Novel Mechanisms of Antigen Processing That Enhance Bcg Vaccine Efficacy

<p><em>Mycobacterium tuberculosis,</em> the causative agent of tuberculosis, is the most lethal single infectious agent afflicting man today causing 2 million deaths per year. The World Health Organization recommends a vaccine as the best option to prevent this disease. The current vaccine, BCG, has a variable efficacy and does not protect adults. It is known that BCG vaccine becomes sequestered in special phagosome compartments of macrophages that do not fuse with lysosomes. Since lysosome fusion is necessary for peptide production and T cell priming leading to protective T_H1 immunity, we hypothesized that vaccine efficacy is reduced and occurs perhaps due to non-lysosome dependent mechanisms. We therefore proposed an in depth analysis of phagosome environment, and its proteome to unravel mechanisms of antigen processing and presentation. We initially discovered that three mechanisms of pH regulation including vacuolar proton ATPase, phagocyte oxidase and superoxide dismutase (SOD) secretion from BCG vaccine affect antigen processing within phagosomes. These studies led to the discovery that a mutant of BCG vaccine which lacked SOD was a better vaccine. Subsequently, the proteomic analysis of vaccine phagosomes led to the discovery of novel protease (γ-secretase) enriched on BCG vaccine phagosomes. We then demonstrated that these proteases generated a peptide from the BCG vaccine which was presented through the MHC-II pathway to T cells and induced a T_H1 response. The specificity of antigen production from γ-secretase was confirmed through siRNA knockdown of the components of the protease namely, nicastrin, presenilin and APH, which led to a decrease in antigen presentation. We therefore conclude that, even though BCG phagosomes are sequestered and do not fuse with lysosomes to generate peptide antigens, there are complex and novel <em>in situ</em> mechanisms within phagosomes that are capable of generating an immune response. We conclude that T_H1 immunity to BCG vaccine arises mostly due to non-lysosome dependent immune mechanisms of macrophages and dendritic cells.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation (PhD)

Year dc:date.available

2011

Author dc:creator

• Singh, Christopher R

Contributors dc:contributor

• Chinnaswamy Jagannath, Ph.D.
• Fernando Cabral, Ph.D.
• Andrew Bean, Ph.D.

• phagosome
• proteomics
• phox (phagocyte oxidase)
• SOD (super oxide dismutase)
• nicastrin
• gamma-secretase
• Immunopathology
• Laboratory and Basic Science Research
• Pathogenic Microbiology

Repository record dc:identifier

https://digitalcommons.library.tmc.edu/utgsbs_dissertations/171

OAI identifier oai:identifier

oai:digitalcommons.library.tmc.edu:utgsbs_dissertations-1201