bactericidal activity generally correlated with induced immunity to gonococcal challenge as detected by the guinea pig subcutaneous chamber model. Sera devoid of bactericidal activity reflected the lack of cross-protection in subcutaneous chambers. Factors affecting the bactericidal assay described in this report include (i) source of complement, (ii) concentration of test antigen and complement activity, and (iii) presence of calcium and magnesium ions and bovine serum albumin in diluent. Poor correlation was observed between agglutinating activity of the immune sera and protection.

Gonococci causing disseminated gonococcal infection are resistant to the bactericidal action of normal human sera

The susceptibility of strains of Neisseria gonorrhoeae to the bactericidal action of normal human sera was determined for isolates from patients with disseminated gonococcal infection and uncomplicated gonorrhea. Serum susceptibility was correlated with penicillin susceptibility and auxotype. 38 of 39 strains (97%) of N. gonorrhoeae from Seattle patients with disseminated gonococcal infection were resistant to the complement-dependent bactericidal action of normal human sera. 36 of these were inhibited by less than or equal to mug/ml of penicillin G and required arginine, hypoxanthine, and uracil for growth on chemically defined medium (Arg-Hyx-Ura- auxotype). 12 of 43 isolates from patients with uncomplicated gonorrhea were also of the Arg-Hyx-Ura-auxotype, inhibited by less than or equal to 0.030 mug/ml of penicillin G, and serum resistant. Of the 31 remaining strains of other auxotypes isolated from patients with uncomplicated gonorrhea, 18 (58.1%) were sensitive to normal human sera in titers ranging from 2 to 2,048. The bactericidal action of normal human sera may prevent the dissemination of serum-sensitive gonococci. However, since only a small proportion of individuals infected by serum-resistant strains develop disseminated gonococcal infection, serum resistance appears to be a necessary but not a sufficient virulence factor for dissemination. Host factors such as menstruation and pharyngeal gonococcal infection may favor the dissemination of serum-resistant strains. Since serum-resistant Arg-Hyx-Ura strains are far more frequently isolated from patients with disseminated gonococcal infection than serum-resistant strains of other auxotypes, Arg-Hyx-Ura-strains may possess other virulence factors in addition to serum resistance.

Inhibition of Neisseria gonorrhoeae by a bacteriocin from Pseudomonas aeruginosa

Supernatants from broth-grown cultures of Pseudomonas aeruginosa PA 103 exhibited bactericidal activity against Neisseria gonorrhoeae. The concentration of the bactericidal substance increased significantly after induction by mitomycin C. Purification was effected by salt fractionation, chromatography on diethylaminoethyl-cellulose, and sedimentation by centrifugation at 100,000 x g for 90 min. Electron microscopy of this purified preparation revealed structures resembling R-type pyocins in both the contracted and uncontracted state. Pyocins in the contracted state were observed in association with the gonococcal cell surface. No loss of bactericidal activity was observed after treatment with proteolytic enzymes. Standard pyocin typing procedures identified the pyocin pattern as 611 131. The bactericidal activity of this pyocin was examined on various species of Neisseria. Out of 56 strains of N. gonorrhoeae from disseminated and nondisseminated infections, all were susceptible to pyocin 611 131. However, only 3 of 20 strains of N. meningitidis and 5 of 16 strains of N. lactamica were susceptible. The bactericidal activity that pyocin 611 131 has for N. gonorrhoeae and other species of Neisseria is significant because it departs from the expected specificity that heretofore has distinguished bacteriocins from most "classical" antibiotics.

The serological classification of Neisseria gonorrhoeae. I. Isolation of the outer membrane complex responsible for serotypic specificity

Neisseria gonorrhoeae has been subdivided into several classes of serological distinct groups. The serotyping system is based upon the antigenic specificity of a protein serotype antigen. This protein is the major polypeptide of the outer membrane of the gonococcus and accounts for over 60% of that membrane's total protein. The serotype antigen complex was isolated by mild extraction of intact organisms in 200 mM lithium acetate buffer, pH 6.0 with 10 mM EDTA for 2 h at 45 degrees C. The extract was fractionated on Sepharose 6B and partially purified by precipitation at pH 4.2 by addition of 10% (vol/vol) acetic acid. Each serotype antigen has a unique subunit molecular size as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Preliminary typing of a gonococcal strain may be performed by comparative SDA-PAGE. To date, 16 different serotypes, representing a diverse distribution, have been isolated.

Specificity of human serum antibodies against endotoxin from N. gonorrhoeae

Sera from patients with gonorrhoea were used to study the specificity of human antibodies against determinant a of endotoxin from gonococcal strains 8551, V, and VII. The sera were tested by an indirect haemagglutination technique before and after absorption with endotoxin from the same strains. The sera were used untreated and treated with mercaptoethanol (ME). The untreated and ME-treated sera showed antibody activity against all the a determinants when examined unabsorbed. After absorption with any of the endotoxin preparations the sera usually demonstrated antibody activity against one or both of the other preparations. The pattern of reactivity thus observed differed from one serum to another. Treatment of sera with ME resulted in an altered pattern of reactivity of four of the five sera. The results indicate multispecificity of human antibodies against the a determinants.