6D and E). Similar results were obtained in immunofluorescence studies of freshly isolated human pDCs. Consistent with results from CAL-1 cells, the nuclear localization of both proteins increased significantly after stimulation with “K” ODN (Fig. 7A and B). Limited IRF-5 and p50 co-localization

was observed in freshly isolated pDCs, presumably reflecting cell activation in vivo or during the purification process. The level of co-localization increased nearly threefold after CpG stimulation (average 8.5 ± 0.9 versus 23.6 ± 1.2 μm2, p < 0.0001, Fig. 7A and B). These findings support the conclusion that “K”-driven pDC stimulation involves the nuclear co-localization of IRF-5 with p50. pDCs make a critical contribution to both the innate and adaptive arms of the immune response. Activated pDCs excel in antigen presentation this website and produce IFNs and other pro-inflammatory cytokines required for host defense [13, 41]. Human pDCs utilize TLR9 to sense the unmethylated CpG motifs present in microbial DNA. “K” ODN have been evaluated in phase I–III clinical trials as immunotherapeutics for the treatment of cancer, allergy, and infectious diseases [4, 42-44]. Understanding the signaling cascades and patterns of gene expression triggered by the recognition of Nutlin 3a “K” ODN by human pDCs is thus of both fundamental and

therapeutic relevance. We and others recently established that “K” ODN induced human pDCs to upregulate the expression see more of two functionally defined groups of genes: those involved in antiviral responses (exemplified by IFN-β) and those involved in pro-inflammatory responses (exemplified by IL-6) [8, 12]. Current studies clarify the regulatory pathways underlying the

activation of those genes by studying CAL-1 cells. Efforts to resolve this issue solely by studying resting human pDCs were impeded by the rarity of such cells (they typically constitute less than 0.5% of PBMCs) and their propensity to activate during the purification process [6, 7]. The use of CAL-1 cells also facilitated analysis of the behavior of intracellular proteins. Unlike previous studies that relied upon protein overexpression models [15, 38, 45], both the level of expression and interaction between cellular proteins could be studied under physiologic conditions in CAL-1 cells. The effect of CpG ODN on murine DCs has been examined extensively. However, human and murine TLR9 molecules differ by 24% at the amino acid level [46] and the hexameric CpG motifs that optimally stimulate human pDCs differ from those most active in mice (and vice versa) [46]. Similarly, the regulatory regions and splice patterns of genes involved in CpG signaling have diverged between mouse and human [47]. Thus, the relevance of results from earlier studies examining mixed populations of murine mDCs and pDCs (both of which respond to CpG stimulation) to human pDCs is unclear.