Natural Development of Antibodies against Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis Protein Antigens during the First 13 Years of Life

Quantity and Quality of Naturally Acquired Antibody Immunity to the Pneumococcal Proteome Throughout Life

BACKGROUND

Young children and older adults are susceptible for invasive pneumococcal disease (IPD) caused by Streptococcus pneumoniae. Pneumococcal protein-specific antibodies play a protective role against IPD; however, not much is known about the pace of acquisition, maturation, and maintenance of these antibodies throughout life.

METHODS

Immunoglobulin G (IgG) and IgA levels, avidity, and/or specificity to the pneumococcal proteome in serum and saliva from healthy young children, adults, and older adults, with known carriage status, were measured by enzyme-linked immunosorbent assay (ELISA) and 2-dimensional western blotting against ΔcpsTIGR4.

RESULTS

Eleven-month-old children, the youngest age group tested, had the lowest pneumococcal proteome-specific IgG and IgA levels and avidity in serum and saliva, followed by 24-month-old children and were further elevated in adult groups. Among adult groups, the parents had the highest serum and saliva IgG and IgA antibody levels. In children, antibody levels and avidity correlated with daycare attendance and presence of siblings, posing as proxy for exposure and immunization. Immunodominance patterns slightly varied throughout life.

CONCLUSIONS

Humoral immunity against the pneumococcal proteome is acquired through multiple episodes of pneumococcal exposure. Low-level and low-avidity antiproteome antibody profiles in young children may contribute to their IPD susceptibility, while in overall antiproteome antibody-proficient older adults other factors likely play a role.

Promoting Fc-Fc interactions between anti-capsular antibodies provides strong immune protection against Streptococcus pneumoniae

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia and an important cause of childhood mortality. Despite the introduction of successful vaccines, the global spread of both non-vaccine serotypes and antibiotic-resistant strains reinforces the development of alternative therapies against this pathogen. One possible route is the development of monoclonal antibodies (mAbs) that induce killing of bacteria via the immune system. Here, we investigate whether mAbs can be used to induce killing of pneumococcal serotypes for which the current vaccines show unsuccessful protection. Our study demonstrates that when human mAbs against pneumococcal capsule polysaccharides (CPS) have a poor capacity to induce complement activation, a critical process for immune protection against pneumococci, their activity can be strongly improved by hexamerization-enhancing mutations. Our data indicate that anti-capsular antibodies may have a low capacity to form higher-order oligomers (IgG hexamers) that are needed to recruit complement component C1. Indeed, specific point mutations in the IgG-Fc domain that strengthen hexamerization strongly enhance C1 recruitment and downstream complement activation on encapsulated pneumococci. Specifically, hexamerization-enhancing mutations E430G or E345K in CPS6-IgG strongly potentiate complement activation on S. pneumoniae strains that express capsular serotype 6 (CPS6), and the highly invasive serotype 19A strain. Furthermore, these mutations improve complement activation via mAbs recognizing CPS3 and CPS8 strains. Importantly, hexamer-enhancing mutations enable mAbs to induce strong opsonophagocytic killing by human neutrophils. Finally, passive immunization with CPS6-IgG1-E345K protected mice from developing severe pneumonia. Altogether, this work provides an important proof of concept for future optimization of antibody therapies against encapsulated bacteria.

Diagnostic applications of microsphere-based flow cytometry: A review

Microsphere-based flow cytometry is a highly sensitive emerging technology for specific detection and clinical analysis of antigens, antibodies, and nucleic acids of interest. In this review, studies that focused on the application of flow cytometry as a viable alternative for the investigation of infectious diseases were analyzed. Many of the studies involve research aimed at epidemiological surveillance, vaccine candidates and early diagnosis, non-infectious diseases, specifically cancer, and emphasize the simultaneous detection of biomarkers for early diagnosis, with accurate results in a non-invasive approach. The possibility of carrying out multiplexed assays affords this technique high versatility and performance, which is evidenced in a series of clinical studies that have verified the ability to detect several molecules in low concentrations and with minimal sample volume. As such, we demonstrate that microsphere-based flow cytometry presents itself as a promising technique that can be adopted as a fundamental element in the development of new diagnostic methods for a number of diseases.

