Immunomodulation and Humoral Immune Response in Teleost Immunized with Aeromonas-Derived Antigenic Extracellular Bioactive Molecules

Abstract

The common use of antimicrobials in food-animal production can lead to drug residues in edible tissues for consumers. However, immunomodulators enhance immune responses and vaccine effectiveness. A new perspective explores bacterial extracellular bioactive molecules (EBMs) in food-animal production to modulate host immune responses, potentially transforming pathogen management and antimicrobial use. This study investigates the immunogenic potential of Aeromonas hydrophila-derived EBMs (Antigens) to enhance the immune system. Four Antigens were administered intraperitoneally to Oreochromis niloticus (Nile Tilapia). Antigens 2 and Antigens 3 boosted fish immune competence within 21 days. Remarkably, Antigens 3 induced robust immunity against A. hydrophila with a single dose, notably enhancing antibody-based immune responses. The increased antibody activity suggests Antigens 3 could be a vaccine candidate, promising further research and potential application in food-animal production to improve disease control. This study highlights immunomodulators' potential in reshaping disease management in the food-animal industry, emphasizing the benefits of focusing on bacterial EBMs to reduce reliance on antimicrobials and achieve sustainable disease prevention.

Keywords: Aeromonas; Antigen; Antimicrobial resistance (AMR); Extracellular bioactive molecules (EBMs); Humoral Immunity; Immunization; Immunomodulation.

Fig. 1

Images of specimens showing various degrees of clinical symptoms post-immunization with Aeromonas-derived antigens. A Image of specimens on the 7th day post-immunization; B image of specimens on the 14th day post-immunization; C image of specimens on the 21st day post-immunization; D image of specimens on the 28th day post-immunization

Fig. 2

Serum antiprotease activity (%) induced by the various antigens from the onset of clinical symptoms on the 14th, 21st, and 28th days post-immunization respectively. Antigen 1 = partially heat-killed bacteria cells at 56 °C for 10 min; Antigen 2 = crude supernatant of homogenized bacterial suspension subjected to ultracentrifugation at 2500 × g for 10 min at 4 °C; Antigen = 0.2 μm filtered crude supernatant (Antigen 2); Antigen = PBS-KCl

Fig. 3

Serum peroxidase activity (UmL⁻¹ of serum) induced by the various antigens from the onset of clinical symptoms on the 14th, 21st, and 28th days post-immunization respectively. Antigen 1 = partially heat-killed bacteria cells at 56 °C for 10 min; Antigen 2 = crude supernatant of homogenized bacterial suspension subjected to ultracentrifugation at 2500 × g for 10 min at 4 °C; Antigen 3 = 0.2 μm filtered crude supernatant (Antigen 2); Antigen 4 = PBS-KCl

Fig. 4

Serum bactericidal activity (UmL⁻¹ of serum) induced by the various antigens from the onset of clinical symptoms on the 14th, 21st, and 28th days post-immunization respectively. A Antigen 1 (partially heat-killed bacteria cells at 56 °C for 10 min); B Antigen 2 (crude supernatant of homogenized bacterial suspension subjected to ultracentrifugation at 2500 × g for 10 min at 4 °C); C Antigen 3 (0.2 μm filtered crude supernatant (Antigen 2)); D Antigen 4 (PBS-KCl)

Fig. 4

Serum bactericidal activity (UmL⁻¹ of serum) induced by the various antigens from the onset of clinical symptoms on the 14th, 21st, and 28th days post-immunization respectively. A Antigen 1 (partially heat-killed bacteria cells at 56 °C for 10 min); B Antigen 2 (crude supernatant of homogenized bacterial suspension subjected to ultracentrifugation at 2500 × g for 10 min at 4 °C); C Antigen 3 (0.2 μm filtered crude supernatant (Antigen 2)); D Antigen 4 (PBS-KCl)

Fig. 4

Serum bactericidal activity (UmL⁻¹ of serum) induced by the various antigens from the onset of clinical symptoms on the 14th, 21st, and 28th days post-immunization respectively. A Antigen 1 (partially heat-killed bacteria cells at 56 °C for 10 min); B Antigen 2 (crude supernatant of homogenized bacterial suspension subjected to ultracentrifugation at 2500 × g for 10 min at 4 °C); C Antigen 3 (0.2 μm filtered crude supernatant (Antigen 2)); D Antigen 4 (PBS-KCl)

Fig. 4

Serum bactericidal activity (UmL⁻¹ of serum) induced by the various antigens from the onset of clinical symptoms on the 14th, 21st, and 28th days post-immunization respectively. A Antigen 1 (partially heat-killed bacteria cells at 56 °C for 10 min); B Antigen 2 (crude supernatant of homogenized bacterial suspension subjected to ultracentrifugation at 2500 × g for 10 min at 4 °C); C Antigen 3 (0.2 μm filtered crude supernatant (Antigen 2)); D Antigen 4 (PBS-KCl)

Fig. 5

Indirect enzyme-linked immunosorbent assay (ELISA) showing the serum activity per concentration (ng/ml) to horseradish peroxidase-labeled secondary antibody (goat anti-rabbit) after polyclonal antibody (PAB) treatment of serum obtained from the respective specimens on the 14th, 21st, and 28th days post-immunization respectively. a Relative serum antibody activities of all Antigens (ng/ml); b Relative serum antibody activity (ng/ml) of Antigen 1 (partially heat-killed bacteria cells at 56 °C for 10 min); c Relative serum antibody activity (ng/ml) of Antigen 2 (crude supernatant of homogenized bacterial suspension subjected to ultracentrifugation at 2500×g for 10 min at 4 °C); d Relative serum antibody activity (ng/ml) of Antigen 3 (0.2 μm filtered crude supernatant (Antigen 2))