Measurement of the humoral immune response against Streptococcus pneumoniae type 3 capsular polysaccharide and oligosaccharide containing antigens by ELISA and ELISPOT techniques

A sensitive ELISA has been developed to study immune responses in mice against Streptococcus pneumoniae type 3 capsular polysaccharide (S3PS) and hexasaccharide (HS)-protein conjugates derived therefrom. An advantage of the described system is that the same microtiter plates can be used for both ELISA and ELISPOT tests with a standardized washing procedure and diluent composition. S3PS induced predominantly IgM antibodies and minute amounts of IgG as measured by ELISA in serum. This was accompanied by large numbers (>14000) of IgM spot-forming cells in the spleen. A shift towards IgG production was achieved by addition of lipid A. HS-protein conjugates induced predominantly IgG antibodies after booster immunization(s). Furthermore these conjugates induced large numbers (>40 000) of IgG spot-forming cells (SFC) in the spleen. ELISA and ELISPOT assays on microtiter plates are both reliable and highly reproducible assays for the evaluation of immune responses to S. pneumoniae antigens.