Resposta imunológica de vacinas experimentais contra Theileria equi e Streptococcus equi subespécie equi em equinos

Abstract

Equine theileriosis is a disease caused by the hemoprotozoan Theileria equi (T. equi), while strangles is caused by the bacterium Streptococcus equi subspecies equi (S. equi), both diseases of clinical importance in equine farms. The aim of this study was to comprehend the dynamics of the immunogenicity of experimental vaccines against T. equi and S. equi. Two experiments were carried out. The first one evaluated the immune response to the vaccination with an experimental recombinant vaccine of EMA-2 protein (rEMA-2) from T. equi in geldings, pregnant mares and foals. Forty horses from a tick-free area were included in this study. AntiEMA-2 specific total IgG, IgG subisotypes and cytokine transcription in peripheral blood mononuclear cells (PBMCs) were evaluated in vaccinated and control animals. A challenge with T. equi was performed in vaccinated and control foals, comparing total IgG levels and subisotypes profile between groups. Geldings and pregnant mares had circulating anti-rEMA-2 antibodies for up to 130 and 140 days after vaccination, respectively. The most detected IgG isotypes in vaccinated animals were IgG3/5, IgG4/7 and IgG1. IL2, IL10, IL12, IL17, IFN-γ, and TNF-α were the most transcribed cytokines in PBMCs of vaccinated horses stimulated with rEMA-2. Challenge with T. equi demonstrated that vaccinated foals had an increase of 33% in specific total IgG four days after the challenge, while controls had no significant response. The second experiment determined specific total IgG and its subisotypes in pregnant mares vaccinated with two experimental vaccines, a rEMA-2 vaccine against T. equi and a vaccine against S. equi, as well as the transfer of passive immunity to their foals. Sixty-four animals, 32 mares and their respective foals, were included in this study. An experimental vaccine of rEMA-2 of T. equi and a S. equi bacterin were used. Mares vaccinated against T. equi showed highest specific IgG levels 14 days after the booster dose, decreasing 30 days after parturition, while mares vaccinated against S. equi had a peak in specific IgG levels seven days after booster vaccination and kept IgG levels for the same period. The most detected IgG isotypes were IgG3/5 and IgG4/7 for both antigens. Maternal antibodies remained circulating in the foals for about two months. Vaccinated pregnant mares had specific antibodies against T. equi and S. equi and transferred a similar profile of IgG and its isotypes to their foals. Maternal antibodies were detected in foals until two months of life. Mares vaccinated with both T. equi and S. equi antigens transferred similar total IgG levels and IgG subisotype profiles to their foals. The data obtained allowed us to understand the dynamics of humoral and cellular responses to vaccination against T. equi, and humoral responses to the vaccine against S. equi.