Neisseria meningitidis, pathogenetic mechanisms to overcome the human immune defences

Neisseria meningitidis is hosted only by humans and colonizes the nasopharynx; it survives in the human body by reaching an equilibrium with its exclusive host. Indeed, while cases of invasive disease are rare, the number of asymptomatic Neisseria meningitides carriers is far higher. The aim of this paper is to summarize the current knowledge of survival strategies of Neisseria meningitides against the human immune defences. Neisseria meningitidis possesses a variety of adaptive characteristics which enable it to avoid being killed by the immune system, such as the capsule, the lipopolysaccharide, groups of proteins that block the action of the antimicrobial proteins (AMP), proteins that inhibit the complement system, and components that prevent both the maturation and the perfect functioning of phagocytes. The main means of adhesion of Neisseria meningitides to the host cells are Pili, constituted by several proteins of whom the most important is Pilin E. Opacity-associated proteins (Opa) and (Opc) are two proteins that make an important contribution to the process of adhesion to the cell. Porins A and B contribute to neisserial adhesion and penetration into the cells, and also inhibit the complement system. Factor H binding protein (fhbp) binds factor H, allowing the bacteria to survive in the blood. Neisserial adhesin A (NadA) is a minor adhesin that is expressed by 50% of the pathogenic strains. NadA is known to be involved in cell adhesion and invasion and in the induction of proinflammatory cytokines. Neisserial heparin binding antigen (NHBA) binds heparin, thus increasing the resistance of the bacterium in the serum.

CEACAM1 negatively regulates IL-1β production in LPS activated neutrophils by recruiting SHP-1 to a SYK-TLR4-CEACAM1 complex

LPS-activated neutrophils secrete IL-1β by activation of TLR-4. Based on studies in macrophages, it is likely that ROS and lysosomal destabilization regulated by Syk activation may also be involved. Since neutrophils have abundant expression of the ITIM-containing co-receptor CEACAM1 and Gram-negative bacteria such as Neisseria utilize CEACAM1 as a receptor that inhibits inflammation, we hypothesized that the overall production of IL-1β in LPS treated neutrophils may be negatively regulated by CEACAM1. We found that LPS treated neutrophils induced phosphorylation of Syk resulting in the formation of a complex including TLR4, p-Syk, and p-CEACAM1, which in turn, recruited the inhibitory phosphatase SHP-1. LPS treatment leads to ROS production, lysosomal damage, caspase-1 activation and IL-1β secretion in neutrophils. The absence of this regulation in Ceacam1^−/− neutrophils led to hyper production of IL-1β in response to LPS. The hyper production of IL-1β was abrogated by in vivo reconstitution of wild type but not ITIM-mutated CEACAM1 bone marrow stem cells. Blocking Syk activation by kinase inhibitors or RNAi reduced Syk phosphorylation, lysosomal destabilization, ROS production, and caspase-1 activation in Ceacam1^−/− neutrophils. We conclude that LPS treatment of neutrophils triggers formation of a complex of TLR4 with pSyk and pCEACAM1, which upon recruitment of SHP-1 to the ITIMs of pCEACAM1, inhibits IL-1β production by the inflammasome. Thus, CEACAM1 fine-tunes IL-1β production in LPS treated neutrophils, explaining why the additional utilization of CEACAM1 as a pathogen receptor would further inhibit inflammation.

Pathogens often evade the immune system by directly binding to and inhibiting neutrophils, abundant white cells that accumulate at the site of infection. For example Gram-negative Neisseria pathogens, such as those that cause gonorrhea or meningitis, bind the neutrophil receptor CEACAM1. Gram-negative bacteria express lipopolysaccharide (LPS) that interacts with toll-like receptor-4 (TLR4) on neutrophils. Since CEACAM1 is an inhibitory receptor, we hypothesized that LPS activation of TLR4 would be inhibited. In this paper we show that this is the case and that the mechanism of LPS inhibition involves induction of a complex between the LPS receptor TLR4, CEACAM1 and an activating kinase called Syk. In the presence of CEACAM1, an inhibitory phosphatase (opposes the kinase) is recruited to the complex that prevents the activation of Syk. The net effect is the inhibition of the pathway that normally leads to the production of the pro-inflammatory cytokine IL-1β. We show that this inhibition is lost in CEACAM1 deficient neutrophils leading to hyper production of IL-1β. We think that CEACAM1 fine-tunes the normal inflammatory response at the site of infection preventing hyper-inflammation, but in the case of Gram-negative pathogens that actually bind to neutrophils, inflammation is further blunted, favoring the infectious process.

Murine glia express the immunosuppressive cytokine, interleukin-10, following exposure toBorrelia burgdorferi orNeisseria meningitidis

There is growing appreciation that resident glial cells can initiate and/or regulate inflammation following trauma or infection in the central nervous system (CNS). We have previously demonstrated the ability of microglia and astrocytes, resident glial cells of the CNS, to respond to bacterial pathogens by rapid production of inflammatory mediators. However, inflammation within the brain parenchyma is notably absent during some chronic bacterial infections in humans and nonhuman primates. In the present study, we demonstrate the ability of the immunosuppressive cytokine, interleukin-10 (IL-10), to inhibit inflammatory immune responses of primary microglia and astrocytes to B. burgdorferi and N. meningitidis, two disparate gram negative bacterial species that can cross the blood-brain barrier in humans. Importantly, we demonstrate that these organisms induce the delayed production of significant quantities of IL-10 by both microglia and astrocytes. Furthermore, we demonstrate that such production occurs independent of the actions of bacterial lipopolysaccharide and is secondary to the autocrine or paracrine actions of other glia-derived soluble mediators. The late onset of IL-10 production by resident glia following activation, the previously documented expression of specific receptors for this cytokine on microglia and astrocytes, and the ability of IL-10 to inhibit bacterially induced immune responses by these cells, suggest a mechanism by which resident glial cells can limit potentially damaging inflammation within the CNS in response to invading pathogens, and could explain the suppression of inflammation seen within the brain parenchyma during chronic bacterial infections.

Characterization and immunogenicity of Kingella kingae outer-membrane proteins

In recent years, Kingella kingae has emerged as an important pediatric pathogen but the antigenicity of the organism and the host immune response have not been studied. Outer membrane proteins (OMPs) of 57 K. kingae isolates were characterized and the immune response of 19 children with invasive infections was studied by immunoblotting. Kingella kingae OMPs were remarkably similar disregarding place and time of isolation and associated clinical condition (asymptomatic carriage, bacteremia, endocarditis, septic arthritis or osteomyelitis). Most OMPs were immunogenic but the specific bands that reacted in each strain and the intensity of the reactions varied substantially. When convalescent sera were reacted with heterologous strains, bands that either were not recognized by the homologous serum or were not present in the homologous strain were visualized. These results demonstrate that OMPs of K. kingae are highly conserved but suggest that some epitopes are polymorphic, resulting in a variable pattern of immune response.

