Role of IL-15 in the IL-12 response of MLN cells to CpG-2006. The kinetics of IL-15 (A) and IL-12/IL-23p40 (B) mRNA production in response to CpG-2006 was determined by quantitative RT-PCR. Experiments were performed with MLN cells isolated from three neonates and three adults. 20 h post-stimulation, MLN cells isolated from three different neonates were recovered and sorted into CD14- and CD14+ cell subsets and IL-15 mRNA was assayed by quantitative RT-PCR in each subset (C). After normalisation with the reference gene (HPRT), the RT-PCR data are reported as means ± SEM values of the ratio of CpG-2006 stimulated to Ctl-ODN stimulated cells (A, B, C). MLN cells, isolated from eight adults, were stimulated with CpG-2006 for 48 h, with or without various amounts of rhIL-15; secreted IL-12 was measured by ELISA (D). The mean ± SEM level of IL-12 secretion is shown for each dose of recombinant cytokine (CpG-2006 - Ctl-ODN). Adult MLN cells were stimulated with CpG-2006 (or Ctl-ODN) and 200 IU/mL of IL-15 in the presence of anti-CD40 mAb or its isotype control and IL-12 was quantified by ELISA 48 h later (CpG-2006 - Ctl-ODN). Data are from one representative animal of five, all giving similar results (E). * p < 0.05; ** p < 0.005.