Mika Lahdenkari

Effects of Ageing and Gender on Naturally Acquired Antibodies to Pneumococcal Capsular Polysaccharides and Virulence-Associated Proteins

ABSTRACT Elderly individuals are susceptible to pneumococcal infections. Although factors contributing to the increased susceptibility of the elderly to bacterial infections may be several, compromised immune function, a consequence of normal human ageing, is widely accepted to play a role. We evaluated the effect of ageing on the concentrations of naturally acquired antibodies to pneumococcal capsular polysaccharides (PPS) and protein antigens. The concentrations of immunoglobulin G (IgG) and IgM antibodies to the PPS of serotypes 3, 4, 6B, 9V, 14, and 23F and IgG antibodies to the pneumococcal virulence-associated proteins CbpA, LytC, PhtD and its C-terminal fragment (PhtD C), NanA, PspA fam1, and PspA fam2 were measured by enzyme immunoassay in the sera of younger (30 to 64 years of age) and elderly (65 to 97 years of age) adults. The concentrations of anti-PPS IgG against serotypes 3 and 6B, of anti-PPS IgM against serotypes 3, 4, 6B, 9V, and 23F, and of anti-protein IgG against all tested antigens were significantly lower in the elderly than in younger adults. A stronger decline in anti-PPS antibody concentrations was seen with age in women compared to men, while anti-protein antibody concentrations were mainly similar between the genders. Age, gender, and the nature of the antigen have substantial and varying effects on the antibody concentrations in the sera of adults.

Antibody response to the pneumococcal proteins pneumococcal surface adhesin A and pneumolysin in children with acute otitis media.

Background. Pneumococcal surface adhesin A (PsaA) and pneumolysin (Ply) are common to virtually all Streptococcus pneumoniae isolates, and they are immunogenic and protective against pneumococcal challenge in experimental animals. We have recently shown production of antibodies to PsaA and Ply in young children, but data on the immune response to these antigens during culture-confirmed pneumococcal infection are lacking. Objectives. To evaluate whether young children respond to S. pneumoniae by producing antibodies to PsaA and Ply during acute otitis media (AOM). Subjects and methods. A cohort of 329 children was followed prospectively from the age of 2 months to the age of 2 years. Paired sera were obtained during episodes of AOM and used to measure antibodies to PsaA and Ply by enzyme-linked immunosorbent assay. S. pneumoniae cultured from the middle ear fluid was taken as evidence of pneumococcal AOM. The presence of S. pneumoniae in the nasopharyngeal aspirate collected in connection of AOM or any other respiratory infection or in the nasopharyngeal swab collected at scheduled visits was taken to indicate pneumococcal carriage and thus a history of previous contact with S. pneumoniae. Results. Children with previous pneumococcal contacts had high anti-PsaA and anti-Ply concentrations in the acute phase sera regardless of the nature (AOM or carriage) of the current pneumococcal contact. Of the children with no previous pneumococcal contact, those with current pneumococcal AOM had lower antibody concentrations than those with current pneumococcal carriage only. Anti-PsaA and anti-Ply responses were found in children with current pneumococcal contact. The antibody response was strongly associated with low acute phase antibody concentration, but not significantly with age and the nature of the current pneumococcal contact. Conclusions. We showed that infants are capable of developing a specific antibody response to the pneumococcal proteins PsaA and Ply during AOM.

Pneumococcal carriage and acute otitis media induce serum antibodies to pneumococcal surface proteins CbpA and PhtD in children

We assessed the development and role of serum anti-CbpA and -PhtD in early childhood in relation to pneumococcal exposure. Serum IgG concentrations to CbpA and PhtD were measured with enzyme immunoassay in serum samples collected at the ages of 6, 12, 18, and 24 months from 50 healthy children and from 50 adults. Furthermore, antibodies to CbpA, PhtD and the C-terminal fragment of PhtD (PhtD C) were measured in serum samples collected at 12 (N=286) and 18 months (N=259) to evaluate the risk of subsequent pneumococcal acute otitis media (AOM) in relation to antibody concentrations. The increase in anti-CbpA and -PhtD concentrations was related to prior pneumococcal exposure. At 12 and 18 months, in the risk model of pneumococcal AOM adjusted for prior pneumococcal AOM, higher concentrations of anti-CbpA, but not anti-PhtD, were associated with a lowered risk of subsequent pneumococcal AOM. In conclusion, pneumococcal exposure induces the development of serum anti-CbpA and -PhtD in early childhood. Anti-CbpA antibodies may play a role in the prevention of subsequent pneumococcal AOM during the second year of life.