Immune response to invasive Kingella kingae infections, age-related incidence of disease, and levels of antibody to outer-membrane proteins

The immune response to Kingella kingae was determined by enzyme-linked immunosorbent assay, using outer-membrane proteins as coating antigen, in 19 children with invasive infection. The age-related incidence of K. kingae disease in southern Israel during 1988-2002 was calculated and correlated with serum antibody levels in healthy children. Significant increases in immunoglobulin G (IgG) levels were found in children convalescing after invasive infections. The incidence was 1.3, 40.3, 23.9, 5.7, and 1.9 cases/100,000 children among those aged 0-5, 6-11, 12-23, 24-35, and 36-47 months, respectively. A low attack rate and undetectable serum IgA and high IgG levels were found during the first 6 months of life, which indicates that protection was conferred by maternally derived immunity. The high attack rate found among 6-24-month-old children coincides with the age at which antibody levels were lowest. Low incidence of disease and increasing antibody levels were found among older children, which probably represents cumulative experience with K. kingae antigens via colonization or infection.

Mucosal vaccination against encapsulated respiratory bacteria--new potentials for conjugate vaccines?

Polysaccharide (PS)-encapsulated bacteria such as Haemophilus influenzae type b (Hib), Streptococcus pneumoniae (pneumococcus), Neisseria meningitides (meningococcus) and group B streptococcus (GBS), cause a major proportion of disease in early childhood. Native PS vaccines are immunogenic and provide protection against disease in healthy adults but do not induce immunological memory. PSs are T-cell-independent antigens and do not elicit antibodies in infants and young children, but by conjugating PS to proteins they become T-cell dependent and immunogenic at an early age. Despite excellent efficacy of PS-protein conjugate vaccines against invasive disease, protection against mucosal infections such as pneumococcal otitis media has been less efficacious. Circulating PS-specific antibodies may protect against infections at mucosal sites, but mucosal immunoglobulin A antibodies may also contribute significantly to protection against mucosal infections. Mucosal immunization of experimental animals with conjugate vaccines against Hib, pneumococcus, meningococcus and GBS induces systemic and mucosal immune responses, which provide protection against carriage, otitis media and invasive disease in a variety of challenge models, providing new means for protection against encapsulated bacteria. In addition, mucosal immunization of neonatal mice with a pneumococcal conjugate and the nontoxic adjuvant LT-K63 has been superior to parenteral immunization in eliciting protective antibodies and PS-specific memory, and thus circumventing the limitations of antibody responses to PS that are responsible for enhanced susceptibility of neonates and infants to infections caused by encapsulated bacteria. Through T-cell dependent enhanced immunogenicity of PS-protein conjugate vaccines, mucosal immunization could be an attractive approach for early life immunization against encapsulated bacteria.

The role of porins in neisserial pathogenesis and immunity

Neisseria meningitidis and Neisseria gonorrhoeae are Gram-negative pathogenic bacteria responsible for bacterial meningitis and septicemia, and the sexually transmitted disease gonorrhea, respectively. Porins are the most represented outer membrane proteins in the pathogenic Neisseria species, functioning as pores for the exchange of ions, and are characterized by a trimeric beta-barrel structure. Neisserial porins have been shown to act as adjuvants in the immune response via activation of B cells and other antigen-presenting cells (APCs). Their effect on the immune response is mediated by upregulation of the costimulatory molecule B7-2 (CD86) on the surface of APCs, an effect that is Toll-like receptor 2- and MyD88-dependent. The effect of neisserial porins on the immune system also involves interaction with components of the complement cascade. Furthermore, neisserial porins co-localize with mitochondria of target cells, where they appear to modulate apoptosis.

Dendritic cell influx differs between the subglottic and glottic mucosae during acute laryngotracheitis induced by a broad spectrum of stimuli

Clinically, the subglottic and glottic mucosae may react differently, eg, during acute laryngotracheitis. In healthy rats, we showed previously that the composition of the mucosal immune system of the larynx also differs between these areas. Neutrophils, lymphocytes, and dendritic cells (DCs) are part of this mucosal immune system. In particular, DCs occupy a key function. They migrate into inflamed mucosae during the early phase of the immune response, which is normally characterized by an influx of neutrophils. Thus, they help to overcome the time lag between the innate and the adaptive immune responses. In the present study, the influx of DCs, neutrophils, and T lymphocytes into the subglottic and glottic mucosae of rats was examined at different time points after challenge with a broad spectrum of stimuli such as dead Moraxella catarrhalis, viable Bordetella pertussis, viable Sendai virus, and the soluble protein ovalbumin. The number of DCs increased rapidly after the application of the antigens. This increase was as rapid as the increase in neutrophils. Depending on the kind of antigen, their number in the mucosa increased up to 1,000 cells per 0.1 mm2 (Sendai virus). The comparison of different mucosal areas shows that an overwhelming number of immunocompetent cells entered the subglottic mucosa, whereas only a few cells migrated into the adjacent glottic mucosa. In conclusion, after inhalation of different kinds of antigens, the subset of immunocompetent cells investigated in this study entered the laryngeal mucosa in high numbers. The number of DCs entering the laryngeal mucosa was higher than the numbers of the other immune cells investigated. This finding underlines their function as first-line sentinels of the mucosal immune system of the larynx. The observation that the number of cells entering the laryngeal mucosa is location-dependent indicates the ability of adjacent laryngeal regions to react differently. This is similar to the clinical observation of a selective subglottic reaction during acute laryngotracheitis.

The outer membrane proteins UspA1 and UspA2 of Moraxella catarrhalis are highly conserved in nasopharyngeal isolates from young children

UspA1 and UspA2 of Moraxella catarrhalis are vaccine candidates. The aims of this study were to determine: (1) the frequencies of occurrence and (2) the degrees of conservation of two surface-exposed epitopes of the uspA1 and uspA2 genes and their respective gene products in 108 nasopharyngeal isolates from young children. The uspA1 and uspA2 genes were detected in 107 (99%) and 108 (100%) isolates, respectively. Twenty-three of 108 uspA2 genes (21%) were identified as the variant gene uspA2H. One-hundred and five isolates (97%) expressed the mAb17C7-reactive epitope shared by UspA1 and UspA2, and 103 isolates (95%) reacted with the UspA1-specific mAb24B5. The only isolate which lacked a uspA1 gene demonstrated reduced adherence to HEp-2 cells and complement sensitivity. The data indicate that both uspA genes and the expression of at least two surface-exposed epitopes are virtually ubiquitous in isolates from a population at risk for otitis media. A vaccine capable of inducing a bactericidal immune response against the mAb17C7- and/or mAb24B5-reactive epitopes appears promising.

Vaccination and otitis media

Acute otitis media (AOM) caused by Streptococcus pneumoniae, Haemophilus influenzae or Moraxella catarrhalis may induce specific systemic and/or local immune responses, which may protect from otitis media caused by the same bacteria. However, earlier clinical trials with pneumococcal capsular polysaccharide vaccines have not been successful in preventing AOM. Recently developed pneumococcal polysaccharide-protein conjugates proved immunogenic even in infants, and a heptavalent pneumococcal CRM 197 conjugate vaccine gave a 57% reduction in the number of pneumococcal AOM episodes caused by the vaccine serotypes in infants in Finland. H. influenzae causing AOM is noncapsulated, and like M. catarrhalis, calls for another kind of vaccine development. Suitable vaccine candidates are not yet available but are under development and being tested for immunogenicity and safety. In some trials influenza vaccines have shown protection from AOM during respective viral epidemics. Passive immunoprophylaxis might be an important alternative for immunocompromised children, although this approach has not been successful so far. Mucosal immunization and the advent of DNA and gene technology will open new interesting prospects in the future.

