Immunogenicity and efficacy of serogroup A and D bacterins againstin mice.

Abstract

INTRODUCTION: is a widespread respiratory pathogen in pigs, causing swine pneumonia and atrophic rhinitis, and the capsular serogroups A and D are the main epidemic serogroups in infected animals. This study investigated the protective effects of serogroup A and D bacterins against current circulatingstrains, to better understand the immunity generated by bacterins. METHOD: 13 serogroup A (seven A: L3 and six A: L6 strains) and 13 serogroup D (all D: L6 strains)strains were isolated, and used as inactivated whole cell antigen to preparebacterins. Mice were immunized with these bacterins at 21-day interval and intraperitoneally challenged with the homologous and heterologousstrains, respectively. The antibody titer levels and immunization protective efficacy of vaccines were evaluated. RESULTS: All of the bacterins tested induced high titer levels of immunoglobulin G antibodies against the parental bacterial antigen in mice. Vaccination with the six A: L6 bacterins provided no protection against the parent strain, but some strains did provide heterologous protection against A: L3 strains. Vaccination with the seven A: L3 bacterins provided 50%-100% protection against the parent strain, but none gave heterologous protection against the A:L6 strains. Immunization with the thirteen D: L6 bacterins offered 60%-100% protection against the parent strain, and almost all D: L6 strains gave cross-protection. DISCUSSION: This study found that the cross-protectivity of serogroup A strains was poor, while serogroup D strains was effective, which provided some insights forvaccine development.