Normal mouse serum-derived factor(s) which inhibits growth of the interleukin-2-dependent cell line CTLL

Evidence is presented for the existence of a serum factor(s) (SF), which inhibits the growth of both the interleukin-2 (IL-2)-dependent cell line CTLL and the 2-day generation of CTL cells. This activity is found in the serum of both nude and euthymic mice and its suppressive effect can be detected about 18 hours after addition to CTLL cultures. The inhibitory activity elutes from a Sepharose 6B gel after the gamma globulin fraction (100-150 kD), and is precipitated by ammonium sulfate at 60 w/v% saturation. IL-3-mediated bone marrow colony formation is not inhibited by SF. It also does not suppress the growth of a panel of different tumor cell lines. The spleen cell responsiveness to both Con A and LPS activation is greatly reduced in the presence of SF. However, binding of radiolabelled IL-2 to CTLL cells was not blocked by SF, although the activity was greatly reduced by absorption to these cells. Our data support the existence of factor(s) in sera that may have a regulatory role on IL-2-mediated functions.