Australian Aboriginal Otitis-Prone Children Produce High-Quality Serum IgG to Putative Nontypeable Haemophilus influenzae Vaccine Antigens at Lower Titres Compared to Non-Aboriginal Children

Background

Nontypeable Haemophilus influenzae (NTHi) is the most common bacterial otopathogen associated with otitis media (OM). NTHi persists in biofilms within the middle ears of children with chronic and recurrent OM. Australian Aboriginal children suffer exceptionally high rates of chronic and recurrent OM compared to non-Aboriginal children. NTHi protein vaccines comprised of antigens associated with both adhesion and persistence in a biofilm are under development and could be beneficial for children with chronic and recurrent OM. Understanding the ontogeny of natural antibody development to these antigens provides insight into the value of vaccinating with particular antigens.

Methods

An in-house multiplex fluorescent bead immunoassay was used to measure serum IgG titres and avidity for three putative vaccine antigens: recombinant soluble PilA (rsPilA), ChimV4, and outer membrane protein 26 (OMP26) in sera from Australian Aboriginal otitis-prone children (n=77), non-Aboriginal otitis-prone children (n=70) and non-otitis-prone children (n=36). Serum IgG titres were adjusted for age, and geometric mean concentrations (GMCs) were compared between groups using a univariate analysis model. Antibody avidity was calculated as a relative avidity index and compared between groups using ANOVA.

Results

Australian Aboriginal otitis-prone children had lower serum IgG titres to rsPilA and ChimV4 than non-Aboriginal otitis-prone children (p<0.001), and non-otitis-prone children (p<0.020). No differences were observed between serum IgG titres from non-Aboriginal otitis-prone children and non-otitis-prone children. There were also no differences in the proportion of high avidity IgG specific for these antigens between these groups. Serum IgG titres to OMP26 were similar between all groups (p>0.670) although otitis-prone children had a higher proportion of high avidity antibodies to this antigen.

Conclusions

Australian Aboriginal otitis-prone children had lower serum IgG titres to 2/3 major NTHi vaccine candidate antigens, suggesting these children are unable to develop persistent IgG responses due to repeated NTHi exposure. These reduced IgG titres may relate to earlier and more frequent exposure to diverse NTHi strains in Aboriginal children through carriage or infection. These data suggest that Aboriginal children may benefit from immunisation with vaccines containing these antigens to increase titres of protective antibodies.

Sputum Proteome Signatures of Mechanically Ventilated Intensive Care Unit Patients Distinguish Samples with or without Anti-pneumococcal Activity

Mechanically ventilated patients are at risk of contracting pneumonia. Therefore, these patients often receive prophylactic systemic antimicrobial therapy. Intriguingly however, a previous study showed that antimicrobial activity in bronchoalveolar aspirates (here referred to as “sputa”) from ventilated patients was only partially explained by antibiotic therapy. Here we report that sputa from these patients presented distinct proteome signatures depending on the presence or absence of antimicrobial activity. Moreover, we show that the same distinction applied to antibodies against Streptococcus pneumoniae, which is a major causative agent of pneumonia. Specifically, the investigated sputa that inhibited growth of S. pneumoniae, while containing subinhibitory levels of the antibiotic cefotaxime, presented elevated levels of proteins implicated in innate immune defenses, including complement and apolipoprotein-associated proteins. In contrast, S. pneumoniae-inhibiting sputa with relatively high cefotaxime concentrations or noninhibiting sputa contained higher levels of proteins involved in inflammatory responses, such as neutrophil elastase-associated proteins. In an immunoproteomics analysis, 18 out of 55 S. pneumoniae antigens tested showed significantly increased levels of IgGs in inhibiting sputa. Hence, proteomics and immunoproteomics revealed elevated levels of antimicrobial host proteins or S. pneumoniae antigen-specific IgGs in pneumococcal growth-inhibiting sputa, thus explaining their anti-pneumococcal activity.