Moraxella catarrhalis: from emerging to established pathogen

Moraxella catarrhalis (formerly known as Branhamella catarrhalis) has emerged as a significant bacterial pathogen of humans over the past two decades. During this period, microbiological and molecular diagnostic techniques have been developed and improved for M. catarrhalis, allowing the adequate determination and taxonomic positioning of this pathogen. Over the same period, studies have revealed its involvement in respiratory (e.g., sinusitis, otitis media, bronchitis, and pneumonia) and ocular infections in children and in laryngitis, bronchitis, and pneumonia in adults. The development of (molecular) epidemiological tools has enabled the national and international distribution of M. catarrhalis strains to be established, and has allowed the monitoring of nosocomial infections and the dynamics of carriage. Indeed, such monitoring has revealed an increasing number of B-lactamase-positive M. catarrhalis isolates (now well above 90%), underscoring the pathogenic potential of this organism. Although a number of putative M. catarrhalis virulence factors have been identified and described in detail, their relationship to actual bacterial adhesion, invasion, complement resistance, etc. (and ultimately their role in infection and immunity), has been established in a only few cases. In the past 10 years, various animal models for the study of M. catarrhalis pathogenicity have been described, although not all of these models are equally suitable for the study of human infection. Techniques involving the molecular manipulation of M. catarrhalis genes and antigens are also advancing our knowledge of the host response to and pathogenesis of this bacterial species in humans, as well as providing insights into possible vaccine candidates. This review aims to outline our current knowledge of M. catarrhalis, an organism that has evolved from an emerging to a well-established human pathogen.

Progress in the prevention of otitis media through immunization

OBJECTIVE

To review the progress that has been made in developing effective vaccines against the major bacterial pathogens responsible for acute otitis media.

DATA SOURCE

Review of the literature with the aid of the MEDLINE database using the search terms otitis media and otitis media and vaccine.

DATA EXTRACTION

Data were collected from clinical trials and laboratory studies.

FINDINGS

The heptavalent pneumococcal conjugated vaccine, Prevnar, reduced the incidence of acute otitis media from all causes by 7% in one study and by 6% in another study. For culture-positive pneumococcal otitis media, the point estimate of efficacy was 66.7% in one study, and the reduction in incidence was 34% in another study. A Phase I clinical trial has been completed successfully for a conjugated vaccine against nontypeable Haemophilus influenzae (NTHi), which has high immunogenicity for mice and rabbits, induces complement-mediated bactericidal activity against NTHi in rabbits, and is protective against NTHi otitis media in chinchillas. A conjugated vaccine against Moraxella catarrhalis elicits strong immune responses in mice and rabbits and induces complement-mediated bactericidal activity in rabbits.

CONCLUSION

The prevention of otitis media is likely to require multivalent pneumococcal, NTHi, and M. catarrhalis vaccines, and these vaccines likely can be developed within a decade.

Vaccines for Moraxella catarrhalis

Vaccine development for Moraxella catarrhalis is in the antigen identification stage. M. catarrhalis does not appear to synthesize secreted antigens such as exotoxins, nor does it appear to possess a carbohydrate capsule. Modified forms of these antigens are usually good vaccine components. There is some interest in whole bacterial cells and membrane fractions, but the search has largely focused on purified outer surface antigens. All of the present antigens have been selected based on the response seen in animals, although the antibody response seen in people exposed to the bacterium provides some guidance. The antibody response provides information related to the cross-strain preservation of epitopes and whether they are surface exposed. Antigens that elicit antibodies that have complement dependent bactericidal capacity, opsonophagocytic activity or interfere with one of the antigen's known functions such as adhesion or nutrient acquisition are particularly valued. In addition to examining the antibody response, some antigens have been evaluated in a murine pulmonary clearance model. Using these assays and model, several vaccine candidates have been identified. The antigens may be roughly classified by the function they serve the bacterium. One set appears to promote adhesion to host tissues and includes the hemagglutinins, ubiquitous surface protein A1 (UspA1), and possibly the CD protein. A second set is involved in nutrient acquisition. This set includes the lactoferrin binding protein A (LbpA) and lactoferrin binding protein B (LbpB), the transferrin binding protein A (TbpA) and transferrin binding protein B (TbpB), the CD and E porins, and the Catarrhalis outer membrane protein B (CopB). A third set is comprised of antigens involved in virulence and it includes lipooligosaccharide (LOS) and the ubiquitous surface protein A2 (UspA2). Antigens of unknown function, such as the 200K protein, may also be vaccine candidates. The antigens that are most suitable will be determined in clinical studies that are only beginning now.

Immune response to surface protein A of Streptococcus pneumoniae and to high-molecular-weight outer membrane protein A of Moraxella catarrhalis in children with acute otitis media

The immune response was evaluated in 11 children with Streptococcus pneumoniae and in 9 children with Moraxella catarrhalis otitis media. The age of the children had a range of 4-32 months. The mean IgG, IgM, and IgA antibody responses to surface protein A (PspA) of S. pneumoniae in sera from children at the acute and convalescent stages were 4864 versus 5831 ng/mL, P<.05, 1075 versus 3752 ng/mL, P<.05, and 67 versus 93 ng/mL, nonsignificant (NS), respectively. The mean IgG, IgM, and IgA antibody responses to the high-molecular-weight outer membrane protein (UspA) of M. catarrhalis in sera from children at acute and convalescent stages were 710 versus 935 mg/mL, NS; 1895 versus 2646 ng/mL, NS; and 121 versus 204 ng/mL, P<.05, respectively. These data show that PspA and UspA are immunogenic in children after otitis media.

Bacteremic Moraxella catarrhalis pneumonia in a patient with immunoglobulin deficiency

A-75-year old woman with agammaglobulinemia developed Moraxella catarrhalis bacteremic pneumonia. M. catarrhalis pneumonia is rarely associated with bacteremia, and neutrophils have been reported as a significant factor in the host defense system against this bacteria. This case suggests that immunoglobulin also plays a key role in the host defense system against M. catarrhalis.

Acute laryngitis in the rat induced by Moraxella catarrhalis and Bordetella pertussis: number of neutrophils, dendritic cells, and T and B lymphocytes accumulating during infection in the laryngeal mucosa strongly differs in adjacent locations

Infectious laryngotracheitis results in fulminant respiratory distress. During the disease, the subglottic mucosa is selectively infected and swollen, the reason for this preference being unknown. Therefore, in the present study the immunoreaction of the laryngeal mucosa was studied in the rat after inhalation of either heat-killed Moraxella catarrhalis (PVG rats) or application of viable Bordetella pertussis (BN rats). The number of neutrophils, macrophages, dendritic cells, and T and B lymphocytes was determined in the mucosa of the supraglottic, glottic, and subglottic area of the larynx as well as in the trachea. After application of the pathogens, the mucosa of the subglottic area was significantly more affected than the glottic mucosa. Already 1 h after application of M. catarrhalis, not only neutrophils but also dendritic cells and T and B lymphocytes were found both subepithelially and within the epithelium. They showed a similar kinetic progression, although at a different level. Two hours after application of M. catarrhalis, at the peak of inflammation, dendritic cells (173 +/- 10 cells/0.1 mm2) outnumbered neutrophils (54 +/- 9 cells/0.1 mm2), T lymphocytes (25 +/- 2 cells/0.1 mm2), and B lymphocytes (4.3 cells/0.1 mm2). The subglottic area (and the trachea) contained about three to five times more cells than the glottic area. In contrast, the number of local macrophages was lower in the subglottic area (24 +/- 5 cells/0.1 mm2) compared with that of the glottic area (38 +/- 6 cells/0.1 mm2), and did not change after application of both M. catarrhalis and B. pertussis. Thus, infectious laryngotracheitis in the rat closely resembles the clinical picture in children. In addition, the present results show a major difference in cellular influx in the mucosa of the glottic and subglottic area. This demonstrates that even in two closely adjacent locations, inflammatory responses of different magnitudes can occur, and it underlines the importance of regulatory mechanisms specific for the respective microenvironment.

