Endocrine Modulation of Immune Function in Aquatic Organisms

The immune systems of aquatic organisms are dynamically regulated by endocrine signals that integrate environmental cues, developmental programmes and stress responses. Central to this regulation are hormonal axes such as the hypothalamic–pituitary–interrenal (HPI) pathway, which governs glucocorticoid release, and the growth hormone–insulin-like growth factor-I (GH–IGF-I) axis, which influences immune organ development and cellular functions. Sex steroids—including oestrogens, androgens and progestins—exert both genomic and non-genomic effects on innate and adaptive immune compartments, altering leukocyte activity, cytokine release and antibody production. Thyroid hormones and neurohormones further modulate leukocyte proliferation and pathogen‐recognition processes. Environmental factors, notably temperature fluctuations and pollutant exposure, intersect with endocrine control to shape seasonal, life‐history and immunotoxicological outcomes in fish, amphibians and aquatic reptiles. An integrated understanding of these signalling networks is essential for managing disease susceptibility in wild populations, optimising health in aquaculture and assessing ecological risks posed by endocrine-disrupting contaminants.

Research from Nature Portfolio

Recent studies have uncovered inherent rhythms in aquatic vertebrate immunity and evaluated cellular assays to predict chemical immunotoxicity. One investigation into a semi‐aquatic snake species demonstrated pronounced circannual oscillations in leukocyte numbers, superoxide‐anion production and lymphocyte proliferation, indicating that seasonal endocrine fluctuations confer temporal adjustments in defence capacity. In parallel, an in vitro assessment using rainbow trout head-kidney leukocytes exposed to known immunomodulatory chemicals revealed that agents such as dexamethasone, benzo(a)pyrene and ethinylestradiol significantly perturbed phagocytosis, oxidative burst and cytokine transcription. Although this assay confirmed immune parameter sensitivity to contaminants, it also highlighted challenges in distinguishing between immunotoxic and inert compounds, underscoring the need for more discriminating biomarkers and integrated testing strategies.

Endocrine Modulation of Immune Function in Aquatic Organisms publication trend

The graph below shows the total number of articles in endocrine modulation of immune function in aquatic organisms across all publications each year (not limited to Nature Index journals).

Technical terms

Hypothalamic–pituitary–interrenal (HPI) axis: The neuroendocrine pathway in fish and amphibians that regulates cortisol release in response to stress and modulates immune activity.

Cortisol: A glucocorticoid hormone released by interrenal tissue that exerts anti‐inflammatory effects and influences leukocyte trafficking.

Insulin-like growth factor-I (IGF-I): A peptide hormone produced by the liver and immune organs that promotes cell growth, survival and innate immune functions.

Oestrogen receptor: A nuclear or membrane‐bound protein that binds oestrogens to regulate gene transcription and rapid signalling in immune cells.

Innate immunity: The non-specific first line of defence involving phagocytic cells, barrier functions and soluble mediators such as complement proteins.

References

1. Annual rhythm in immune functions of blood leucocytes in an ophidian, Natrix piscator. Scientific Reports (2024).
2. Evaluation of an in vitro assay to screen for the immunotoxic potential of chemicals to fish. Scientific Reports (2021).
3. Endocrine and Local IGF-I in the Bony Fish Immune System. Biology (2016).
4. Effects of Sex Steroids on Fish Leukocytes. Biology (2018).
5. Ecological Risks Due to Immunotoxicological Effects on Aquatic Organisms. International Journal of Molecular Sciences (2021).