Antibodies to pneumococcal surface protein A families 1 and 2 in serum and saliva of children and the risk of pneumococcal acute otitis media.

BACKGROUND Pneumococcal surface protein A (PspA) is a highly variable yet cross-reactive protein that exists as 2 major families. We assessed the development of human serum and salivary antibodies against the PspA families 1 (PspA1) and 2 (PspA2) in early childhood and their role in the prevention of pneumococcal acute otitis media (AOM). METHODS Serum levels of IgG and salivary levels of IgA antibodies to PspA1 and PspA2 were measured by use of enzyme immunoassay from the samples from the Finnish Otitis Media Cohort Study obtained at the ages of 12 months (287 and 160 samples, respectively) and 18 months (258 and 131 samples, respectively). The Cox proportional hazard model was used to evaluate the relative risk (RR) of pneumococcal AOM during the 6 months after sampling relative to concentration of serum or presence of salivary anti-PspA in the samples. RESULTS Anti-PspA1 and anti-PspA2 concentrations at 12 and 18 months were related to prior culture-confirmed pneumococcal exposure. The concentrations of serum anti-PspA were not significantly associated with the risk of pneumococcal AOM. At 18 months, the presence of salivary anti-PspA was significantly associated with a lower risk of pneumococcal AOM during the 6 months after sampling (RR, 0.27 [95% confidence interval, 0.11-0.69]). CONCLUSIONS The lowered risk of pneumococcal AOM associated with the presence of salivary anti-PspA at 18 months suggests that mucosal anti-PspA antibodies have a role in the prevention of pneumococcal AOM.

Does the Presence of Pneumococcal DNA in Middle-Ear Fluid Indicate Pneumococcal Etiology in Acute Otitis Media?

Bacterial culture of middle-ear fluid (MEF), the standard for etiologic diagnosis of acute otitis media (AOM), has revealed Streptococcus pneumoniae (Pnc) to be a major pathogen responsible for one-third of AOM cases. In the present study, we compared the results of polymerase chain reaction (PCR) based on the amplification of the pneumolysin gene with the results of pneumococcal culture, for 2595 MEF samples obtained during AOM events in 831 children who were followed from 2-24 months of age in the Finnish Otitis Media Vaccine Trial. PCR results were positive for 47.1% of the MEF samples, and culture results were positive for 27.3% of the samples. PCR-positive, culture-negative samples were associated with previous Pnc AOM in a time-dependent pattern, concurrent antibiotic treatment, low volume of MEF, and concurrent nasopharyngeal carriage. PCR-positive AOM represented a clinically less severe disease, compared with culture-positive Pnc AOM. A positive PCR result seemed to indicate the presence of viable, although often nonculturable, Pnc.

Long-term effect of pneumococcal conjugate vaccines on tympanostomy tube placements.

Background: We have previously shown that the 7-valent pneumococcal conjugate vaccine (PncCRM) given in infancy is effective in reducing tympanostomy tube placements up to 4 to 5 years of age. This study aimed to assess the effectiveness of pneumococcal conjugate vaccines PncCRM and PncOMPC from 2 up to 13 years of age. Methods: Altogether 2497 children participated in the Finnish Otitis Media Vaccine trial conducted in 1995 to 1999 and were vaccinated at 2, 4, 6 and 12 months of age with PncCRM or PncOMPC or hepatitis B vaccine as controls. The data for tympanostomy tube placements were collected from health registers including hospital and private office operations. Vaccine efficacy was estimated by comparing incidences of tympanostomies from 2 to 12–13 years of age in each of the pneumococcal vaccine groups with the control group. Results: Register data were searched for 2474 subjects. A total of 535 tympanostomy tube placements were identified in the health registers from 1998 through 2008 with a cumulative incidence of 14.6% from 2 to 13 years of age in the control group. The vaccine impact was age-dependent: from 2 through 5 years of age the vaccine effectiveness was 34% (95% confidence interval: 1% to 52%) for PncCRM and 6% (–28 to 31) for the PncOMPC vaccine. For the age group of 6 to 12–13 years the vaccine effectiveness estimates for the PncCRM and PncOMPC groups were –13% (–137 to 46) and –2% (–123 to 54), respectively. Conclusions: PncCRM vaccine reduced the tympanostomy tube placements up to 5 years of age. No impact on new surgical procedures could be demonstrated after that but the benefit achieved was sustained.

