Immunopathogenesis of Spinal Tuberculosis (TB) - Project Summary:
Tuberculosis (TB), caused by the intracellular bacteria Mycobacterium tuberculosis (Mtb), is the second-
leading cause of death worldwide from infection. Following inhalation, Mtb are phagocytosed by macrophages
at the epithelial barrier of the lung, eliciting an inflammatory response and recruitment of other immune cells
from the blood. While in the circulation, infected phagocytes can disseminate throughout the body, leading to
infectious foci at extrapulmonary (EP) sites. There is limited understanding of EPTB disease pathogenesis,
which hinders the control of the epidemic. In immune-competent adults, the hallmark response to Mtb is the
formation of a granuloma at the site of infection, an organized collection of immune cells, which limits the
spread of the bacilli and can control their growth. Prior studies of the granulomatous response in TB, derived
mostly from the examination of surgically resected human lung tissue and animal models of pulmonary TB,
have shown that, as granulomas mature and enlarge in the lung, they can become centrally necrotic, liquefy
and ultimately drain, creating cavities. In EP sites, draining of the liquefied material is hampered and the
cellular aggregates form abscesses rather than cavities. The tissue composition and microenvironment of the
skeletal system varies greatly from that of the lung. In the spine, Mtb infection is relatively well contained in the
form of a "cold" epidural abscess, in association with bone and cartilage destruction, which may cause collapse
of the spinal column, deformity and neurological complications. We hypothesize that much of the pathogenesis
and tissue destruction in the spine is caused by an excessive immune response due to an imbalance between
inflammation and wound healing. The proposed study aims to elucidate the unique immunopathogenesis of
spinal TB to ultimately reduce the morbidity and mortality associated with this manifestation of TB. We will
define immune and tissue-remodeling mediators that contribute to spinal TB infection, by performing
microarray analysis on isolated, histologically-distinct regions of excised granulomatous tissue from spinal TB
patients undergoing surgical treatment in Durban, South Africa. The processes that drive and characterize
spinal TB will be confirmed by determining the presence of specific proteins and mRNAs, as well as lipid
species, within the tissue. The expression of spinal TB-associated factors identified in the tissue will be
interrogated in the peripheral blood of the same patients, to identify novel systemic biomarkers. TB is a major
opportunistic infection in HIV patients and HIV infects many of the same cells that orchestrate immunity to TB,
such as activated CD4 T cells and macrophages. We will therefore investigate the impact of HIV status on the
immunopathogenesis of spinal TB. This study will address an outstanding question in TB research, namely a
molecular definition of the immunological and pathological features of EPTB. Ultimately, the results of this
project can contribute towards improved diagnostic and/or monitoring strategies in TB patients.
