BackgroundProlonged indoor heat exposure disrupts immune homeostasis and can precipitate acute systemic inflammation. However, the core temperature threshold triggering sex-specific immune cell (leukocytes and neutrophils) mobilization during passive indoor heat stress remains undefined.MethodsWe studied 68 males and 46 females exposed to wet-bulb temperatures (Tw) of 32–35 °C.
Rectal temperature (Trec) was continuously monitored, and blood samples were collected at 0.5 °C increments up to 38.9 °C. Leukocyte and neutrophil counts were modeled using quadratic and segmented mixed-effects models to identify inflection points of immune activation.ResultsBoth leukocytes and neutrophils increased nonlinearly with rising Trec (p < 0.05).
Estimated Trec breakpoints occurred at approximately 38 °C, with overlapping 95% confidence intervals across sexes and cell types, indicating a transition to more rapid immune cell mobilization. This breakpoint was comparable to commonly cited thresholds for limiting excessive heat strain.
Below the breakpoint, females exhibited steeper increases in both leukocytes and neutrophils, whereas above it, males showed greater acceleration, particularly for leukocytes.
Frontiers in Immunology published a clinical update in Infectious Disease on 22 Apr 2026.
The item focuses on Core temperature-dependent leukocyte and neutrophil responses during prolonged heat exposure.
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