Fetal bovine serum contains an inhibitor of interleukin-1

Abstract

The keratinocyte cell line COLO-16 constitutively produces factors with interleukin-1 (IL-1) activity including IL-1α and IL-1β. IL-1 activity assayed by thymocyte proliferation from cell supernatants was 20–50% less if cells were maintained in media containing 10% fetal bovine serum (FBS) compared to media without serum 24 h prior to harvest. The increased IL-1 activity in supernatants from cells in serum free media was not due to increased cellular levels of IL-1α or IL-1β mRNA. Similarly, IL-1 activity recovered from conditioned supernatants of COS cells transfected with expresion vectors containing IL-1β cDNA was ≈ 22–45% less in cells grown in 20% FBS medium compared to similar cultures grown for 3 days post transfection in 1% FBS. When serial dilutions of recombinant IL-1 were made in buffer containing 10% FBS and assayed by a thymocyte proliferation method, a 30–50% decrease in activity was observed. IL-1 activity was also measured by its ability to induce prostaglandin E 2 synthesis by fibroblasts. When COS conditioned supernatants were applied to fibroblast cultures there was 30% less prostaglandin E 2 activity from fibroblasts treated with COS supernatants containing 20% FBS, compared to supernatants containing 1% FBS. The inhibitor molecule was partially purified by gel filtration and found to have a molecular weight of ≈ 85,000. The presence of FBS in cell-conditioned media significantly reduces the sensitivity of IL-1 detection by bioassay techniques.