A sequential study of incomplete Freund's adjuvant-induced peritonitis in Atlantic cod

Area of Science:

• Immunology
• Veterinary Pathology
• Aquaculture

Background:

• Understanding host defense mechanisms is crucial for developing effective vaccines and diagnostics.
• Vaccine adjuvants, like incomplete Freund's adjuvant (IFA), elicit specific host responses that require detailed study.
• Atlantic cod (Gadus morhua) immune responses to adjuvants are not fully characterized.

Purpose of the Study:

• To investigate the sequential morphological changes in Atlantic cod peritoneum following intraperitoneal injection of incomplete Freund's adjuvant (IFA).
• To characterize the inflammatory cell processing and host defense reactions to IFA.
• To elucidate the patterns of peritoneal tissue response and cell involvement.

Main Methods:

• Sequential morphological study involving necropsy, histology, and electron microscopy.
• Analysis of peritoneal tissue responses in Atlantic cod after intraperitoneal IFA injection.
• Assessment of leukocyte morphology, enzyme content, apoptotic cells, and IFN-γ expression.

Main Results:

• An extensive inflammatory response was observed, characterized by specific leukocyte morphology, enzyme activity, apoptotic cells, and interferon-gamma (IFN-γ) expression.
• Two distinct patterns of IFA droplet processing by inflammatory cells were identified.
• The second pattern involved a stratified cellular response with macrophage-like cells (MLCs) undergoing apoptosis, and oil droplets were found within and outside MLCs.

Conclusions:

• Atlantic cod mount a significant inflammatory response to IFA, involving complex cellular interactions and macrophage-like cells (MLCs).
• The observed stratified inflammatory response is similar to other teleosts, suggesting conserved defense mechanisms or sequential development.
• The high number of dead MLCs indicates a substantial contribution to the overall inflammatory process.