Recently some authers af us have described successful production of human recombinant interleu- kin 2 (rlL 2). In concideration of future application in vitro and in vivo of rIL 2, this study was carried out in an attempt to confirm the biological activities of the rIL 2 and compare with those of human natural IL 2 (nlL 2) on a per unit basis. The two IL 2 preparations induced CTLL-2 cell proliferation at the equivalent level. This result showed that nIL 2 and rIL 2 activity could be evaluated with same assay system. Dose response of IL 2 in lymphokine-activated killer (LAK) cell induction was also similar. Greatest activity of LAK cells was induced with 500-1,000 U/ml (target, Raji) or 100 1,000 U/ml (target, K -562) of IL Z, and the activity decreases over 5,000 U/ml of rIL 2. In LAK cell induction kinetics, peak activity was seen after 4 (targe, Raji) to 5 day-culture (target, K-562) with rlL 2 and nIL 2. Thereafter, activity of LAK cells generated with nIL 2 declind whereas it was sustained (target, K-562) or enhanced successively (target, Raji) with rIL 2. Similar results were also seen in a prolonged activation of LAK cells for 9~14 days. Augmentation effect of IL2 on natural killer cell activity by 24 hr-treatment was comparable between nlL 2 and rlL 2 except that higher peak activity was observed with rIL 2 than with nIL 2. These data suggested that nIL 2 might be different from rIL 2 in some biological activities, although we cannot exclusively rule out the possibility that some other related lymphakines are present in nlL 2 preparation. Subsequent experiments for elucidation of the mechanisms for the differential activities demonstrated that the functional differences of the two IL 2 preparations observed above were due to neither lability nor poor IFN induction of nIL 2. Thus, it was assumed that activation or proliferation of any other cell populations than LAK effector or precursor cells, e.g., suppressor cells, might be involved in the mechanism.
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