Inhibitory effect of sera from patients with liver cirrhosis on natural killer activity

The effect of sera from patients with liver cirrhosis (LC) and from healthy donors on natural killer (NK) activity of normal peripheral blood mononuclear cells (PBMC) was investigated. PBMC from a healthy donor were pre‐incubated for 3 h at 37°C in media containing 50% test sera and washed twice with phosphate‐buffered saline (PBS). Cytotoxic activity was determined using ⁵¹Cr‐labelled K‐562 cells as target. It was demonstrated that sera from both healthy donors and patients with LC suppressed the NK activity of normal PBMC compared with a PBS control. But the level of inhibition caused by patients’ sera (n= 30) was significantly higher than that caused by normal sera (n= 30; P < 0.001, Wilcoxon rank sum test). Sera from a patient with LC and a healthy subject were fractionated by a Sephacryl S‐300 column and the effect of five fractions on NK activity of normal MNC was assessed. Fractions 3 and 4 from both sera had inhibitory effects although Fraction 5 revealed an enhancing effect. These results suggest that human sera contain factors which both inhibit and enhance NK activity and that their net effects are inhibition. Since it is known that IgG is eluted in Fraction 4, IgG was separated from sera with a DEAE‐Sephacel column and its effect on NK activity was examined. IgG from patients’ sera was observed to suppress NK activity more often than those from healthy donors at the same concentrations.