Defense mechanisms involving Fc-dependent functions of immunoglobulin A and their subversion by bacterial immunoglobulin A proteases

Mucosal immune responses to meningococcal group C conjugate and group A and C polysaccharide vaccines in adolescents

Previous studies in children have shown that Haemophilus influenzae type b (Hib) polysaccharide conjugate vaccines can reduce nasopharyngeal carriage of H. influenzae and provide herd immunity and suggest that this effect is mediated through mucosal antibodies. As this phenomenon may operate in other invasive bacterial infections which are propagated by nasopharyngeal carriage, mucosal antibody responses to meningococcal C conjugate and A/C polysaccharide vaccines were investigated. A total of 106 school children aged 11 to 17 years were randomized to receive a single dose of either conjugate or polysaccharide vaccine in an observer-blind study. Before and at 1, 6, and 12 months after immunization, samples of unstimulated saliva were collected and assayed by enzyme-linked immunosorbent assay for group C polysaccharide-specific immunoglobulin A (IgA), IgA1, IgA2 and secretory component, IgG antibodies, and total IgG and IgA. A subset of serum samples were also assayed for specific IgA and IgG antibodies. The concentrations of specific IgA and IgG in saliva were expressed both as nanograms per milliliter and as nanograms per microgram of total IgA or IgG. One month after immunization, significant increases in antibody titers (both IgA and IgG) were observed in saliva in both groups. There were significant subsequent falls in antibody titers by 6 months. Anti-meningococcal C-specific secretory component and IgA antibody titers were closely correlated (r = 0.85, P < 0.001), but there was no significant correlation between salivary and serum IgA titers, suggesting that IgA antibodies are locally produced. Significant correlation was found between salivary and serum IgG titers (r = 0.52, P < 0.01), suggesting that salivary IgG may be serum derived. Compared with polysaccharide vaccine, the conjugate vaccine induced significantly higher salivary IgG responses (P < 0.05), although there were no significant differences between salivary IgA responses to the two vaccines. The conjugate vaccine induced greater salivary IgG responses than a polysaccharide vaccine. Both vaccines induced significant salivary IgA antibodies. Further studies are needed to establish the functional significance of these mucosal responses.

Interference with virus and bacteria replication by the tissue specific expression of antibodies and interfering molecules

Historically, protection against virus infections has relied on the use of vaccines, but the induction of an immune response requires several days and in certain situations, like in newborn animals that may be infected at birth and die in a few days, there is not sufficient time to elicit a protective immune response. Immediate protection in new born could be provided either by vectors that express virus-interfering molecules in a tissue specific form, or by the production of animals expressing resistance to virus replication. The mucosal surface is the largest body surface susceptible to virus infection that can serve for virus entry. Then, it is of high interest to develop strategies to prevent infections of these areas. Virus growth can be interfered intracellularly, extracellularly or both. The antibodies neutralize virus intra- and extracellularly and their molecular biology is well known. In addition, antibodies efficiently neutralize viruses in the mucosal areas. The autonomy of antibody molecules in virus neutralization makes them functional in cells different from those that produce the antibodies and in the extracellular medium. These properties have identified antibodies as very useful molecules to be expressed by vectors or in transgenic animals to provide resistance to virus infection. A similar role could be played by antimicrobial peptides in the case of bacteria. Intracellular interference with virus growth (intracellular immunity) can be mediated by molecules of very different nature: (i) full length or single chain antibodies; (ii) mutant viral proteins that strongly interfere with the replication of the wild type virus (dominant-negative mutants); (iii) antisense RNA and ribozyme sequences; and (iv) the product of antiviral genes such as the Mx proteins. All these molecules inhibiting virus replication may be used to obtain transgenic animals with resistance to viral infection built in their genomes. We have developed two strategies to target into mucosal areas either antibodies to provide immediate protection, or antigens to elicit immune responses in the enteric or respiratory surfaces in order to prevent virus infection. One strategy is based on the development of expression vectors using coronavirus derived defective RNA minigenomes, and the other relies on the development of transgenic animals providing virus neutralizing antibodies in the milk during lactation. Two types of expression vectors are being engineered based on transmissible gastroenteritis coronavirus (TGEV) defective minigenomes. The first one is a helper virus dependent expression system and the second is based on self-replicating RNAs including the information required to encode the TGEV replicase. The minigenomes expressing the heterologous gene have been improved by using a two-step amplification system based on cytomegalovirus (CMV) and viral promoters. Expression levels around 5 micrograms per 10(6) cells were obtained. The engineered minigenomes will be useful to understand the mechanism of coronavirus replication and for the tissue specific expression of antigen, antibody or virus interfering molecules. To protect from viral infections of the enteric tract, transgenic animals secreting virus neutralizing recombinant antibodies in the milk during lactation have been developed. Neutralizing antibodies with isotypes IgG1 or IgA were produced in the milk with titers of 10(6) in RIA that reduced virus infectivity by one million-fold. The recombinant antibodies recognized a conserved epitope apparently essential for virus replication. Antibody expression levels were transgene transgene copy number independent and were related to the transgene integration site. This strategy may be of general use since it could be applied to protect newborn animals against infections of the enteric tract by viruses or bacteria for which a protective MAb has been identified. Alternatively, the same strategy could be used to target the expression of antibio

Cysteine proteinases and the pathogenesis of amebiasis

Amebiasis is a major cause of morbidity and mortality throughout the tropical world. Entamoeba histolytica is now recognized as a separate species from the morphologically identical E. dispar, which cannot invade. Cysteine proteinases are a key virulence factor of E. histolytica and play a role in intestinal invasion by degrading the extracellular matrix and circumventing the host immune response through cleavage of secretory immunoglobulin A (sIgA), IgG, and activation of complement. Cysteine proteinases are encoded by at least seven genes, several of which are found in E. histolytica but not E. dispar. A number of new animal models, including the formation of liver abscesses in SCID mice and intestinal infection in human intestinal xenografts, have proven useful to confirm the critical role of cysteine proteinases in invasion. Detailed structural analysis of cysteine proteinases should provide further insights into their biochemical function and may facilitate the design of specific inhibitors which could be used as potential chemotherapeutic agents in the future.

Bacterial proteinases as targets for the development of second-generation antibiotics

The emergence of bacterial pathogen resistance to common antibiotics strongly supports the necessity to develop alternative mechanisms for combating drug-resistant forms of these infective organisms. Currently, few pharmaceutical companies have attempted to investigate the possibility of interrupting metabolic pathways other than those that are known to be involved in cell wall biosynthesis. In this review, we describe multiple, novel roles for bacterial proteinases during infection using, as a specific example, the enzymes from the organism Porphyromonas gingivalis, a periodontopathogen, which is known to be involved in the development and progression of periodontal disease. In this manner, we are able to justify the concept of developing synthetic inhibitors against members of this class of enzymes as potential second-generation antibiotics. Such compounds could not only prove valuable in retarding the growth and proliferation of bacterial pathogens but also lead to the use of this class of inhibitors against invasion by other infective organisms.

An ELISA method to measure total and specific human secretory IgA subclasses based on selective degradation by IgA1-protease

We have taken advantage of the property of IgA1-proteases to selectively cleave the human IgA1 subclass into Fabalpha and Fcalpha-J chain-secretory component (Fcalpha-J-SC) fragments in order to design a novel ELISA method for measuring the two secretory IgA (S-IgA) subclasses in secretions. The assay is based on the loss of detection of S-IgA1 by a combination of peroxidase-labelled antibodies to secretory component and Fab following IgA1-protease treatment. The specificity is that of the protease and the sensitivity of the detection is 5 ng/ml. Moreover, the use of purified S-IgA1 and S-IgA2 controls is not necessary. The assay has been successfully applied to the analysis of colostral S-IgA antibodies (Abs) to HIV-1-gp160 from HIV-1 positive women. The major subclass of colostral S-IgA antibodies to gp160 was found to be of the alpha1 isotype but the specific activity of anti-HIV-gp160 S-IgA2 was, however, higher than that of S-IgA1.

