In vivo humoral immune responses to isolated pneumococcal polysaccharides are dependent on the presence of associated TLR ligands.
We determined whether T cell-independent Ig isotype responses to isolated pneumococcal polysaccharides (PPS) required TLR signaling in vivo. IgG anti-PPS responses to PPS3, PPS14, and C-polysaccharide (C-PS) were virtually undetectable in TLR2(-/-) mice, whereas specific IgM induction was variably reduced compared with wild-type mice. All PPS-containing preparations induced IL-6 and TNF-alpha from wild-type, but not TLR2-/-, macrophages. TLR2 activity was distinct from that of PPS, in that it was phenol extractable. Immunization of wild-type mice with phenol-extracted PPS14 also resulted in a marked reduction in the IgG, although not the IgM-anti-PPS14, response compared with untreated PPS14. The commercial 23-valent PPS vaccine, Pneumovax-23 also contained TLR ligands (TLR2 and TLR4), which were absolutely critical for the IgG-inducing activity of the vaccine in mice. Finally, the commercial pneumococcal conjugate vaccine, Prevnar, contained a TLR2 ligand(s) that substantially enhanced both the primary and secondary anti-PPS responses in mice, especially the type 1 IgG isotypes. These data strongly suggest the absolute need for a distinct, TLR-dependent second signal for inducing in vivo IgG T cell-independent humoral immune responses to isolated pneumococcal polysaccharide Ags and highlight the potential importance of previously unappreciated copurified and/or contaminating TLR ligands in PPS vaccine preparations.
Sen
Goutam
G
Department of Pathology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA.
Khan
Abdul Q
AQ
Chen
Quanyi
Q
Snapper
Clifford M
CM
D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood*; D016667:Bacterial Capsules / Q000276:immunology; D016207:Cytokines / Q000096:biosynthesis; D007074:Immunoglobulin G / Q000097:blood; D007075:Immunoglobulin M / Q000097:blood; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D022242:Pneumococcal Vaccines / Q000276:immunology*; D011135:Polysaccharides, Bacterial / Q000276:immunology*; D011971:Receptors, Immunologic / Q000502:physiology*; D013296:Streptococcus pneumoniae / Q000276:immunology*; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4
D000907:Antibodies, Bacterial; D016207:Cytokines; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D022242:Pneumococcal Vaccines; D011135:Polysaccharides, Bacterial; D011971:Receptors, Immunologic; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4