IgG multimers, and not monomers, cause ADCC of IVIg-DCs by NK cells. (A,B) Culture medium (CTRL), IVIgs, and humanized monoclonal antibody trastuzumab (HRC) were heated at 63°C for 30 minutes (░) or left untreated (■) before addition to immature blood DCs during their maturation with proinflammatory cytokines. IVIgs and HRCs were added to the DCs in a concentration of 10 mg/mL. After 18 hours of maturation, all additions were removed, and allogeneic NK cells were added at a ratio of DC/NK of 1:6. Percentages of 7-AAD⁺ DCs (A) and CD69 expression on NK cells (B) were determined after 18 and 48 hours of DC-NK coculture, respectively (N = 4; Wilcoxon test for paired data, *P < .05). Error bars represent SD.