Moraxella catarrhalis bacteremia: a 10-year experience

BACKGROUND

Moraxella catarrhalis commonly inhabits the upper respiratory tract and is a cause of acute otitis media and sinusitis in children. It is an infrequent cause of invasive disease.

METHODS

We reviewed records of all patients with positive blood cultures for M catarrhalis admitted to our hospital during the 10-year period (1988 through 1997).

RESULTS

Eleven cases were identified. Age range was 11 to 32 months. Four (44%) had risk factors for infection, including sickle cell disease (2), acquired immunodeficiency syndrome (AIDS) (1), and leukopenia (1). Upper respiratory symptoms and fever were present in all patients. Ten had acute otitis media, five had sinusitis, and three had pneumonia. All isolates were beta-lactamase producers. Treatment included intravenous cefuroxime (8), cefotaxime (2), and ceftazidime (1), followed by oral amoxicillin/clavulanate or cefuroxime axetil.

CONCLUSION

Moraxella catarrhalis bacteremia should be considered in febrile young children with upper respiratory infections and/or acute otitis media especially in those with underlying immune dysfunction.

Antibody response to outer membrane proteins of Moraxella catarrhalis in children with otitis media

BACKGROUND

Moraxella catarrhalis is an important cause of bacterial otitis media, and a vaccine to prevent this disease would be highly desirable. Analysis of the dominant antigens on the surface of M. catarrhalis recognized by the human immune response to infection might aid in such a search. Such analysis would be most informative when studied in the eventual target age group for the vaccine; thus we have studied the immune response to M. catarrhalis in infants with otitis media.

METHODS

Eighteen infants (mean age, 9.4 months) experiencing an episode of otitis media caused by M. catarrhalis were studied. Acute and convalescent antibody responses were studied by whole cell enzyme-linked immunosorbent assay (heterologous strain) and by immunoblotting of outer membrane proteins (OMPs).

RESULTS

Specific IgG was detected in 17% of acute serum samples and in 61% of convalescent sera. A rise in specific IgG was detected in 10 of 12 (83%) children 8 months of age or older, compared with 1 of 6 (17%) in younger patients (P = 0.0128). Immunoblotting revealed antibody binding to several OMPs with some detectable cross-reactivity. Four dominant OMP targets were identified, corresponding to UspA, TbpB, CopB and a approximately 60-kDa protein.

CONCLUSIONS

A combination of antigens might form the most suitable basis for a M. catarrhalis vaccine designed to prevent otitis media in this age group.

Analysis of antigenic structure and human immune response to outer membrane protein CD of Moraxella catarrhalis

Moraxella catarrhalis is an important cause of otitis media in children and lower respiratory tract infections in adults with chronic obstructive pulmonary disease (COPD). Outer membrane protein CD (OMP CD) is a 45-kDa protein which is a potential vaccine antigen to prevent infections caused by M. catarrhalis. Eight monoclonal antibodies were used to study the antigenic structure of the OMP CD molecule by assaying recombinant peptides corresponding to the sequence of the protein. This approach identified two surface-exposed epitopes, including one near the amino terminus (amino acids 25 to 44) and one in the central region of the molecule (amino acids 261 to 331). Assays with serum and sputum supernatants of adults with COPD revealed variable levels of antibodies to OMP CD among individuals. To determine which portions of the OMP CD molecule were recognized by human antibodies, three human serum samples were studied with six recombinant peptides which span the sequence of OMP CD. All three sera contained immunoglobulin G antibodies which recognized exclusively the peptide corresponding to amino acids 203 to 260 by immunoblot assay. Adsorption experiments with whole bacteria established that some of the human antibodies are directed at surface-exposed epitopes on OMP CD. We conclude that OMP CD is a highly conserved molecule which contains at least two separate epitopes which are exposed on the bacterial surface. While individual adults with COPD show variability in the immune response to OMP CD, a specific region of the OMP CD molecule (amino acids 203 to 260) is important as a target of the human immune response.

Analysis of the immunological responses to transferrin and lactoferrin receptor proteins from Moraxella catarrhalis

Moraxella catarrhalis expresses surface receptor proteins that specifically bind host transferrin (Tf) and lactoferrin (Lf) in the first step of the iron acquisition pathway. Acute- and convalescent-phase antisera from a series of patients with M. catarrhalis pulmonary infections were tested against Tf and Lf receptor proteins purified from the corresponding isolates. After the purified proteins had been separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting, we observed strong reactivity against Tf-binding protein B (TbpB; also called OMP1) and Lf-binding protein B (LbpB) but little or no reactivity against Tf-binding protein A (TbpA) or Lf-binding protein A (LbpA), using the convalescent-phase antisera. Considerable antigenic heterogeneity was observed when TbpBs and LbpBs isolated from different strains were tested with the convalescent-phase antisera. Comparison to the reactivity against electroblotted total cellular proteins revealed that the immune response against LbpB and TbpB constitutes a significant portion of the total detectable immune response to M. catarrhalis proteins. Preparations of affinity-isolated TbpA and LbpA reacted with convalescent-phase antisera in a solid-phase binding assay, but blocking with soluble TbpB, soluble LbpB, or extracts from an LbpA(-) mutant demonstrated that this reactivity was attributed to contaminants in the TbpA and LbpA preparations. These studies demonstrate the immunogenicity of M. catarrhalis TbpB and LbpB in humans and support their potential as vaccine candidates.

Moraxella catarrhalis-induced purulent otitis media in the rat middle ear. Structure, protection, and serum antibodies

To study the effects of viable and heat-killed Moraxella catarrhalis bacteria on the middle ear mucosa and to evaluate the protection after whole-cell immunizations, Sprague-Dawley rats were challenged and rechallenged with four different M. catarrhalis strains. The animals were monitored by clinical observations, bacterial and histological samples from middle ears, and serum IgG levels. Only viable bacteria at a high concentration induced purulent otitis media, which was culture positive in 58% of the cases on day 4. The infection was characterized by a mild acute reaction lasting otomicroscopically about 8 days, together with quantitative and qualitative changes of the goblet cells. Structurally the mucosal effects of the heat-killed bacteria were less pronounced in the early phase compared to the viable bacteria, but similar at the end of the experiment at 6 months. The intrabullar and subcutaneous immunizations evoked an IgG antibody response in all animals, and the protection rate after immunization was 50% or more. The induced protection was not strain-specific. The study showed the rat to be a possible alternative for the study of different aspects of M. catarrhalis otitis media, an infection that is clinically and structurally different from that elicited by Streptococcus pneumoniae and Haemophilus influenzae in the rat.

