| dc.description.abstract | Dendritic cells (DCs) are antigen presenting cells (APCs) that play a crucial role in the innate and adaptive immunity. Upon capturing antigen, DCs migrate from peripheral tissues to local lymphoid organs, differentiate into APCs, and then activate antigen-specific T cells. It is well known that elevation of intracellular cAMP concentration attenuates many inflammatory responses in almost all inflammatory cell types, including DCs. Type 4 phosphodieasterases (PDE4s) are predominant cAMP-hydrolyzing PDEs in immune/inflammatory cells which affect inflammatory responses by regulating intracellular cAMP concentration and cAMP signal pathways. Our previous study showed that the PDE4 inhibitor rolipram significantly downregulated the differentiation of mouse bone marrow (BM) cells into immature dendritic cells (imDCs). However, among the four PDE4 isoforms (PDE4A, 4B, 4C and 4D) which isoform is responsible for this differentiation remained to be delineated. Additionally, it is unclear whether PDE4s are involved in DC maturation and their immune functions. In this study, we first used GM-CSF to induce wild-type and PDE4-deficient mouse bone marrow cells to differentiate into immature DCs (imDCs). Flow cytometry analysis revealed that the wild-type CD11c+ population (i.e. imDC) reached 86.8 ± 0.6 % and ablation of PDE4B, but not of PDE4A or PDE4D, significantly reduced the imDC population, indicating that the inhibitory effect of rolipram on imDC differentiation is mediated by inhibition of only PDE4B. Contrarily, DC maturation (identified as CD11c+CD86+) induced by lipopolysaccharide (LPS) or the antigen ovalbumin (OVA) was not altered by rolipram or PDE4 ablation. However, the CD11c+CD86+ population was found to be increased when the imDCs were cultured in the presence of rolipram alone or these cells were PDE4B deficient. Moreover, during LPS- or OVA-induced BMDC maturation, rolipram significantly increased the CD11c+CXCR4+ population and this induction of CXCR4+ cells was demonstrated to be mediated by inhibition of PDE4B, but not PDE4A or PDE4D. In a functional study, we found that the ability of mature DCs to activate T cell proliferation was not affected by ablation of PDE4, as demonstrated by coculturing PDE4-deficient DCs and OVA-primed spleen CD4+ T cells in the presence of OVA. Taken together, these findings demonstrate that PDE4B is involved in the differentiation of imDCs and the CXCR4 expression in mDCs. The data also form the experimental basis for the development of PDE4B selective inhibitors for the treatment of inflammatory diseases that are mediated by DCs. | en_US |