Effect of IL-6 on the antigen-presenting ability (to autologous cells) of myeloma DCs derived from CD34⁺progenitors in the presence of GM-CSF, TNF-α, SCF, and FLT3-L (G+T+S+F) and grown in FCS (A) or autologous serum (B).

CD3⁺ cells (1 × 10⁵) were incubated with a fixed number (3000) of DCs pulsed with TT or KLH. Results report the mean ± SD of 5 different experiments. Autologous DCs alone gave 2500 ± 400 cpm. The addition of IL-6 (A) to the culture of CD34⁺ cells significantly inhibited the development of functional APCs (P < .002). The inhibitory effect of IL-6 was abrogated by anti–IL-6 antibodies. Similarly, the addition of autologous serum in place of FCS significantly reduced the antigen-presentation capacity of DCs (P < .03). However, neutralizing experiments with anti–IL-6 antibodies did not fully reverse the APC ability of DCs (P < .05 compared with G+T+S+F). *P < .05.