Bacteriology of the middle meatus in children

Little is known about the bacteriology of the middle meatus in children. Therefore, middle meatal samples were obtained from 50 children who underwent adenoidectomy or adenotonsillectomy, while a group of 50 children submitted to minor non-ENT surgical procedures, were used as a control group. Haemophilus influenzae, Moraxella catarrhalis and Streptococcus pneumoniae were the most frequent cultured organisms, not only in the ENT group (in 68, 50 and 60% of the children respectively) but also in the control group (40, 34 and 50%). These three potential pathogens were more frequently seen among the children of the ENT group but only for H. influenzae was the observed difference statistically significant (P = 0.009). On semiquantitative analysis, there seemed to be more negative cultures or cultures with only a few colonies in the control group, while the richer cultures were obtained from the ENT group. Again, only for H. influenzae, these differences reached a statistical significance (P = 0.003). Streptococcus viridans and Neisseria species, both organisms that might be able to inhibit colonisation by some of the pathogens, were more frequently cultured in the control than in the ENT group: Strep. viridans 30 vs. 10% (P = 0.025) and Neisseria species 14 vs. 2% (P = 0.069).

Pathogenic neisseriae: complexity of pathogen-host cell interplay

Recent studies have provided insight into the function of important neisserial adhesins (pili and Opa) and their interaction with cellular receptors, including members of heparan sulfate proteoglycan, CD66, and integrin receptor families. These interactions not only allow colonization of the human mucosa but also stimulate cellular signaling cascades involving phosphatidylcholine-dependent phospholipase C, acidic sphingomyelinase and protein kinase C in epithelial cells, and Src-related kinases, Rac1, p21-activated kinase, and Jun N-terminal kinase in phagocytic cells. Activation of these pathways is essential for cellular entry and intracellular accommodation of the pathogens but also leads to early induction of cytokine release, thus priming the immune response. Detailed knowledge of the cellular signaling cascades that are activated by infection will aid us in applying both current and novel interfering drugs (in addition to classical antibiotic therapy) as therapy and prophylaxis for persistent or otherwise difficult-to-treat bacterial infections, including periodontal infections.

Antibodies specific to outer membrane antigens of Moraxella catarrhalis in sera and middle ear effusions from children with otitis media with effusion

OBJECTIVE

Recent studies have shown that bacterial DNA is present in a significant percentage of middle ear effusions, suggesting that persistent bacterial infection may be more important in pathogenesis and recurrence of otitis media with effusion (OME) than previously considered. Although Moraxella (M.) catarrhalis is one of the most common pathogens of otitis media, relatively little is known about immune response to the organism. The objective of the present study is to investigate how systemic and local immune activities against M. catarrhalis may be associated with severity of OME.

METHODS

The antibody levels specific to outer membrane antigens of M. catarrhalis in sera and middle ear effusions (MEEs) from 59 children with OME were measured by enzyme-linked immunosorbent assay. Their ages ranged from 1 to 12 years with a median 5.0 years. The children were followed 1 year prospectively and classified into two groups with or without recurrent/persistent OME according to severity of OME during the follow-up 1 year.

RESULTS

Serum IgG, IgM, and IgA antibodies specific to outer membrane antigens of M. catarrhalis were detected in all samples and the median levels were 35, 0.93, and 1.2 microg/ml respectively. The MEE IgG, IgM, IgA, and secretory IgA antibodies were detected in over 95% samples tested and the median levels were 371, 158, 20, and 50 ng/mg total protein respectively. A comparison between acute and subacute/chronic phases revealed that the median levels of MEE IgG and IgM antibodies were higher at the acute phase (692 vs. 340, P = 0.06; 35 vs. 10, P = 0.02, respectively); while the MEE secretory IgA antibody level was increased at the subacute/chronic phase (74 vs. 35, P = 0.02). Either serum or MEE IgG antibody level was significantly lower in recurrent/persistent OME group than that in nonrecurrent/non-persistent OME group (13 vs. 43 ,microg/ml, P = 0.009; 238 vs. 577 ng/mg protein, P = 0.006, respectively).

CONCLUSIONS

These data provide additional information on the immunologic aspects of children with OME. Decreased serum and MEE IgG antibody levels specific to outer membrane antigens of M. catarrhalis may lead to failure to eliminate this organism, resulting in persistent and/or recurrent appearance of MEE.

Enhancement of pulmonary clearance of Moraxella (Branhamella) catarrhalis following immunization with outer membrane protein CD in a mouse model

Moraxella (Branhamella) catarrhalis is an important human respiratory tract pathogen. Outer membrane protein (OMP) CD is highly conserved among strains and has characteristics that indicate it may be an effective vaccine antigen. This study investigated the effect of immunization with OMP CD on pulmonary clearance following intratracheal challenge of mice with M. catarrhalis. Two routes of immunization were studied: mucosal immunization (intra-Peyer's patch followed by intratracheal boost) and intramuscular immunization with OMP CD. Both resulted in enhanced pulmonary clearance of M. catarrhalis compared with sham-immunized controls. Immunization with OMP CD induced specific antibodies in serum and bronchoalveolar lavage fluid and induced a specific lymphocyte proliferative response in T cells from mesenteric lymph nodes from mice mucosally immunized with OMP CD. On the basis of these results, OMP CD should undergo continued testing to determine whether it will induce a protective immune response in humans.

Serum antibodies specific to CD outer membrane protein of Moraxella catarrhalis, P6 outer membrane protein of non-typeable Haemophilus influenzae and capsular polysaccharides of Streptococcus pneumoniae in children with otitis media with effusion

We measured the levels of serum IgG antibodies to CD outer membrane protein of Moraxella catarrhalis, P6 outer membrane protein of non-typeable Haemophilus influenzae and capsular polysaccharides of Streptococcus pneumoniae in 168 children with otitis media with effusion (OME) who were followed prospectively, using ELISA. Serum IgG antibodies to CD, P6 and pneumococcal capsular polysaccharides were detected in all samples. The anti-pneumococcal polysaccharides antibody level was highest, followed by the anti-P6 antibody level and anti-CD antibody was lowest (median:interquartile ranges were 45.9:19.1-100 microg/ml, 15.6:9.70-23.2 microg/ml and 1.06:0.73-1.87 microg/ml, respectively). In children aged 0-6 years, there were positive correlations among the antibody levels (anti-CD vs anti-P6, r=0.325, p <0.001; anti-CD vs anti-polysaccharide, r=0.397, p <0.0001; anti-P6 vs anti-polysaccharide, r=0.175, p=0.057). However, no relationship was seen in children aged 7-15 years. Children were classified according to severity of OME during the 1-year follow-up. In children aged 0-6 years, the severity of OME correlated inversely with the levels of anti-CD antibody (r=-.23, p=0.012), of anti-P6 antibody (r=-0.292, p=0.0015), and of anti-pneumococcal polysaccharides antibody (r=-0.25, p=0.0064). However, no correlation was found between antibody levels and severity of OME in children aged 7-15 years. These data suggest that persistence and/or recurrence of OME may be due to an insufficient serum antibody response to middle ear pathogens in young children.

