Background: Our previous studies have shown an antibody-secreting cell (ASC) response to pneumococcal vaccines in adults and suggested that a high IgA ASC response is an indicator of a secretory IgA response in saliva. We believe that the mucosal immune response is potentially an important characteristic of the pneumococcal vaccines and should thus be measured when the new pneumococcal conjugate vaccines are evaluated.
Objectives: To study mucosal and serum antibody responses to pneumococcal conjugate vaccines in toddlers.
Methods: Each investigational vaccine, containing either 3 or 10 microg of pneumococcal PS serotypes 6B, 14, 19F and 23F conjugated to either diphtheria toxoid (PncD) or tetanus protein (PncT), was administered to 10 children (a total of 40 children). The ASC response was measured on Day 7 after immunization by enzyme-linked immunospot assay, and the salivary and serum antibodies were measured before and 7 and 28 days after the immunization by enzyme immunoassay.
Results: The vaccines studied induced ASC responses to the pneumococcal polysaccharides (PS) in all children vaccinated. The ASC responses to the PS components of the vaccine (the geometric mean number of ASCs varying from 120 to 160 ASC/10(6) cells) were lower than those seen earlier in adults after conjugate vaccine (240 to 2015 ASC/10(6) cells), but comparable with those seen earlier in adults after pneumococcal PS vaccine (113 to 136 ASC/10(6) cells). The ASC response was clearly dominated by IgA-secreting cells. Salivary IgA responses were detected in 35% of the children, but IgG was rarely detected in saliva. A positive correlation was demonstrated between the number of IgA ASCs and salivary IgA concentration (r = 0.70, P = 0.01), suggesting that a high number of IgA ASCs after parenteral immunization is an indicator of a secretory IgA response in saliva. On Day 28 after immunization increased serum concentrations of IgG were detected in most vaccinees (75 to 95%, depending on the serotype).
Conclusions: Both mucosal and systemic antibody responses were induced by PncD and PncT vaccines in toddlers.