Antibody-secreting cells and their relation to humoral antibodies in serum and in nasopharyngeal aspirates in children with pneumococcal acute otitis media.

Mucosal and systemic antibody responses to pneumococcal capsular polysaccharide were studied in 17 children with culture-verified pneumococcal acute otitis media. Serotype-specific antibody-secreting cells (ASCs) in peripheral blood and antibodies in acute and convalescent sera and nasopharyngeal aspirates were measured. A polysaccharide-specific ASC response was induced in all subjects. The response was age dependent, and the dominant antibody class was IgA. Three children > 24 months old had > 100 IgA-class ASCs/10(6) cells and serum and nasopharyngeal IgA responses; 2 had only a nasopharyngeal IgA response. None of 8 children < 24 months old showed a systemic response; however, a nasopharyngeal IgA response was detected in 1. Results suggest that whole pneumococci can induce a mucosal polysaccharide-specific antibody response independent of the systemic response. Results are also in accordance with earlier studies suggesting that the mucosal immune system matures earlier in life than does the systemic immune response.