Isolation and characterization of two proteins from Moraxella catarrhalis that bear a common epitope

The UspA1 and UspA2 proteins of Moraxella catarrhalis are potential vaccine candidates for preventing disease caused by this organism. We have characterized both proteins and evaluated their vaccine potential using both in vitro and in vivo assays. Both proteins were purified from the O35E isolate by Triton X-100 extraction, followed by ion-exchange and hydroxyapatite chromatography. Analysis of the sequences of internal peptides, prepared by enzymatic and chemical cleavage of the proteins, revealed that UspA1 and UspA2 exhibited distinct structural differences but shared a common sequence including an epitope recognized by the monoclonal antibody 17C7. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), purified UspA1 exhibited a molecular weight of approximately 350, 000 when unheated and a molecular weight of 100,000 after being heated for 10 min at 100 degreesC. In contrast, purified UspA2 exhibited an apparent molecular weight of 240,000 by SDS-PAGE that did not change with the length of time of heating. Their sizes as determined by gel filtration were 1,150,000 and 830,000 for UspA1 and UspA2, respectively. Preliminary results indicate the proteins have separate functions in bacterial pathogenesis. Purified UspA1 was found to bind HEp-2 cells, and sera against UspA1, but not against UspA2, blocked binding of the O35E isolate to the HEp-2 cells. UspA1 also bound fibronectin and appears to have a role in bacterial attachment. Purified UspA2, however, did not bind fibronectin but had an affinity for vitronectin. Both proteins elicited bactericidal antibodies in mice to homologous and heterologous disease isolates. Finally, mice immunized with each of the proteins, followed by pulmonary challenge with either the homologous or a heterologous isolate, cleared the bacteria more rapidly than mock-immunized mice. These results suggest that UspA1 and UspA2 serve different virulence functions and that both are promising vaccine candidates.

Human antibody response to Moraxella catarrhalis antigens

Moraxella catarrhalis was isolated from 68 of 200 (34%) sputum and 56 (28%) nasopharyngeal swab samples of patients with community-acquired pneumonia. Of the 68 pneumonia patients, 42 (61.8%) were males and 26 (38.2%) females. Fifty one of the 68 patients (75%) had chronic underlying diseases. beta-lactamase was produced by 37 (54.4%) of the 68 sputum samples and 32(57.1%) of the 56 nasopharyngeal isolates. In an ELISA using outer membrane protein antigens of M. catarrhalis against patient sera showed 40 of 68 (58.8%), and 43 of 68 (63.2%) significant increase in convalescent to acute sera when IgA, IgM and IgG3 were used respectively. In control sera only of 30(3.3%) and none showed significant antibody rise when IgA, IgM and IgG3 conjugates were used respectively (P < 0.05).

Outer-membrane antigen expression by Moraxella (Branhamella) catarrhalis influences pulmonary clearance

Moraxella (Branhamella) catarrhalis is a common respiratory tract pathogen in man. The bacterium shows a strong tendency to form aggregates in vitro. A variant strain of M. catarrhalis that showed a reduced tendency to form aggregates was selected by successive in-vitro passage in broth culture from which aggregates had settled. The non-clumping variant strain showed alteration in expression of outer-membrane antigens, including the HMW-OMP, an outer-membrane protein of c. 200 kDa, outer-membrane protein CD and lipo-oligosaccharide. A mouse model for pulmonary challenge with M. catarrhalis revealed significant differences in the rate of clearance of the isogenic variant strains from the lung. The parent strain caused enhanced recruitment of neutrophils to the lung and more rapid clearance of bacteria from the lungs in comparison to the non-clumping variant. It is concluded that alteration of expression of surface molecules by M. catarrhalis has a significant impact in an in-vivo model of pulmonary clearance.

Fimbriae-mediated host-pathogen cross-talk

Recent studies show that the coupling of fimbrial adhesins of uropathogenic Escherichia coli and pathogenic Neisseria species to their complementary receptors on host cells is a dynamic event, involving specific signaling to the bacteria as well as to the host cell. These studies have unveiled intriguing and novel mechanisms by which bacteria utilize their fimbriae to promote virulence at the mucosal surface and in deeper tissue.

Studies on haemagglutination and serum resistance status of strains of Moraxella catarrhalis isolated from the elderly

A total of 40 strains of Moraxella catarrhalis, isolated from the sputum of elderly persons with respiratory tract infections and from nasopharyngeal swabs from healthy elderly, were examined for haemagglutination of human red blood cells and resistance to bactericidal activity in normal human serum (NHS). 15 of 20 strains isolated from the infected elderly and 3 of 20 strains isolated from the healthy elderly showed haemagglutinating properties (p < 0.001). Similarly, 13 of 20 strains from the infected group and 2 of 20 strains from the healthy group were found to be resistant to the bactericidal activity of NHS (p < 0.001). Strains of M. catarrhalis which were associated with respiratory tract infections in the elderly, in contrast to strains colonizing the healthy elderly, were found to be predominantly haemagglutinating for human red blood cells and resistant to complement killing in NHS.

Immunoglobulin-coated bacteria in effusions obtained during chronic maxillary sinusitis

Local protection of the maxillary sinuses against bacterial invasion takes both specific and non-specific forms. The present study is intended to evaluate the participation of the specific protective factors, immunoglobulins IgG, secretory IgA, IgM and complement, in protecting the maxillary sinuses during chronic maxillary sinusitis (CMS). We collected 47 sinus effusion samples from 37 patients (17 male, 20 female) with current CMS of at least 3 months' duration. Patients' ages ranged from 3 to 80 years. The effusion material was subjected to qualitative and quantitative bacteriological analyses, while bacterial coating with IgG, SIgA, IgM and C3b was determined using an immunofluorescence technique. Detectable bacteria were harboured by 55% of the samples, the most common species being Moraxella catarrhalis, Streptococcus pneumoniae and Staphylococcus aureus. The bacterial counts ranged from 0 to 10(9) per ml effusion. Half of the samples hosting detectable bacteria showed microorganisms coated with protective immunoglobulins. Antibacterial factors had completely eradicated the microorganisms in 45% of the CMS cases and coated the organisms with specific immunoglobulins in a further 28%.

Dendritic cells are recruited into the airway epithelium during the inflammatory response to a broad spectrum of stimuli

A key rate-limiting step in the adaptive immune response at peripheral challenge sites is the transmission of antigen signals to T cells in regional lymph nodes. Recent evidence suggests that specialized dendritic cells (DC) fulfill this surveillance function in the resting state, but their relatively slow turnover in most peripheral tissues brings into question their effectiveness in signaling the arrival of highly pathogenic sources of antigen which require immediate mobilization of the full range of host defenses for maintenance of homeostasis. However, the present report demonstrates that recruitment of a wave of DC into the respiratory tract mucosa is a universal feature of the acute cellular response to local challenge with bacterial, viral, and soluble protein antigens. Consistent with this finding, we also demonstrate that freshly isolated respiratory mucosal DC respond in vitro to a variety of CC chemokines as well as complementary cleavage products and N-formyl-methionyl-leucine-phenylalanine. This suggests that rapid amplification of specific antigen surveillance at peripheral challenge sites is an integral feature of the innate immune response at mucosal surfaces, and serves as an "early warning system" to alert the adaptive immune system to incoming pathogens.

