Apoptosis of human neutrophils is accelerated at 39.5 C as compared to 37C

Human neutrophils (PMNs) are central to innate immunity and responsible for clearance of pathogens. PMNs undergo a tightly regulated apoptosis program that facilitates their clearance while preventing leakage of their pro‐inflammatory contents into the cellular microenvironment. Our laboratory is focused on the immunomodulatory effects of fever, specifically how exposure to febrile range temperature (39.5¢XC, FRT) increases PMN‐dependent pathogen clearance and collateral tissue injury. In the present study we studied the effect of FRT on PMN apoptosis by isolating PMNs from healthy human volunteers and incubating them at 37„aC or 39.5„aC in RPMI media containing 10% FBS. Apoptosis was sequentially assessed by morphological analysis, flow cytometry after propidium iodide staining, Western blotting of caspase 3 and Bid, ELISA of cytochrome c release, and caspase activity. We found that PMN apoptosis was accelerated at FRT (over 2–3 fold) accompanied with rapid cleavage of caspase 3, ‐8, and ‐9 and Bid in comparison to cells at 37¢XC. Inhibitiors of caspase 3, ‐8, and ‐9 conferred greater protection from apoptosis in the warmer cells. These data suggest that, in the absence of exogenous survival factors, PMNs undergo earlier apoptosis at FRT due to accelerated activation of the intrinsic (mitochondrial) apoptosis pathway. This process may facilitate resolution of inflammation during febrile illnesses.