Characteristics in adherence of streptococci and Staphylococcus aureus isolated from various infective skin lesions: serum IgA decreases adherence of Streptococcus pyogenes but not Staphylococcus aureus

We characterized adherence of streptococci and Staphylococcus aureus strains isolated from various infective skin lesions in terms of hydrophobicity, negative charge, tube adherence, slime production, and influence on adherence to coverslips by plasma and serum immunoglobulins. High hydrophobicity was more frequently observed in Streptococcus pyogenes strains than in Streptococcus agalactiae strains (P < 0.01) and S. aureus strains (P < 0.001) and slime production was more frequently observed in S. agalactiae strains than in S. pyogenes strains (P < 0.05). Serum IgA decreased adherence to coverslips of S. pyogenes strains but not that of S. aureus strains.

Validation of a gastrointestinal explant system for measurement of mucosal antibody production

A gastrointestinal explant culture system was developed and compared to the mononuclear cell extraction and enzyme-linked immunospot assay method for measurement of immunoglobulin A (IgA) and IgG antibody-secreting cells (ASCs) in gastric antral and duodenal biopsies of non-Helicobacter pylori-infected volunteers. IgA and IgG were detected in explant supernatants during 6 to 7 days of culture in all subjects. IgA containing secretory component was also detected throughout the culture period, although peak production occurred only in the first 3 days. During 7 days of culture, the cumulative geometric mean IgA levels produced were 2.2 and 8.02 microg/ml/10 mg of antral and duodenal biopsy tissues, respectively, while the cumulative geometric mean IgG levels were 1.54 and 2.92 microg/ml/10 mg of antral and duodenal biopsy tissues, respectively. Cycloheximide treatment resulted in a >90% reduction in both immunoglobulin classes after 6 days of treatment compared to levels in untreated controls. The detection of IgA and IgG ASCs extracted from biopsies on days 1 and 6 of culture confirmed that the antibody detected was derived from mucosal lamina propria. The IgA and IgG ASC responses were positively correlated with antibody concentrations detected in culture supernatants (r = 0.87 and 0.85, respectively). These results validate the potential usefulness of our gastrointestinal explant system for the evaluation of mucosal effector B-cell function.

Experimental gonococcal genital tract infection and opacity protein expression in estradiol-treated mice

The development of effective prophylactic agents against gonorrhea and the study of adaptation by Neisseria gonorrhoeae to the urogenital mucosa are hindered by the lack of a well-established animal model of gonococcal genital tract infection. Here, a murine model of long-term gonococcal genital tract infection is described. Female BALB/c mice were treated with 17-beta-estradiol and inoculated intravaginally with wild-type gonococcal strain FA1090 or MS11. N. gonorrhoeae was recovered from vaginal swabs for an average of 12 to 13 days following inoculation with 10(6) CFU of either strain. Inflammation occurred in over 80% of infected mice, and diplococci were associated with epithelial cells and neutrophils in stained vaginal smears. Ascended infection occurred in 17 to 20% of mice inoculated with strain FA1090. An outbred mouse strain (SLC:ddY) previously reported to be naturally susceptible to N. gonorrhoeae was also tested; however, as with BALB/c mice, estradiol was required for prolonged infection. Although piliation was not maintained during experimental murine infection, 46 to 100% of vaginal isolates from four of eight BALB/c mice and three of four SLC:ddY mice expressed one or more opacity (Opa) proteins within 4 days after inoculation with an Opa-negative variant of strain FA1090. The observed selection for and/or induction of gonococcal Opa protein expression during murine infection appears to parallel events that occur during experimental urethritis in volunteers.

Killing of Streptococcus pneumoniae by capsular polysaccharide-specific polymeric IgA, complement, and phagocytes

The role of IgA in the control of invasive mucosal pathogens such as Streptococcus pneumoniae is poorly understood. We demonstrate that human pneumococcal capsular polysaccharide-specific IgA initiated dose-dependent killing of S. pneumoniae with complement and phagocytes. The majority of specific IgA in serum was of the polymeric form (pIgA), and the efficiency of pIgA-initiated killing exceeded that of monomeric IgA-initiated killing. In the absence of complement, specific IgA induced minimal bacterial adherence, uptake, and killing. Killing of S. pneumoniae by resting phagocytes with immune IgA required complement, predominantly via the C2-independent alternative pathway, which requires factor B, but not calcium. Both S. pneumoniae-bound IgA and complement were involved, as demonstrated by a 50% decrease in killing with blocking of Fcalpha receptor (CD89) and CR1/CR3 (CD35/CD11b). However, IgA-mediated killing by phagocytes could be reproduced in the absence of opsonic complement by pre-activating phagocytes with the inflammatory products C5a and TNF-alpha. Thus, S. pneumoniae capsule-specific IgA may show distinct roles in effecting clearance of S. pneumoniae in the presence or absence of inflammation. These data suggest mechanisms whereby pIgA may serve to control pneumococcal infections locally and upon the pathogen's entry into the bloodstream.

Human opsonins induced during meningococcal disease recognize outer membrane proteins PorA and PorB

Human opsonins directed against specific meningococcal outer membrane structures in sera obtained during meningococcal disease were quantified with a recently developed antigen-specific, opsonin-dependent phagocytosis and oxidative burst assay. Outer membrane vesicles (OMVs) and PorA (class 1) and PorB (class 3) proteins purified from mutants of the same strain (44/76; B:15:P1.7. 16) were adsorbed to fluorescent beads, opsonized with acute- and convalescent-phase sera from 40 patients with meningococcal disease, and exposed to human leukocytes. Flow cytometric quantitation of the resulting leukocyte phagocytosis products (PPs) demonstrated that disease-induced serum opsonins recognized meningococcal OMV components and both porins. The PPPorA and PPPorB values induced by convalescent-phase sera correlated positively with the PPOMV values. However, the PPPorB values were higher than the PPPorA values in convalescent-phase sera (medians [ranges] of 754 [17 to 1,057] and 107 [4 to 458], respectively) (P < 0.0001) and correlated positively with higher levels of immunoglobulin G against PorB than against PorA as evaluated by enzyme-linked immunosorbent assay. Extensive individual variations in the anti-OMV and antiporin serum opsonic activities between patients infected by serotypes and serosubtypes homologous and heterologous to the target antigens were observed. Simultaneously measured oxidative burst activity correlated with the opsonophagocytosis, an indication that both of these important steps in the in vitro phagocytic elimination of meningococci are initiated by opsonins directed against OMV components, including PorA and PorB. In conclusion, human patient opsonins against meningococcal OMV components and in particular PorB epitopes were identified by this new method, which might facilitate selection of opsonin-inducing meningococcal antigens for inclusion in future vaccines.

