Effects of repeated hyperthermal stress on blood cells in vivo

The effects of repeated hyperthermal stress on blood cells were examined in seven healthy subjects who took three 3-minute 47 degrees C hotspring baths daily for three consecutive weeks. After a 3-minute 47 degrees C bath, the sublingual temperature was transiently increased about 1.8 degrees C, returning to the baseline level within 60 min. Two weeks after completing the 3-week bathing period, monocytes were increased and eosinophils were decreased significantly. Total lymphocytes and CD3+ cells tended to be decreased. Interestingly, CD4+ cells were decreased significantly at the time of completing the 3-week bathing period and returned to the baseline level two weeks later. These findings suggest that repeated hyperthermal stress may induce alteration of the blood cells.