8 More recently it has also been suggested that TLRs may have a role to play in directing haematopoiesis at the progenitor Fostamatinib molecular weight cell level. TLRs have been shown to be expressed on haematopoietic stem cells (HSCs) and early progenitors in the bone marrow. Stimulation with ligands for TLR2 and TLR4 induced proliferation

and increased the production of mature progeny.7 Furthermore, stimulation of granulocyte/monocyte progenitor (GMP) and common myeloid progenitor (CMP) cultures with lipopolysaccharide (LPS) resulted in a loss of dependence on the growth factors macrophage colony-stimulating factor (M-CSF) and granulocyte–macrophage colony-stimulating factor (GM-CSF) for cell survival and differentiation in vitro. Ligands for TLR2 and TLR4 thus appear to act on haemopoietic progenitor cells to bias haemopoiesis towards monocyte and macrophage production. McGettrick and O’Neill8 reviewed this role Akt inhibitor for TLRs in haematopoiesis, suggesting that TLRs can supply initiation, survival and proliferation cues in a way similar to

that of endogenous cytokines. The cytokine TNF-α is a potential product of TLR signalling and has been found to affect the generation of dendritic cells (DCs) from haematopoietic progenitors in the bone marrow. Studies have shown that TNF-α, along with GM-CSF, is involved in the in vitro differentiation of CD34+ cells into cells displaying a DC phenotype,9 while interleukin (IL)-6 has been shown to suppress monocyte differentiation into DCs and to promote the development of macrophages.10 In addition there are also reports that IL-6, in conjunction with GM-CSF or Flt-3,11 can initiate in vivo DC differentiation Baricitinib from CD34+ progenitors. Type-1 interferons (IFN-αβ) are produced following TLR signalling initiated by viral PAMPs and in response to viral infection, and there is also evidence to suggest that IFN-αβ is involved in the generation and

maturation of DCs. The capacity of type 1 IFNs to induce DC maturation has been well documented; they have been shown to increase the capacity of DCs to stimulate T lymphocytes through the upregulated expression of specific costimulatory molecules, including CD86.12–14 Reports have also suggested that DCs generated in vitro from monocyte precursors display enhanced maturation and function in response to IFN-α. Santini et al.14 showed that treatment of monocytes with IFN-α led to the rapid acquisition of high levels of CD40, CD80 and CD86, whereas Radvanyi et al.13 demonstrated that the addition of IFN-α to cultures of human peripheral blood mononuclear cells cultured with GM-CSF and TNF-α greatly increased the expression of CD86 on developing DCs. The hypothesis of this study was that TLR-mediated signalling initiated by bacterial and viral products would lead to changes in mature leucocyte production from murine bone marrow in vitro.