Interleukin-4 and interferon-gamma synergistically increase secretory component gene expression, but are additive in stimulating secretory immunoglobulin A release by Calu-3 airway epithelial cells

Interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) synergize to express polymeric immunoglobulin receptor (pIgR) but their combined effect, and that of IL-4 alone, on secretory immunoglobulin A (sIgA) release is unknown. Recently, we have developed an airway epithelial cell model that allows assessment of the integrated effect of a stimulus on pIgR gene and protein expression and sIgA release. With this model we show here that IL-4 and IFN-gamma dose-dependently increased pIgR mRNA and protein expression, and sIgA release. IFN-gamma and IL-4 induced similar maximal expression of pIgR, but IFN-gamma enhanced sIgA release more than IL-4. When added together, IL-4 and IFN-gamma synergistically increased pIgR mRNA and protein expression, but sIgA release was stimulated in an additive manner. Thus, IL-4 and IFN-gamma may be implicated in the increase of sIgA levels as found in mucosal inflammatory diseases. In addition, our results indicate that transport and release of empty pIgR is subject to regulatory mechanisms different from those of pIgR with bound dimeric IgA.

Mucosal Immunity to Influenza Without IgA: An IgA Knockout Mouse Model

IgA knockout mice (IgA−/−) were generated by gene targeting and were used to determine the role of IgA in protection against mucosal infection by influenza and the value of immunization for preferential induction of secretory IgA. Aerosol challenge of naive IgA−/− mice and their wild-type IgA+/+ littermates with sublethal and lethal doses of influenza virus resulted in similar levels of pulmonary virus infection and mortality. Intranasal and i.p. immunization with influenza vaccine plus cholera toxin/cholera toxin B induced significant mucosal and serum influenza hemagglutinin-specific IgA Abs in IgA+/+ (but not IgA−/−) mice as well as IgG and IgM Abs in both IgA−/− and IgA+/+ mice; both exhibited similar levels of pulmonary and nasal virus replication and mortality following a lethal influenza virus challenge. Monoclonal anti-hemagglutinin IgG1, IgG2a, IgM, and polymeric IgA Abs were equally effective in preventing influenza virus infection in IgA−/− mice. These results indicate that IgA is not required for prevention of influenza virus infection and disease. Indeed, while mucosal immunization for selective induction of IgA against influenza may constitute a useful approach for control of influenza and other respiratory viral infections, strategies that stimulate other Igs in addition may be more desirable.

Immunogenicity of intranasally administered meningococcal native outer membrane vesicles in mice

Colonization of the human nasopharyngeal region by Neisseria meningitidis is believed to lead to natural immunity. Although the presence of bactericidal antibody in serum has been correlated with immunity to meningococcal disease, mucosal immunity at the portal of entry may also play an important role. This study was undertaken to examine in mice the possibility of safely using native outer membrane vesicles (NOMV) not exposed to detergent as an intranasal (i.n.) vaccine. The mucosal and systemic responses of mice to intranasal and intraperitoneal (i.p.) vaccination with NOMV were compared over a range of doses from 0.1 to 20 microgram. Intranasal vaccination of mice with NOMV induced a strong systemic bactericidal antibody response, as well as a strong local immunoglobulin A immune response in the lung as determined by assay of lung lavage fluid by enzyme-linked immunosorbent assay and lung antibody secreting cells by enzyme-linked immunospot assay. However, 8- to 10-fold-higher doses of NOMV were required i.n. compared to i.p. to elicit an equivalent bactericidal antibody response in serum. Some NOMV vaccine was aspirated into the lungs of mice during i.n. immunization and resulted in an acute inflammatory response that peaked at 1 to 2 days postimmunization and was cleared by day 7. These results indicate that i.n. delivery of meningococcal NOMV in mice is highly effective in eliciting the production of both a mucosal immune response and a systemic bactericidal antibody response.

Evaluation of immunoglobulin A1 (IgA1) protease and IgA1 protease-inhibitory activity in human female genital infection with Neisseria gonorrhoeae

Immunoglobulin A1 (IgA1) protease, an enzyme that selectively cleaves human IgA1, may be a virulence factor for pathogenic organisms such as Neisseria gonorrhoeae. Host protection from the effects of IgA1 protease includes antibody-mediated inhibition of IgA1 protease activity, and it is believed that the relative balance between IgA1 protease and inhibitory antibodies contributes to the pathogenesis of disease caused by IgA1 protease-producing organisms. We have examined the levels of these two opposing factors in genital tract secretions and sera from women with uncomplicated infection with N. gonorrhoeae. When IgA1 in cervical mucus was examined by Western blotting, no evidence of cleavage fragments characteristic of IgA1 protease activity was seen in gonococcus-infected or control patients. Cleavage fragments typical of IgA1 protease were detected, however, after the addition of exogenous IgA1 protease to cervical mucus. Degraded IgA1 was detected in some vaginal wash samples, but the fragment pattern was not typical of IgA1 protease activity. All N. gonorrhoeae isolates from the infected patients produced IgA1 protease in vitro. All but two serum samples and 16 of 65 cervical mucus samples displayed inhibitory activity against gonococcal IgA1 protease, but there was no significant difference in the level of inhibitory activity between gonococcus-infected and noninfected patients in either cervical mucus or serum. There was no difference in the levels of IgA1 protease-inhibitory activity in serum or cervical mucus collected from patients at recruitment and 2 weeks later. These results suggest that cleavage of IgA1 by gonococcal IgA1 protease within the lumen of the female lower genital tract is unlikely to be a significant factor in the pathogenesis of infections by N. gonorrhoeae.

Immunity to vaginal HSV-2 infection in immunoglobulin A knockout mice

An immunoglobulin A (IgA) knockout (KO) mouse was used to study the role of IgA in protective immunity against vaginal infection with herpes simplex virus-type 2 (HSV-2). Intact and KO mice were immunized intravaginally (IVAG) with attenuated HSV-2, challenged IVAG with wild-type virus 6 weeks later and evaluated for vaginal infection and neurological disease. Non-immunized/challenged intact and KO mice showed vaginal infection and succumbed to neurological disease, while immunized/challenged mice exhibited reduced or no vaginal infection and no neurological disease. Log 2.5 enzyme-linked immunoassay (ELISA) titres of viral IgA, immunoglobulin G (IgG) and immunoglobulin M (IgM) in vaginal secretions collected from intact immune mice before challenge were 0.6+/-0.3, 6.4+/-0.32 and 0.0, while those in KO immune mice were 0.0, 6.7+/-0.19 and 3.0+/-0.29, respectively. Twenty-four hours after challenge, the percentage of vaginal epithelium that was infected in non-immune intact and KO mice was 2.0+/-0.6 and 2.4+/-0.6, which was reduced to 0.2+/-0.1 and 0.1+/-0.06 in immune intact and KO mice, respectively. No shed virus protein was detected in vaginal secretions 3 days after challenge in any immune mouse, whereas titres were 1400 and 1700 in the two groups of non-immune mice. Thus, immune protection against vaginal HSV-2 infection was similar in both KO and intact mice, indicating that this mucosal immunity does not depend mainly on IgA.

