CHARACTERIZATION OF CHEMOKINE AND DENDRITIC CELL POPULATIONS IN PULMONARY GRANULOMAS FROM CYNOMOLGUS MACAQUESINFECTED WITH MYCOBACTERIUM TUBERCULOSIS

摘要

One-third of the world's population is infected with Mycobacterium tuberculosis, which causes over 2 million deaths annually. M. tuberculosis typically infects humans through the inhalation of aerosolized microorganisms and the host's immune system controls the infection by developing a granuloma, which consists predominantly of macrophages and lymphocytes. The factors initiating the formation and maintenance of these granulomas are not well understood, but immune cells are likely recruited to the site of inflammation to maintain immune control of the infection. Chemokines and cytokines play important roles in cell trafficking and migration of immune cells, and DC initiate an adaptive immune response. My hypothesis is that DC (in conjunction with macrophages) recruit immune cells to the granulomatous site by the expression of IFN-g-inducible chemokines, which are expressed due to mycobacterial antigen stimulation. To determine local cytokine- and chemokine-specific and DC-associated mRNA expression patterns in granulomatous lesions, I performed in situ hybridization (ISH) on paraformaldehyde-fixed, cryopreserved lung tissue sections obtained from cynomolgus macaques (Macaca fascicularis) infected with a low dose of virulent M. tuberculosis. In addition, we evaluated the presence of mycobacterial 16S rRNA to determine the distribution of the mycobacteria and the mycobacterial burden within the granulomas. To model the immune environment in the pulmonary granulomas, I infected human monocyte-derived DC with M. tuberculosis in the presence of IFN-g. Although I found an abundant expression of the IFN-g-inducible chemokines and numerous DC-associated genes within the granulomas, the IFN-g-inducible chemokine expression was predominantly produced by macrophages. The presence of DC in the granuloma may serve to skew the immune response to a type I environment, but our data do not suggest a direct role in the production of IFN-g-inducible chemokines. These studies provide further information on the potential roles for chemokines and DC in granuloma formation and maintenance as well as the composition of local DC populations. These studies further illustrate the complex microenvironment of granulomas, which are important in the control of tuberculosis infection. Further understanding of granuloma formation and maintenance could lead to the development of therapeutic treatments needed to reduce this public health epidemic.