Subcutaneous <i>Streptococcus dysgalactiae</i> GAPDH vaccine in mice induces a proficient innate immune response.

Abstract

<h4>Background</h4>Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) on the surface of <i>Streptococcus dysgalactiae</i>, coded with gapC, is a glycolytic enzyme that was reported to be a moonlighting protein and virulence factor.<h4>Objective</h4>This study assessed GAPDH as a potential immunization candidate protein to prevent streptococcus infections.<h4>Methods</h4>Mice were vaccinated subcutaneously with recombinant GAPDH and challenged with <i>S. dysgalactiae in vivo</i>. They were then evaluated using histological methods. rGAPDH of mouse bone marrow-derived dendritic cells (BMDCs) was evaluated using immunoblotting, reverse transcription quantitative polymerase chain reaction, and enzyme-linked immunosorbent assay methods.<h4>Results</h4>Vaccination with rGAPDH improved the survival rates and decreased the bacterial burdens in the mammary glands compared to the control group. The mechanism by which rGAPDH vaccination protects against <i>S. dysgalactiae</i> was investigated. <i>In vitro</i> experiments showed that rGAPDH boosted the generation of interleukin-10 and tumor necrosis factor-α. Treatment of BMDCs with TAK-242, a toll-like receptor 4 inhibitor, or C29, a toll-like receptor 2 inhibitor, reduced cytokines substantially, suggesting that rGAPDH may be a potential ligand for both TLR2 and TLR4. Subsequent investigations showed that rGAPDH may activate the phosphorylation of MAPKs and nuclear factor-κB.<h4>Conclusions</h4>GAPDH is a promising immunization candidate protein for targeting virulence and enhancing immune-mediated protection. Further investigations are warranted to understand the mechanisms underlying the activation of BMDCs by rGAPDH in a TLR2- and TLR4-dependent manner and the regulation of inflammatory cytokines contributing to mastitis pathogenesis.