Effects of hyperthermia on human natural killer cells

Lymphocytes from healthy blood donors were exposed to temperatures between 37 degrees C and 42 degrees C for up to three hours and then tested for natural killer (NK) activity using K562 cells as targets in a 3-h 51Cr-release assay. For a given level of hyperthermia a semilogarithmic decrease in NK activity relative to the treatment period was seen. NK effectors exposed to 42 degrees C for one hour lost 90% of their cytotoxic capacity compared to effectors kept at 37 degrees C. The depression in NK activity could Not be repaired by overnight incubation at 37 degrees C or by interferon treatment. Heating also inhibited the induction of NK-like cells during mixed lymphocyte culture (MLC), while exposure of either responder or stimulator cells to hyperthermia did not affect the degree of MLC-proliferation. The heating only slightly decreased lymphocyte viability--as determined by trypan blue exclusion--whereas a marked and permanent reduction in the number of cells bearing Fc-receptors for IgG occurred. The content of E-rosetting cells decreased initially, but was normalized after overnight incubation. The findings indicate that NK cells and T cells are differentially sensitive to in vitro hyperthermic treatment.