Abstract: The invention pertains to a method to produce a vaccine to protect a pig against a pathogenic infection with Streptococcus suis, the method comprising recombinantly expressing an IgM protease antigen in E. coli bacteria, subjecting the E. coli bacteria to a high pressure homogenisation operation at a pressure of at least 500 bar to induce lysis of the E. coli bacteria and release of the IgM protease antigen into the supernatant of the lysate, separating the supernatant from the pellet and mixing the supernatant comprising the IgM protease antigen with a pharmaceutically acceptable carrier to constitute the vaccine. The invention also pertains to a vaccine produced with this method.