10 - Stress and Disease Resistance: Immune System and Immunoendocrine Interactions

1. Introduction 2. Effects of Stressors on the Immune Response 2.1. Suppressive Versus Enhancing Effects 2.2. Perception of Stress After Immune Stimulation: Systemic Versus Local Responses 2.3. Stress and the Cellular and Humoral Immune Response 3. Organization of the Immune Response Following Stress: The Neuroimmunoendocrine Connection and the Role of the Head Kidney 4. Effects of Hormones on the Immune System 4.1. Hypothalamic Hormones 4.2. Pituitary Hormones 4.3. Interrenal Hormones 4.4. Receptor-Mediating Action of Cortisol in Fish Immunity During Stress Response 4.5. Somatotropic Axis and Fish Immune System 5. Environmental Stressors and Fish Immunity 5.1. Environmental Salinity 5.2. Temperature and Seasonality 6. Future Directions The endocrine-immune relationship of fish, particularly related to the stress response, is mediated by the close interaction of hormones and cytokines. In essence, stress can depress certain elements of the immune system and render fish vulnerable to infection and disease. This chapter summarizes the effects of stressors on disease resistance and the immune system and updates the knowledge on endocrine regulation of the immune system in fish, the effects at systemic and local levels, and the organization of the immune responses under stressed conditions, with special emphasis on the roles of hormones, their receptors, and system interactions. Basically, low levels of severity of stress (eustress) may lead to enhanced immune competence while greater severities tend to be immunosuppressive. The immune response to stressors are mediated by the endocrine system at both central and peripheral levels.