Investigating the Role of mce2 Operon in B.tb Infection

Olivera Marjanovic, UC San Francisco

The objective of my dissertation project is to characterize the mechanism of latency of Mycobacterium tuberculosis (M. tuberculosis) by studying an operon that may play a role in the regulation of host immune response in a mouse model of tuberculosis (TB).

Global epidemics of tuberculosis and HIV and their interaction represent one of the most significant challenges to global public health. An estimated one third of the world population is infected with M. tuberculosis, of whom more than 8 million develop active disease each year. It is estimated that at the end of 2004, 40 million people were living with HIV/AIDS, and the total death toll from HIV/AIDS was estimated to be 3.1 million. Furthermore, about 10% of the total global burden of tuberculosis is thought to occur in people with HIV infection. Therefore, in order to control tuberculosis in areas with high co-infection rates strategies must be developed to prevent tuberculosis in HIV-infected individuals. More specifically, since 1/3 of the world population is latently infected with Mycobacterium tuberculosis and HIV infection is a potent risk factor for reactivation of latent TB, efforts must be directed toward treatment of latent TB or prevention of reactivation of latent TB. The proposed project here aims to study a set of mycobacterial genes and their involvement in TB latency establishment. Identifying gene products involved in establishment of TB latency could lead to development of novel therapeutic vaccines to prevent reactivation of latent TB, a major burden contributor to those infected with HIV/AIDS.

M.tuberculosis has 4 related sets of an operon called mce (mce1-4). The mce1 operon has been previously shown to be important for bacterial latency of M.tuberculosis in mice. Its disruption causes the mutant M.tuberculosis to become hypervirulent in mice. The mce3 and mce4 operons appear to exhibit a different phenotype in mice. Their disruption causes M.tuberculosis to be attenuated in mice. The role of mce2 operon in infection is not yet known. In order to study the effects of mce2 operon on bacterial latency, deletion of the entire operon will be carried out by means of homologous recombination on both the H37Rv and mce1k/o bacterial strains. These bacterial mutants will further be characterized for both intracellular as well as extracellular growth kinetics. Cytokine and chemokine production, as well as NO, from murine macrophages will be evaluated in response to infection with our mutants. Finally, in vivo mouse studies will be conducted to determine the effect of mce2 operon single deletion and mce1/2 double operon deletion on bacterial and host survival as well as its impact on granuloma formation. The results from these experiments should tell us whether or not the mce2 operon contributes to M.tuberculosis latency, and whether it interacts with the mce1 operon to influence infection outcome. Thus, the analysis of the role of the mce2 operon will complete the story of the family of mce operons in TB latency.