[Study of lymphocyte and NK cell activity during mild hypothermia therapy]

Infectious disease is a common complication of mild hypothermia therapy. However, very little has been reported about immune response during hypothermia. In the present study, the number and subset of peripheral lymphocytes and mitogen response to phytohaemagglutinin (PHA) and concanavalin A (Con-A) were examined in 14 patients who received mild hypothermia therapy. NK cell ratio and activity were also examined in the same patients. Six out of 14 patients had complicated infectious diseases during mild hypothermia therapy. Five of them had pneumonia and the remaining one had thrombophlebitis. The number of peripheral lymphocytes decreased in patients whose rectal temperature was less than 34.5 degrees C, whereas mitogen response of lymphocytes to PHA and Con-A remained unchanged in patients whose rectal temperature was above 34.0 degrees C. NK cell ratio and cytotoxicity decreased in patients whose rectal temperature was less than 34.5 degrees C, including infectious cases. These results suggested that, under hypothermia therapy, immune responses of the patients whose rectal temperature was less than 34.5 degrees C were disturbed because of the reduced number of peripheral lymphocytes and depression of NK cell activity.