Measurement of Serum Interleukin-2 Activity

The accurate measurement of serum interleukin-2 activity is crucial for assessing the efficacy and toxicity of systemic immunotherapy with recombinant interleukin-2. Incubation of serum at 56 °C for 30 minutes facilitates the bioassay for interleukin-2 activity by destroying the interleukin-2 Inhibitory activity native to human serum. As this report will demonstrate, however, 30% to 50% of interleukin-2 activity in serum taken from patients or normal volunteers was destroyed by heating at 56°C. No loss of recombinant interleukin-2 activity occured during heating in serum-free media. The percentage of interleukin-2 activity lost at 56°C varied from patient to patient and also varied with the time of exposure. Native serum interleukin-2 inhibitory activity can be removed, and interleukin-2 activity can be assessed accurately in serial dilutions of the serum beyond 1:64.