Comparative Study of Immunogenic Properties of Purified Capsular Polysaccharides from Streptococcus suis Serotypes 3, 7, 8, and 9: the Serotype 3 Polysaccharide Induces an Opsonizing IgG Response

• Published in: Infection and immunity 2020-09, Vol.88 (10)
• Main Authors: Goyette-Desjardins, Guillaume, Auger, Jean-Philippe, Dolbec, Dominic, Vinogradov, Evgeny, Okura, Masatoshi, Takamatsu, Daisuke, Van Calsteren, Marie-Rose, Gottschalk, Marcelo, Segura, Mariela
• Format: Article
• Language: English
• Subjects: Adjuvants, Immunologic - administration & dosage; Animals; Antigens, Bacterial - administration & dosage; Antigens, Bacterial - chemistry; Antigens, Bacterial - immunology; Bacterial Capsules - genetics; Bacterial Capsules - immunology; Chemokines - immunology; Dendritic Cells - immunology; Immunization; Immunoglobulin G - immunology; Immunoglobulin M - immunology; Mice; Microbial Immunity and Vaccines; Myeloid Differentiation Factor 88 - immunology; Polysaccharides, Bacterial - administration & dosage; Polysaccharides, Bacterial - chemistry; Polysaccharides, Bacterial - immunology; Serogroup; Streptococcal Infections - immunology; Streptococcal Infections - microbiology; Streptococcus suis - genetics; Streptococcus suis - immunology; Toll-Like Receptor 2 - immunology
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.00377-20

is an encapsulated bacterium and one of the most important swine pathogens and a zoonotic agent for which no effective vaccine exists. Bacterial capsular polysaccharides (CPSs) are poorly immunogenic, but anti-CPS antibodies are essential to the host defense against encapsulated bacteria. In addition to the previously known serotypes 2 and 14, which are nonimmunogenic, we have recently purified and described the CPS structures for serotypes 1, 1/2, 3, 7, 8, and 9. Here, we aimed to elucidate how these new structurally diverse CPSs interact with the immune system to generate anti-CPS antibody responses. CPS-stimulated dendritic cells produced significant levels of C-C motif chemokine ligand 3 (CCL3), partially via Toll-like receptor 2 (TLR2)- and myeloid differentiation factor 88-dependent pathways, and CCL2, via TLR-independent mechanisms. Mice immunized with purified serotype 3 CPS adjuvanted with TiterMax Gold produced an opsonizing IgG response, whereas other CPSs or adjuvants were negative. Mice hyperimmunized with heat-killed serotypes 3 and 9 both produced anti-CPS type 1 IgGs, whereas serotypes 7 and 8 remained negative. Also, mice infected with sublethal doses of serotype 3 produced primary anti-CPS IgM and IgG responses, of which only IgM were boosted after a secondary infection. In contrast, mice sublethally infected with serotype 9 produced weak anti-CPS IgM and IgG responses following a secondary infection. This study provides important information on the divergent evolution of CPS serotypes with highly different structural and/or biochemical properties within and their interaction with the immune system.