Histologic and immunohistochemical evaluation of Nile tilapia (Oreochromis niloticus) vaccinated against Streptococcus agalactiae

Abstract

The infection caused by Streptococcus agalactiae causes great losses in intensive farming of tilapia in Brazil and one of the solutions to minimize these losses is the use of vaccines . This study is evaluating the responses of tissues and their participation in the humoral immune response induced by the vaccine against S. agalactiae . For this, we used 206 Nile tilapia ( Oreochromis niloticus ) with an average weight of 200 ± 25 g . Will determine the bacterial concentration lethal to 50.0 % of the fish ( LC50 ) and assessed the relative percentage survival ( PRS ) tilapia vaccinated with soluble or insoluble portions of the antigen , resulting from the process of sonication of S. agalactiae . For both are divided into four groups (n = 20 ) and group 1 (G1) injected with 0.65% saline (control), group 2 ( G2) injected with PBS + Freund's incomplete adjuvant , group 3 (G3 ) immunized with the soluble portion of sonicated antigen + Freund's incomplete adjuvant and group 4 (G4) insoluble portion immunized with sonicated antigen + Freund's incomplete adjuvant . After 21 days of immunization the fish will be challenged with an inoculum of S. agalactiae and evaluated for 15 days . Subsequently be prepared vaccine containing antigens of the major portion of which has given PRS + incomplete Freund's adjuvant (1:1 ) with ¶ l final volume of 200 . To evaluate the humoral immune response will be used two groups ( n = 63 ) , namely , group injected with 0.65 % saline ( control) and group immunized with the vaccine incorporated with the product of sonication of S. agalactiae which produced greater PRS . The vaccine will be saline and applied via intracelomic ( ic ) . In all groups will be collected blood and organs pre immunization and sequential samples after immunization in times of 7 , 14 , 21 , 28 , 35 , 42 , 60 and 90 days to evaluate the immune response through direct agglutination test in plate and for making the histological slides and immunohistochemistry . The results are compared by analysis of variance ( ANOVA ) at 5 % probability and the difference between the averages will be compared by Tukey test later.