Graduate Student - Ph.D.

Molecular Pathology and Laboratory Medicine

University of Texas Health Science Center at Houston (Houston, TX)

Graduate Student - Ph.D.

University of Texas M. D. Anderson Cancer Center (Houston, TX)

Chinnaswamy Jagannath

I am inveestigating a Human macrophage model for the study of non-replicating persistenct Mycobacterium tuberculosis (Mtb).

Tuberculosis is the leading causes of death due to infections in mankind today. Nearly 1/3rd of the human population is latently infected with Mycobacterium tuberculosis and the pathogen reactivates to cause most of the adult disease. The pathogenic mechanisms of latent tuberculosis and reactivation remain unclear essentially due to the lack of reliable models. We have developed a novel cell culture model for the study of dormant/latent organisms. Methods: Human THP1 macrophages were activated with vitamin D3 and retinoic acid (RAVD) and infected with Mtb followed by repeated activation with RAVD. Control macrophages were activated with phorbol myristyl acetate (PMA). Macrophaegs were lysed and plated for colonies of Mtb at weekly intervals. Macrophages were also phenotyped to study expression of receptors and evaluated for bactericidal function using immunostains for phagocyte oxidase (phox) and Iinducible nitric oxide synthase (iNOS). Results: Mtb grew in PMA THPs over 7 days and by day 14 the cells were completely destroyed due to the excessive growth of Mtb. In contrast, RAVD was bacteriostatic to Mtb in macrophages over 7 days and after 3 weeks of RAVD treatment, bacterial counts declined to nearly undetectable levels. Microscopy of the cultures showed persistent bacteria that stained for phox and iNOS. mRNA extracted from RAVD showed messages for antigen 85B, a marker of metabolism in Mtb, although organisms did not grow on media suggesting that they are dormant organisms. Thus we suggest that activation with RAVD induces bactericidal activity in macrophages that leads to the persistence of Mtb in a dormant condition in macrophages. We propose that this cell culture model would be useful to study the molecular mechanisms of latent tuberculosis and devise methods for its control.

2005-2010 NIH Ruth L. Kirschstein Predoctoral Fellowship