Nevertheless, the similar numbers of moDCs found 24 h after infection with attenuated and PLX-4720 price virulent strains offers an explanation as to why the virulence of a STm strain for a particular mouse strain does not impede Th1 differentiation 36. Similar to previous reports 24, 25, 37, we show that moDCs responding to STm are the major synthesizers of TNF-α. This reflects the cytokine

profile from TipDCs after L. monocytogenes infection 17. In contrast, cDCs were the primary producers of IL-12, a cytokine required for the persistence of Th1 responses after STm infection but not for their induction 38. There may be some pathogen specificity in the cytokine signature of moDCs since the predominant source of IL-12 after influenza infection was moDCs rather than in cDCs 20. In studies identifying inflammatory cell recruitment after STm 24, 37, Wick and co-workers found limited potential

for CD11cintCD11b+ cells to prime OVA-specific OTII CD4+ T cells after in vitro infection with STm expressing OVA, although these cells could present OVA peptide. The differences in the findings between these studies are likely to primarily reflect methodological differences. In the current study, moDCs were crucial in the first 24 h after infection. Their early presence is important since this website depleting monocytes in vivo before infection impaired Th1 priming, whereas depleting from 72 h after infection did not. These differences were not due to depletion-induced changes in bacterial burdens. In a previous report on the use of clodronate before and during STm infection, the effects of clodronate depletion depended

upon the virulence of the strain used. Thus, in an attenuated strain similar to that used in most experiments here, bacterial colonization was not affected by depletion, whereas infection with a virulent strain of STm was affected by clodronate treatment so that mice actually had improved survival and lower bacterial colonization after clodronate treatment 30. Direct involvement of moDCs in priming is shown using sorted moDCs. Using naive, transgenic see more FliC-specific CD4+ T cells, we show that moDCs can drive IFN-γ production and this was abrogated after neutralization of TNF-α. The effects of TNF-α neutralization on diminishing moDCs-mediated Th1 priming were only apparent when moDCs were cultured on their own with T cells and not when they were co-cultured with cDCs. This effect is striking, although the reason for it is unclear. It suggests that there is some compensatory mechanism for the loss of TNF-α at play when different DC subsets are cultured together with T cells. The details of this cellular collaboration and its mechanism are currently under investigation.