Evaluation of the Potency of Two Pyolysin-Derived Recombinant Proteins as Vaccine Candidates of Trueperella Pyogenes in a Mouse Model: Pyolysin Oligomerization and Structural Change Affect the Efficacy of Pyolysin-Based Vaccines

<i>Trueperella pyogenes</i> (<i>T. pyogenes</i>) is an important opportunistic pathogen in livestock and wild animals. However, only one commercial <i>T. pyogenes</i> vaccine is currently available, and its immunoprotective effect is not ideal. Pyolysin (PLO) is one of the important virulence factors expressed by <i>T. pyogenes</i> and one of the targets for the development of new <i>T. pyogenes</i> vaccines. In this study, we constructed two recombinant antigens, tPLOA1 (contains amino acids 1-110 and domain 4 of the PLO molecule) and tPLOA2 (contains amino acids 190-296 and domain 4 of the PLO molecule). Vaccines were prepared by mixing the two recombinant antigens with incomplete Freund's adjuvant or sheep red blood cell membrane and provided partial immune protection to immunized mice against the lethal challenge of <i>T. pyogenes.</i> Analysis of the PLO-specific IgG levels of immunized mice indicated that the antibody-inducing potency and immunoprotective efficacy of PLO-based vaccines are affected by the oligomerization and structural changes of PLO after binding to a cholesterol-containing membrane. In addition, the titer of anti-hemolysis antibodies is not a suitable indicator of the immunoprotective effect of these vaccines in PLO-based vaccine-immunized animals. The results provide new insights into the development of <i>T. pyogenes</i> vaccines.