Effects of blocking IL-15 or IL-6 in myeloma cell lines.

(A) Increase in apoptosis by blocking IL-15 or IL-6 in myeloma cell lines producing IL-15. ARH-77, LP-1, and RPMI 8226 cells were cultured in RPMI-1640 supplemented with 10% FCS or 0.5% FCS. Neutralizing agents anti–IL-15 (5 μg/mL) or anti–IL-6 (5 μg/mL) mAbs were added alone or in combination with recombinant IL-15 (10 ng/mL) or IL-6 (100 ng/mL), respectively. Bars indicate the mean percentages of apoptotic cells ± SEM (standard error of mean), which was determined after a 3-day cultivation in 4 independent experiments. (B) Effects of blocking IL-15 in the MC-Car cell line without detectable intracellular IL-15 protein. MC-Car cells were treated as described for part A. Bars indicate the mean percentages of apoptotic cells ± SEM of 4 independent experiments. Statistical analysis revealed no significant effects of blocking either autocrine IL-15 (P = 0.7) or IL-6 (P =0.3).