Dendritic Cells in Granulomas Figure 1. Inflammatory DCs present in both acute and chronic mycobacterium-induced granulomas. C57BL/6 mice were systemically infected intraperitoneally with BCG. Three, six and ten weeks post infection livers were harvested, and granuloma-infiltrating cells were isolated. A, FACS analysis of CD11c and CD11b populations in liver granulomas. Plot obtained from gate of SSC high FSC high population, excluding lymphocytes. B, Phenotypic analysis of CD11c+ cells from gating shown in A. Graph shows absolute number of cells per gram of liver tissue of cells positive for designated DC subsets listed below graph. C, Absolute number of CD11c+ cells per gram of tissue, population obtained from gate shown in A. Statistical differences among groups shown on graph. FACS plots and graphs generated from 3–7 mice pooled per time point for granuloma preparation and representative of three independent experiments. doi:10.1371/journal.pone.0011453.g001 granulomas from CD11c-EYFP mice infected with dsRED BCG (Fig. 3A). In both acute and chronic granulomas some BCG was located in CD11c-EYFP+ cells, detected by red rods located in homogenous green cytoplasmic fluorescence. Although the expected majority of bacteria were in macrophage-like cells 2 (CD11c-EYFP ), there was significantly more BCG per cell in those CD11c-EYFP+ cells that were infected compared to than 2 non-DCs (CD11c-EYFP ) both in acute and chronic lesions (Fig. 3A Right). Flow cytometric analysis of granuloma CD11b+ and CD11c+ cells from mice systemically infected with GFP-BCG further confirmed that both DC-like cells (CD11c+) and macro- phage-like cells (CD11c2CD11b+) are infected at acute and chronic time points (Fig. 3B). Although the CD11c2CD11b+ cell population had a higher frequency of GFP BCG-infected cells at 10 weeks (8.61% compared to 1.17% of CD11c+ cells) (Fig. 3B), the 1.17% of CD11c+ cells infected had a higher GFP fluorescence intensity than CD11c2CD11b+ cells, 28.7% compared to 17.3%, respectively (Fig. 3C). The higher frequency of GFP intensity indicates more GFP+ bacilli per cell. These data suggest that while macrophage-like cells (CD11c2CD11b+) are more frequently infected, DC-like cells (CD11c+), when infected, contain more bacteria per cell. CD11c+ cells in chronic granulomas display decreased expression of MHCII and T cell co-stimulatory molecules, and increased expression of inhibitory molecules DCs are equipped with an array of receptors that facilitate T cell activation. To investigate the phenotype of DCs in granulomas throughout infection, wild-type mice were infected with BCG and PLoS ONE | www.plosone.org 3 July 2010 | Volume 5 | Issue 7 | e11453