Is there any specific association between respiratory viruses and bacteria in acute otitis media of young children

Summary Background Respiratory viral infections are usually preceding or coinciding with acute otitis media (AOM) in children. It is not known if a given viral infection would facilitate invasion of bacterial pathogens into the middle ear in a species-specific way. We reanalysed the microbiological results of the two prospective Finnish Otitis Media (FinOM) studies for this purpose. Methods The children had been followed from 2 months to 2 years of age in specific study clinics and all referred AOM events were analysed. Combined results of virus detection tests from middle ear fluid and nasopharyngeal aspirate and those of bacterial culture from middle ear fluid were cross-tabulated for 529 AOM events in the FinOM Cohort Study and for 364 events in the FinOM Vaccine Trial. Results In both studies the main bacterial pathogens were Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis while the main viruses detected were rhinoviruses and respiratory syncytial virus (plus enteroviruses in the Vaccine Trial). No distinct species-specific associations were observed between the viral and bacterial findings. Conclusion We did not find support to the theory that respiratory infection caused by a given viral species would favour growth of a certain bacterial pathogen in the MEF more than another.

Serum antibodies to the pneumococcal surface proteins PhtB and PhtE in Finnish infants and adults.

We examined naturally acquired antibodies to pneumococcal vaccine candidate proteins PhtB and PhtE in children during their first 2 years of life. Prior culture-confirmed pneumococcal exposure was shown to induce the development of anti-PhtB and -PhtE antibodies. The anti-PhtB or -PhtE antibody concentrations were not significantly associated with a decreased risk of subsequent pneumococcal acute otitis media.

Do Antibodies to Pneumococcal Surface Adhesin A Prevent Pneumococcal Involvement in Acute Otitis Media

Antibodies to the pneumococcal (Pnc) surface protein PsaA are immunogenic and protective in experimental animal models, but their role in protection from Pnc disease in humans is not known. In the present study, the ability of antibodies to PsaA to prevent the progression of Pnc carriage to Pnc acute otitis media (Pnc AOM) was evaluated. Antibodies to PsaA were measured in acute-phase serum samples of children with AOM and with Streptococcus pneumoniae cultured from the nasopharynx. The risk of Pnc AOM was evaluated by a logistic regression model with anti-PsaA concentration as the predictive variable. Higher concentrations of antibodies to PsaA were associated with lower risk of the Pnc nasopharyngeal carriage progression to Pnc AOM. This was true in children 9-24 months old (odds ratio [OR], 0.49; 95% confidence interval [CI], 0.31-0.78) but not in children <9 months old (OR, 0.81; 95% CI, 0.48-1.35).

Distribution of Pneumococcal Surface Protein A Families 1 and 2 among Streptococcus pneumoniae Isolates from Children in Finland Who Had Acute Otitis Media or Were Nasopharyngeal Carriers

ABSTRACT PspA is a structurally variable surface protein important to the virulence of pneumococci. PspAs are serologically cross-reactive and exist as two major families. In this study, we determined the distribution of PspA families 1 and 2 among pneumococcal strains isolated from the middle ear fluid (MEF) of children with acute otitis media and from nasopharyngeal specimens of children with pneumococcal carriage. We characterized the association between the two PspA families, capsular serotypes, and multilocus sequence types (STs) of the pneumococcal isolates. MEF isolates (n = 201) of 109 patients and nasopharyngeal isolates (n = 173) of 49 children were PspA family typed by whole-cell enzyme immunoassay (EIA). Genetic typing (PCR) of PspA family was done for 60 isolates to confirm EIA typing results. The prevalences of PspA families 1 and 2 were similar among pneumococci isolated from MEF (51% and 45%, respectively) and nasopharyngeal specimens (48% each). Isolates of certain capsule types as well as isolates of certain STs showed statistical associations with either family 1 or family 2 PspA. Pneumococci from seven children with multiple pneumococcal isolates appeared to express serologically different PspA families in different isolates of the same serotype; in three of the children the STs of the isolates were the same, suggesting that antigenic changes in the PspA expressed may have taken place. The majority of the isolates (97%) belonged to either PspA family 1 or family 2, suggesting that a combination including the two main PspA families would make a good vaccine candidate.