Serum antibody response to outer membrane proteins of Moraxella (Branhamella) catarrhalis in patients with bronchopulmonary infection

A Western blot (immunoblot) method for detecting antibodies against outer membrane protein (OMP) epitopes of Moraxella (Branhamella) catarrhalis was evaluated. Paired serum samples from patients suspected of M. catarrhalis (n = 38) and non-M. catarrhalis (n = 25) bronchopulmonary infection were examined for the presence of antibodies of the immunoglobulin M (IgM), IgG, and IgA classes to OMPs from M. catarrhalis by a gel electrophoresis-immunoperoxidase technique (Western blotting); sera from 40 healthy adult blood donors were also included. A significantly (P = 0.004) more frequent occurrence of IgM-class antibodies and/or an increase in the number of IgG-class antibodies against different M. catarrhalis OMPs from acute- to convalescent-phase serum samples was found for patients with M. catarrhalis (79%) than for patients without M. catarrhalis (40%). IgM-class antibodies against OMPs of M. catarrhalis were found in acute- and/or convalescent-phase serum samples form 58% of patients with M. catarrhalis and 32% of patients without M. catarrhalis. Fifty percent of patients with M. catarrhalis and 16% of patients without M. catarrhalis had, from acute- to convalescent-phase serum samples, an increased number of IgG-class antibodies directed against different OMPs. A total of 34% of patients with M. catarrhalis and 4% of patients without M. catarrhalis had, from acute- to convalescent-phase serum samples, an increased number of IgA-class antibodies directed against different OMPs. The present study indicates that M. catarrhalis is one of the bacteria involved in acute exacerbations of chronic bronchitis.

Branhamella catarrhalis: epidemiology, surface antigenic structure, and immune response

Over the past decade, Branhamella catarrhalis has emerged as an important human pathogen. The bacterium is a common cause of otitis media in children and of lower respiratory tract infections in adults with chronic obstructive pulmonary disease. B. catarrhalis is exclusively a human pathogen. It colonizes the respiratory tract of a small proportion of adults and a larger proportion of children. Studies involving restriction enzyme analysis of genomic DNA show that colonization is a dynamic process, with the human host eliminating and acquiring new strains frequently. The surface of B. catarrhalis contains outer membrane proteins, lipooligosaccharide, and pili. The genes which encode several outer membrane proteins have been cloned, and some of these proteins are being studied as potential vaccine antigens. Analysis of the immune response has been limited by the lack of an adequate animal model of B. catarrhalis infection. New information regarding outer membrane structure should guide studies of the human immune response to B. catarrhalis. Immunoassays which specifically detect antibodies to determinants exposed on the bacterial surface will elucidate the most relevant immune response. The recognition of B. catarrhalis as an important human pathogen has stimulated research on the epidemiology and surface structures of the bacterium. Future studies to understand the mechanisms of infection and to elucidate the human immune response to infection hold promise of developing new methods to treat and prevent infections caused by B. catarrhalis.

The protective efficacy of cloned Moraxella bovis pili in monovalent and multivalent vaccine formulations against experimentally induced infectious bovine keratoconjunctivitis (IBK)

Calves were vaccinated with cloned Moraxella bovis pili of serogroup C (experiment 1) or B (experiment 2) either as a monovalent formulation or as part of a multivalent preparation with pili of six other serogroups. Within 4 weeks of the second vaccine dose vaccinated calves and non-vaccinated controls were challenged via the ocular route with either virulent M. bovis strain Dal2d (serogroup C) or M. bovis strain 3WO7 (serogroup B) in experiments 1 and 2, respectively. Calves vaccinated with multivalent vaccines had significantly lower antibody titres than those vaccinated with monovalent preparations. Nevertheless, the levels of protection against infectious bovine keratoconjunctivitis (IBK) achieved with multivalent vaccines were 72% and 83% for the groups challenged with M. bovis strains of serogroups B and C, respectively. The serogroup C monovalent vaccine gave 100% protection against experimentally induced IBK and M. bovis isolates cultured from the eyes 6 days post-challenge were identified as belonging solely to serogroup C. Unexpectedly, only 25% protection was achieved against homologous strain challenge of calves that received the monovalent serogroup B vaccine. Furthermore, the majority of M. bovis isolates recovered from calves in this group belonged to serogroup C, as did half of those isolates cultured from the multivalent vaccinates. The remaining bacterial isolates from the latter group, together with all isolates from the non-vaccinated controls, belonged to serogroup B. Results are consistent with the hypothesis that derivatives of the serogroup B challenge inoculum had expressed serogroup C pilus antigen within 6 days of the challenge, possibly as a result of pilus gene inversion occurring in response to the presence of specific antibody in eye tissues and tears.

Emergence of a new virulent clone within the electrophoretic type 5 complex of serogroup B meningococci in Norway

An increase in B:15:P1.12 meningococci among isolates from patients with Neisseria meningitidis infection in Norway in recent years led to further characterization of such strains. Between 1987 and 1992, B:15:P1.12 strains constituted 9.8% (24 strains) of B:15 isolates. The B:15:P1.12 strains belonged to the electrophoretic type 5 (ET-5) complex, but 17 (71%) strains were a new clone (ET-5c) not found elsewhere in the world. All but one strain of ET-5c were responsible for a localized outbreak of systemic meningococcal disease in western Norway. A novel monoclonal antibody (202,G-12), developed against the unknown variable region 2 on the class 1 protein of one of these strains, bound to 19 of the 15:P1.12 strains, 4 strains bound the subtype P1.13 reference monoclonal antibody MN24H10.75, and the remaining strain showed no reaction. Sequencing of porA genes demonstrated a series of nine threonine residues in the deduced variable region 2 of the latter strain, while four and five threonine residues were found in the corresponding regions of strains reacting with the monoclonal antibodies 202,G-12 and MN24H10.75, respectively. Epitope mapping with synthetic peptides showed that 202,G-12 bound to a sequence of 11 amino acids which included the four threonine residues specific for subtype P1.13a. Immunoglobulin G antibodies against the P1.7,16 subtype protein, induced in volunteers after vaccination with the Norwegian meningococcal vaccine, did not cross-react on immunoblots with the subtype protein of clone ET-5c. Thus, postvaccination class 1 protein antibodies, assumed to be protective, may not be effective against infection with the new clone.

Lack of serotype-specific antibody response to lipopolysaccharide antigens of Moraxella catarrhalis during lower respiratory tract infection

An enzyme immunoassay (EIA) was used to determine the antibody response to different serotypes of lipopolysaccharide (LPS) antigens of Moraxella catarrhalis in adult patients with lower respiratory tract infections (LRTI). Moraxella catarrhalis was isolated from sputum or nasopharyngeal samples from 20 patients with LRTI. Sixteen of the isolates were serotype A, four were type B and none were type C. The antibody response to the different LPS serotypes was determined in paired sera from patients suffering from LRTI. In addition to the 20 patients with Moraxella catarrhalis isolated (Group 1), a group of seven patients with LRTI of unknown etiology (Group 2) and a group of ten patients with LRTI of known other bacterial etiology (Group 3) were selected for this study. An increase in antibody levels of > 1.5-fold (convalescent-/acute-phase serum) was recorded in approximately half of the patients, not only in the first group (Moraxella catarrhalis isolated) but also in the other two groups. However, in the first and second groups there was a correlation between an increase in antibody levels in the LPS EIA and in an EIA using whole bacterial cells as antigen. In the group of patients in whom Moraxella catarrhalis was isolated, the antibody response to LPS antigens was not serotype specific. The antibody response to type-A and type-B LPS was more predominant than the response to type-C LPS in most patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Human immune response against outer membrane proteins of Moraxella (Branhamella) catarrhalis determined by immunoblotting and enzyme immunoassay

