Development of antibodies against pneumococcal proteins alpha-enolase, immunoglobulin A1 protease, streptococcal lipoprotein rotamase A, and putative proteinase maturation protein A in relation to pneumococcal carriage and Otitis Media.

Surface associated pneumococcal proteins alpha-enolase (Eno), immunoglobulin A1 protease (Iga), streptococcal lipoprotein rotamase A (SlrA), and putative proteinase maturation protein A (PpmA) have potential as candidates for future protein-based anti-pneumococcal vaccines. The immunogenicity of these proteins were studied in a cohort of 329 children during their first two years of life. During the first recorded episode of otitis media, acute and convalescent phase sera were available from 151 children. Concentrations of antibodies against Eno, Iga, SlrA and PpmA were measured by EIA and detected in 99% (300/302), 95% (288/302), 95% (288/302), and 83% (251/302) of the sera, respectively. There were no statistically significant differences between the groups of children with and without a history of pneumococcal contact or with respect to the type of pneumococcal contact. Despite a mean overall decrease in the antibody titers in the convalescent sera following AOM, several children were able to respond with a more than twofold increase in antibody titer in response to AOM. The majority of the children with increased antibody concentrations appeared in the groups, which were colonized with pneumococci at the time of serum collection, but were recorded as having no prior contact with pneumococci. In conclusion, SlrA, PpmA, Eno and Iga are immunogenic proteins that elicit antibody responses early in life. No significant correlation between antibody titers to these proteins and pneumococcal carriage or infection was found. Presumably, this results from the presence of cross-reactive epitopes on commensal bacteria.