E-041. Changing Frequency, Phenotype and Location of Dendritic Cells in Mycobacterium-Induced Granulomas at Different Phases of Infection

H. A. Vonderheid, P. D. Hulseberg, M. Sandor;
Univ. of Wisconsin, Madison, WI.

During most stages of mycobacterial infections, bacteria are contained within granulomatous lesions. Dendritic cells (DCs), important regulators of both T cells and NK cells, have been shown to be present within these lesions. However, many questions remain regarding the role DCs play in mycobacterial granulomas. Questions include the frequency of DCs in granulomas, their traffic into and out of the lesion over the course of infection, their phenotype and maturation status over time, their ability to sample and process granulomatous antigens in order to induce systemic immunity and what T cell populations they induce after sampling. By isolating granulomatous lesions from Mycobacterium bovis (BCG) infected mice over the course of infection, from early acute stages to latent chronic stages, we were able to answer some of these key questions. By flow cytometric analysis and fluorescent microscopy, we have found that both the frequency and location of DCs within the granuloma change over the course of infection. Phenotypic analysis of DC subsets by flow cytometry shows the predominant DC population over the course of infection to be monocyte-derived ‘inflammatory’ DCs. Further phenotypic analysis suggests that early lesions contain mature DCs expressing high levels of T cell costimulatory molecules and are mainly found in the T cell-rich lymphoid cuff region. However, during chronic infection, mature DCs with a phenotype associated less with activation and more with inhibitory functions are largely found in the center of lesions. Taken together, the DCs changing quantity, phenotype and location over the course of infection suggest a complex and changing role that DCs may play throughout the disease in both regulation and maintenance of granulomas. These data imply that in early granulomas DCs are reactivating T cells locally, while during the chronic phase the DCs are inhibiting T cell activity within the lesions.