T Cell-Mediated Humoral Immune Responses to Type 3 Capsular Polysaccharide of Streptococcus pneumoniae

Most pathogenic bacteria express surface carbohydrates called capsular polysaccharides (CPSs). CPSs are important vaccine targets because they are easily accessible and recognizable by the immune system. However, CPS-specific adaptive humoral immune responses can only be achieved by the covalent conjugation of CPSs with carrier proteins to produce glycoconjugate vaccines. We previously described a mechanism by which a model glycoconjugate vaccine can activate the adaptive immune system and demonstrated that the mammalian CD4⁺ T cell repertoire contains a population of carbohydrate-specific T cells. In this study, we use glycoconjugates of type 3 Streptococcus pneumoniae CPS (Pn3P) to assess whether the carbohydrate-specific adaptive immune response exemplified in our previous study can be applied to the conjugates of this lethal pathogen. In this article, we provide evidence for the functional roles of Pn3P-specific CD4⁺ T cells utilizing mouse immunization schemes that induce Pn3P-specific IgG responses in a carbohydrate-specific T cell-dependent manner.