Mycobacterium Tuberculosis - Macrophage Interaction

Mycobacterium tuberculosis is one of the most important infectious agents yet identified, being responsible for an estimated annual death rate of 2-3 millions. Mycobacterium tuberculosis is an intracellular pathogen which survives within macrophages. Immunological effector molecules, cytokines and chemokines and their receptors, in the initial interaction between macrophages and Mycobacterium tuberculosis are thought to play a key role in determining the outcome of infection. But chemokines and their receptors in M. tuberculosis have been investigated to a limited extent. To know more about the changes of the chemokines and their receptors in macrophage infected with Mycobacterium tuberculosis, we established the human macrophage cell line U937 as an in vitro model for infection with Mycobacterium tuberculosisi H37Rv, carried out gene microarray, Semi-quantification RT-PCR, flow cytometry to detect the profile of chemokins and their receptors in U937 on different infection phase (after infection 6, 12 and 24). The analysis of the transcriptome using microarray show that many genes were up-regulated at 6 hr and 12 hr. There are total 25 genes up-regulated and 22 of them up-regulated significantly at 24 hr. The results of some genes including IL-8, MIP1-α , RANTES, CXCR4 and CCR5 could be confirmed by Semi-quantification RT-PCR. Flow cytometry demonstrated infection with H37Rv could increase the expression of CCR5 and CXCR4 on the U937.In order to detect the up-regulation of CCR5 and CXCR4 as a unique phenomenon of MTB infection or a ubiquitous phenomenon of pathogenic bacteria, we investigated the expression changes of these two chemokine receptors in macrophages attacked by another bacterium Actinobacillus actinomycetemcomitans (AA) (from mRNA level and protein level). To reveal the molecular mechanism of this expression changes, p38 MAPK special inhibitor SB203580 was used and the expression of CCR5 and CXCR4 negative regulator YY1 transfactor was analyzed. Finally we conclude that the up-regulation of CCR5 and CXCR4 can at least partially contribute to the down-regulation of transfactor YY1 which is p38 MAPK pathway dependent and this up-regulation has little relationship with MTB and HIV co-infection.