IVIg-mediated COX-2 induction and PGE₂production in DCs are F(ab′)₂dependent. (A,D) Western-blot analysis of COX-2 expression in DCs. DCs were cultured in GM-CSF and IL-4 alone (Ctr) or with IVIg or equimolar concentrations of either F(ab′)₂ fragments or Fc fragments of IVIg or HSA for 24 hours (A). In some experiments, DCs were preincubated with blocking antibodies to DC-SIGN or isotype control antibodies followed by treatment with equimolar concentrations of either IVIg or F(ab′)₂ fragment of IVIg (D). Representative blot of 6 to 7 experiments is shown. (B,E) The fold changes in the COX-2 expression (mean ± SEM, n = 6-7) based on densitometry analysis of western blots in the above experiments. AU, arbitrary units. (C) Secretion (mean ± SEM, n = 7) of PGE₂ by DC that were treated as explained above, *P < .05; **P < .01; ***P < .001.