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<p>Prolonged immersion in thermoneutral water reproduces several physiological adaptations of orbital flight but its endocrine‑immune consequences remain incompletely characterised. We investigated stress hormones and immune markers in two healthy divers undergoing a 25‑h shallow‑water immersion and compared the findings with contemporary microgravity literature. Peripheral blood was collected one day before and &lt; 15 min after immersion. Flow cytometry, 51Cr‑release assay, lymphocyte proliferation, intracellular cytokine PCR and routine endocrinology panels were performed. All data were corrected for plasma‑volume shifts. Cortisol, growth hormone and prolactin increased by 45–100%, whereas testosterone declined modestly. CD56⁺ natural killer (NK)‑cell frequency fell (‑25% and ‑32%) without loss of cytotoxicity. PBMC proliferation in response to phytohaemagglutinin decreased (‑30% to ‑45%). A Th1 → Th2 cytokine shift was evident with lower IFN‑γ and higher IL‑4 expression. These responses mirror patterns reported after head‑down bed rest and long‑duration spaceflight. Extended shallow‑water immersion is sufficient to activate the neuro‑endocrine stress axis and induce selective, microgravity‑like immune alterations. Thermoneutral immersion may therefore serve as a cost‑effective analogue for mechanistic studies and countermeasure testing.</p>

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Immunological and Hormonal Changes During a 25‑h Shallow‑Water Immersion: a Two‑Case Report

  • 期刊论文

  • 发表日期：

    2026年2月28日

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  • Luca Bonanni,
  • Gino Chioetto,
  • Nicola Ferri

摘要

Prolonged immersion in thermoneutral water reproduces several physiological adaptations of orbital flight but its endocrine‑immune consequences remain incompletely characterised. We investigated stress hormones and immune markers in two healthy divers undergoing a 25‑h shallow‑water immersion and compared the findings with contemporary microgravity literature. Peripheral blood was collected one day before and < 15 min after immersion. Flow cytometry, 51Cr‑release assay, lymphocyte proliferation, intracellular cytokine PCR and routine endocrinology panels were performed. All data were corrected for plasma‑volume shifts. Cortisol, growth hormone and prolactin increased by 45–100%, whereas testosterone declined modestly. CD56⁺ natural killer (NK)‑cell frequency fell (‑25% and ‑32%) without loss of cytotoxicity. PBMC proliferation in response to phytohaemagglutinin decreased (‑30% to ‑45%). A Th1 → Th2 cytokine shift was evident with lower IFN‑γ and higher IL‑4 expression. These responses mirror patterns reported after head‑down bed rest and long‑duration spaceflight. Extended shallow‑water immersion is sufficient to activate the neuro‑endocrine stress axis and induce selective, microgravity‑like immune alterations. Thermoneutral immersion may therefore serve as a cost‑effective analogue for mechanistic studies and countermeasure testing.