Pneumococcal antibodies in IgA of serum and external secretions.

An indirect immuno-fluorescent method is described for the detection of group and type specific antibodies against pneumococci. The localization of these antibodies in the various immunoglobulin classes can be established by this method. Difficulties may be encountered, due to masking of sites on the antigen by antibodies, present in excess in a particular class of immunoglobulin. Relatively high titres of group specific and type specific antibodies against pneumococcus types, 3, 6, 9, 14 and 24 could be demonstrated in colostrum IgA. Occasionally these antibodies were also found in serum IgA. Group specific antibodies were detected in low titres in IgA of saliva and nasal secretions. The findings are discussed in relation to the concept of the secretory IgA system.