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In contrast to other pneumococcal serotypes, which are thought to be T-independent antigens, type 1 Streptococcus pneumoniae polysaccharide (Sp1) is a zwitterionic polysaccharide (ZPS). It has previously been shown to be processed and presented by antigen-presenting cells utilizing the MHC-II pathway, which leads to Sp1-induced T cell proliferation, a hallmark of thymus-dependent immune responses. We used peripheral blood mononuclear cells obtained from adults enrolled in a randomised clinical trial to investigate memory B cell responses following immunisation with the 23-valent pneumococcal plain polysaccharide vaccine. Administration of this serotype 1 containing vaccine resulted in the depletion of serotype 1 antigen-specific pre-existing memory B cells compared to baseline. This finding indicates that this ZPS is not processed by a classical TD mechanism within the MHC-II pathway.

Original publication




Journal article



Publication Date





368 - 372


Aged, Antigens, Bacterial, B-Lymphocytes, Cells, Cultured, Female, Heptavalent Pneumococcal Conjugate Vaccine, Humans, Immunoglobulin G, Immunologic Memory, Male, Middle Aged, Pneumococcal Infections, Pneumococcal Vaccines, Polysaccharides, Bacterial, Streptococcus pneumoniae, Vaccination