Expression of Streptococcus mutans wall-associated protein A gene in Chinese hamster ovary cells: prospect for a dental caries DNA vaccine

Streptococcus mutans wall-associated protein A promotes TLR4-induced dendritic cell maturation

Dendritic cells orchestrate innate and adaptive immune responses, which are central to establishing efficient responses to vaccination. Wall-associated protein A (WapA) of Streptococcus mutans was previously used as a vaccine in animal studies for immunization against dental caries. However, as a cell surface protein, whether WapA activates innate immune responses and the effects of WapA on DCs remain unclear. In this study, WapA was cloned into the GST fusion vector pEBG, which can be expressed efficiently in mammalian cells. We found that when added before stimulation with LPS, purified WapA-GST protein increased TLR4-induced NF-κB and MAPK signalling pathway activation. Pretreatment with WapA-GST also increased LPS-induced proinflammatory cytokine production by DCs, including IL-12, IL-6 and TNF-α. Furthermore, expression of the DC maturation markers CD80/86, CD40 and MHC II was also increased by WapA pretreatment. These data indicate that WapA is recognized by DCs and promotes DC maturation.

Enhancement of salivary IgA response to a DNA vaccine against Streptococcus mutans wall-associated protein A in mice by plasmid-based adjuvants

A specific salivary IgA (sIgA) response was obtained in mice by intranasal immunization with a naked DNA vaccine consisting of the Streptococcus mutans wall-associated protein A gene (wapA) inserted into the mammalian expression vector pcDNA3.1/V5/His-TOPO. In the present study, the vaccine, referred to as pcDNA-wapA, was administered with or without the cationic lipid DMRIE-C. No mucosal response was observed in mice immunized with the vaccine alone, whereas a weak and temporal sIgA response was obtained when the vaccine was mixed with DMRIE-C. To investigate the use of pcDNA containing the interleukin 5 (IL-5) gene (pcDNA-il-5) or the cholera toxin B gene (pcDNA-ctb) as genetic adjuvants, these constructs were used in co-immunization studies. The enhancement effect was transient with pcDNA-il-5, but longer lasting with pcDNA-ctb, thus supporting the use of the latter as a genetic adjuvant to DNA vaccine.

Identification and characterization of collagen-binding activity in Streptococcus mutans wall-associated protein: A possible implication in dental root caries and endocarditis

Streptococcus mutans is implicated in coronal and dental root decay, and in endocarditis. Comparative study of the amino acid sequence of S. mutans 47 kDa wall-associated protein A (WapA) revealed a collagen-binding domain (CBD) at the N-terminal region. Recombinant AgA (WapA truncated at the carboxyterminal end) was isolated, biotin-labeled, and analyzed by Solid Phase Binding Assay. The results showed that biotin-labeled AgA bound significantly and in a dose-dependent manner to immobilized collagen type I, and to a lesser extent to fibronectin, but not to collagen type IV or laminin. Binding of biotin-labeled S. mutans cells to collagen-coated surfaces was significantly inhibited by antibody to WapA or AgA (P<0.001). The results obtained confirmed the collagen-binding activity of CBD in AgA and WapA, and suggested that WapA may be used, not only as a vaccine against coronal and dental root caries, but also against S. mutans-mediated endocarditis.

Differential immunogenicity of a DNA vaccine containing the Streptococcus mutans wall-associated protein A gene versus that containing a truncated derivative antigen A lacking in the hydrophobic carboxyterminal region

Two plasmid DNA constructs were obtained by cloning separately into the eukaryotic expression vector pcDNA3.1/V5-His-TOPO the wall-associated protein A (wapA) gene of Streptococcus mutans GS-5 or its truncated derivative antigen A (agA) gene encoding a known candidate antigen for dental caries vaccine. The immunogenicity of the two constructs, designated pcDNA-wapA and pcDNA-agA, was compared by intranasal immunization of two groups of mice using the cationic DMRIE-C (1,2-dimyristyloxypropyl-3-dimethylhydroxy ethyl ammonium bromide-cholesterol) as an adjuvant. Immunization with pcDNA-wapA or pcDNA- agA resulted in specific salivary IgA and systemic IgG antibodies to the target antigens after two doses given at 3-week intervals. Higher salivary IgA level was observed in the mice immunized with the pcDNA-wapA vaccine compared to those immunized with the pcDNA-agA vaccine. Furthermore, anti-WapA antibody inhibited S. mutans sucrose-dependent adherence suggesting a potential protection against S. mutans colonization of the tooth, while anti-AgA had no significant effect. Indeed, prediction and analysis of protein epitopes showed that WapA contains highly promiscuous MHC-II binding motifs in addition to those found in AgA. Immunodot assay confirmed that WapA bound biotin-labeled dextran, whereas AgA did not. These data indicated that full-length WapA is a better candidate vaccine antigen than the soluble AgA, which is truncated in the hydrophobic membrane and wall-spanning region.