DETERMINATION OF HAPTOGLOBIN EXPRESSION IN IL-6 TREATED HEPG2 CELLS BY ELISA AND BY RNA HYBRIDIZATION - EVALUATION OF A QUANTITATIVE METHODTO MEASURE IL-6

Interleukin-6 (IL-6) is known to be an important modulator of acute ph ase (AP) protein expression in hepatocytes both in vivo and in vitro. In the present study the inducing activity of IL-6 on the expression o f the AP protein haptoglobin (HP) by the human hepatoma cell line HepG 2, has been evaluated. HP mRNA inducibility was analysed by Northern a nd slot-blot hybridization, while HP protein was detected by means of an ELISA procedure. A dose-response relationship from 0.3 to 4.8 ng/ml of a human recombinant IL-6 preparation derived from a Chinese hamste r ovary (CHO) cell line was observed after 48 h of treatment. Comparab le results were obtained by analysing both HP mRNA expression and HP p rotein secretion. Detectable induction of HP protein secretion was obs erved with as little as 25 pg/ml of IL-6. The effect of IL-6 was poten tiated by dexamethasone, while an inhibition on HP mRNA inducibility c ould be prevented by lowering the foetal calf serum (FCS) concentratio n to 1%. Preliminary data indicate that neither IL-1 beta nor TNF-alph a were able to induce significantly HP mRNA expression and protein sec retion. The activity ratio between two IL-6 preparations (from CHO and E. coli cells) obtained with a conventional IL-6 bioassay (i.e., T116 5 cell growth assay) was comparable to that obtained in the induction of HP expression. The nominal specific activity of the CHO-derived IL- 6 was two to three times higher with both responses.