The data obtained (Fig. S1) were essentially identical to those shown in Fig. 6c when anti-TNF-α was added on day 0 only. Therefore, although TNF-α was capable of modulating BMDC production, it did not appear to be directly involved in the changes induced Pritelivir in vitro by ligands for TLR4 or TLR9, suggesting that other molecules were likely

to be responsible. The aim of the present study was to investigate whether bacterial and viral products are able to affect the generation of DCs from BM in vitro. Our data suggested that inactivated influenza A viruses and the TLR3 ligands Poly I and Poly I:C reduce cellular proliferation in the cultures and cause a diminution in BMDC production. These data complement and extend those of previous studies, which suggest that Poly I:C inhibits granulocyte colony formation by bone marrow cells in vivo.20. Viral infections result in the secretion of type 1 IFNs (IFN-αβ), which are crucial mediators of the antiviral response, and there is evidence to suggest that IFN-αβ inhibits the in vitro differentiation of DC from CD14+ precursors.21 Experiments with IFNAR-deficient bone marrow cells have shown that the IFNAR is required to buy PD98059 modulate the changes in BMDC production induced by culture with influenza viruses.

This role was confirmed by observations showing that recombinant IFN-α was able to replicate the effects, and neutralizing antibody to IFN-α was able to block them. These data are supported by other studies demonstrating an inhibitory effect of IFN-αβ on DC differentiation from monocyte-derived precursors,21 and by evidence which suggests that type 1 IFNs Orotidine 5′-phosphate decarboxylase are cytotoxic for granulocytic progenitor cells in vitro.22 More recently, transient suppression of haematopoiesis in vivo has been shown to be caused by high levels of IFN-αβ.23 Taken together, this evidence suggests that IFN-αβ inhibits the differentiation of haematopoietic progenitors in a way that leads to reduced BMDC production. In vivo infection with influenza virus induces

a transient, but significant, loss of bone marrow B-lineage cells.24 A similar reduction in bone marrow B-lineage cells was observed during acute infection with lymphocytic choriomeningitis virus (LCMV) in mice.4 This bone marrow B-cell depletion accompanying acute influenza infection was found to be mediated by a mechanism involving TNF-α and LT-α. Interestingly, bone marrow B-cell depletion following infection with LCMV or influenza virus does not appear to be mediated by IFN-αβ.4 This contrasts with our data which show that in vitro BMDC depletion in response to influenza virus is IFN-αβ dependent, suggesting that there are differences in the signalling pathways activated in BMDC and bone marrow B-precursor cells following the recognition of influenza virus.