Transgenic mice secreting coronavirus neutralizing antibodies into the milk

Ten lines of transgenic mice secreting transmissible gastroenteritis coronavirus (TGEV) neutralizing recombinant monoclonal antibodies (rMAbs) into the milk were generated. The rMAb light- and heavy-chain genes were assembled by fusing the genes encoding the variable modules of the murine MAb 6A.C3, which binds an interspecies conserved coronavirus epitope essential for virus infectivity, and a constant module from a porcine myeloma with the immunoglobulin A (IgA) isotype. The chimeric antibody led to dimer formation in the presence of J chain. The neutralization specific activity of the recombinant antibody produced in transiently or stably transformed cells was 50-fold higher than that of a monomeric rMAb with the IgG1 isotype and an identical binding site. This rMAb had titers of up to 10(4) by radioimmunoassay (RIA) and neutralized virus infectivity up to 10(4)-fold. Of 23 transgenic mice, 17 integrated both light and heavy chains, and at least 10 of them transmitted both genes to the progeny, leading to 100% of animals secreting functional TGEV neutralizing antibody during lactation. Selected mice produced milk with TGEV-specific antibody titers higher than 10(6) as determined by RIA, neutralized virus infectivity by 10(6)-fold, and produced up to 6 mg of antibody per ml. Antibody expression levels were transgene copy number independent and integration site dependent. Comicroinjection of the genomic beta-lactoglobulin gene with rMAb light- and heavy-chain genes led to the generation of transgenic mice carrying the three transgenes. The highest antibody titers were produced by transgenic mice that had integrated the antibody and beta-lactoglobulin genes, although the number of transgenic animals generated does not allow a definitive conclusion on the enhancing effect of beta-lactoglobulin cointegration. This approach may lead to the generation of transgenic animals providing lactogenic immunity to their progeny against enteric pathogens.

IgA1 protease production by bacteria colonizing the upper respiratory tract

Thirty-eight clinical isolates of Haemophilus influenzae and ten clinical isolates of Streptococcus pneumoniae were examined for IgA1 protease production. A suspension of surface material of each individual strain was incubated with human secretory IgA; IgA1 cleavage products were detected by SDS-PAGE and immunoblotting. The high incidence of IgA1 protease-positive strains (68.4% of the examined H. influenzae and 100% of the examined S. pneumoniae strains) confirms that IgA1 protease activity is a frequent characteristic of these two species. Yet the presence of this enzyme is, if at all, only a minor decisive factor for the induction of symptomatic infections of the upper respiratory tract by IgA1 protease-positive bacteria.

Oral microbial ecology and the role of salivary immunoglobulin A

In the oral cavity, indigenous bacteria are often associated with two major oral diseases, caries and periodontal diseases. These diseases seem to appear following an imbalance in the oral resident microbiota, leading to the emergence of potentially pathogenic bacteria. To define the process involved in caries and periodontal diseases, it is necessary to understand the ecology of the oral cavity and to identify the factors responsible for the transition of the oral microbiota from a commensal to a pathogenic relationship with the host. The regulatory forces influencing the oral ecosystem can be divided into three major categories: host related, microbe related, and external factors. Among host factors, secretory immunoglobulin A (SIgA) constitutes the main specific immune defense mechanism in saliva and may play an important role in the homeostasis of the oral microbiota. Naturally occurring SIgA antibodies that are reactive against a variety of indigenous bacteria are detectable in saliva. These antibodies may control the oral microbiota by reducing the adherence of bacteria to the oral mucosa and teeth. It is thought that protection against bacterial etiologic agents of caries and periodontal diseases could be conferred by the induction of SIgA antibodies via the stimulation of the mucosal immune system. However, elucidation of the role of the SIgA immune system in controlling the oral indigenous microbiota is a prerequisite for the development of effective vaccines against these diseases. The role of SIgA antibodies in the acquisition and the regulation of the indigenous microbiota is still controversial. Our review discusses the importance of SIgA among the multiple factors that control the oral microbiota. It describes the oral ecosystems, the principal factors that may control the oral microbiota, a basic knowledge of the secretory immune system, the biological functions of SIgA, and, finally, experiments related to the role of SIgA in oral microbial ecology.

Both IgM and IgG anti-VSG antibodies initiate a cycle of aggregation-disaggregation of bloodstream forms of Trypanosoma brucei without damage to the parasite

Bloodstream forms of Trypanosoma brucei, when aggregated in the presence of either acute immune plasma, acute immune serum, purified IgM anti-VSG antibodies or purified IgG anti-VSG antibodies, subsequently disaggregated with a t1/2 for disaggregation of 15 min at 37 degrees C as long as the trypanosomes were metabolically active at the beginning of the experiment and maintained during the experiment in a suitable supporting medium. The t1/2 for disaggregation was found to be directly dependent upon temperature and inversely proportional to the antibody concentration. The trypanosomes were always motile and metabolically active during aggregation and after disaggregation and were fully infective for a mammalian host following disaggregation as well as able to grow and divide normally during axenic culture. The disaggregation was strictly energy dependent and was inhibited when intracellular ATP levels were reduced by salicylhydroxamic acid or following addition of oligomycin while respiring glucose. In addition the process of disaggregation was dependent upon normal endosomal activity as evidenced by its sensitivity to a wide variety of inhibitors of various endosomal functions. Disaggregation was not due to separation of immunoglobulin chains by either disulphide reduction or disulphide exchange reactions and gross proteolytic cleavage of the immunoglobulins attached to the surface of the parasite was not detected. In addition, gross cleavage or release of the VSG from the surface of the cell did not occur during disaggregation but proteolytic cleavage of a small proportion of either the VSG or the immunoglobulins could not be eliminated from consideration. Finally the mechanism of disaggregation was found to be a regulated process, independent of Ca2+ movements but dependent upon the activity of protein kinase C or related kinases and inhibited by the activity of protein kinase A as evidenced by the effects of a panel of inhibitors and cAMP analogues on the process of disaggregation. The mechanism of disaggregation displayed by trypanosomes aggregated by anti-VSG antibody is proposed to form part of the parasite's defence against the host immune system and functions to aid survival of trypanosomes in the presence of antibody in the host prior to the occurrence of a VSG switching event.

Subclass distribution of IgA antibodies in saliva and serum after immunization with Haemophilus influenzae type b conjugate vaccines

IgA subclass distribution of antibodies against capsular polysaccharide (PS) of Haemophilus influenzae type b (Hib) was studied in saliva and serum samples of children vaccinated with two (n = 58) or three doses (n = 53) of Hib vaccine. One month after the second dose of Hib conjugate vaccine, at 7 months old, 40% of the children had IgA1 and 41% had IgA2 anti-Hib PS antibodies in saliva. One month after the third dose, at 15-25 months old, IgA1 was the predominating subclass; 72% of the children had IgA1, 26% had IgA2 anti-Hib PS in saliva. The mean concentration of IgA1 anti-Hib PS, expressed as optical density (OD) values, was significantly higher after three doses (OD 80.7) than after two doses (OD 18.9). The mean concentration of IgA2 did not change significantly after the third dose (OD 23.8 after two doses, OD 18.1 after three doses). In serum, IgA1 anti-Hib PS predominated both after two (17% had IgA1, none had IgA2) and three doses (72% had IgA1, 4% had IgA2) of Hib vaccine. In conclusion, both IgA1 and IgA2 anti-Hib PS were found in saliva of immunized children after two doses of Hib conjugate vaccine, whereas the third vaccine dose induced a shift towards IgA1 anti-Hib PS dominance in saliva.

Protective immunity against HSV-2 in the mouse vagina

Herpes simplex virus type 2 (HSV-2) is a sexually transmitted pathogen that infects the genital tract. The high prevalence of HSV-2 in humans underscores the need to develop an effective vaccine. Efforts to develop vaccines to protect women against this and other sexually transmitted pathogens would be facilitated by a better understanding of the immune mechanisms that protect the female reproductive tract against infections in animal models. Such information would be invaluable in developing vaccine strategies to promote the type and magnitude of immune responses in the genital tract that would effectively protect against infection. This review focuses on recent studies using a progestin-treated adult mouse model to explore mucosal immunity to HSV-2 in the vagina. Evidence indicating a major role for both humoral and T cell immunity is presented.