IMPORTANCE Respiratory pathogens like Streptococcus pneumoniae can cause severe pneumonia. Nonetheless, mechanically ventilated intensive care patients, who have a high risk of contracting pneumonia, rarely develop pneumococcal pneumonia. This suggests the presence of potentially protective antimicrobial agents in their lung environment. Our present study shows for the first time that bronchoalveolar aspirates, “sputa,” of ventilated patients in a Dutch intensive care unit were characterized by three distinct groups of proteome abundance signatures that can explain their anti-pneumococcal activity. Importantly, this anti-pneumococcal sputum activity was related either to elevated levels of antimicrobial host proteins or to antibiotics and S. pneumoniae-specific antibodies. Further, the sputum composition of some patients changed over time. Therefore, we conclude that our study may provide a novel tool to measure changes that are indicative of infection-related conditions in the lungs of mechanically ventilated patients.

Seroepidemiological analysis of anti-pneumococcal surface protein A (PspA) immunoglobulin G by clades in Japanese population

BACKGROUND

Pneumococcal surface protein A (PspA) is one of the candidates of the novel pneumococcal protein vaccines. The seroepidemiology of naturally acquired anti-PspA immunoglobulin G (IgG) by clades, across a wide range of ages has not been investigated.

METHODS

We examined the concentrations of anti-PspA IgG by clades (1, 2, 3, 4, and 5) in 397 sera from persons aged 0-≥70 years by enzyme-linked immunosorbent assay, and determined the geometric mean concentrations (GMCs) by age group. The relationships between concentrations of anti-PspA IgG antibody for each clade for each person were also assessed.

RESULTS

GMC of anti-PspA IgG was lowest, highest, and plateaued in those aged 6-11 months, 5-9-years, and 20-49 years, respectively. It gradually declined in those aged > 70 years. GMCs patterns in different age groups were similar for all clades. Correlations were found especially within the same PspA family (between clades 1 and 2 or clades 4 and 5).

CONCLUSIONS

Our data suggested that most people acquired anti-PspA IgG across clades 1, 2, 3, 4, and 5 during childhood. These results would be a fundamental data of clade-specific anti-PspA IgG antibodies.

Immune exclusion by naturally acquired secretory IgA against pneumococcal pilus-1

Successful infection by mucosal pathogens requires overcoming the mucus barrier. To better understand this key step, we performed a survey of the interactions between human respiratory mucus and the human pathogen Streptococcus pneumoniae. Pneumococcal adherence to adult human nasal fluid was seen only by isolates expressing pilus-1. Robust binding was independent of pilus-1 adhesive properties but required Fab-dependent recognition of RrgB, the pilus shaft protein, by naturally acquired secretory IgA (sIgA). Pilus-1 binding by specific sIgA led to bacterial agglutination, but adherence required interaction of agglutinated pneumococci and entrapment in mucus particles. To test the effect of these interactions in vivo, pneumococci were preincubated with human sIgA before intranasal challenge in a mouse model of colonization. sIgA treatment resulted in rapid immune exclusion of pilus-expressing pneumococci. Our findings predict that immune exclusion would select for nonpiliated isolates in individuals who acquired RrgB-specific sIgA from prior episodes of colonization with piliated strains. Accordingly, genomic data comparing isolates carried by mothers and their children showed that mothers are less likely to be colonized with pilus-expressing strains. Our study provides a specific example of immune exclusion involving naturally acquired antibody in the human host, a major factor driving pneumococcal adaptation.

