Antibody and splenocyte proliferation response to whole inactivated Streptococcus pneumoniae serotype 1, 3 and 6B in mice.

Animal models of infection and protection on the topic of the Streptococcus pneumoniae (S. pneumoniae) have encountered many difficulties generated by low immunogenicity, a characteristic of polysaccharide capsular bacteria and difference of virulence between serotypes and strains. We have explored the immune response after immunization with heat inactivated S. pneumoniae serotype 1, 3 and 6B in C57BL/6 mice by IgM and IgG detection, and by splenocyte in vitro 5-ethynyl-2'-deoxyuridine (EdU) incorporation after antigen specific stimulation, as a proposed method of cellular immune response evaluation. Antibody titer persistence after immunization was not lengthy while antigen specific proliferation response detected by EdU assay was remnant. Intraperitoneal (i.p.) challenge with serotype 6B S. pneumoniae proved that antibody titers and the detected specific cellular immune response do not cover seroprotective necessity and do not confer improved immunologic memory in comparison to non-immunized mice, which show natural resistance.