Diet modulates the relationship between immune gene expression and functional immune responses

Area of Science:

• Nutritional immunology
• Insect physiology
• Host-parasite interactions

Background:

• Immune system investment is resource-dependent.
• Dietary quantity is a poor proxy for nutritional quality.
• Nutrient balance, not just amount, impacts fitness.

Purpose of the Study:

• To investigate how nutrient balance and amount affect immune response to infection.
• To utilize the Geometric Framework for Nutrition (GFN) for this assessment.
• To analyze immune gene expression and functional immune responses in caterpillars.

Main Methods:

• Spodoptera littoralis caterpillars were fed 20 diets varying in protein, carbohydrate, and calorie content.
• Insects were challenged with live or dead Xenorhabdus nematophila bacteria.
• Immune gene expression and functional immune responses (PPO, Lysozyme) were measured.

Main Results:

• Dietary protein availability was the strongest predictor of functional immune response.
• Immune gene expression varied unpredictably with diet, unlike functional immunity.
• IMD pathway genes (Moricin, Relish) were upregulated by both live and dead bacteria.

Conclusions:

• Diet composition, particularly protein, is crucial for mounting an effective immune response.
• Immune gene expression is not always a reliable proxy for immune investment.
• Nutritional strategies can significantly influence host defense capabilities.