Immune effector activities in challenged rohu, Labeo rohita after vaccinating with Aeromonas bacterin

The present study assessed the efficacy of formalin inactivated Aeromonas vaccines by determining the cellular immune-effector activities such as production of oxidative radical (ROS) and nitrite and lymphocyte proliferation in challenged rohu, Labeo rohita upon vaccination with Aeromonas hydrophila (AH), Aeromonas caviae (AC) and a cocktail of both (CKTL). The relative percentage survival was much higher in AH group (68.89) than in the AC (28.89) and CKTL (20.00) groups. The vaccinated L. rohita showed high immune-effector activities in the first 15 days post-vaccination, which subsequently lowered at different post-challenge periods. The vaccination activated the synthesis of ROS in leucocytic cells of all vaccinated groups up on challenge with A. hydrophila-C36 strain as immediate protection against the bacteria and the activities of blood phagocytes progressively waned as the disease process progressed. The production of nitrite was higher in AH group when stimulated with OMP antigen than that of somatic antigen and LPS; while in AC group, both OMP and somatic antigen stimulation resulted in higher nitrite production. On the other hand, the cocktail group showed higher nitrite production upon somatic antigen stimulation followed by OMP and LPS. A high level of non-specific lymphocyte proliferation was observed on the 10th day post-vaccination and the 5th day post-challenge periods and an antigen specific proliferation when stimulated with somatic and OMP antigens on the 15th day post-challenge. The stimulation by specific somatic and OMP antigens resulted in higher HK leucocyte proliferation in A. hydrophila vaccinated group. The experiment revealed that the highest protection was generated in the AH group compared to the other two groups and this might be explained by the specific cellular immune response generated in this vaccinated group against the specific antigen as assessed at 15 days post-challenge.

► The vaccinated L. rohita showed high immune-effector activities in first 15 days post-vaccination.
► The relative percentage survival with A. hydrophila inactivated vaccine was 68.89.
► Aeromonas hydrophila vaccinated group provided highest protection than the other two groups.