Fig. 1.

IL-18 and immobilized IgG costimulate IFN-γ production by human NK cells. a Enriched human NK cells were incubated overnight in medium alone or medium containing 1, 10, or 100 ng/mL IL-18 as indicated and then plated overnight in the presence (striped bars) or absence (solid bars) of immobilized IgG. Supernatant IFN-γ levels were measured by ELISA. P value for comparison of medium alone versus medium plus IgG is 0.001 and for comparisons of IgG alone versus IgG plus IL-18 1, 10, or 100 ng/mL is 0.312, 0.033, 0.012, respectively. b Enriched human NK cells were incubated in wells precoated or not with immobilized IgG in medium with or without 100 ng/mL IL-18 as indicated in the presence (striped bars) or absence (solid bars) of F(ab′)2 fragments of CD16 monoclonal antibody 3G8. P value for comparison of presence versus absence of CD16 F(ab′)2 fragments for medium, IgG, IL-18, or IgG plus IL-18 is 0.023, 0.013, 0.019, 0.006, respectively. Results shown represent mean ± SE of data from 3 (a) or 5 (b) separate experiments