Immunogenicity of Escherichia coli Expressing Streptococcus equi subsp. equi Recombinant SeM

HIGHLIGHTS

E. coli BL21 as a suitable expression and delivery vaccine system;

rSeM protein protect mice against S. equi infection;

E. coli cells enhance the immune response against S. equi;

rSeM protein, purified or not, presented immunogenicity in horses.

Abstract

The Equine Strangles, caused by Streptococcus equi subs. equi, is a contagious disease, causing high rates of morbidity been responsible for important economic losses. The M protein synthesized by S. equi plays an important role in the pathogenesis and is a promising candidate for a vaccine antigen. The innate immune system is responsible for the first immune response against microorganisms, this response is mediated by receptors that detect PAMPs and their activation trigger crucial modulation of the adaptative immune response. This work describes the immune response of S. equi subs. equi. recombinant SeM protein, using Escherichia coli BL21 (DE3) as an expression and delivery vaccine system. To characterize and to determine the vaccine efficacy, mice were vaccinated as followed: 1. Recombinant E. coli expressing rSeM protein; 2. The same recombinant E. coli, inactivated adsorbed in Alumen; 3. Purified rSeM protein adsorbed in Alumen; 4. Inactivated S. equi whole cells adsorbed in Alumen; 5. Control group. All vaccinated mice developed protective response against S. equi infection, however the groups that received the E. coli expressing rSeM presented significant higher IgG level than other vaccinated groups. The recombinant E. coli delivery vaccine system also induced a highest IgG response than inactivated S. equi or purified rSeM vaccines in horses. This study evidence that the recombinant E. coli, live or inactivated, enhanced the humoral response, reaching significant higher antibodies levels than those obtained in the vaccination with the bacterin or purified antigen, showing the feasibility of producing low-cost vaccines against strangles.

Keywords:
Streptococcus equi; SeM protein; PAMPs; recombinant E. coli.