Surface Immunogenic Protein of Streptococcus Group B is an Agonist of Toll-Like Receptors 2 and 4 and a Potential Immune Adjuvant

Abstract

Vaccine-induced protection against pathogens, especially subunit-based vaccines, are related to antigen properties but mainly in their ability to stimulate the immune system by the use of an adjuvant. Modern vaccines are formulated with a high level of antigen purity, where an efficient adjuvant is necessary. In this context, the use of protein Toll-Like Receptor (TLR) agonists as vaccine adjuvants has been highlighted because of their optimal immunogenicity and minimal toxicity. The Surface Immunogenic Protein (SIP) from Group B Streptococcus (GBS) has gained importance as a new potential protein-based vaccine. Recently, we reported that recombinant SIP (rSIP) expressed by E. coli and purified by High Performance Liquid Chromatography (HPLC) alone induces a protective humoral immune response. In this study, we present the immunomodulatory properties of rSIP as a protein-based adjuvant, as an agonist of TLR. To this end, we showed that C57BL/6 bone marrow-derived dendritic cells pulsed by rSIP resulted in enhanced CD40, CD80, CD86, and Major Histocompatibility Complex (MHC) class II as well as increased secretion proinflammatory cytokines Interleukin (IL)-6, Interferon (IFN)-γ, Tumor Necrosis Factor (TNF)-α, and IL-10. Next, we investigated the in vivo effect of rSIP in the absence or presence of ovalbumin (OVA) on antigen-specific antibody secretion in C57BL/6 mice. Immunization with rSIP plus OVA showed that anti-OVA IgG2a and IgG1a increased significantly compared with OVA alone in C57BL/6 mice. Also, the immunization of rSIP plus OVA generates increased serum cytokines levels characterized by IL-12p70, IL-10, IL-4, and IFN-γ. Interestingly, we observed that rSIP stimulate Toll Like Receptor (TLR)2 and TLR4, individually expressed by Human embryonic kidney (HEK) 293-derived TLR reporter cells. These findings suggest that rSIP is a new potential protein TLR agonist adjuvant and may be employed in the development of new vaccines.

Hyaluronidase Impairs Neutrophil Function and Promotes Group BStreptococcusInvasion and Preterm Labor in Nonhuman Primates

“…Given the in vivo and in vitro data obtained in this study, we propose that HylB may dampen proinflammatory cascades and microbicidal activity of first-line innate immune defenses such as neutrophils, thereby promoting bacterial replication and invasion of the amniotic cavity and fetus. We hypothesize that once bacteria have invaded the fetal niche, other proinflammatory, surface-associated bacterial factors (e.g., capsular polysaccharides [ 41 ], surface immunogenic protein [ 42 ], pilus [ 43 ]) overcome the immune-dampening effects of GBS HylB-digested HA fragments, triggering host PRRs and resulting in systemic fetal inflammation. A systemic fetal inflammatory response in GB37-infected fetuses may have triggered parturition in these animals, akin to fetal inflammatory response syndrome, which has been linked to preterm labor in humans ( 44 , 45 ).…”

Mucosal Vaccination with Lactococcus lactis-Secreting Surface Immunological Protein Induces Humoral and Cellular Immune Protection against Group B Streptococcus in a Murine Model

“…SIP is considered a putative target for the development of a GBS vaccine because it is highly conserved among all GBS serotypes and induces a protective humoral and cellular immune response [13,19]. Moreover, rSIP is an agonist of toll-like receptor 2 (TLR2) and TLR4, which suggests a dual role in the generation of innate and adaptive immune responses against bacterial infection [15]. Previously, we demonstrated that an oral vaccination strategy composed of SIP plus alum adjuvant induces a reduction of GBS vaginal colonization, as well as opsonic antibodies [30].…”

“…Following the manufacturer’s instructions, we used the automated NucliSENS-EasyMAG platform (Biomerieux, Marcy l’Etoile, France) to purify total nucleic acids from 600,000 splenocytes contained in 500 μL of RPMI 1640 medium with 10% FBS, 25 mM β-mercaptoethanol, and penicillin/streptomycin. The splenocytes were obtained from the spleens of experimental mice and pulsed with SIP protein (purified by HPLC, as described by Diaz-Dinamarca et al [ 15 ]). The eluates were treated with DNase (Invitrogen, Carlsbad, CA, USA) to degrade the DNA in the sample.…”

“…An animal model demonstrated that specific antibodies against SIP could cross the placenta to confer protection to newborns against diseases caused by GBS [14]. We also recently reported that SIP is a toll-like receptor (TLR)-2 and TLR-4 protein agonist, suggesting potential as a new immune adjuvant [15]. In addition, SIP has been used in the development of a vaccine for GBS infection in a Nile tilapia (Oreochromis niloticus) model and generated an increase in innate immunity [16,17].…”

Surface immunogenic protein from Streptococcus agalactiae and Fissurella latimarginata hemocyanin are TLR4 ligands and activate MyD88- and TRIF dependent signaling pathways

“…In contrast to hemocyanins, including the FLH used in this study, the recombinant surface immunogenic protein (rSIP) from Group B Streptococcus is a small protein. It was previously expressed in Escherichia coli and Pichia pastoris and had a molecular weight of 53 kDa with a β-folded structure and the ability to form dimers ( 27 ). This recombinant protein was analyzed as a vaccine against GBS in a preclinical trial.…”