Comparative analysis of immunoglobulin A1 protease activity among bacteria representing different genera, species, and strains

Immunoglobulin A1 (IgA1) proteases cleaving human IgA1 in the hinge region are produced constitutively by a number of pathogens, including Haemophilus influenzae, Neisseria meningitidis, Neisseria gonorrhoeae, and Streptococcus pneumoniae, as well as by some members of the resident oropharyngeal flora. Whereas IgA1 proteases have been shown to interfere with the functions of IgA antibodies in vitro, the exact role of these enzymes in the relationship of bacteria to a human host capable of responding with enzyme-neutralizing antibodies is not clear. Conceivably, the role of IgA1 proteases may depend on the quantity of IgA1 protease generated as well as on the balance between secreted and cell-associated forms of the enzyme. Therefore, we have compared levels of IgA1 protease activity in cultures of 38 bacterial strains representing different genera and species as well as strains of different pathogenic potential. Wide variation in activity generation rate was found overall and within some species. High activity was not an exclusive property of bacteria with documented pathogenicity. Almost all activity of H. influenzae, N. meningitidis, and N. gonorrhoeae strains was present in the supernatant. In contrast, large proportions of the activity in Streptococcus, Prevotella, and Capnocytophaga species was cell associated at early stationary phase, suggesting that the enzyme may play the role of a surface antigen. Partial release of cell-associated activity occurred during stationary phase. Within some taxa, the degree of activity variation correlated with degree of antigenic diversity of the enzyme as determined previously. This finding may indicate that the variation observed is of biological significance.

Inhibition of Prevotella and Capnocytophaga immunoglobulin A1 proteases by human serum

Oral Prevotella and Capnocytophaga species, regularly isolated from periodontal pockets and associated with extraoral infections, secret specific immunoglobulin A1 (IgA1) proteases cleaving human IgA1 in the hinge region into intact Fab and Fc fragments. To investigate whether these enzymes are subject to inhibition in vivo in humans, we tested 34 sera from periodontally diseased and healthy individuals in an enzyme-linked immunosorbent assay for the presence and titers of inhibition of seven Prevotella and Capnocytophaga proteases. All or nearly all of the sera inhibited the IgA1 protease activity of Prevotella buccae, Prevotella oris, and Prevotella loescheii. A minor proportion of the sera inhibited Prevotella buccalis, Prevotella denticola, and Prevotella melaninogenica IgA1 proteases, while no sera inhibited Capnocytophaga ochracea IgA1 protease. All inhibition titers were low, ranging from 5 to 55, with titer being defined as the reciprocal of the dilution of serum causing 50% inhibition of one defined unit of protease activity. No correlation between periodontal disease status and the presence, absence, or titer of inhibition was observed. The nature of the low titers of inhibition in all sera of the IgA1 proteases of P. buccae, P. oris, and P. loescheii was further examined. In size exclusion chromatography, inhibitory activity corresponded to the peak volume of IgA. Additional inhibition of the P. oris IgA1 protease was found in fractions containing both IgA and IgG. Purification of the IgG fractions of five sera by passage of the sera on a protein G column resulted in recovery of inhibitory IgG antibodies against all three IgA1 proteases, with the highest titer being for the P. oris enzyme. These finding indicate that inhibitory activity is associated with enzyme-neutralizing antibodies.

Comparison of the oral, rectal, and vaginal immunization routes for induction of antibodies in rectal and genital tract secretions of women

To determine which mucosal immunization routes may be optimal for induction of antibodies in the rectum and female genital tract, groups of women were immunized a total of three times either orally, rectally, or vaginally with a cholera vaccine containing killed Vibrio cholerae cells and the recombinant cholera toxin B (CTB) subunit. Systemic and mucosal antibody responses were assessed at 2-week intervals by quantitation of CTB-specific antibodies in serum and in secretions collected directly from mucosal surfaces of the oral cavity, rectum, cervix, and vagina with absorbent wicks. The three immunization routes increased levels of specific immunoglobulin G (IgG) in serum and specific IgA in saliva to similar extents. Rectal immunization was superior to other routes for inducing high levels of specific IgA and IgG in rectal secretions but was least effective for generating antibodies in female genital tract secretions. Only vaginal immunization significantly increased both specific IgA and specific IgG in both the cervix and the vagina. In addition, local production of CTB-specific IgG in the genital tract could be demonstrated only in vaginally immunized women. Vaginal immunization did not generate antibodies in the rectum, however. Thus, generation of optimal immune responses to sexually transmitted organisms in both the rectal and the genital mucosae of women may require local immunization at both of these sites.

Mucosal immunogenicity of a recombinant Salmonella typhimurium-cloned heterologous antigen in the absence or presence of coexpressed cholera toxin A2 and B subunits

An avirulent Salmonella typhimurium vaccine strain expressing a streptococcal protein adhesin and a similar clone which produces the same streptococcal antigen linked to the cholera toxin (CT) A2 and B subunits (CTA2/B) were compared for the ability to induce antibody responses to the expressed heterologous antigen after oral or intranasal immunization of mice. Expression of cloned immunogens in these systems is temperature regulated, being optimal at 37 degrees C, and the two clones under comparison were shown to produce similar levels of the streptococcal antigen. Both clones were found to stimulate high levels of serum immunoglobulin G (IgG) and mucosal IgA antibodies to the cloned immunogen. A consistent trend was observed toward higher mucosal IgA but lower serum IgG responses in the case of the S. typhimurium vector that coexpressed CTA2/B, a potential mucosal adjuvant, regardless of the route of administration. Also noteworthy was the capacity of these antigen delivery systems to induce anamnestic systemic and secretory responses to the cloned immunogen 15 weeks after the primary immunization, despite preexisting immunity to the Salmonella vectors. These antibody responses were sustained for at least 7 months following the booster immunization, at which time the secretory IgA antibody levels were significantly higher in mice given the Salmonella clone that coexpressed CTA2/B. Although the serum IgG response against the Salmonella vector was characterized by a high IgG2a/IgG1 ratio (indicative of the T helper type 1 [Th1]/Th2 profile), a mixed IgG1 and IgG2a pattern was observed for the carried heterologous antigen, which displayed a dominant IgG1 response when administered as a purified immunogen. Our findings indicate that the recombinant streptococcal antigen and CTA2/B are strong immunogens when expressed by the antigen delivery system used in this study and suggest that CTA2/B may have an additional immunoenhancing activity in the mucosal compartment besides its ability to target antigen uptake into the mucosal inductive sites. CTA2/B may thus be useful as an S. typhimurium-cloned adjuvant for coexpressed protein antigens.

The lysosomal/phagosomal membrane protein h-lamp-1 is a target of the IgA1 protease of Neisseria gonorrhoeae

Lysosomal/phagosomal membranes of mammalian cells are coated by highly conserved glycoproteins (lamps) that are thought to protect the membranes from degradation. Interestingly, we identified an amino acid sequence in human lamp-1 characteristic of a cleavage site for the Neisseria gonorrhoeae IgA1 protease. Furthermore, gonococci are detected in h-lamp-1-positive vacuoles after their uptake by professional phagocytes and epithelial cells. Here we demonstrate cleavage of glycosylated h-lamp-1 by the secreted gonococcal IgA1 protease. The cleavage was observed with h-lamp-1 purified from epithelial cells but not from professional phagocytes. The biological role of lamp-1 cleavage by the gonococcal protease is discussed.

Recognition of immunoglobulin A1 by oral actinomyces and streptococcal lectins

Actinomyces naeslundii and Streptococcus gordonii, oral bacteria that possess Gal/GalNAc- and sialic acid-reactive lectins, respectively, were adherent to immobilized secretory immunoglobulin A (IgA) and two IgA1 myeloma proteins but not to two IgA2 myeloma proteins. Apparently, O-linked oligosaccharides at the hinge region of the IgA1 heavy chain are receptors for lectin-mediated adhesion of these bacteria.

