INFLUENCE OF FETAL CALF SERUM ON GROWTH-INHIBITORY ACTIVITY OF HUMAN RECOMBINANT γ-INTERFERON (GI-3) IN VITRO

Abstract

The growth-inhibitory activity of human recombinant γ-interferon (rIFN-γ: GI-3) against 30 human cultured cell lines derived from leukemias and lymphoma (9 T-cell, 13 B-cell, 2 nonTnonB and 6 myeloid cell lines) was measured quantitatively by in vitro regrowth assay. Only three myelomonocytoid cell lines (HL-60, U937 and THP-1-0) were found to be sensitive, and HL-60 was the most sensitive. However, the sensitivity of HL-60 was found to be much influenced by both the batch and the concentration of fetal calf serum (FCS) used in the experiment. In the experiments using a certain FCS, GI-3 had a high antiproliferative activity against HL-60 at the optimal concentration (10⁴-10⁵ U/ml), when assayed in medium containing 10% FCS. Both lower and higher concentrations of the interferon than 10⁴-10⁵ U/ml resulted in decreased antiproliferative activity. When a high concentration (30%) of the FCS was employed in the assay, the antiproliferative activity of GI-3 was also much reduced. In the experiments using the other FCS, no antiproliferative activity of GI-3 against HL-60 was observed on assay in the medium containing 10% FCS, but significant antiproliferative activity was observed in the medium containing 30% FCS from the same source. Experiments using serum-free culture medium revealed that GI-3 itself had both a slight growth-inhibitory action at the optimal concentrations (at about 10⁴ U/ml) and growth-enhancing activity at high (10⁶U/ml) concentration. The antiviral titer of GI-3 was stable during 72hr of incubation in growth medium with or without cells. These findings suggest that there are cofactors in the serum which positively or negatively influence the growth-regulatory activity of GI-3 against HL-60 cells.