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.