Figure 1 Dendritic cells mature after they phagocytose M. tuberculosis. A. Human monocytes were separated from buffy coats by plastic adherence and cultured for 6 days in the presence of recombinant human IL-4 (40 ng/ml) and GM-CSF (50 ng/ml) to allow differentiation to DCs. Cells were analysed for CD14 and DC-SIGN expression by flow cytometry. DCs were CD14- and DC-SIGN+ (typically > 85% of gated cells; both before and after infection with Mtb). Plots show uninfected, OICR-9429 price immature DCs after 6 days of cytokine treatment from 1 representative

donor of 3.. B. DCs were infected with live H37Ra at MOI 1 for 24 h and visualised by light microscopy. C. DCs were infected with live Mtb H37Rv at MOI 10 overnight. Bacteria were stained with auramine and nuclei with Hoechst and were visualised by confocal microscopy. Similar results were obtained with iH37Rv, live H37Ra and streptomycin-killed H37Ra (data not shown). D. DCs were infected with live Mtb H37Ra or streptomycin-killed

H37Ra at MOI 1 for 48 h. Surface expression of CD83 and CD86 was assessed by flow cytometry. The histograms show 1 representative donor of 3. Maturation was assessed in DCs infected with H37Ra. In controlled experiments, Selleck AZD2281 DCs were infected with live or dead Mtb H37Ra or at MOI 1for 24 h. Approximately 60% of cells had phagocytosed mycobacteria at this time point. The cells were washed to remove extracellular mycobacteria and either analysed or incubated for a further 24 or 48 h before analysis. DCs infected with live H37Ra displayed a mature phenotype, up-regulating

CD83 and CD86 after 48 h infection with Mtb (Figure 1D). Streptomycin-killed H37Ra did not induce DC maturation. To assess the relationship between intracellular infection and DC viability, we infected human monocyte-derived MG-132 clinical trial DCs with Mtb strains H37Ra and H37Rv. Viability of infected DCs (infected with 10 bacilli per cell) was assessed by PI exclusion and quantified on a GE IN Cell Analyzer 1000. Infection of DCs with either live strain was followed by cell death after 24-72 hours (Figures 2A and 2B), whereas dead bacilli (streptomycin-killed or irradiated) did not elicit this response. Incubation times with each strain were optimised to provide a significant increase in the percentage of PI positive cells above background (40-60%) while at the same time minimizing the cellular disintegration that occurs in the late stages of cell death and would lead to an underestimate of the numbers of dead cells. Longer incubation times led to the death of the majority of infected cells (> 95%). The virulent H37Rv strain induced cell death at a faster rate than an equivalent MOI of the attenuated H37Ra strain and as a consequence, the PI exclusion assay was carried out 24 h after infection in H37Rv-infected DCs and 72 h in H37Ra-infected cells. Cell death also occurred with live H37Ra infection at the lower MOIs of 1 and 5 after 72 h (Figure 2C). Figure 2 Live M.