Sleeping With the Enemy? The Current Knowledge of Piscine Orthoreovirus (PRV) Immune Response Elicited to Counteract Infection.

Piscine orthoreovirus (PRV) is a virus in the genus Orthoreovirus of the Reoviridae family, first described in 2010 associated with Heart and Skeletal Muscle Inflammation (HSMI) in Atlantic salmon (Salmo salar). Three phases of PRV infection have been described, the early entry and dissemination, the acute dissemination phase, and the persistence phase. Depending on the PRV genotype and the host, infection can last for life. Mechanisms of immune response to PRV infection have been just beginning to be studied and the knowledge in this matter is here revised. PRV induces a classical antiviral immune response in experimental infection of salmonid erythrocytes, including transcriptional upregulation of ifn-α, rig-i, mx, and pkr. In addition, transcript upregulation of tcra, tcrb, cd2, il-2, cd4-1, ifn-γ, il-12, and il-18 has been observed in Atlantic salmon infected with PRV, indicating that PRV elicited a Th1 type response probably as a host defense strategy. The high expression levels of cd8a, cd8b, and granzyme-A in PRV-infected fish suggest a positive modulatory effect on the CTL-mediated immune response. This is consistent with PRV-dependent upregulation of the genes involved in antigen presentation, including MHC class I, transporters, and proteasome components. We also review the potential immune mechanisms associated with the persistence phenotype of PRV-infected fish and its consequence for the development of a secondary infection. In this scenario, the application of a vaccination strategy is an urgent and challenging task due to the emergence of this viral infection that threatens salmon farming.

Thymomodulin enhances vaccination responses against Streptococcus agalactiae in Nile tilapia / Timomodulina melhora as respostas vacinais contra Streptococcus agalactiae em tilápia-do-Nilo

Streptococcosis caused by Streptococcus agalactiae is a major economic problem for Nile tilapia Oreochromis niloticus production worldwide. Inactivated vaccines are considered an efficient method for controlling streptococcosis. However, during the vaccination process, stress during fish handling could affect the immune response. Immunomodulators, such as thymomodulin, act on the immune system and can improve vaccination responses. Thus, the aim of this study was to assess the immunomodulatory effect of thymomodulin in O. niloticus vaccinated against S. agalactiae. For this, fish were distributed in a factorial design (2x2x6), corresponding to two levels of thymomodulin supplementation (0.0 and 0.3%), two treatments (sterile phosphate buffered saline and inactivated S. agalactiae vaccine). Initially, fish received thymomodulin supplementation for 30 days. Next, fish were vaccinated by injection intraperitoneal (i.p.) of heat inactivated S. agalactiae vaccine. 15 days after vaccination, all fish were challenged i.p. with S. agalactiae and blood samples were collected at 7, 14, 21 days post infection (DPI).Results revealed that fish supplemented with thymomodulin vaccinated or not developed better protection against S. agalactiae than vaccinated fish without thymomodulin. Furthermore, fish vaccinated and supplemented with thymomodulin presented high levels of antibodies after 14 and21 DPI, suggesting that thymomodulin can promote the immune response in Nile tilapia.

A estreptococose causada pelo Streptococcus agalactiae é um grande problema econômico para a produção de tilápia-do-nilo Oreochromis niloticus em todo o mundo. As vacinas inativadas são consideradas um método eficiente para o controle da estreptococose. No entanto, durante o processo de vacinação o estresse durante o manejo dos peixes pode afetar sua resposta imune. Imunomoduladores como a timomodulina, atuam no sistema imunológico e podem melhorar as respostas vacinais. Assim, o objetivo deste estudo foi avaliar o efeito imunomodulador da timomodulina em O. niloticus vacinado contra S. agalactiae. Para isso, os peixes foram distribuídos em esquema fatorial (2x2x6), correspondendo a dois níveis de suplementação de timodulina (0,0 e 0,3%), dois tratamentos (solução salina tamponada com fosfato estéril e vacina S. agalactiae inativada). Inicialmente, os peixes receberam suplementação de timomodulina por 30 dias. Em seguida, os peixes foram vacinados por via intraperitoneal (i.p.) da vacina de S. agalactiae inativada pelo calor. 15 dias após a vacinação, todos os peixes foram desafiados i.p. com S. agalactiae e amostras de sangue foram coletadas aos 7, 14, 21 dias após a infecção (DPI). Os resultados revelaram que os peixes suplementados com timomodulina vacinados ou não desenvolveram melhor proteção contra S. agalactiae do que os peixes vacinados sem timomodulina. Além disso, os peixes vacinados e suplementados com timomodulina apresentaram altos níveis de anticorpos após 14 e 21 DPI, sugerindo que a timomodulina pode promover a resposta imune em tilápia-do-nilo.