Vasoactive intestinal peptide induces S(alpha)/S(mu) switch circular DNA in human B cells

Vasoactive intestinal peptide (VIP), a major neurotransmitter of peripheral nerves, has been suggested to function in host defense by regulating local human immune function. Indirect evidence has been marshaled that VIP can function as a switch factor for IgA in human Ig isotype recombination. In this study we directly tested the ability of VIP to function as a factor driving human B cells into IgA producing cells by assessing its ability to induce switch circular DNA representing direct mu to alpha switching. In addition we determined the generation of alpha germ-line transcripts and measured the level of IgA protein produced. Stimulation with VIP and CD40 mAb induced IgA production by human IgD+ B cells while VIP or CD40 alone failed to do so. Stimulation of purified IgD+ B cells with VIP plus CD40 mAb induced generation of switch circular DNA representing in vitro driven isotype switching from mu to alpha. CD40 mAb alone induced alpha germ-line transcripts but not IgA switch circles. Thus VIP, a neurogenic factor, can induce alpha-specific switching in CD40-activated human B cells and may thereby play an important role in directing the humoral immune response at mucosal surfaces.

A method for titration of inhibiting antibodies to bacterial immunoglobulin A1 proteases in human serum and secretions

Bacterial IgA1 proteases specifically cleave IgA1, including S-IgA1, molecules into Fab alpha and Fc alpha fragments. Hereby these enzymes interfere with the protective functions of antibodies belonging to this isotype. Antibodies inhibiting IgA1 proteases have been detected in humans, but the titration of such antibodies is a matter of methodological concern. Because human serum and secretions contain IgA1 substrate, it is impossible to provide uniform substrate conditions for samples of IgA1 protease incubated with inhibitors differing in their origin and state of dilution. This study demonstrates that such variations in substrate are not prohibitive for a reliable titration of inhibiting antibodies. This was evident from experiments demonstrating that the variations do not interfere with the quantification of residual IgA1 protease activity provided the activity is measured in terms of the proportion of IgA1 substrate cleaved during incubation. Proportions of cleaved IgA1 were measured by exploiting the differential reactivity of cleaved and intact IgA1 molecules in an ELISA using anti-Fc alpha and enzyme-conjugated anti-light chain antibodies for catching and development, respectively. A protocol for the titration of IgA1 protease-inhibiting antibodies based on this ELISA is described. By application of the protocol to chromatographic fractions of saliva, IgA1 protease-inhibiting activity was found to co-purify with salivary S-IgA.

Immunity at mucosal surfaces

The mucosae form a barrier between our bodies and a hostile external environment. Diseases and extrinsic factors which impair mucosal function may lead to serious consequences. The mucosal immune system is the primary mediator of specific immunity at mucosal surfaces. As such, it is responsible for maintaining homeostasis and for defense against both overt and opportunistic pathogens. For this reason, it is also the target of many new vaccine strategies for the induction of mucosal immunity. This brief review will examine the mucosal immune system, its role in maintaining the integrity of the mucosa, and some of the strategies aimed at enhancing specific immunity.

Localization of the binding site for the monocyte immunoglobulin (Ig) A-Fc receptor (CD89) to the domain boundary between Calpha2 and Calpha3 in human IgA1

Immunoglobulin (Ig) A serves as the first line of humoral defense at all mucosal surfaces and is present in large quantities of blood. In playing its role in humoral immunity, IgA interacts with a variety of effector molecules present both in serum and on the surfaces of immune and inflammatory cells. To study these interactions, we previously established expression of human IgA1 in insect cells using recombinant baculoviruses and showed that the expressed antibody is a structurally and functionally intact polypeptide useful for examining the molecular properties of IgA. Indeed, since the C alpha 2 N-linked glycosylation site lies near the Fab-distal pole of C alpha 2, the inability of a mutant IgA1 lacking C alpha 2 N-glycosylation to bind its cognate receptor suggested that the monocyte Fc alpha receptor (mFcalphaR) recognizes IgA at a hinge-distal site encompassing the boundary between the C alpha 2 and C alpha 3 domains. In this report, we utilize both domain-swapped IgA/IgG and point-mutated IgA chimeras to verify the above hypothesis. Using an antigen-specific rosetting assay and a mFc alpha R-expressing cell line, we show that (a) C alpha 2 and C alpha 3 together are necessary and sufficient for binding; (b) neither the IgA hinge nor the tailpiece is necessary for binding; (c) mutations away from the interdomain boundary do not affect binding; and (d) mutations located near the three-dimensional boundary between C alpha 2 and C alpha 3 completely disrupt binding. Taken together, these results localize the mFc alpha R recognition site on IgA to the boundary region between the second and third constant domains--a site analogous to that recognized by Staphylococcus aureus protein A on IgG. The use of this hinge-distal site is, to date, unique among Fc receptors of the Ig superfamily.

Evidence of bovine immunoglobulin G1 (IgG1) protease activity in partially purified culture supernate of Pasteurella haemolytica A1

In the bovine respiratory tract, IgG1 is a major secretory immunoglobulin (Ig), and both IgG1 and IgG2 are believed to be important in defense against pneumonic pasteurellosis (shipping fever) in calves. Here we provide evidence for hydrolysis of IgG1 in the presence of partially purified culture supernate (ppCS) from the respiratory pathogen Pasteurella haemolytica A1. Bovine IgG1 was hydrolysed sequentially into three distinct bands (approximately 39, 12, and 7 kDa respectively). Furthermore, partial hydrolysis of bovine IgG2 was observed, but neither bovine IgA nor IgM were affected by incubation with ppCS. These findings suggest that the production of an IgG1-specific protease by P. haemolytica A1 may be a virulence mechanism contributing to the pathogenesis of bovine pneumonic pasteurellosis.

Evidence of recombination and an antigenically diverse immunoglobulin A1 protease among strains of Streptococcus pneumoniae

The genetic relationships among 114 isolates of Streptococcus pneumoniae representing mainly nine serotypes that frequently cause severe childhood disease in Northern Europe were examined by use of multilocus enzyme electrophoresis. A comparison was made of the corresponding antigenic variations of excreted immunoglobulin A1 (IgA1) proteases detected by enzyme neutralization assays. Allelic variation at 13 gene loci among 70 electrophoretic types disclosed a comparatively low mean genetic diversity per locus (H = 0.319). In contrast, IgA1 proteases showed extensive antigenic diversity as 17 different inhibition types were distinguished. A lack of overall clonality was apparent from the linkage equilibrium of alleles harbored by 28 isolates chosen to represent the genetic diversity of the study population. However, certain clones, such as those marked by identical electrophoretic type, serotype, and IgA1 protease type, persisted for a sufficiently long time to enable clonal spread between distant geographic areas. Among clonally related isolates, examples illustrating a shift of capsular serotype or IgA1 protease type supported the view that recombination occurs in vivo in corresponding genes. In conclusion, over time, horizontal genetic exchange appears to be sufficiently frequent to disrupt the clonal structure otherwise generated by binary fission in natural populations of S. pneumoniae. The clonal instability combined with considerable antigenic heterogeneity renders the pneumococcal IgA1 protease less attractive as a potential component of future vaccines.

Are bacterial proteinases pathogenic factors?

Evidence is rapidly accumulating that suggests that the growth and proliferation of pathogenic bacteria depend on proteolytic enzymes of the invading organism and of the host. Proteinase inhibitors targeting bacterial proteinases may be useful antimicrobial agents.