Assessment of an Antibody-in-Lymphocyte Supernatant Assay for the Etiological Diagnosis of Pneumococcal Pneumonia in Children

New diagnostic tests for the etiology of childhood pneumonia are needed. We evaluated the antibody-in-lymphocyte supernatant (ALS) assay to detect immunoglobulin (Ig) G secretion from ex vivo peripheral blood mononuclear cell (PBMC) culture, as a potential diagnostic test for pneumococcal pneumonia. We enrolled 348 children with pneumonia admitted to Patan Hospital, Kathmandu, Nepal between December 2015 and September 2016. PBMCs sampled from participants were incubated for 48 h before harvesting of cell culture supernatant (ALS). We used a fluorescence-based multiplexed immunoassay to measure the concentration of IgG in ALS against five conserved pneumococcal protein antigens. Of children with pneumonia, 68 had a confirmed etiological diagnosis: 12 children had pneumococcal pneumonia (defined as blood or pleural fluid culture-confirmed; or plasma CRP concentration ≥60 mg/l and nasopharyngeal carriage of serotype 1 pneumococci), and 56 children had non-pneumococcal pneumonia. Children with non-pneumococcal pneumonia had either a bacterial pathogen isolated from blood (six children); or C-reactive protein <60 mg/l, absence of radiographic consolidation and detection of a pathogenic virus by multiplex PCR (respiratory syncytial virus, influenza viruses, or parainfluenza viruses; 23 children). Concentrations of ALS IgG to all five pneumococcal proteins were significantly higher in children with pneumococcal pneumonia than in children with non-pneumococcal pneumonia. The concentration of IgG in ALS to the best-performing antigen discriminated between children with pneumococcal and non-pneumococcal pneumonia with a sensitivity of 1.0 (95% CI 0.73-1.0), specificity of 0.66 (95% CI 0.52-0.78) and area under the receiver-operating characteristic curve (AUROCC) 0.85 (95% CI 0.75-0.94). Children with pneumococcal pneumonia were older than children with non-pneumococcal pneumonia (median 5.6 and 2.0 years, respectively, p < 0.001). When the analysis was limited to children ≥2 years of age, assay of IgG ALS to pneumococcal proteins was unable to discriminate between children with pneumococcal pneumonia and non-pneumococcal pneumonia (AUROCC 0.67, 95% CI 0.47-0.88). This method detected spontaneous secretion of IgG to pneumococcal protein antigens from cultured PBMCs. However, when stratified by age group, assay of IgG in ALS to pneumococcal proteins showed limited utility as a test to discriminate between pneumococcal and non-pneumococcal pneumonia in children.

Determination of avidity of IgG against protein antigens from Streptococcus pneumoniae: assay development and preliminary application in clinical settings

The measurement of antibody levels is a common test for the diagnosis of Streptococcus pneumoniae infection in research. However, the quality of antibody response, reflected by avidity, has not been adequately evaluated. We aimed to evaluate the role of avidity of IgG against eight pneumococcal proteins in etiologic diagnosis. Eight pneumococcal proteins (Ply, CbpA, PspA1 and 2, PcpA, PhtD, StkP-C, and PcsB-N) were used to develop a multiplex bead-based avidity immunoassay. The assay was tested for effects of the chaotropic agent, multiplexing, and repeatability. The developed assay was applied to paired samples from children with or without pneumococcal disease (n = 38 for each group), determined by either serology, polymerase chain reaction (PCR), or blood culture. We found a good correlation between singleplex and multiplex assays, with r ≥ 0.94.The assay was reproducible, with mean inter-assay variation ≤ 9% and intra-assay variation < 6%. Children with pneumococcal disease had lower median avidity indexes in the acute phase of disease for PspA1 and 2 (p = 0.042), PcpA (p = 0.002), PhtD (p = 0.014), and StkP-C (p < 0.001). When the use of IgG avidity as a diagnostic tool for pneumococcal infection was evaluated, the highest discriminative power was found for StkP-C, followed by PcpA (area under the curve [95% confidence interval, CI]: 0.868 [0.759-0.977] and 0.743 [0.607-879], respectively). The developed assay was robust and had no deleterious influence from multiplexing. Children with pneumococcal disease had lower median avidity against five pneumococcal proteins in the acute phase of disease compared to children without disease.