IL18 and hepatocellular carcinoma: To validate DTP vaccination as a suitable model for evaluating NK cell recall responses, PBMC were incubated overnight with TT, DT or inactivated whole cell pertussis with or without low concentrations of the cytokines IL-12 and IL-18 (LCC) or, as a positive control, with a high concentration of cytokines IL-12 and IL-18 (HCC), stained for NK cell phenotypic and functional markers, and examined by flow cytometry (Fig. 1).