Neisseria gonorrhoeae IgA1 proteases share epitopes recognized by neutralizing antibodies

The antigenic diversity among IgA1 proteases of 61 Neisseria gonorrhoeae strains isolated during a period of 23 years and on four continents was examined in enzyme neutralization assays employing rabbit antisera raised against selected IgA1 proteases. The antigenic analyses were compared with results of iga gene-region RFLP patterns and enzyme cleavage specificity for substrate IgA1. Type 1 IgA1 proteases were antigenically uniform while six different antigenic types were detected among type 2 enzymes. Extensive cross-reactions of antibodies against the different antigenic types suggested only minor differences in relevant epitopes. Epitopes previously found to be common to all Neisseria meningitidis IgA1 proteases were also shared by all N. gonorrhoeae IgA1 proteases in the collection. Human sera from patients with gonorrhoea showed broadly cross-reactive neutralizing activity at titers comparable to those of sera from immunized rabbits. In conclusion, N. gonorrhoeae IgA1 proteases show a remarkable lack of diversity of epitopes recognized by enzyme-neutralizing antibodies. If future studies confirm that cleavage of IgA1 is an important step in gonococcal infections, Neisseria IgA1 proteases may be attractive vaccine candidates.

Selective neutralization of a bacterial enterotoxin by serum immunoglobulin A in response to mucosal disease

One-third of convalescent-phase serum samples (6 of 18) from patients with Clostridium difficle-associated diarrhea demonstrated neutralization of the clostridial enterotoxin, toxin A. Although appreciable amounts of toxin A-specific immunoglobulin G (IgG) and IgA were present in these sera, the ability to neutralize the cytotoxic activity of toxin A on OTF9-63 cells in vitro was confined to the IgA fraction and the IgA1 subclass in serum samples from all six patients. In contrast to the patients with C. difficile diarrhea, this activity was present in both the IgA and IgG fractions in sera from two C. difficile-infected patients without diarrhea, one of whom presented with a splenic abscess. Sera and purified IgA which neutralized the cytotoxicity of toxin A on OTF9-63 cell cultures in vitro also neutralized the enterotoxicity of toxin A in rabbit ileal loops in vivo. This activity was not Fc dependent, since IgA retained neutralizing activity after pepsin digestion and F(ab')2 purification. The transition from nonneutralizing toxin A-specific IgA in the acute-phase sera to neutralizing specific IgA in the convalescent-phase sera was accompanied by a shift from a polymeric to a predominantly monomeric form of specific IgA. However, the neutralizing activity in convalescent-phase sera was present as both monomeric and polymeric IgA. Convalescent-phase sera from other patients with C. difficile diarrhea that failed to neutralize toxin A also failed to produce a predominantly monomeric-form specific IgA response. We conclude that serum IgA, not IgG, characteristically neutralizes toxin A in patients with C. difficile diarrhea who develop neutralizing systemic responses. This neutralization of an enteric bacterial toxin is a unique and selective role for serum IgA which provides a novel functional link between the systemic and mucosal immune systems.

Generation and assembly of secretory antibodies in plants

Four transgenic Nicotiana tabacum plants were generated that expressed a murine monoclonal antibody kappa chain, a hybrid immunoglobulin A-G heavy chain, a murine joining chain, and a rabbit secretory component, respectively. Successive sexual crosses between these plants and filial recombinants resulted in plants that expressed all four protein chains simultaneously. These chains were assembled into a functional, high molecular weight secretory immunoglobulin that recognized the native streptococcal antigen I/II cell surface adhesion molecule. In plants, single cells are able to assemble secretory antibodies, whereas two different cell types are required in mammals. Transgenic plants may be suitable for large-scale production of recombinant secretory immunoglobulin A for passive mucosal immunotherapy. Plant cells also possess the requisite mechanisms for assembly and expression of other complex recombinant protein molecules.

Active release of bound antibody by Streptococcus mutans

Previous studies have shown that Streptococcus mutants is capable of releasing many surface protein antigens, particularly antigen P1. Antigen P1 is immunodominant and has been implicated in adherence of S. mutants to the acquired pellicles. The purpose of this study is to investigate the significance of release of this antigen by the cells. S. mutants NG8 (serotype c) was incubated with an anti-P1 rabbit immunoglobulin G (IgG) or a human colostral IgA which contains natural anti-P1 activity. Results indicated that the bound antibodies were released by the cells in a pH- and time-dependent manner. The optimal pH for release was between 6 and 8, and the release rate reached a plateau in 1 h at 37 degrees C. The release of bound antibodies was considered an active process, since heat-killed cells remained capable of antibody binding but failed to release the antibodies. The release was also dependent on the age of the culture, with early-exponential-phase cells releasing the maximum amount of bound IgG. The released IgG was isolated by polyethylene glycol precipitation and protein A-Sepharose column chromatography and found to be associated with antigen P1, indicating that the antibodies were released together with the antigen in the form of immune complexes. The binding of S. mutans by secretory IgA (SIgA) inhibited the adherence of the cells to salivary agglutinin-coated hydroxylapatite. However, when the SIgA-coated S. mutans was allowed to release the bound antibodies, the inhibitory effect of SIgA on adherence was abrogated. These results suggest that S. mutans is capable of shedding surface-bound antibodies in the form of antibody-antigen immune complexes. Such an action may be a strategy employed by the cells to counter the neutralizing effect of naturally occurring antibodies in the oral cavity.

HIV-1 recombinant gp160 vaccine induced antibodies in serum and saliva. The NIAID AIDS Vaccine Clinical Trials Network

As part of a phase I safety and immunogenicity trial of a vaccinia-expressed HIV-1 recombinant gp160 (rgp160) candidate vaccine, we measured serum and saliva antibody responses in low risk, uninfected volunteers. Six healthy adult volunteers received 50 micrograms doses of rgp160 vaccine adjuvanted in alum and deoxycholate at months 0, 1, 6, and 12. A 200 micrograms rgp160 immunization was given to four volunteers at 18 months. The vaccine induced anti-envelope glycoprotein IgG and IgA serum antibodies in all six volunteers. Saliva antibodies to envelope glycoprotein appeared in some volunteers at certain timepoints. Three volunteers appeared to transiently develop vaccine-induced secretory IgA antibody to envelope glycoprotein in whole saliva.

Current status of meningococcal group B vaccine candidates: capsular or noncapsular?

Meningococcal meningitis is a severe, life-threatening infection for which no adequate vaccine exists. Current vaccines, based on the group-specific capsular polysaccharides, provide short-term protection in adults against serogroups A and C but are ineffective in infants and do not induce protection against group B strains, the predominant cause of infection in western countries, because the purified serogroup B polysaccharide fails to elicit human bactericidal antibodies. Because of the poor immunogenicity of group B capsular polysaccharide, different noncapsular antigens have been considered for inclusion in a vaccine against this serogroup: outer membrane proteins, lipooligosaccharides, iron-regulated proteins, Lip, pili, CtrA, and the immunoglobulin A proteases. Alternatively, attempts to increase the immunogenicity of the capsular polysaccharide have been made by using noncovalent complexes with outer membrane proteins, chemical modifications, and structural analogs. Here, we review the strategies employed for the development of a vaccine for Neisseria meningitidis serogroup B; the difficulties associated with the different approaches are discussed.

