A Critical Rectal Temperature Defines Sex-Specific Leukocyte and Neutrophil Activation During Prolonged Passive Heat Exposure in Young Adults

BackgroundProlonged heat exposure disrupts immune homeostasis and can precipitate acute systemic inflammation. However, the core temperature threshold that triggers sex-specific leukocyte and neutrophil activation during passive heat stress remains undefined. MethodsWe studied 52 males and 58 females exposed to wet-bulb temperatures of 32-35 {degrees}C. Rectal temperature (Trec) was continuously monitored, and blood samples were collected at 0.5 {degrees}C increments up to 38.6 {degrees}C. Leukocyte and neutrophil counts were modeled using quadratic and segmented regression to identify inflection points of immune activation. ResultsBoth leukocytes and neutrophils increased nonlinearly with rising Trec (p View larger version (22K): org.highwire.dtl.DTLVardef@9620dorg.highwire.dtl.DTLVardef@47beborg.highwire.dtl.DTLVardef@6396daorg.highwire.dtl.DTLVardef@44c890_HPS_FORMAT_FIGEXP M_FIG C_FIG