The role of Moraxella (Branhamella) catarrhalis as a respiratory tract pathogen is increasingly recognized. We looked at the human immune response against individual outer membrane proteins of M. catarrhalis and against the 81-kDa CopB protein, which has previously been shown to be a target for protective antibodies. Paired serum samples from six elderly patients with pneumonia were tested by Western blot (immunoblot) analysis by using outer membrane vesicles of M. catarrhalis 035E as antigen. All of the six convalescent-phase serum samples reacted with a protein which migrated at the position of the CopB protein and with a high-molecular-weight protein of M. catarrhalis; three serum samples also reacted with a 34-kDa outer membrane protein. Paired serum samples from 18 patients, 10 of which had M. catarrhalis infection on the basis of previous serology results, were tested by enzyme immunoassay (EIA) with the CopB protein and whole cells of M. catarrhalis 035E as antigens. Nine patients showed a significant rise in EIA titer between acute- and convalescent-phase sera when whole bacterial cells were used as antigens. Six (67%) patient samples that were positive by the EIA with the whole-cell antigen were also positive by the EIA with the CopB antigen, and six of nine patient samples negative by the EIA with the whole-cell antigen were also negative by the EIA with the CopB antigen. These results suggest that both the CopB and a high-molecular-weight protein are major targets of the immune response against M. catarrhalis, and further studies with greater amounts of patient materials are needed to elucidate the usefulness of CopB as an antigen in etiologic studies.

Serum antibody response to proteins of Moraxella (Branhamella) catarrhalis in patients with lower respiratory tract infection

We searched for antibodies against Moraxella (Branhamella) catarrhalis proteins in the sera of patients with lower respiratory tract infection. Sera from 48 patients with M. catarrhalis and 39 patients without M. catarrhalis in their lower respiratory tract specimens were studied by a gel electrophoresis-immunoperoxidase technique; sera from 23 healthy adult blood donors were also included. Immunoglobulin G (IgG) antibodies against a 28-kDa protein were found significantly more frequently in patients with M. catarrhalis in lower respiratory tract specimens (71%) than in patients without M. catarrhalis in lower respiratory tract specimens (28%) or healthy adult blood donors (22%). Seroconversion, from the acute to the convalescent stages, occurred in at least eight patients with M. catarrhalis and in one patient without detectable M. catarrhalis. IgG antibodies against other M. catarrhalis proteins were found in most sera, including those obtained from blood donors. By adsorption experiments the 28-kDa protein was demonstrated to be surface exposed. IgM antibodies against an 85-kDa protein were found in serum from one patient from whom M. catarrhalis and Streptococcus pneumoniae were isolated from the lower respiratory tract, while IgA antibodies against M. catarrhalis proteins could not be detected in any serum specimen.

A large, antigenically conserved protein on the surface of Moraxella catarrhalis is a target for protective antibodies

A monoclonal antibody (MAb) to Moraxella catarrhalis O35E bound to a surface-exposed epitope of a proteinaceous antigen of this organism. The antigen, designated UspA, was present in every strain of the pathogen tested in a colony blot RIA. UspA had a molecular mass on SDS-PAGE that varied between 300 and 400 kDa, depending on the individual M. catarrhalis strain. Passive immunization of mice with the UspA-reactive Mab enhanced pulmonary clearance of M. catarrhalis. Use of this Mab to screen a M. catarrhalis genomic DNA library permitted identification of a recombinant bacteriophage expressing the M. catarrhalis UspA protein. The recombinant UspA protein was used in Western blot analysis with sera from patients with M. catarrhalis pneumonia. Convalescent-phase sera but not acute-phase sera from these patients contained antibodies to this M. catarrhalis surface protein, indicating that M. catarrhalis strains growing in vivo express this molecule.

Immune response to Moraxella catarrhalis in children with otitis media: opsonophagocytosis with antigen-coated latex beads

Opsonic antibody activity against Moraxella catarrhalis was determined in sera from children with otitis media. The antibody was determined with a new assay utilizing outer membrane antigen-coated latex beads. Antigen-coated beads opsonized in heat-inactivated pooled human serum phagocytosed 47.5 +/- 36.1 beads per 100 neutrophils compared to 15.6 +/- 10.2 beads per 100 neutrophils opsonized in hypogammaglobulinemic serum (p < .025). Antigen-coated beads opsonized in homologous sera from 11 children with M. catarrhalis otitis media demonstrated increased opsonic activity in convalescent sera (34.6 +/- 27.1) compared to acute sera (15.5 +/- 6.7; p < .05). These data suggest that infection with M catarrhalis is associated with the development of opsonic antibody.

Polymorphism of the complement C8A and -B genes in two families with C8 beta deficiency and neisserial infections

Serum samples from members of two Italian families with complement C8 beta deficiency were studied by SDS-PAGE under nonreducing conditions and by IEF. The proband of family I had suffered from two episodes of purulent meningitis and two of her uncles had suffered from only one episode, while the proband of family II had suffered from three different episodes. In contrast to previous findings, where C8 beta deficiency was cosegregating with C8A (alpha-gamma) allotype A, the proband of family II had the C8A allotype B. In addition, in one of her sons a novel variant of the C8 beta chain was detected. Studies at the DNA level in family I, using a recently described PCR system, demonstrate the presence of a C-T exchange, which creates a stop codon in exon 9 of the C8B gene, as cause for the C8 beta deficiency. The mutated allele does not carry the TaqI polymorphic restriction site located in intron 11 of the C8B gene. These findings provide evidence for multiple recombination events within the genetic region of the defective C8B gene.

Significance of isolation of Moraxella catarrhalis in routine cultures from the respiratory tract in adults: antibody response studied in a whole cell EIA

The significance of the isolation of Moraxella catarrhalis from sputum or nasopharynx was studied in patients treated at an infectious disease clinic. A whole-cell enzyme immunoassay was used to detect a specific antibody response to M. catarrhalis during infection. In all, 27 patients with respiratory tract infections and 4 with other infections were studied. Titre rises were recorded in 11/23 patients with lower respiratory tract infections, whereas patients with common cold or infections elsewhere all had negative serology. In patients with acute bronchitis, 7/10 patients responded with a significant titre rise. Patients with a low titre in their acute serum sample were those who responded with a titre increase during infection. The findings indicate that isolation of M. catarrhalis from sputa and nasopharyngeal samples in adults is of value for the etiological diagnosis of acute bronchitis and other lower respiratory tract infections, and is therefore important for the choice of drug for treatment, as many isolates are resistant to beta-lactam antibiotics.

A mutation affecting expression of a major outer membrane protein of Moraxella catarrhalis alters serum resistance and survival in vivo

A major outer membrane protein (CopB) of Moraxella catarrhalis is a target for antibodies that enhance clearance of this organism from the lungs of mice. A mini-Tn10kan transposon was inserted into the cloned copB gene from M. catarrhalis O35E, and an isogenic mutant unable to express the CopB protein was constructed by transforming this mutated gene into the wild-type strain. The mutant grew at the same rate as the wild-type parent strain in broth. Unlike the serum-resistant parent strain, this mutant was sensitive to killing by normal human serum, and its ability to survive and grow in the lungs of animals was impaired. Genetic restoration of CopB protein expression resulted in the simultaneous acquisition of wild-type levels of serum resistance and the ability to resist pulmonary clearance in vivo. Thus, the CopB protein of M. catarrhalis may be important in the interaction between this organism and the defense mechanisms of the respiratory tract.