Recombinant human IgA expressed in insect cells

IgA serves as the first line of humoral defense at all mucosal surfaces and is present in large quantities in serum. To map the sites of interaction of immune effector molecules with the IgA constant region (C alpha), we have expressed soluble, chimeric human IgA in insect cells using recombinant baculoviruses. This antibody is correctly assembled into heavy chain/light chain heterodimers, N-glycosylated, and secreted by the insect cells; further, when coexpressed with a human J chain, the antibodies can assemble into dimers. The recombinant protein is authentic by a number of criteria, including antigen-binding, recognition by monoclonal antibodies, complement fixation via the alternative pathway, and specific binding to the monocyte IgA Fc receptor. We have also constructed viruses which encode structurally altered IgA heavy chains. Using one of these variant viruses, we have shown that glycosylation of the second domain of C alpha is required for interaction with the monocyte IgA Fc receptor. This system should prove useful in further characterization of the structure-function relationships in human C alpha.

Heavy-chain isotype patterns of human antibody-secreting cells induced by Haemophilus influenzae type b conjugate vaccines in relation to age and preimmunity

The influence of preexisting immunity on the heavy-chain isotypes of circulating antibody-secreting cells (AbSC) induced by vaccination with Haemophilus influenzae type b (Hib) capsular polysaccharide (HibCP) coupled to tetanus toxoid (TT) or diphtheria toxoid (DT) and by vaccination with TT or DT alone in 51 healthy adults and 9 infants was studied. In adults, the isotypes of TT and DT AbSC were dominated by immunoglobulin G1 (IgG1) followed by IgG4 and IgA1. HibCP AbSC were dominated by the isotype IgA1 followed by (in decreasing order) IgG2, IgA2, IgM, and IgG1. The isotype distributions of TT and DT AbSC were independent of whether the toxoids were coupled to HibCP, and the isotypes of HibCP AbSC were not influenced by the nature of the carrier (TT or DT). Furthermore, the isotype distributions were unaffected by recent immunization with components of the conjugates, although this reduced the numbers of AbSC. The heavy-chain gene usage of HibCP AbSC in adults differed clearly from that in infants, which was restricted largely to the genes mu, gamma 1, and alpha 1, all lying upstream in the heavy-chain constant-region gene locus, while the usage in adults also, to different extents, involved the downstream genes gamma 2 and alpha 2. The ratio between the numbers of HibCP AbSC using heavy-chain genes from the downstream duplication unit (gamma 2, gamma 4, and alpha 2) and those using genes from the upstream duplication unit (gamma 3, gamma 1, and alpha 1) correlated with the preimmunization level of natural HibCP antibodies (r = 0.59; P = 0.00002). A possible role of natural exposure for Hib or cross-reactive bacteria on the mucosal surfaces in the shaping of the isotype response to HibCP conjugate vaccines is discussed.

Antigenic relationships among immunoglobulin A1 proteases from Haemophilus, Neisseria, and Streptococcus species

To investigate the antigenic variation and relationships of immunoglobulin A1 (IgA1) proteases among different species and genera, we examined a comprehensive collection of serine type and metallo-type IgA1 proteases and corresponding antisera in enzyme neutralization assays. Sharing of neutralizing epitopes of metallo-type IgA1 proteases from Streptococcus pneumoniae, Streptococcus sanguis, Streptococcus mitis, and Streptococcus oralis and of serine type IgA1 proteases from Haemophilus and pathogenic Neisseria species was extremely limited. A number of limited to strong cross-reactions in such epitopes were found among serine type IgA1 proteases released by members of the genera Haemophilus and Neisseria, reflecting the common origin of their iga gene. However, the relatively limited prevalence of shared "neutralizing" epitopes of IgA1 proteases from the two genera indicates that they rarely induce immunity to each other. In contrast, extensive sharing of neutralizing epitopes was found between N. meningitidis and N. gonorrhoeae IgA1 proteases, making them potentially attractive vaccine components. Among metallo-type IgA1 proteases, several pneumococcal proteases were found to induce neutralizing antibodies to IgA1 proteases of oral streptococci whereas the opposite was not the case.

Pioneer oral streptococci produce immunoglobulin A1 protease

As part of a longitudinal study of the relationship between bacterial colonization and the secretory immune response, 367 isolates of pioneer viridans streptococci collected from 40 breast- and bottle-fed neonates within the first month postpartum were tested for the production of immunoglobulin A1 (IgA1) protease and glycosidases. Fifty percent of the streptococci isolated produced IgA1 protease, including all isolates of Streptococcus oralis and S. sanguis, 60.7% of S. mitis biovar 1 isolates, and some isolates that could not be identified. Three cleavage patterns of alpha 1 heavy chains were observed. Six isolates of S. mitis biovar 1 that did not produce IgA1 protease attacked the alpha 1 chain. Incubation of IgA1 protease-negative S. mitis biovar 1 isolates with IgA1, either prior to or together with S. sanguis, rendered the IgA1 paraprotein resistant to cleavage by the IgA1 protease of S. sanguis. The ability of some pioneer streptococci in the human oral cavity to produce IgA1 protease and of others to modify the susceptibility of IgA1 to cleavage by IgA1 protease perhaps enhances their ability to survive in this habitat.

Systemic and mucosal immune responses in mice orally immunized with avirulent Salmonella typhimurium expressing a cloned Porphyromonas gingivalis hemagglutinin

Porphyromonas gingivalis produces a variety of virulence factors that may have a function in the periodontal disease process. Determination of the role of these various factors in pathogenesis and identification of a means for protecting the host from the destructive effects of this organism are areas of vigorous investigation. In this study we demonstrate the potential of avirulent Salmonella typhimurium strains to stimulate a specific systemic and mucosal immune response to a cloned P. gingivalis hemagglutinin (HagB). An avirulent strain of S. typhimurium, chi 4072, expressing the hagB gene of P. gingivalis 381 on the plasmid pDMD1 was intragastrically administered to BALB/c mice. These mice mounted a serum immunoglobulin G (IgG) and IgA primary response against the hagB gene product and a mucosal immune response as measured by evaluation of saliva. IgA antibodies were also detected in bile. These results demonstrate the feasibility of using attenuated S. typhimurium strains as carriers of P. gingivalis virulence factors for subsequent evaluation of the systemic and mucosal immune response against these antigens. This system will provide a means for evaluating the virulence factors of P. gingivalis for their suitability in the construction of potential vaccines.

Immunoglobulin A (IgA), IgA1, and IgA2 antibodies to Candida albicans in whole and parotid saliva in human immunodeficiency virus infection and AIDS

Human immunodeficiency virus (HIV)-infected individuals are predisposed to recurrent oral candidiasis, and, although it has been assumed that this is because of deficient mucosal immune responses, this has not been properly established. The present study aimed to compare the concentrations and secretion rates of immunoglobulin A (IgA) and IgA subclass antibodies to Candida albicans in whole and parotid saliva samples from HIV-infected patients, AIDS patients, and control subjects. Levels of IgA antibody to Candida species in whole saliva were higher in the HIV group than in the controls and were highest in the AIDS group (P < 0.05). In parotid saliva, the mean antibody levels were significantly greater in HIV-positive patients than in controls (P < 0.05) but fell to lower levels in the AIDS group. The secretion rates of Candida antibodies in parotid saliva were reduced in AIDS patients compared with HIV patients. The specific activities of the IgA antibodies and both subclasses were significantly higher in the HIV and AIDS patients than in the controls in both whole and parotid saliva (P < 0.05). Antibody levels were significantly correlated with the numbers of Candida organisms isolated from saliva (P < 0.05). These results suggest clear differences in salivary antibody profiles among HIV-infected. AIDS, and control subjects and are indicative of a response to antigenic challenge by infecting Candida species. No obvious defect in the mucosal immune response in the HIV or AIDS groups that might account for the increased prevalence of candidiasis was apparent.