Circulating antibody secreting cell response to parenteral pneumococcal vaccines as an indicator of a salivary IgA antibody response.

This study assessed the mucosal immune response in healthy adult volunteers immunized parenterally with either pneumococcal polysaccharide (N = 8) or pneumococcal polysaccharide-protein conjugate (N = 10) vaccine with an aim to evaluate the relevance of antibody secreting cell (ASC) response after parenteral vaccination. An ASC response to the four types of capsular polysaccharide tested was observed in all vaccinees 7-9 days after immunization. IgA was the predominant class in the ASC response, and IgG the next common, with very few IgM ASCs. The IgA/IgG ratio in the ASC response was higher after immunization with the polysaccharide than the conjugate vaccine. Antibodies of the IgA class were frequently seen in the saliva already before immunization; especially to serotypes 14 and 19F. A twofold increase of the type specific secretory IgA antibodies in saliva was found in eight of the 16 instances in which the specific IgA ASC response was > 100 ASC per 10(6) cells and in only one of the 52 instances with fewer ASCs. We conclude that the ASC response in the peripheral blood is a useful parameter of the antibody response to pneumococcal vaccines and a good indicator of a secretory IgA response in the saliva.