Characteristics of Immune Responses to Native and Protein Conjugated Pneumococcal Polysaccharide Type 14

The immune response to pneumococcal polysaccharide type 14 (PPS‐14), induced by native PPS‐14 was compared with the response induced by PPS‐14 conjugated with CRM197 (PPS‐14‐CRM197). In our animal model, immunization with PPS‐14‐CRM197 gave a significant enhancement of anti‐PPS‐14 serum titres for IgM and IgG. but not for IgA. Also an increase in total number of anti‐PPS‐14 antibody‐secreting ceils was found. Using immunohistochemical techniques, a different distribution pattern of specific antibody‐containing cells in spleen section after immunization with PPS‐I4‐CRM197 was observed. Furthermore, a higher number of IFN‐γ producing cells was found after immunization with PPS‐14‐CRM197, as compared with immunization with PPS‐14. This enhanced IFN‐γ production may be the cause for enhanced IgG response observed after immunization with PPS‐14‐CRM197. The specific immune response was less affected by splenectomy in animals immunized with PPS‐14‐CRM197 than with PPS‐14. However, an age‐related response to the native as well as the conjugated form of the PPS‐14 was observed, since no effect of conjugation with CRM197 was seen in the onset of the immune response to PPS‐14 in young animals. In conclusion, our results affirm the hypothesis that conjugation of polysaccharides changes the characteristics of the antigen towards a thymus‐dependent antigen.